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Acoustic properties of PMMA: towards Bragg gratings in

ultrasonic particle separation

Michael Rowlands

20145343

School of Mechanical and Chemical Engineering University of Western Australia

Supervisor: Professor Adrian Keating

School of Mechanical and Chemical Engineering University of Western Australia

Final Year Project Thesis

School of Mechanical and Chemical Engineering

University of Western Australia

Submitted: November 7th, 2011

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Project Summary

Ongoing microfluidics research at the University of Western Australia (UWA) aims to

develop low-cost poly (methyl methacrylate) (PMMA) as an alternative platform for

acoustophoresis - particle separation using acoustic energy. Widespread use of

acoustophoresis has been limited by the high cost and complex fabrication methods

required for the silicon devices typically used. The hurdle facing PMMA is its poor

acoustic properties. Its acoustic inefficiency requires the use of high power levels to

achieve acoustophoresis, producing excessive heat which is damaging to biological

cells. Following on from promising but inconclusive previous studies addressing this,

this project aimed to make progress towards incorporating Bragg gratings into PMMA

devices in an attempt to make them more acoustically efficient. This was undertaken

through the following means:

1. The causes of previously unexplained results at UWA were resolved through an

experimental investigation into the design and manufacturing processes used.

2. A test rig was created to measure acoustic attenuation in plastics. A software

tool was created to automate the tests to achieve higher-resolution, more

repeatable results than would be possible manually.

3. Tests were undertaken to experimentally investigate the acoustic properties of

PMMA.

Key Findings:

• Fluid channels were reduced in width by 38 �m in light of issues identified with

the design and fabrication process.

• The means to experimentally measure the acoustic attenuation properties of a

plastic were developed, including a detailed study into the issues involved.

• The acoustic attenuation coefficient � of PMMA was measured experimentally

as 25 ± 4.25 Np/m, which compares favourably to the literature (Treiber et al.

(2009) report a value of 21.88 NP/m).

• A large body of future work was identified which will allow the impact of Bragg

gratings on acoustic transmission through PMMA to be quantitatively assessed,

and pave the way for more optimal particle separation devices in the future.

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Letter of Transmittal

Michael Rowlands 11 Mardella St

Coolbinia, WA, 6050

7th November, 2011

Professor David Smith Dean Faculty of Engineering University of Western Australia 35 Stirling Highway Crawley, WA, 6009

Dear Professor Smith

I am pleased to submit this thesis, entitled “Acoustic properties of PMMA: towards Bragg gratings in ultrasonic particle separation”, as part of the requirement for the degree of Bachelor of Engineering.

Yours Sincerely

Michael Rowlands 20145343

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Acknowledgements

First and foremost, I would like to thank my supervisor Adrian Keating, for not only

providing invaluable academic guidance and feedback throughout the course of the

project, but also making himself available despite his busy schedule. Thanks also to the

other students completing final year projects this year in the SAIL lab who helped keep

me sane during the long days and nights spent in there.

A very special thank you to Leonie Yann, Greg Rowlands, Timothy Rowlands and

Robyn Lieblich, all of whom were all coerced into proof reading draft versions of this

paper at some point.

Lastly, I would like to thank: my family, who have always supported me in all my

endeavours; my friends, who have provided me with a much needed release from study

throughout the year; and my partner Sarah Lumsden, for putting up with my diminished

presence this past year without a single word of complaint.

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Table of Contents

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Nomenclature

c Speed of sound

CSV Comma separated values

Fr Acoustic radiation force

HBM Human breast milk

I Acoustic sound wave intensity

MSDS Material safety data sheet

PCB Printed circuit board

PDMS Polydimethylsiloxane

PMMA Poly (methyl methacrylate)

P0 Pressure Amplitude

PPE Personal protective equipment

SAIL Sensors and advanced instrumentation laboratory

SMR Surface-mounted resonator

USW Ultrasonic standing wave

UV Ultraviolet

UWA University of Western Australia

V Measured Voltage

Vp Particle Volume

Vpp Peak-to-peak voltage

Z Acoustic impedance

� Compressibility

� Wavelength

� Density

� Acoustic contrast factor

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Chapter 1: Overview

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1.1 Introduction and Objectives

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There is a demand for cheap, portable particle separators to enable point of care analysis

of biological fluids (Pamme 2007). The use of ultrasonic energy to form standing waves

capable of separating particles in a microfluidic flow (known as acoustophoresis) has

the potential to achieve this. The acoustic force exerted on particles suspended in a fluid

flow moves them to pressure nodes across the flow’s width, allowing them to be

collected at separate outlets (Figure 1-1).

Figure 1-1: A 1 wavelength acoustophoresis particle separator, with pressure and force

profiles across the channel and particle trajectories along the flow (Diagram not to scale).

Currently, the high cost of typically silicon acoustophoresis devices prevents its

widespread application. Cheaper materials such as plastics are not used for

acoustophoresis due to their acoustic inefficiency. The excess heat that this generates

can damage biological fluids. Methods such as the focusing of acoustic energy in these

devices through the use of Bragg reflectors have been explored to theoretically avoid

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the losses that cause heating. Results of these efforts are inconclusive, and the acoustic

losses in the plastics used need to be better understood in order to predict the influence

of Bragg gratings on these devices.

This project continued ongoing research efforts at the University of Western Australia

(UWA). The overall aim was to make significant progress towards acoustophoresis

devices suitable for the analysis of sensitive biological fluids made using a low-cost

plastic - poly (methyl methacrylate) (PMMA) - and simple fabrication processes. This

aim was addressed through the following specific objectives:

• Investigate the causes of previously unexplained experimental results

• Refine the existing fabrication process

• Design an experimental setup for investigating acoustic losses and the influence

of Bragg reflectors on these losses

• Determine experimentally the acoustic losses of PMMA

Through these objectives, this project aimed to lay the groundwork for a structured

approach towards the novel application of Bragg reflectors in PMMA acoustophoresis.

Successful completion of these objectives would be a substantial progression towards

the long-term objective at UWA of a commercial device for the automatic analysis of

human breast milk.

1.2 Background and Current State of the Art

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1.2.1 Microfluidics and Lab on Chip

Microfluidics is an emerging field referring to a range of devices and methods for

controlling and manipulating fluid flows with length scales less than a millimetre

(Stone, Stroock & Ajdari 2004). First made possible by the emergence of

microelectronics and dating back to 1979 (Terry, Jerman & Angell 1979), microfluidics

has the potential to revolutionise the way laboratory biological and chemical analysis is

performed (Squires & Quake 2005). Many laboratory functions that have traditionally

been performed manually have been scaled down onto chips typically less than a few

square centimetres. An example of a microfluidics platform combining multiple

processes onto a single chip is illustrated in Figure 1-2. The literature describes many

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microfluidic devices including valves, pumps, actuators, switches, sensors, dispensers,

mixers, filters, separators, heaters (Stone, Stroock & Ajdari 2004).

Figure 1-2: Microfluidic system used for tissue organisation, culture and analysis (El-

Ali, Sorger & Jensen 2006) via Doncon (2010).

Microfluidic devices offer many advantages over their traditional counterparts; they are

often more cost-effective, only require small reagent volumes, minimising waste, have a

small footprint, require diminished labour and are more portable (El-Ali, Sorger &

Jensen 2006). Most current efforts in microfluidics concern applications in chemistry,

biology and medicine, but there also exist applications for control systems and heat

management (Squires & Quake 2005).

Many microfluidics devices rely on the unique fluid flow characteristics observed at the

microlitre scale, where flows have been observed to be purely laminar (Hansen &

Quake 2003). This flow profile enables devices such as particle separators to be

effective; once a particle has been moved to a certain location within the fluid channel,

it will remain there as it flows along the channel’s length.

1.2.2 Particle Separators

The ability to separate solid particles from a fluid is important for the pre-treatment

phase of biological samples (Grenvall et al. 2009). Many different particle separation

approaches have been reported in the microfluidics literature. The main advantage of

this group of particle separators over traditional processes is their ability to be operated

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in a continuous, flow-through manner (Pamme 2007). All of these methods apply a

force on the particles, moving them predictably within the fluid channel. The means of

exerting the necessary forces vary, and include acoustic (used in the present research at

UWA), magnetic, dielectric, optical and passive geometry-based techniques (Laurell,

Petersson & Nilsson 2007). Each of these approaches has advantages and limitations,

and an overview of these is presented in Table 3 in Appendix A.1

1.2.3 Acoustophoresis

The use of acoustic pressure to separate particles (so-called acoustophoresis) is the

focus of the present microfluidics research at UWA, of which the current project is a

part. It has potential in biological fields where a minimum of mechanical stress applied

to the cells is desired due to its non-contact mode of particle handling (Laurell,

Petersson & Nilsson 2007). Other attractive properties of acoustophoresis include its

flexibility (acoustophoresis can separate based on size, compressibility and density), its

ability to separate particles from of tenths of micrometres up to tens of micrometres

(Laurell, Petersson & Nilsson 2007) and also its reasonably high flow-rates.

In acoustophoresis, ultrasonic waves are applied to a microfluidic channel, usually by

means of a piezoelectric transducer (Laurell, Petersson & Nilsson 2007). One of the

channel’s dimensions is chosen to correspond to a resonant mode of the ultrasonic

wavelength. This causes reflections at the channel walls to interfere constructively and

create an ultrasonic standing wave (USW) between them (Laurell, Petersson & Nilsson

2007). This creates a sinusoidally varying pressure distribution along the channel in this

dimension (Figure 1-3), with sound pressure maxima (antinodes) at the channel walls

(Hagsater et al. 2007). Note that all future references to ‘nodes’ and ‘antinodes’ refer to

this pressure distribution. Suspended particles travelling through the USW are subjected

to what is known as the primary acoustic radiation force (Laurell, Petersson & Nilsson

2007). This is a non-linear effect which causes particles to be attracted to either the

nodes or antinodes of the standing wave and is defined by equation (1) (Laurell,

Petersson & Nilsson 2007).

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It can be seen that Fr is proportional to the square of the pressure amplitude P0 and the

volume of the particle Vp, and inversely proportional to the ultrasonic wavelength �. x

is the particle’s distance from a pressure node and � and � denote the compressibility

and density of the particle (p) and the suspending medium (m), respectively. The

magnitude and direction of the force to which particles are subjected is defined by the

acoustic contrast factor, �. A function of the relative densities and compressibilities of

the liquid and suspended particles, � is defined in equation (2) (Laurell, Petersson &

Nilsson 2007).

� �� 4�5�

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Lipid particles in milk, for example, are more compressible than water, resulting in a

negative contrast factor, so will move towards pressure antinodes (Hagsater et al. 2007).

Conversely, polystyrene beads have a positive contrast factor and will move to pressure

nodes (Doncon 2010). Figure 1-3 shows a plot of the acoustic pressure distribution

across the channel width of a single-wavelength fluid channel and resultant acoustic

radiation force using the parameters of Doncon (2010), who separated polystyrene

microbeads from a water solution at 2 MHz.

Figure 1-3: Pressure distribution and acoustic radiation force experienced by

polystyrene microbeads in water at 2 MHz across the width of a single-wavelength

resonator. Pressure amplitude is not known so y the axis is not scaled.

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Developed by Nilsson et al. (2004), the usual means of achieving particle separation by

acoustophoresis is by use of a ‘layered resonator’ (Laurell, Petersson & Nilsson 2007).

The layers consist of an ultrasonic transducer mounted below a resonator into which a

microfluidic channel has been defined, and a reflector layer on top to confine the

acoustic energy to the fluid channel (Figure 1-4). Somewhat counter-intuitively, a

standing wave can be obtained orthogonal to the flow channel (Figure 1-4A), thus

sorting the particles across the channel’s width. The mechanism by which acoustic

energy is coupled into this lateral mode has been investigated by Townsend et al.

(2006). It is predicted that the gradients of potential energy density in this lateral mode

may be as large as 85% of that observed in the dominant planar mode. It is in this lateral

mode of operation that particle separation has been achieved in research at UWA

(Harris, Keating & Hill 2010). At UWA, the fluid channel has been designed to be a

single wavelength in width. This will cause two bands of the positive-contrast-factor

polystyrene bead and water combination under test as shown in Figure 1-1.

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Figure 1-4: Ultrasonic standing waves (USW) generated in a ‘layered resonator’

acoustophoresis device. A) Operating in the ‘lateral mode’ and B) in the ‘planar mode’.

The transducer vibrates in the z direction (Doncon 2010).

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1.2.4 Resonators

An ideal resonator material requires high acoustic impedance, ensuring efficient energy

reflection at the fluid channel walls. The reflection coefficient R between two materials

determines the fraction of energy reflected by an incident acoustic wave travelling from

one material to the other, given by equation (3) (Kuttruff 2007).

� ! � "# � ""# "� (3)

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Z0, Z1 are the acoustic impedances of the two materials, given by:

� " � �$� (4)

Where, for each medium:� = density and c = Speed of sound. The reflection coefficient

will be between -1 and 1, with 1 representing total reflection and no phase change, 0

representing no reflection and -1 representing total reflection with a 180° phase change

(Kuttruff 2007). Table 4 in Appendix A.2 shows the acoustic impedances and reflection

coefficients with water of some commonly used materials within microfluidics. When

the acoustic impedances of two materials are similar, they are said to be well ‘matched’,

and energy transfer between them is efficient.

Silicon and glass possess favourable acoustic properties, reflecting 86% and 79% of

incident acoustic energy at a water/resonator interface, respectively. Manufacturing

processes also exist for these materials to create perfectly straight and parallel channel

sidewalls within them. Fluid channels can be defined in silicon and glass materials

using photolithography and micromachining methods established from years of

microelectronics development (Duffy et al. 1998). In the ongoing work at UWA, the

fluid channel has been designed to be a single wavelength in width. This will cause two

bands of the positive-contrast-factor polystyrene bead and water combination under test

as shown in Figure 1-1. However, the manufacturing processes for these materials are

expensive, time-consuming and complex (Tan et al. 2001), (Rhee & Burns 2008),

greatly limiting access to this technology.

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1.2.5 Polymers in microfluidics

Rhee and Burns (2008) summarise recent attempts to develop simpler and cheaper

fabrication methods for microfluidic devices. Polymers such as polydimethylsiloxane

(PDMS) and poly (methyl methacrylate) (PMMA) are identified as cheaper and less

fragile alternatives to glass and silicon for microfluidic systems. Several microfluidic

systems have been fabricated using PDMS (Duffy et al. 1998), however these typically

still required an expensive master mask (Effenhauser et al. 1997). PMMA is beginning

to see widespread use in microfluidics, but not in acoustophoresis due to its poor

acoustic properties (Treiber et al. 2009). Glynne-Jones et al. (2009) demonstrated a

‘quarter-wave thin-reflector’, the first PMMA microfluidic device relying on acoustic

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energy. However, due to this device’s design the reflection properties of the material

were of minimal importance. Harris, Keating and Hill (2010) demonstrated an

acoustophoresis particle separator constructed from PMMA with fluid channels defined

using a simple hot-embossing process. However, the power input required for particle

separation was significantly higher than on similar equivalent silicon or glass devices.

This generated a large amount of heat, which will be damaging to biological fluids.

1.2.5.1 Dealing with excess heat

The ultimate objective of ongoing microfluidics research at UWA is to achieve

separation of lipid particles from human breast milk at temperatures safely below 39°C.

Operating piezoelectric transducers at high power levels generates a significant amount

of heat (Ferroperm Piezoceramics A/S ® 2011). This is unacceptable in biological

applications where temperatures above 39°C will damage the sample (Hansen & Quake

2003). This has been dealt with previously in microfluidics by employing aluminium

spacers as heat-sinks and using peltiers to remove excess heat (Grenvall et al. 2009).

1.2.6 Bragg Gratings

Bragg gratings are commonplace in optics and often integrated within optic fibres

(Tsuda 2006). In optics, they consist of a periodic variation in the refractive index of a

medium (Figure 1-5) which causes light to be reflected constructively at the target

wavelength and allowed to pass almost unaffected at all other frequencies (Othonos

1997) as shown in Figure 1-6. This occurs because at the target frequency the

amplitudes of the reflected field contributions from different parts of the grating are all

in phase, and add up constructively (Paschotta 2008).

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Figure 1-5: A quarter-wavelength distributed Bragg reflector (DBR), showing the

acoustic energy field as an incident wave is reflected.

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The typical design in acoustics is the ‘quarter-wave stack’ also known as a Distributed

Bragg Reflector (DBF), in which the consecutive regions of high and low acoustic

impedance are designed to be the thickness of one quarter-wavelength of the desired

stop-band frequency (El Boudouti et al. 2009). Quarter-wave stacks have been a topic of

research since 1965 (Lakin, McCarron & Rose 1995), and are more recently finding

application as narrow bandpass filters in wireless transmission systems (Kone et al.

2010).

Figure 1-6: Characteristic reflectivity spectrum of a distributed Bragg Reflector (DBR)

with a centre frequency of 2 MHz. Modified from Paschotta (2008).

1.2.6.1 Application in Acoustophoresis at UWA

Recently Doncon (2010), working in the Advanced Sensors and Instrumentation

Laboratory (SAIL) at UWA, addressed the issue of excessive heat in PMMA

acoustophoresis through a novel application of Bragg gratings. A DBR, designed to

reflect at the resonant frequency of the main channel, was placed on either side of it in

an attempt to better focus the acoustic energy, similar to a Fabry-Perot microresonator

in optics (Chen 2011). This was expected to minimise the acoustic losses in PMMA that

generate unwanted heat. The gratings were implemented using water-filled fluid

channels as the low-impedance medium and the PMMA between these channels as the

high-impedance medium. This configuration is shown in Figure 2-1. Although the

reflectivity coefficient between water and PMMA is only 0.34 (Doncon 2010), weak

index modulations have been shown to be sufficient for achieving nearly total reflection

in surface mounted resonator (SMR) devices (Marksteiner et al. 2005). Doncon (2010)

achieved limited success, with acoustophoresis achieved at lower power levels than

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previously seen in PMMA, but unexpected and poorly explained particle separation

behaviour was observed with four bands of particles appearing when only two were

expected. An objective of the present project was to conduct a thorough investigation

into the design and fabrication processes used by Doncon (2010) and eliminate all

possible sources of error.

1.2.7 Acoustic Attenuation Coefficient (�)

The acoustic attenuation coefficient (�) is one of the fundamental acoustic parameters of

a material (Treiber et al. 2009), describing the characteristic losses as acoustic energy

passes through it. It is analogous to the optical attenuation coefficient in optics, which

describes the attenuation of optical energy through a length of fibre, for example (Chen

& Chi 1993). A number of techniques have been presented for the measurement of

acoustic attenuation (Treiber et al. 2009). In all of these, an acoustic signal is generated

by a transmitter transducer, coupled through a test specimen and measured by a receiver

transducer.

1.2.7.1 Measuring �

The contact transducer approach involves a transducer coupled to either side of a

material sample with a coupling agent liquid or a permanent bond (Treiber et al. 2009).

This approach is widely employed due to its simple and flexible experimental setup

(Treiber et al. 2009). However, the coupling conditions between the transducer and

specimen have the potential to vary largely between tests and these variations are

difficult to measure (Treiber et al. 2009). This can result in erroneous and inconsistent

measurements.

Immersion techniques overcome this inconsistency by immersing the test specimen,

transmitting transducer and receiving transducer in a liquid to ensure excellent coupling

of the ultrasonic energy through the specimen (Hartmann & Jarzynsk 1974). However,

this approach was deemed inappropriate for the present investigation due to the thin

nature of the samples under test (the PMMA used was 1.36mm thick). This method

relies on completely obstructing the sound beam with the test specimen, which would

not be possible with samples of this thickness and the comparatively large (6×6mm

square) transducers available.

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There are two main approaches used to measure � for a sample (Treiber et al. 2009).

The first tests a sample of accurately known length, observing the measured frequency

spectra for a period of time after the initial pulse is transmitted in order to determine the

energy intensity after multiple internal reflections within the specimen (Treiber et al.

2009). This approach, referred to as the ‘double echo’ method can suffer from a poor

signal-to-noise ratio when the attenuation is high or the sample is thick (Treiber et al.

2009). Reference-based measurements utilise a material sample with a well-known

attenuation value against which the frequency spectra of subsequently tested specimens

are compared (Sears & Bonner 1981). This is also not appropriate for the present

investigation as this project seeks to establish acoustic impedance tests for the first time

in the SAIL, and as such no suitable reference sample is available.

Figure 1-7: Through-transmission (S1) and ‘double-echo’ (S2) sound intensity

measurements in a contact transducer arrangement (Treiber et al. 2009).

The ‘through-transmission technique’, adopted for the present investigation into

PMMA, is similar to the ‘cutback method’ used to measure fiber transmission losses in

optics (Dupuis et al. 2009). The sample length through which acoustic energy is

transmitted is varied, and the amplitude of the measured output is used to calculate the

attenuation coefficient �. This approach eliminates the need to estimate the input energy

levels; plotting the logarithm of the measured intensity against sample length gives the

attenuation directly (Dupuis et al. 2009). This approach is particularly prone to coupling

variations, as replacing the sample between tests changes the coupling conditions each

time. A thorough investigation into the coupling conditions was therefore required.

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1.2.8 Attenuation Properties of PMMA

PMMA is an acoustically lossy material (Treiber et al. 2009). However, values available

in the literature for these losses vary dramatically (Treiber et al. 2009). This large

variation is attributed to compositional difference between PMMA samples tested

(Treiber et al. 2009). Because of this, it was desired to gain a better understanding of the

acoustic losses of PMMA in use at UWA. This understanding will enable future work to

explore whether or not the inclusion of Bragg gratings is a feasible approach towards

reducing the power required to obtain particle separation.

1.3 Report Organisation

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The work done in this project involved separate paths of design and investigation that

stand on their own, and are presented as such in this paper. Following the suggested

thesis format of displaying all experimental processes followed by a presentation and

discussion of all results would require the reader to endure long passages of unrelated

content between reading about a process undertaken and learning of its outcomes.

Dividing up the ‘process’ and ‘results and discussion’ sections within specific chapters

allows the reader to follow a more logical and coherent path through the work presented

in this report. The structure of the remaining chapters is as follows:

Chapter 2: Investigating Previous Results

2-1: Experimental Method

2-2: Results and Discussion

Chapter 3: Acoustic Transmission Test

3-1: Design Approach


Chapter 4: Experimental Safety

Chapter 5: Attenuation Properties of PMMA

5-1: Experimental Method and Data Extraction


Chapter 6: Conclusions and Future Work

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Chapter 2: Investigating Previous Results

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2.1 Experimental Method

To achieve this project’s objective of determining the cause of the previously

unexplained results of the study undertaken by Doncon (2010) at UWA, the experiment

has been repeated in the present work in an attempt to reproduce these results.

Improvements were then made to the identified shortcomings in the experimental setup

and tests repeated once more. Finally, a thorough investigation into the design and

fabrication process of the PMMA devices used by Doncon (2010) was undertaken to

identify and eliminate any sources of error.

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2.1.1 Experiment of Doncon (2010)

Doncon (2010) attempted particle separation on a PMMA resonator with seven Bragg

gratings either side of the main fluid channel, as shown in Figure 2-1.

Figure 2-1: Design of the acoustophoresis device tested by Doncon (2010), with seven

Bragg gratings either side of the main channel (Doncon 2010).

The devices were tested by actuating a piezoelectric transducer with an AC signal from

a signal generator while a microbead (Polystyrene, from Polysciences® Inc.) and water

mixture was input into the device using a syringe pump. The PMMA device was held in

place using the test rig design by Doncon (2010). A transducer was mounted on the

underside of the PMMA device, an aluminium spacer placed between the transducer

and the PMMA device with a thin layer of coupling paste between the transducer and

the spacer, and between the spacer and the PMMA device to ensure good ultrasonic

coupling. A steel bolt was fastened onto the underside of the transducer to press it

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firmly against the device. This experimental setup is shown in Figure 2-2. Particle

separation performance was then observed using an oscilloscope, microscope, and

image capture equipment and software (Doncon 2010).

Figure 2-2: Experimental setup for particle separation, in action under the microscope

(top inset). Isometric and photo insets from Doncon (2010) (Diagram not to scale).

2.1.1.1 Previous Results

Particle separation was achieved by Doncon (2010) at lower power levels than

previously reported on PMMA devices. The main fluid channel was designed to be a

single wavelength in width in water at 2 MHz, which predicts two bands of microbeads

to form within the flow corresponding to the two pressure node locations as shown

previously in Figure 1-1. However, four particle bands were observed instead of the two

predicted by the theory. No adequate explanation was provided for this (Doncon 2010)

and possible causes have been explored experimentally in the present research.

2.1.1.2 Re-Creating the Experiment

In order to investigate these unexplained results, the test setup of Doncon (2010) was re-

created as faithfully as possible. The signal generator (Agilent ® 3320A), syringe pump

(KD Scientific ® KDS230), piezoelectric transducers (Pz27, from Ferroperm

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Piezoceramics A/S®), microscope, image capture equipment (Olympus® U-TV0.5XC-

3 camera connected to an Olympus® BX51 microscope and a PC) and software

(Olympus® Soft Imaging Solutions (SIS) analySIS™ software package) were identical

to those used by Doncon (2010). The oscilloscope used to monitor the input voltage

(Rigol® 1204B) was different to the original, but this will have no influence on the

outcomes. All input and output test parameters for the tests in which Doncon (2010)

observed particle separation are listed in Table 5, Appendix A.3. These parameters were

identical in the present tests. The PMMA device used was the original fabricated and

tested by Doncon (2010). Note that significantly lower concentrations of microbeads

were used in the current tests due to their high cost. Repeating the experiment as

described above, the results were quantitatively the same as Doncon (2010) observed–

four particle bands formed where only two were expected (Figure 2-3).

2.1.2 Improving Experimental Setup

Shortcomings were identified with the experimental setup used, improvements made

and the tests repeated a second time to observe any impact of these changes on particle

separation behaviour.

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Figure 2-3: A) Particle separation results of Doncon (2010). The microbeads formed

four bands within the main fluid channel (1-4, above) instead of the expected two.

B) Re-created particle separation showing qualitatively similar results. Note the lower

microbead concentration used in repeated tests to minimise waste.

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2.1.2.1 Transducer Backing

Doncon (2010) noted that particle separation was only observed when a force was

applied to the rear of the transducer, coupling it more effectively with the PMMA

device. A steel bolt on the underside of the transducer applied this force (Figure 2-2).

With the transducer backed by air, over 99% of the acoustic energy at the air/transducer

interface will be reflected internally due to the poor acoustic matching of air and the

ceramic (Kuttruff 2007). However, due to the better acoustic matching of the ceramic

and steel, roughly half of the energy at this interface will be coupled into the steel bolt

and lost (Doncon 2010).

A spring-loaded backing comprised of polypropylene drinking straw segments was used

in place of the steel bolt to minimise these losses. Four straws were cut to length and

fixed atop a spring in the arrangement shown in Figure 2-4 C) and D) using an epoxy

resin. The tips of the drinking straws were then cut at an angle to reduce contact area

with the transducer (Figure 2-4 D).

Figure 2-4: A) Cross-section of a drinking straw, showing the outer diameter (OD) and

wall thickness. B) Top face of a typical hex bolt. C) The drinking straw arrangement

used. D) Spring-back array of drinking straws used to apply pressure to the transducer.

Straws were chosen for their relative strength and cross-sectional area comprised largely

of air. Furthermore, the polypropylene from which the drinking straws are made is

poorly acoustically matched with the transducer (Hartmann & Jarzynsk 1974), so even

the areas in contact will not transmit acoustic energy efficiently. The outer diameter

(OD) of the straws used and the thickness of the plastic from which they are made

(Figure 2-4, A) were measured to be 5.32 mm and 0.08 mm, respectively. The resulting

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cross-section is comprised of 97% air and only 3% plastic (Table 1) for a single

drinking straw. The four straw array used (Figure 2-4 C) has a slightly higher ratio of air

to plastic still due to the inability of the straws’ circular cross-sections to tessellate

(Table 1).

Single Straw Straw Array

Total cross-sectional

area

16.71 mm2 113.21 mm2

Air cross-section 16.21 mm2 111.12 mm2

Plastic cross-section 0.503 mm2 2.01 mm2

Percentage air 97.00% 98.22%

Table 1: Cross-section composition of a single drinking straw and the four-straw array

with which the steel bolt was replaced.

2.1.2.2 Power Amplifier

Doncon (2010) powered the transducer directly from the function generator at its

maximum available output. The heavy loading of the high-impedance transducer, as

well as operating the amplifier at its voltage limits, may have been applying a distorted

signal to the Piezo, in turn creating undesired resonant modes in the PMMA. After the

tests in Doncon (2010) had been completed, Dr. Nick Harris (School of Electronics and

Computer Science, University of Southampton) provided Doncon with an amplifier

capable of dealing with the high-frequency 2MHz signal. This was included in the

signal path between the function generator and the transducer in order to supply higher

voltages to the transducer, but particle separation was not re-tested by Doncon (2010)

after its inclusion. It has been included in the present tests, with the signal delivered to

the transducer measured on an oscilloscope during all tests to ensure that a clean sine

wave was being delivered, and that the peak to peak voltage (Vpp) was accurately

known.

2.1.2.3 Impact

Repeating the test with the amplifier included and the bolt replaced had no qualitative

effect on the results: four particle bands were still formed where only two were

expected. Following these tests, it was concluded that the extra particle bands were not

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caused by shortcomings of the experimental setup or human error, prompting an

investigation into the physical properties of the resonator itself.

2.1.3 Investigating Manufacturing Tolerances

If the centre channel or Bragg gratings of the PMMA devices were not the specified

resonant widths, exciting them at 2 MHz could cause interference patterns resulting in

extra pressure nodes formed across the channel, accounting for the extra particle bands

observed. An investigation was performed to determine the accuracy of the device

dimensions, and the source of any deviation from the design parameter.

2.1.3.1 Device Manufacturing Process

The fabrication process for the PMMA devices established at UWA and detailed by

Doncon (2010) involves multiple stages.

1. Design the resonator using Microsoft® VisioTM

2. Print the designs to a Bromide mask

3. Expose the design onto photoresist on a blank PCB

4. Develop the PCB to remove unwanted photoresist

5. Etch away excess copper to create a master PCB mould

6. Imprint the design onto a PMMA sheet using the master PCB and a hot

embossing process

7. Drill holes for inlet and outlet tubing

8. Seal the fluid channels by bonding the resonator to a thinner PMMA top sheet

9. Secure inlet and outlet tubing in place using an epoxy glue

The section ‘2.3 Fabrication Process’ from (Doncon 2010) provides full fabrication

details and has been reproduced in Appendix B:. Each stage above presents an

opportunity for error to be introduced. Doncon (2010) reports on device feature

variation throughout the fabrication process. Design features were found to vary

predictably in size from the bromide mask to the PCB mould (step 2 to step 5), and

again from the mould to the final PMMA device (5 to 6). However, all measurements

were given as relative sizes from one stage to the next, with no absolute measurements

of a complete device presented (Doncon 2010).

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2.1.3.2 Measuring Each Stage

Two of Doncon’s (2010) final PMMA devices were obtained, along with the PCBs used

to press them, the Bromide masks used to etch the PCBs and the Microsoft® VisioTM

file containing the original designs. An investigation was undertaken to determine the

error present in the final devices and at what stage in the manufacturing process this

error was introduced. This error was characterised and where possible, its sources

eliminated. This investigation was undertaken using the image capture equipment and

software described previously in section 2.1.1.2. The AnalySISTM software package

includes the ability to precisely measure features of microscope images. The three

features identified in Figure 2-5 were measured at each stage of the fabrication process

and compared. The two devices obtained were manufactured from different bromide

masks, but the measured feature sizes were designed to be identical on both.

Device designs were revised based on the findings of these investigations and re-drawn

using Microsoft ® VisioTM. The revised designs were printed onto Bromide

transparencies at local printing specialist Type Tamer.

Figure 2-5: Cross-section of PMMA device showing nominal values for the three

dimensions measured. (A) Fluid-filled gratings. B) PMMA (C) Main fluid channel. All

measurements are in �m.

2.1.3.3 Printing Tolerances

An investigation was also undertaken into the characteristic changes in feature sizes

between designs drawn in Microsoft ® VisioTM and submitted to Type Tamer for

printing, and the bromide masks returned. The three key feature sizes shown in Figure

2-5 were measured on the bromide masks of a number of designs and compared with

the nominal design dimensions to characterise the printing tolerance at Type Tamer. To

determine whether the minimum possible feature size using the present fabrication

methods is limited by this printing process, a scale bar was also printed at Type Tamer

with lines of varying thicknesses ranging from 10�m up to 10mm in size (Figure 6-6,

Appendix C.1).

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2.1.3.4 From Mask to Final Device

The three stages involved in taking the bromide mask to a PCB mould (steps 3, 4 and 5

in 2.1.3.1) were not reported on individually by Doncon (2010), with only the overall

change in feature size over this series of processes recorded. Any error introduced in

these steps therefore could not be accounted for with any degree of certainty. To

investigate the behaviour at each of these stages, the original bromide masks were used

to perform these three steps of the fabrication process, and the same three key feature

sizes measured as described in section 2.1.3.2 throughout. A large but predictable and

consistent shrinkage of features was observed during the etching of the PCBs when the

etching tank conditions (heat, concentration of etchant, aeration, etching time) were

carefully controlled (Doncon 2010). A similar investigation has been repeated in the

present work due to the unknown microscope calibration state used previously (refer to

section 2.1.3.5). A number of PCBs etched by Doncon (2010) and the bromide masks

on which they were based were obtained for these measurements.

2.1.3.5 Calibrating Microscope

No mention was made by Doncon (2010) as to whether or not the AnalySIS™

measurement software was calibrated for use with the Olympus BX-51 microscope

before measurements were taken, or if correct calibration was assumed. In order to

eliminate this as a possible source of error, two calibration pieces were obtained, one

with 100�m increments and the second with smaller, 10�m increments. Figure 6-9 in

Appendix C.2 shows an annotated image of the calibration pieces used. A series of five

images were measured for each piece at both 5x and 20x magnification in both the X

and Y directions. The averages from the five measurements were used to determine the

�m/pixel value to be used in the software.

2.1.4 Poorly Defined Sidewalls

During the investigation into feature size, the fluid channels on the final PMMA devices

were observed to have very poorly defined sidewalls (Figure 2-6). The resultant uneven

and no longer perfectly parallel channels created far from ideal conditions for the

formation of a standing wave between them (Nilsson et al. 2004).

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Figure 2-6: A segment of a PMMA resonator, showing poorly-defined and uneven

channel sidewalls.

Doncon (2010) commented on these sidewalls, attributing the poor properties entirely to

the uneven etching of the PCB mask and deemed an unavoidable, inherent drawback of

the fabrication method. However, an investigation in the present work revealed that

during the ultraviolet (UV) exposure of the mask onto the photoresist (step 3 in section

2.1.3.1) by Doncon (2010), the bromide mask was always placed upside-down during

the UV exposure of the PCBs (Figure 2-7). This is evident from the name and date

stamp on each design, which would need to be have been mirrored to appear correct on

the final devices, but were not. A utility knife was used to carefully scrape away a small

area of the bromide on one of the unused masks, verifying the side of the transparency

that had been printed onto and confirming the mistake in the original designs.

Figure 2-7: Ultraviolet (UV) light exposure setup shown schematically with the mask

placed: A) Correctly; and B) Upside-down, causing poorly defined features to be

exposed in the photoresist layer as some light refracts within the transparency layer.

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In the present investigation, a single bromide mask was exposed onto two separate

PCBs: one correctly and the other upside-down. Their features examined under the

microscope after developing to remove excess photoresist (Steps 3 and 4 in 2.1.3.1), but

before etching (step 5). Previously, designs had not been investigated at this stage.

2.2 Results and Discussion

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2.2.1 Measuring Feature Sizes

The measured feature sizes on the final PMMA devices of Doncon (2010) were found

to vary significantly between the two devices, and neither device closely matched the

nominal design dimensions. These results, as well as the same measurements taken

from the two corresponding bromide masks are shown in Figure 2-8.

The first significant observation from Figure 2-8 is that both bromide masks had

virtually identical feature sizes with the exception of the centre fluid channel

measurements. For both the gratings and PMMA sections the error between the two

masks is less than 0.1%, proving that the masks supplied by Type Tamer are controlled

to sufficiently tight tolerances. The centre channel measurements differed between the

two masks by a larger 2.36%. This can be attributed to the fact that there was only a

single instance of this feature to measure on each mask, compared to the average of

seven measurements each for the gratings and PMMA sections. Any inaccuracies and

quantization effects in the measurement software (the number of pixels on the screen

limits the smallest measurable increments) will be amplified for a single measurement.

Also, this feature is too large to display in a single image at 20× magnification so had to

be measured at 5× whereas all other measurements were taken at 20×. The quantization

effects are significantly larger at the lower magnification value due to fewer pixels

representing the same distance. Similarly, errors due to any misalignment between the

measurement axis and the masks will also have a larger impact.

The second interesting point to note is that the features on both masks are dramatically

different from the design dimensions, with the gratings 104.3�m (56%) larger than

designed at 289.7�m and the PMMA gaps 115.84�m (36%) smaller at 207.9�m. Any

variation between the design and the bromide mask must come from the printing

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process at Type Tamer. Given the tightly controlled tolerances between masks, it

seemed unlikely that this could account for such a large variation. Significantly, the

combined width of 1 grating + 1 PMMA segment was found to closely match the

corresponding dimensions on the original design (to within 2.3%). This indicated that

somewhere in the design or manufacturing process, the width of the fluid channels only

had been affected, while leaving the pitch from one grating to the next correct.

Figure 2-8: Results of PMMA device and bromide mask measurements:

A) Microscope image of a bromide mask at 5× magnification showing: 1 – Centre

Channel; 2 – Gratings; 3 - PMMA; and 4 – Grating + PMMA.

B) Average measured feature sizes on the two Bromide masks (A and B).

C) Average measured feature sizes on the two corresponding PMMA devices.

Upon examination of the original Microsoft Visio™ designs of Doncon (2010), two

issues were identified. Firstly, the Bragg gratings in the design were only specified at a

width of 175�m instead of the desired 185�m. However, the measured Bragg gratings

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on the bromide masks were already significantly larger than 185�m design, so

increasing this would not eliminate the issue. The resonator designs in Visio are

comprised largely of black rectangles which define the main channel and Bragg gratings

(Figure 6-10). By default, a newly placed rectangle in Visio has a line defining its

boundary, with a thickness of ‘0.24 point’. Microsoft adheres to the PostScript

definition of a ‘point’, whereby 1 point is equivalent to 1/72 of an inch (Adobe Systems

Incorporated 1999) giving a ‘0.24 point’ line a thickness of 84.7�m – 46% of the total

design thickness (185�m) of a single grating. This thickness was being inadvertently

added to each fluid channel (and hence removed from the PMMA spacing in-between

two channels). The impact of this oversight is illustrated in Figure 6-10, Appendix C.3.

2.2.2 Poorly-Defined Sidewalls

Exposing the photoresist incorrectly (as discussed in section 2.1.4) was found to create a

‘shadowing’ effect at the edge of each feature, likely as a result of light bending within

the transparency layer between the design and the photoresist. This caused the definition

of the fluid channel edges to become blurred in the photoresist (Figure 2-9 A). The

designs exposed correctly exhibited dramatically more well-defined channel edges

(Figure 2-9 B).

Figure 2-9: PCBs with UV-exposed photoresist before etching with; (A) Bromide mask

placed upside down during exposure, channel edges are ‘shadowed’ and poorly

defined. (B) Mask placed the correct way up, edges clearly defined.

These two PCBs were then etched and close-ups of a portion of each are shown in

Figure 2-10. As expected, the design features are much more clearly defined on the

correctly-exposed PCB. This improvement is expected to carry across to PMMA

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devices subsequently hot-pressed from these PCB moulds, and this impact should be

verified and characterised in future work. Note that for images of etched PCBs, the

features appear as the lighter region as copper is more reflective than the substrate

material. This is reversed from previous images of the photoresist on a copper substrate.

2.2.3 Shrinking During Etching

Repeating the comparison performed by Doncon (2010) between feature sizes of the

bromide masks and PCB moulds etched from them, found comparable shrinkage of the

fluid channels during the PCB fabrication process. On average, channel width on the

final devices was found to be 64.8�m smaller than on the corresponding masks. This

compares well with Doncon’s (2010) figure of 63.8�m for the same tests on a single

device.

Figure 2-10: Microscope images at 5× magnification of etched PCB moulds.

A) Etched from upside-down photoresist exposure.

B) Etched with the mask placed correctly during UV exposure.

2.2.3.1 Printing Tolerances

Features on the bromide masks from Type Tamer were measured to be an average of

26.7�m larger than their nominal dimensions. 94% of features measured falling within

the range of 27±7�m. The spread of measurements is shown in a histogram in Figure

6-7 (Appendix C.1) Future designs printed at Type Tamer should allow for this 27�m

increase in feature size, removing it from the width of each fluid channel feature.

However, measurements will need to be repeated with each subsequent print run to

confirm the repeatability of this tolerance.

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Measurements of the scale bar printed indicated that this is a fixed offset and not a

function of the overall feature size (Illustrated in Figure 6-8, Appendix C.1,). At line

widths below a nominal value of 50�m (measured at 77.99�m) unpredictability was

observed in the offset value. Approximately 80�m thus becomes the lower limit of

channel width possible using masks printed at Type Tamer. Caution should be exercised

in this lower size ranger however, as the 7�m fluctuation observed represents a much

larger percentage of the overall feature size at these length scales.

2.2.4 Revised Designs

In light of the above investigations, the resonator designs were revised introducing the

following changes:

• Bragg grating width increased 10�m to the correct size of 185�m

• Unwanted line fill removed from fluid channels

• Overall, 38�m added to the width of each feature:

o 65�m added to counteract the shrinking observed during PCB etching

o 27�m removed to account for variation in printing at Type Tamer

• In anticipation of variations during fabrication, designs duplicated twice; once

with channels 10% smaller than final required size, and again increased by 10%

2.2.5 Significance and Future Work

The deviation between the nominal design dimensions and those measured on the

PMMA devices tested by Doncon (2010) are substantial. It is expected that resolving

the design and fabrication issues identified here will eliminate the unexpected particle

separation behaviour observed. In future work, new devices should be manufactured

from the revised designs, observing the improved fabrication procedures described here.

Final device dimensions should be measured to verify that they closely resemble the

expected dimensions. The experiment of Doncon (2010) should then be repeated once

more with a correctly dimensioned device and particle separation behaviour observed.

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Chapter 3: Acoustic Transmission Test

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3.1 Design Approach

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An acoustic transmission test was designed to allow the acoustic attenuation properties

of a rigid material to be determined experimentally. This was a necessary step towards

achieving this project’s objective of investigating the acoustic properties of the PMMA

samples in use for ongoing microfluidics research at UWA.

3.1.1 Requirements

The following requirements were identified for the experimental setup:

• Able to test samples up to 50mm in length in varying thicknesses

• Makes use of existing piezoelectric transducers in the SAIL

• Minimal in cost

3.1.2 Approach Adopted

An approach based on a through-transmission, ‘cut-back’ style test was decided upon,

as this presented the most accessible option with the limited resources available. The

test designed involved two piezoelectric transducers (a transmitter and a receiver)

mounted on either side of a length of PMMA (Figure 3-1). A voltage is applied to the

transmitter by means of a signal generator, and the receiver transducer voltage was

measured on an oscilloscope.

Figure 3-1: Transmission test designed to characterise the acoustic losses in PMMA.

An AC electrical signal at the transmitter generates an acoustic wave which propagates

through the PMMA, and is measured at the receiver.

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3.1.3 Test Rig

A test rig was required to hold the two piezoelectric transducers and the PMMA length

under test in the position illustrated in Figure 3-1. The design requirements were:

• Transducers separable by 5-50mm, with or without a PMMA sample

• PMMA quickly and easily exchanged

• Pressure applied to transducers reproducible and consistent from 5-50mm

• Transducers mounted to minimise acoustic coupling away from test sample

3.1.4 Test Rig

A mechanism powered by a constant-force spring was identified as a suitable solution.

Constant-force springs are used in a variety of applications such as electric motors and

window-sash counterbalances. They take the form of a tightly-wound spiral and when a

load is applied, the spring uncoils. As the load increases, it quickly approaches a

constant value which is maintained as the spring is extended infinitely (Ohtsuki,

Ohshima & Itoh 2001). A device from iCandy Creative® designed to push stock to the

front of a retail display was leveraged to create the jig (Figure 3-2). The device

consisted of a rail and an upright, pushed by a constant-force spring.

To create the jig, the existing upright was secured in place, with a second upright

mounted on the same rail and allowed to move. The spring pushes the two uprights

together, creating a reproducible and constant applied force between the two faces at a

range of separation distances. In order to keep the transducers in without a PMMA

specimen installed, drinking straw segments were simply wedged between the two

uprights to maintain the required separation distance. Lengths of straws were measured

using vernier calipers and cut to the lengths required to obtain 5-50mm separation

between the transducers to match the PMMA specimens tested. The transducers were

attached to the faces of the pushers using drinking straws as spacers for reasons detailed

previously in section 2.1.2.1. The straws were attached to the uprights using Blu-Tac™

as this allowed minor adjustments to be made to the transducers in order to obtain the

best possible contact with the PMMA for each test.

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Figure 3-2: Schematic of the jig designed and built to conduct transmission tests.

PMMA and transducers are held as shown in Figure 3-1, applying a constant force

across all PMMA lengths tested. The cardboard guide in view (A) prevents the PMMA

from rotating out of plane with the applied force (Not to scale).

Although convenient for short sample lengths (<20mm), attempting to position the

sample in the test rig as shown in Figure 3-2 becomes very difficult to achieve. This is

due to the moment applied to the sample when it is not perfectly aligned between the

two transducers. A series of cardboard guides were fabricated for samples of varying

length to prevent rotation of the sample, making them easy to align repeatedly and

consistently. Low acoustic impedance cardboard was used in order to minimise acoustic

coupling with the PMMA. Tests were performed with and without the guides in place to

confirm that they had no measurable impact on the results.

3.1.5 Performing the Test

The acoustic transmission tests consisted of the following steps:

1. PMMA polished smooth on opposite ends using P100 wet/dry sandpaper

2. Liberal amounts of coupling paste applied to both ends of the PMMA

3. The ‘sliding end’ of the test rig pulled back (Figure 3-2

4. PMMA placed into cardboard guide (Figure 3-2)

5. Sliding end allowed to return, applying pressure between transducers (Figure

3-2)

6. Cables connected from Signal generator to input transducers

7. Oscilloscope probe connected to one receiver wire, the other grounded

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8. Signal generator powered on and measured output observed on oscilloscope

9. Frequency adjusted as required

10. Voltage output of function generator slowly increased until sufficiently large

voltage observed on the receiver, and voltage recorded

11. Function generator powered off before handling PMMA to avoid contact with

harmful ultrasonic energy (See Chapter 5: Experimental Safety)

12. Sample moved a small amount; signal generator powered on once again and

measured output voltage and position of sample recorded

13. Step 12 repeated until optimal acoustic coupling achieved (highest voltage)

14. Frequency varied incrementally across desired range, recording output voltage

3.1.6 Automation

Ultimately, steps 1-14 above will need to be performed over a range of frequencies and

under a number of different conditions (Described fully in Chapter 5: Attenuation

Properties of PMMA). Preliminary tests revealed that to manually do this at a

reasonable resolution is very time-consuming, and prone to human error. Figure 3-3

shows a manually measured transmission spectra centred on the 2 MHz resonance of the

transducers.

Figure 3-3: Manual voltage measurements for a 20mm PMMA sample from 1 to 3 MHz

at a resolution of 0.1 MHz.

Clearly, considerable information is missing at this resolution. A computer program was

written to interface with both the function generator and oscilloscope, to automatically

sweep across the desired frequency range and log voltage readings from the

oscilloscope. Both devices were controlled remotely through a USB-serial connection.

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This was done to allow a larger number of data points to be collected on each test than

would be possible manually. Requirements for the software tool were:

• Interfaces with the oscilloscope and function generator

• User-selectable start and end frequencies, sweeping rate and voltage amplitude

• Logs the peak to peak voltage (Vpp) from the oscilloscope at each frequency step

3.1.6.1 Interfacing with Laboratory Equipment

Fortunately, both the oscilloscope and the function generator have been designed with

Interchangeable Virtual Instrument (IVI) drivers. Drivers for the function generator and

oscilloscope were downloaded from the Agilent® and Rigol® websites, respectively.

These drivers detect the hardware automatically when plugged into a PC, and assign

them an IVI address. The Agilent ® I/O Libraries suite (also available for free

download from the Agilent® website) provides a set of standard input and output

functionality for communicating with IVI devices. This includes functions to establish

connections to IVI-enabled hardware and send and receive pre-defined serial

commands. These work with not only the Agilent® function generator but also the

Rigol® oscilloscope, as both are designed to the IVI standard. This functionality is

provided in a number of programming languages, including Microsoft® C# .NETTM.

This was selected as the programming platform due to the author’s previous familiarity

with this development environment and the included graphical user interface (GUI)

editor which allows a user-friendly application to be developed quickly.

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3.2.1 Automation Software Tool

A software tool to automate the transducer characterisation and transmission tests was

developed and tested in light of the original requirements. In meeting those

requirements, a graphical user interface (GUI) was developed (Figure 3-4) that allows

the user to enter a number of parameters through simple text fields, open and close

connections with the oscilloscope and function generator and run the automated tests.

Measurements are logged automatically. Full application source code is provided in

Appendix D.1.

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3.2.1.1 User Parameters

As indicated on Figure 3-4, there are three sets of information required from the user in

order to define and set up an automated test. All input parameters are defined, along

with the values that each parameter can take in Table 6. Formal parameter definitions

and restrictions are given in Table 6, Appendix D.2.

Figure 3-4: Graphical user interface(GUI) of the automation software, showing

parameters for test run from 1-3 MHz in steps of 1 kHz at 2.5V amplitude. 1), 2) and 3)

indicate the parameters required to define a test as described in section 3.2.1.1.

1) Oscilloscope and function generator VISA addresses:

The IVI addresses of the oscilloscope and function generator must first be obtained

by plugging in the USB connections, opening the Agilent ® I/O Libraries suite and

observing the assigned addresses. These addresses are copied and pasted into the

text boxes for the two devices. The VISA address is a string of letter and numbers

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separated by colons. For reference, on the author’s PC the oscilloscope’s address

was ‘USB0%2391%5970%30D3090541%0%INSTR’. Pressing the ‘Set I/O’ button

will establish a connection with each device. The corresponding ‘Close I /O’ button

will become available upon successful connection.

2) Frequency sweep test parameters:

The user must then enter the following parameters to define an automated test:

• Start and end frequencies for the frequency sweep

• Size of the frequency steps between samples

• Peak to peak voltage amplitude of the function generator’s output

• Delay time between successive samples

3) Oscilloscope setup conditions:

The application developed takes advantage of the DS1204B oscilloscope’s ‘auto

scale’ feature rather than hard-coding in axis x and y axis scales. This increases the

tool’s flexibility, allowing it to be used under a range of measurement conditions

without any change in end-user behaviour required. Initially, this function was

invoked at the beginning of each test with the signal generator’s output conditions

set to the start conditions defined by the user.

However, this resulted in the scale settings not always being set appropriately for

the frequencies and voltages of a particular test. This occurred particularly in tests

where the frequency sweep began away from the transmitter transducer’s resonance

and passed over it during the course of the test, where larger voltages are measured.

The oscilloscope reports the value of MAX_INT (32767 Volts) when the waveform

is larger than the current scale settings allow to be displayed on the screen.

Conversely, with the scales set too large, accuracy of the measurements decreases as

the quantisation steps increase (Rigol®, 2010). This means inappropriate set scale

dimensions will result in significant data loss. The functionality was added to allow

the user to define the desired auto-scale conditions to be used at the beginning of a

test to address this. By selecting a frequency near resonance, and a voltage slightly

higher than will be used in subsequent tests, consistent and reliable auto-scaling was

achieved.

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3.2.1.2 Data Logging

For each frequency step, the peak to peak voltage of the oscilloscope is stored in a

comma separated values (CSV) file. These files will open natively in Microsoft® Excel

in the format shown in Figure 3-5.

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file. Each row represents a single sample.

3.2.1.3 Performance Assessment

The developed software tool was tested extensively and found to satisfy all required

design criteria. It successfully interfaces with both the oscilloscope and function

generator, allows the user to define the test they want to perform and sets both pieces of

hardware appropriately. Results are logged automatically into a user-friendly format.

The tool allows an arbitrarily large number of data points to be collected for each test,

enabling a complete and accurate picture of the frequency-dependant behaviour of the

device under test. A comparison between the manual measurements presented

previously in Figure 3-3 and those made possible by the automation software are

compared in Appendix D.3, Figure 6-11.

The upper speed limit at which the automated tests can be performed was explored

experimentally. Times between samples greater than 100ms produced reliable,

repeatable results. At rates faster than this, the time taken to request and retrieve a

voltage reading from the oscilloscope begins to exceed this interval on occasion, with

reported values defaulting to MAX_INT. As the oscilloscope is operating in an

averaging mode in these tests, it is also necessary to ensure that sufficient time is being

allowed at each frequency for the voltage to reach a steady state over 8 samples. If it is

not, then peaks at resonance in particular will become flattened. This is not a limitation

of the software, but a physical limitation of the transducers under test and the

measurement equipment used.

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3.2.2 Electrical Noise and Cross-Talk

The measured voltage signal in the transmission tests was found to contain a large

common mode 50Hz signal as well as the desired 2MHz. This noise had a peak to peak

voltage (VPP) of up to 3.5V, dominating the signal at lower voltages and when coupled

through any length of PMMA. An electromagnetically shielded box was fabricated by

covering a cardboard box in aluminium foil which was then grounded (Celozzi, Rodolfo

& Lovat 2008). The entire test rig was placed inside this box in an attempt to eliminate

the unwanted signal. Repeating the tests showed that the 50Hz signal had been

eliminated below any detectable level.

A clear sine wave at 2MHz could then be measured at the receiver when driving the

transmitter, even at low voltages and through lengths of PMMA up to the largest

available length (50mm). However, the signal was still obscured by approximately

20mVpp of what appeared to be random noise. Setting the oscilloscope to a time-

averaging mode of data acquisition eliminated this completely, confirming that this was

in fact random noise and not a deterministic signal.

To mitigate this in the present tests, the decision was made to apply a constant AC

signal to the test specimens and allow the measured voltage to reach a steady-state. This

is in contrast to reported attenuation testing methods, where short ultrasonic pulses are

typically used (Treiber et al. 2009). However, this approach is consistent with the

operating mode of the ultimate PMMA acoustophoresis devices being developed at

UWA for which this test has been designed. A sample size of 8 samples was found to be

sufficient to eliminate the random noise entirely, reducing the noise floor to the

measurement limit of the oscilloscope (4mV). All subsequent transmission tests were

performed in this time-averaging mode to allow more precise voltage values to be

obtained.

3.2.3 Acoustic and Electrical Coupling through Air

In attenuation tests, the literature reports that there is often a ‘reference’ or ‘background

signal level, measured in the absence of a test specimen which must be subtracted from

the total measured signal in order to obtain only the sample’s contribution to the

transmitted signal (Dupuis et al. 2009). When powering the transmitter transducer, a

clear signal was observed on the receiver with no physical contact between the two

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transducers. This represents a combination of electrical and acoustic signals that

together comprise the ‘reference signal’ for the present experimental setup.

An experimental investigation was undertaken to characterise the relative contributions

of electrical cross-talk and acoustic coupling to this reference signal. In order to

minimise electrical cross-talk, the wires leading to both transducers were twisted

together and shielded as close to the transducers as possible within the experimental

configuration (Celozzi, Rodolfo & Lovat 2008). This reduced the signal level, but did

not eliminate it. Subsequently, transmission tests were performed in the absence of a

test specimen to characterise this reference signal as a function of frequency over the

target range of 1 to 3 MHz. These tests were repeated at separation distances of 5-

50mm. A representative sample of these results is given in Figure 3-6, with full test

results in Appendix E.2.

Figure 3-6: Representative results of the measured reference signal due to acoustic and

electromagnetic coupling through air at three distances.

Tests were repeated with the receiver replaced by a roughly equivalent electronic circuit

to measure the energy coupled electronically in the absence of any acoustic signal

(Figure 3-7). This circuit simply consisted of a resistor and capacitor in parallel

(Ferroperm Piezoceramics: A/S ® 2011) as shown in Figure 6-12 of Appendix E.1.

Figure 3-7 shows a clear peak around the nominal 2 MHz resonance of the transducers

in both the electrical and acoustic components of the signal. Electrical coupling

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accounts for roughly 20% of the reference signal at resonance, and is not subject to the

oscillations observed in the combined acoustic/electric signal. The estimated electrical

signal surpasses the reference signal at higher frequencies, however, this is not possible,

which indicates that the capacitance and resistance values used in the circuit do not

accurately model the transducer in this region. The voltage magnitude in these tests is

very small, peaking at less than 20mV peak to peak. This is due to the poor acoustic

transmission between air and the transducers, and effective electromagnetic shielding.

Dupuis et al. (2009) note that the reference signal in attenuation tests typically falls into

the noise floor of the detector. This is true of the current experimental setup when not

operating in a time-averaging mode of operation.

Figure 3-7: The electrical and acoustic components of the reference signal at 5mm

separation, receiver transducer has been replaced with an equivalent electronic circuit.

3.2.4 Impact of Bragg Gratings

Although the Bragg gratings in PMMA acoustophoresis devices at UWA are only

shallow compared to the total device depth (65�m compared to the 1360�m resonator),

successful reflection has been achieved at similarly small depth ratios in optics (Hill &

Meltz 1997). The transmission tests described here will allow future work to investigate

the ability of Bragg gratings to influence the acoustic transmission properties of a length

of PMMA using the setup shown in Figure 3-8. A number of 20± 0.5mm PMMA

lengths have been cut by the Mechanical and Materials Engineering workshop into

which distributed Bragg reflectors comprised of between 1 and 7 fluid-filled channels

should be fabricated in future work. Comparing the transmission responses of these

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different configurations will allow the impact of Bragg gratings on acoustic energy

transmission within the devices to be measured and characterised, leading to more

optimal Bragg reflector designs.

Figure 3-8: Test designed for future work to investigate the influence of Bragg gratings

on acoustic transmission. The sample shown has seven periodic variations.

3.2.5 Improving Contact Area

Tapered attachments to the test rig as shown in Figure 3-9 may assist in achieving a

higher level of acoustic energy transfer into PMMA devices. The impact on transducer

surface areas in contact with the PMMA should also be investigated in future work.

Figure 3-9: Concept for increasing coupling efficiency into sample in future work.

3.2.6 Characterising Transducers

Doncon (2010) found that transducers of the same type can have significantly different

frequency responses. Measuring these allows the transducers’ correct operation to be

verified, those with the most ideal characteristics to be selected from a batch and to

predict experimental results more accurately. Previously at UWA, this was done using a

network analyser borrowed from the department of electrical engineering at UWA, and

access to this equipment is limited (Doncon 2010). The automation software developed

for the attenuation tests was expanded to fulfil this role.

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When a piezoelectric transducer is driven at its resonance at fixed voltage, its

impedance is lowered and current drawn from the power supply increases (Ferroperm

Piezoceramics: A/S ® 2011). A Jaycar QM-1538 multimeter was placed in series

between the power supply and the amplifier circuit driving the piezoelectric transducer

to measure the current drawn. This multimeter allows data logging to a PC through a

USB serial cable and the provided Data LoggerTM software. By synchronising the

automation tool previously discussed with Data Logger, frequency response plots of

transducers were obtained (Figure 3-6).These proved very repeatable (Figure 3-10) with

93.2% of data points falling within ± 1mA (0.69% of the current drawn at resonance)

between successive tests. The larger errors all occurred around resonance, where the

current drawn was changing rapidly. Sweeping frequencies at a slower rate may

improve the accuracy, however, the performance presented here was deemed sufficient

for the present work. The amplifier driving the transducer approaches its gain-

bandwidth product limit at approximately 4.7MHz. This explains the erratic behaviour

above this frequency in Figure 3-10.

3.2.6.1 Characterising the Attenuation Test Transducers

The frequency responses of the transmitter and receiver transducer used in the

attenuation tests were obtained. The responses of the two transducers was found to

deviate significantly around the nominal resonance of 2 MHz (Figure 6-12), with only

the transmitter exhibiting a clear resonant peak. After characterising the two transducers

individually, attempts were made to determine the combined resonance of the two

transducers when placed ‘back to back’. A second transducer was mechanically

attached to the first using coupling paste and separated by a small piece of silicon which

isolates the two transducers electrically. The silicon is expected to have minimal impact

on acoustic energy transmission due to its good acoustic matching with the transducers.

This is representative of the configuration to be used ultimately in the PMMA

attenuation tests.

Figure 3-11 shows that measured transducer response is clearly impacted by the

presence of the second transducer. The resonant peak has been flattened and the overall

current drawn is lower. This may be due to the electro-mechanical response of

transducer B, the mechanical loading of the system due to the extra mass of the

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transducer or both. The same test was repeated with a length of PMMA between the two

transducers (Figure 3-11). The result is similar to the back to back tests, but with the

resonant peak reduced further still. These preliminary results are inconclusive and

should be explored in future work.

Figure 3-10: Automated transducer characterisation test results for two consecutive

runs. Very good repeatability observed, with the two runs distinguishable visually only

at resonance and above the operating frequency of the amplifier.

Figure 3-11: Measured frequency response of two PZ27 transducers (A and B)

individually, and the combined response tested ‘back to back’.

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Chapter 4: Experimental Safety

4.1 Laboratory Safety Training

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All experimental work was performed in the Sensors and Advanced Instrumentation

Lab (SAIL) at UWA (room G55). This room contains a variety of specialty equipment,

much of which has accompanying inherent safety issues. It is necessary that all

personnel working in such an environment are aware of all products and equipment in

use, as well as the relevant safety procedures. At the beginning of the semester, a safety

induction was conducted by area coordinator Adrian Keating and attended by all

students working in the lab. The induction covered:

• Personal protective equipment (PPE)

• Instrument documentation and equipment usage journals

• Location of first aid kits

• Location and correct usage of fire extinguishers and alarm switches

• Location of safety showers and eye basins

• Fire and first aid officer contact details

• Proper labeling of hazards

• General laboratory and safety procedures

• Emergency and evacuation procedures

At the conclusion of the induction a ‘Project Safety Induction Form’ was signed by the

author and submitted to the School of Mechanical Engineering to indicate that all

appropriate training had been undertaken to enable work to be performed safely in the

SAIL without supervision. In addition to the general safety procedures, safety and

correct usage training was performed for the following equipment and procedures

specific to the present work:

• Carver Inc® 3889 automatic hydraulic press

• Olympus® BX51TM microscope

• PCB etching

• Global Machinery Company® (GMC) LSR13DP drill press

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4.2 Project-Specific Risks

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A number of risks were identified related to the fabrication of PMMA microfluidic

devices and the two experimental investigations undertaken (particle separation and

PMMA transmission). A risk and mitigation matrix has been constructed according to

the UWA Safety & Health Risk Management Procedure (University Safety Committee

2011), with a ‘score’ assigned to the consequences, likelihood and exposure levels

involved with each risk (Table 8, Table 9 and Table 10 in Appendix F:, respectively).

The product of these scores determines the severity of the risk and the level of

preventative control measures that need to be in place to mitigate it. All identified risks

are listed below, and full details of the risk assessment performed and the control

strategies put in place to mitigate these risks are presented in Table 7 of Appendix F.1.

4.2.1 Chemicals

The following hazardous chemicals are used in the fabrication of PMMA devices:

Ammonium Persulphate, Sodium hydroxide, Ethanol, Acetone, Isopropanol, Epoxy

glue.

4.2.2 Hydraulic Press

A hydraulic hot press is used to emboss the fluid channels onto PMMA. This piece of

equipment generates considerable heat and applies a large force between its platens.

This poses potential risks of burns and crushing injury to operators of this equipment. If

used inappropriately, samples in the press also have the ability to become airborne,

creating a projectile risk also. It is equipped with a safety shield and interlocks which

will disable the press when the shield is not in place. The platens will remain hot after

the press has been shut down.

4.2.3 UV Light Box

During PCB fabrication, an ultraviolet (UV) light box is used to expose the design onto

photoresist. Operating this light with the box open, or with any cracks/holes in the box

would expose the operator to damaging UV light.

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4.2.4 Etching Tank Heater

The glass casing of the heater within the etching tank in the SAIL has previously

shattered when setting the heater temperature too high or it is handled roughly (Godfrey

2010). There is a risk of electrocution if the heater is operated whilst broken.

4.2.5 Drill Press

A drill press is used to create holes in the PMMA devices in order to attach the inlet and

outlet tubing.

4.2.6 Ultrasonic Transducer

Direct contact with an ultrasonic source can cause heating and cavitation to occur

(Health Canada 2008). This can result in tissue damage.

4.2.7 Soldering

Wires were soldered to the piezoelectric transducers. Soldering irons get very hot and

are a burning hazard. The solder used was not lead-free and its use also poses a risk.

4.2.8 Microbeads

The polystyrene microbeads used during particle separation experiments were 3�m in

diameter and can cause irritation of the eyes and skin. They can also cause irritation to

the respiratory system if inhaled. However, the microbeads are packaged in solution and

unlikely to become airborne. When pumping a fluid through the microfluidic devices

during particle separation experiments, there is the potential for the tubing to ‘blow off’

of the syringe tip causing the microbead solution to squirt out.

4.2.9 Syringes

Although the syringes used have ‘blunt’ tips, there is still the potential for cuts resulting

from careless handling. There is also the potential for mistaking the contents of a

syringe, which could lead to contamination of the experiments.

4.2.10 Lasers

Lasers were in use by fellow students working in the SAIL throughout the year. These

have the potential to cause eyesight damage when viewed directly, or through a

microscope.

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4.2.11 Power Supply, Signal Generator and Faulty Lab Equipment

The DC power supply and signal generator used during the experimental investigations

have the potential to expose the operator to electrical shock if used incorrectly.

4.3 Other Safety Issues

4.3.1 Workshop Safety

Cutting of the PMMA samples was performed by the UWA Mechanical and Materials

Engineering Workshop. PMMA is not considered a hazardous material, and as such

these cuts did not present any danger to the workshop staff outside of the normal

dangers associated with using their machinery. No extra precautions beyond those

already existing in the workshop were required.

4.3.2 Incidents

No incidents or injuries eventuated during the current project work. In the event of such

an occurrence, an incident report form needs to be submitted to the UWA health and

safety office within 24 hours.

4.3.3 Implementation Safety Issues

The overall aim of ongoing research at UWA, of which the current project is a part, is to

produce an integrated acoustophoresis unit that can be used by the general public.

Future work will need to ensure it is not possible for end users to be electrocuted. This

should be easily safeguarded against by ultimately integrating the power supply to the

transducer within the unit. Another requirement will be to avoid ultrasonic energy from

reaching the end user due to the potentially damaging effects described previously.

Designing the final system so that a material with very low acoustic impedance (such as

air) is placed between the transducer and the end-user will ensure very little ultrasonic

energy reaches them.

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Chapter 5: Attenuation Properties of PMMA

5.1 Experimental Method and Data Extraction

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5.1.1 Measuring the Attenuation Coefficient

Because of the large compositional differences between PMMA samples and resultant

variation in measured � values reported in the literature, an experimental investigation

was undertaken to determine the attenuation coefficient of the PMMA in use for

microfluidics at UWA. A series of tests were performed on PMMA samples of varying

length and data collected using the automatic tests described in ‘Chapter 3: Acoustic

Transmission Test .’

This section details the parameters used in these tests and the process by which the raw

data obtained is used to calculate the attenuation coefficient, �, of the PMMA used in

microfluidics research at UWA. Subsequent investigations into the acoustic coupling

efficiency and factors affecting it are also presented. Finally, experiments are described

for the quantitative assessment of the impact of fluid-filled Bragg gratings on the

acoustic properties of PMMA.

5.1.2 Attenuation of a Plane Wave

In physical terms, the attenuation coefficient � describes how quickly the intensity of a

sound wave is reduced as it passes through a medium. As ultrasound travels through

PMMA, the amplitude of the acoustic intensity is expected to decay exponentially

according to the equation for a decaying plane wave (Treiber, 2009). That is:

� &# � &'()*� 4.5�

Where:

I1 = Output wave intensity at distance x mm travelled through PMMA

I0 = Input power intensity at distance = 0 mm

� = Attenuation coefficient for PMMA, in Nepers per mm (Np/mm)

Note: A neper is a unit expressing the ratio of two numbers as a natural logarithm

(Treiber et al. 2009).

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Sound intensity is defined as acoustic power per unit cross-sectional area through a

medium. The cross-sectional area is held constant in the present tests, and acoustic

power is proportional to the square of the acoustic pressure (Kuttruff 2007). Acoustic

pressure is proportional to the mechanical strain induced in the piezoelectric transducer

by the sound wave, which in turn is proportional to the voltage it produces (Ferroperm

Piezoceramics: A/S ® 2011). As all other parameters are assumed constant for each test,

the decay of voltage amplitude (V) will vary proportional to the square of the acoustic

attenuation value (�) for sound intensity. So, equation (5) with respect to the measured

voltage becomes:

� �# � ��'()*�� 4/5�

Or, more naturally:

� �# � �'(�)*�� 4'5�

Plotting the logarithm of the measured voltages as a function of distance the acoustic

wave has travelled through PMMA, the 2� coefficient for PMMA can be obtained

directly. This measurement will be performed at a number of frequencies centred on

2MHz.

5.1.3 Test Specimens

The PMMA thickness for these test samples was chosen to be equal to the thickness of

the sheets from which acoustophoresis devices have previously been fabricated:

1.36mm. Lengths were cut from 5-50mm in 5mm increments to a nominal tolerance of

± 0.5mm at the Mechanical and Materials Engineering Workshop. A comparison

between the nominal and actual lengths shows that the cut lengths fell comfortably

within this tolerance (measured lengths shown in Table 11, Appendix G.1). The widths

were arbitrarily chosen to be approximately 16.5mm, as this allowed three samples to be

fabricated from each existing 50mm PMMA square readily available in the SAIL. This

dimension was not expected to have any influence on the attenuation results. The

smallest available transducers (6x6x1mm Pz27) were chosen for these tests to maximise

the fraction of the total available surface area of the transducers in contact with the

PMMA. The transmitter was powered with a sine wave using the signal generator and

amplifier arrangement described above for the particle separation tests.

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5.1.4 Attenuation Tests

Using the automatic transmission tests described in Chapter 3:, measurements were

performed over a frequency range of 1-3 MHz at a resolution of 1 kHz. By fixing the

frequency and taking the corresponding data points from each transmission test, a plot

can be drawn from which the acoustic attenuation is obtained at that frequency as

described in section 5.1.2. Frequencies were arbitrarily fixed at 0.2 MHz intervals over

the tested range to obtain 11 experimental values of �.

5.1.5 Coupling efficiency

Acoustic attenuation tests are particularly prone to variations in the coupling conditions

between tests, as the samples are replaced for each measurement. An investigation was

started into the manner in which the coupling of ultrasonic energy into and out of

PMMA is affected by use of coupling paste and a force backing.


5.2.1 Attenuation Coefficients

A representative sample of transmission tests performed on PMMA samples from 5 –

50mm in length is given in Figure 5-1 and full results are in Appendix G.2.

Figure 5-1: Measured transmission spectra between 1 and 3MHz for four PMMA

lengths. Fixing the frequency at 1.8 MHz gives data points for plot in Figure 5-2.

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Fixing the frequency (for example at 1.8 MHz as in Figure 5-1), the intersection with

each transmission test corresponds to a data point on the plot of measured output

voltage variation with distance (Figure 5-2) for that frequency.

Figure 5-2: Measured output decreases exponentially with distance through PMMA.

Figure 5-2 shows that at 1.8 MHz, the voltage decrease with distance fits an exponential

curve very accurately. Plotting the natural log of the same data gives a linear regression,

the gradient of which is equal to 2� in units of Np/mm according to equation (7). The

linear gradients were measured at 0.2 MHz intervals from 1MHz to 3 MHz; values for �

were calculated from these and then converted to the standard units of Np/m. Results

are shown in Table 1 . All plots from which attenuation values have been calculated are

presented in Appendix G.3.

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Table 2: Summary of Measured attenuation coefficients for PMMA.

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Taking the average of the measured values, excluding the outliers at 2.8 and 3 MHz, the

attenuation coefficient of the PMMA tested, it was found that:

� = 25 ± 4.25 Np/m.�

5.2.2 Linear Increase with Frequency

The value of � is known to increase linearly with frequency in PMMA (Treiber et al.

2009) so it is usual to compare not the attenuation coefficient, but the attenuation-

wavelength product (��) which is a constant as frequency varies (Asay, Lamberso &

Guenther 1969). Plotting the measured � values as a function of frequency, the expected

linear behaviour can be observed for data points between 1.2 and 2 MHz. The gradient

obtained from these points corresponds to a 10.25Np/m increase in attenuation per

MHz. This compares reasonably to the increase of 12.8Np/m reported by Treiber et al.

(2009). Assuming this variation in attenuation across all frequencies, an estimate for ��

was obtained.

Figure 5-3: Data points between 1.2 and 2 MHz exhibit the expected linear increase in

attenuation with frequency.

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Considering the first term of the linear regression, the attenuation per wavelength is

defined as:

� +, � -.��/ 0 1/� (8)

(Treiber et al. 2009). The frequency terms cancel to give a constant, and substituting the

value for the speed of sound in PMMA as 2590m/s (Doncon 2010) gives:

� 23 � 4� 45678 (9)

5.2.3 Comparison with Literature

In the literature, measured values for �� vary from as low as 0.02Np up to 0.036 Np

(Treiber et al. 2009). This large variation is attributed not to differences in measurement

techniques, but to compositional variations between PMMA samples tested (Treiber et

al. 2009). The value measured here falls comfortably within this range. Only a single

explicit attenuation value was able to be located in the literature for 2MHz, and this was

22.92 NP/m by Treiber et al. (2009). Perhaps surprisingly, given the extremely large

variations reported for the �� product (Hartmann & Jarzynsk 1974), (Asay, Lamberso &

Guenther 1969) the attenuation coefficient of 25 Np/m measured in the present work

agrees with this value to within 9%.

5.2.4 Reliability

The attenuation value of 25±4.25 Np/m presented for PMMA at 2 MHz is considered

reliable. It was obtained by averaging 9 separate measurements at varying frequencies

centred around 2 MHz. The effect of a linear increase in attenuation with frequency will

be negated by an equal number of data points included both above and below 2 MHz. In

contrast to this, the +, product of 0.027Np presented will need to be verified in future

tests. This figure was obtained from only a small portion of a single data set (see Figure

5-3), so it is not considered robust. It is presented here as a starting point only, with a

more complete investigation into variation in acoustic attenuation of PMMA with

frequency required in future work. Internal reflections within the PMMA causing

oscillations in the measured voltage output (See 5.2.5, below) are identified as a major

source of error in these measurements. Eliminating or allowing for these oscillations in

future measurements will allow more representative results to be obtained throughout

the frequency spectrum. Ideally, the receiver transducer should have a resonant

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frequency much higher than the transmitter as measurements taken far below resonance

are more consistent and reliable (Stansfield 1991). This explains the poor adherence to

the expected linear increase in measured attenuation values as frequencies exceed the

receiver’s 2 MHz resonance.

5.2.5 Internal Reflections

The frequency spectra of measured PMMA samples oscillations can be observed in the

measured voltages (Figure 5-1, Figure 5-4, Figure 5-5). These oscillations increase in

frequency but decrease in magnitude at longer PMMA lengths. It is suspected that these

oscillations correspond to internal reflections within the sample. The frequency is

predicted to be a function of the time taken for the wave to travel within the PMMA

from one end to the other and back again. This was not explored further due to time

limitations but should be the focus of future work. Removing these oscillations will

allow more consistent and accurate attenuation values to be measured.

5.2.6 Coupling Efficiency

A preliminary investigation was performed into the impact of various experimental

conditions on acoustic coupling efficiency. Figure 5-4 shows the impact of removing

all coupling paste between the two transducers and the PMMA.

Figure 5-4: Transmission spectra of four separate tests performed on a 20mm PMMA

sample, one performed ‘dry’ without any coupling paste.

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Figure 5-5 shows the impact of removing the force applied between the two transducers.

Figure 5-5: Removing the spring force between the two transducers negatively impacts

acoustic coupling.

It can be seen that both of these parameters are of critical importance in efficiently

transferring acoustic energy into and out of the PMMA. The absence of either one

significantly reduces the acoustic energy coupled into the PMMA. Future work should

perform a thorough investigation into these issues to quantify the variation in coupling

efficiency between tests, assigning ‘coupling coefficient’ to the combined impact of all

factors affecting coupling.

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Chapter 6: Conclusions & Future Work

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6.1 Conclusions and Future Work

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This project achieved its overall aim of making a substantial contribution towards

acoustically efficient ultrasonic particle separation devices in the ongoing research effort at

the University of Western Australia. All of this project’s original objectives have been

achieved.

The key outcomes presented in this project are:

• Fluid channels reduced in width by 38 �m in light of issues identified with design and

fabrication process

• Experimental setup for measuring acoustic transmission and attenuation properties

designed, constructed and evaluated

o Software tool written to automate these tests

• Acoustic attenuation coefficient � of PMMA measured experimentally

o 25 ± 4.25 Np/m

o Compares favourably to literature (Treiber et al. (2009) report a value of

21.88)

Preliminary investigations conducted in this project identified and laid the groundwork for a

large body of future work, described throughout this paper. Of particular importance are:

• Transmission test setup and software should be leveraged in future work to investigate:

o Impact of Bragg gratings on acoustic transmission through PMMA (Section 3.2.4)

o Factors affecting acoustic coupling, and how this varies between tests (Section 5.2.6)

o Impact of internal reflections within the PMMA on measured attenuation coefficient

(Section 5.2.5)

• Tests of Doncon (2010) should be repeated with the fabrication improvements

implemented here, and impact on particle separation behaviour gauged

• Thorough investigation into the coupling of acoustic energy and impact of Bragg gratings

into the lateral mode when fired in from beneath the device should be conducted:

o Configuration currently used in final devices, so understanding acoustic

behaviour in this mode of operation is essential

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• Particle separation should be attempted mounting transducer on the side of the

PMMA device, not underneath it

o Increased acoustic efficiency through Bragg gratings may allow this to

become a viable alternative

o Previously, losses have been too great

• Investigate impact of varying Bragg grating depth

o Deeper gratings theoretically offer better reflection

o PCBs available with varying copper thicknesses to allow gratings of different

depths to be fabricated and compared

Through the completion of this project’s objectives and future work identified, significant

progress has been made towards gaining a better understanding of the impact Bragg gratings

have on acoustophoresis in PMMA devices. This understanding will guide the design of more

efficient resonator devices, towards the ultimate objective at UWA of achieving a cheap,

portable particle separator for the analysis of human breast milk.

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References

Adobe System Incorporated 1999, Postscript Language Reference. Available from:

http://partners.adobe.com/public/developer/en/ps/PLRM.pdf. [30 September 2011]

Asay, JR, Lamberso, DL & Guenther, AH 1969, 'Pressure and temperature dependence of

acoustic velocities in polymethylmethacrylate', Journal of Applied Physics, vol. 40, no. 4, pp.

1768-1775.

Celozzi, S, Rodolfo, A & Lovat, G 2008, Electromagnetic Shielding, Wiley-Interscience:

IEEE Press, Hoboken, N.J.

Chen, CY & Chi, S 1993, 'Attenuation and fluorescence characteristics of optical signals

propagating in an erbium-doped fiber', Ieee Photonics Technology Letters, vol. 5, no. 9, pp.

1020-1022.

Chen, M 2011, 'Frequency-tunable terahertz electromagnetic-pulses generation based on an

optical fabry-perot microresonator with variable birefringence material', Microwave and

Optical Technology Letters, vol. 53, no. 12, pp. 2879-2882.

Doncon, AW 2010, 'Ultrasonic Particle Separation in a Microfluidic Device for Lab-on-a-

Chip Analysis of Biological Fluids', School of Mechanical Engineering,University of

Western Australia, Perth.

Duffy, DC, McDonald, JC, Schueller, OJA & Whitesides, GM 1998, 'Rapid prototyping of

microfluidic systems in poly(dimethylsiloxane)', Analytical Chemistry, vol. 70, no. 23, pp.

4974-4984.

Dupuis, A, Allard, JF, Morris, D, Stoeffler, K, Dubois, C & Skorobogatiy, M 2009,

'Fabrication and THz loss measurements of porous subwavelength fibers using a directional

coupler method', Optics Express, vol. 17, no. 10, pp. 8012-8028.

�� ./

Effenhauser, CS, Bruin, GJM, Paulus, A & Ehrat, M 1997, 'Integrated capillary

electrophoresis on flexible silicone microdevices: Analysis of DNA restriction fragments and

detection of single DNA molecules on microchips', Analytical Chemistry, vol. 69, no. 17, pp.

3451-3457.

El-Ali, J, Sorger, PK & Jensen, KF 2006, 'Cells on chips', Nature, vol. 442, no. 7101, pp.

403-411.

El Boudouti, EH, Djafari-Rouhani, B, Akjouj, A & Dobrzynski, L 2009, 'Acoustic waves in

solid and fluid layered materials', Surface Science Reports, vol. 64, no. 11, pp. 471-594.

Ferroperm Piezoceramics A/S ® 2011, Pz27 (Navy II), Ferroperm Piezoceramics A/S ®.

Available from:

<http://app04.swwwing.net/files/files/Pz27%2520Datasheet.pdf> [October 2011].

Glynne-Jones, P, Boltryk, RJ, Hill, M, Harris, NR & Baclet, P 2009, 'Robust acoustic particle

manipulation: A thin-reflector design for moving particles to a surface', Journal of the

Acoustical Society of America, vol. 126, no. 3, pp. EL75-EL79.

Godfrey, CM 2010, 'High Resolution Separation of Microparticles by Size Using

Microfluidics', School of Mechanical Engineering, University of Western Australia, Perth.

Grenvall, C, Augustsson, P, Folkenberg, JR & Laurell, T 2009, 'Harmonic Microchip

Acoustophoresis: A Route to Online Raw Milk Sample Precondition in Protein and Lipid

Content Quality Control', Analytical Chemistry, vol. 81, no. 15, pp. 6195-6200.

Hagsater, SM, Jensen, TG, Bruus, H & Kutter, JP 2007, 'Acoustic resonances in microfluidic

chips: full-image micro-PIV experiments and numerical simulations', Lab on a Chip, vol. 7,

no. 10, pp. 1336-1344.

Hansen, C & Quake, SR 2003, 'Microfluidics in structural biology: smaller, faster... better',

Current Opinion in Structural Biology, vol. 13, no. 5, pp. 538-544.

�� .'

Harris, NR, Keating, A & Hill, M 2010, 'A Lateral Mode Flow-through PMMA Ultrasonic

Separator', APCOT2010 Perth, Western Australia.

Hartmann, B & Jarzynsk.J 1974, 'Immersion apparatus for ultrasonic measurements in

polymers', Journal of the Acoustical Society of America, vol. 56, no. 5, pp. 1469-1477.

Health Canada 2008, Guidelines for the Safe Use of Ultrasound, Health Canada, Government

of Canada. Available from:

<http://www.hc-sc.gc.ca/ewh-semt/pubs/radiation/safety-code_24-securite/health-sante-

eng.php> [September 2011].

Hill, KO & Meltz, G 1997, 'Fiber Bragg grating technology fundamentals and overview',

Journal of Lightwave Technology, vol. 15, no. 8, pp. 1263-1276.

Kone, I, Domingue, F, Reinhardt, A, Jacquinot, H, Borel, M, Gorisse, M, Parat, G, Casset, F,

Pellissier-Tanon, D, Carpentier, JF, Buchaillot, L & Dubus, B 2010, 'Guided acoustic wave

resonators using an acoustic Bragg mirror', Applied Physics Letters, vol. 96, no. 22.

Kuttruff, H 2007, Acoustics: An Introduction, Taylor & Francis, Hoboken.

Lakin, KM, McCarron, KT & Rose, RE 1995, 'Solidly mounted resonators and filters', 1995

Ieee Ultrasonics Symposium Proceedings, vols. 1 and 2, pp. 905-908.

Laurell, T, Petersson, F & Nilsson, A 2007, 'Chip integrated strategies for acoustic separation

and manipulation of cells and particles', Chemical Society Reviews, vol. 36, no. 3, pp. 492-

506.

Marksteiner, S, Kaitila, J, Fattinger, GG, Aigner, R & Ieee 2005, 'Optimization of acoustic

mirrors for solidly mounted BAW resonators', 2005 IEEE Ultrasonics Symposium, vols. 1-4,

pp. 329-332.

Nilsson, A, Petersson, F, Jonsson, H & Laurell, T 2004, 'Acoustic control of suspended

particles in micro fluidic chips', Lab on a Chip, vol. 4, no. 2, pp. 131-135.

�� .6

Ohtsuki, A, Ohshima, S & Itoh, D 2001, 'Analysis on characteristics of a C-shaped constant-

force spring with a guide', Jsme International Journal Series C-Mechanical Systems Machine

Elements and Manufacturing, vol. 44, no. 2, pp. 494-499.

Othonos, A 1997, 'Fiber Bragg gratings', Review of Scientific Instruments, vol. 68, no. 12, pp.

4309-4341.

Pamme, N 2007, 'Continuous flow separations in microfluidic devices', Lab on a Chip, vol. 7,

no. 12, pp. 1644-1659.

Paschotta, R 2008, Encyclopedia of Laser Physics and Technology: Volume 1, Wiley-VCH,

Weinheim.

Rhee, M & Burns, MA 2008, 'Microfluidic assembly blocks', Lab on a Chip, vol. 8, no. 8, pp.

1365-1373.

Sears, FM & Bonner, BP 1981, 'Ultrasonic-attenuation measurement by spectral ratios

utilizing signal-processing techniques', Ieee Transactions on Geoscience and Remote

Sensing, vol. 19, no. 2, pp. 95-99.

Squires, TM & Quake, SR 2005, 'Microfluidics: Fluid physics at the nanoliter scale', Reviews

of Modern Physics, vol. 77, no. 3, pp. 977-1026.

Stansfield, D 1991, Underwater Electroacoustic Transducers, Peninsula Publishing, Los

Altos Hills.

Stone, HA, Stroock, AD & Ajdari, A 2004, 'Engineering flows in small devices:

Microfluidics toward a lab-on-a-chip', Annual Review of Fluid Mechanics, vol. 36, pp. 381-

411.

Tan, AM, Rodgers, K, Murrihy, JP, O'Mathuna, C & Glennon, JD 2001, 'Rapid fabrication of

microfluidic devices in poly(dimethylsiloxane) by photocopying', Lab on a Chip, vol. 1, no.

1, pp. 7-9.

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Terry, SC, Jerman, JH & Angell, JB 1979, 'Gas-chromatographic air analyzer fabricated on a

silicon-wafer', Ieee Transactions on Electron Devices, vol. 26, no. 12, pp. 1880-1886.

Townsend, RJ, Hill, M, Harris, NR & White, NM 2006, 'Investigation of two-dimensional

acoustic resonant modes in a particle separator', Ultrasonics, vol. 44, pp. 467-471.

Treiber, M, Kim, J-Y, Jacobs, LJ & Qu, J 2009, 'Correction for partial reflection in ultrasonic

attenuation measurements using contact transducers', Journal of the Acoustical Society of

America, vol. 125, no. 5, pp. 2946-2953.

Tsuda, H 2006, 'Ultrasound and damage detection in CFRP using fiber Bragg grating

sensors', Composites Science and Technology, vol. 66, no. 5, pp. 676-683.

University Safety Committee 2011, UWA Safety & Health Risk Management Procedure,

Safety & Health, University of Western Australia. Available from:

< http://www.safety.uwa.edu.au/safety_management> [October 2011]

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Appendix A: Microfluidics Background

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Appendix A.1 Comparison Of Microfluidic Particle Separators

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Laurell, 2010); (Pamme, 2007) via Doncon (2010))

Appendix A.2 Acoustic Properties of Common Microfluidic Materials

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Table 4: Acoustic properties of microfluidic device materials (Kutruff 2007; Laurell,

Petersson & Nilsson 2007

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Appendix A.3 Test Parameters of Doncon (2010)

Transducer size: 12×12×1mm

Number of Bragg gratings

each side of fluid channel: 7

Microbead diameter 3 �m

Flow rate 3�L/min

Drive Frequency 2.05 MHz

Equivalent Channel Width 1 Wavelength

AC Input Voltage 12.6Vpp

Aluminium Spacer 10×10×5 mm

Coupling Paste Unick® silicone heat transfer

compound

Table 5: Experimental configuration in which Doncon (2010) observed particle separation

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Appendix B: Fabrication Process

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Appendix B.1 Fabrication Process: Re-produced from Doncon (2010)

The fabrication process to be used has already been established by Professor Keating, Dr.

Harris and Christopher Godfrey (undergraduate student, School of Mechanical and Chemical

Engineering, UWA) (Godfrey, 2010; Harris, Keating, & Hill, 2010). The process can be

separated into two distinct stages: mould fabrication and device fabrication, as illustrated in

Figure 6-1.

Figure 6-1: The mould and device fabrication processes.

6.1.1 Mould Fabrication

A printed circuit board (PCB) was used as the mould to imprint the PMMA. The method

chosen to etch the PCBs was based upon the equipment available in The Sensors and

Advanced Instrumentation Laboratory (SAIL), School of Mechanical and Chemical

Engineering. Christopher Godfrey produced a set of instructions for etching PCBs using this

equipment (Godfrey, 2010). Using experiences from this project more detail was added to

these instructions and some parameters were changed in order to achieve a better result. The

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revised instructions are in appendix A (note: Not included here, MR). The instructions are

now included in the ‘Safety Procedures and Operating Guide’ for SAIL.

The first step to etch the PCB was to print a mask onto a transparency. This was initially

done using a laser printer and a standard sheet of overhead transparency. The result was

analysed under a microscope and the quality was deemed not accurate enough to produce a

mould. Masks were reprinted using a local specialist printing company – Type Tamer. Type

Tamer used a high quality printing process to print the masks onto a bromide transparency.

A comparison of the two masks is shown in Figure 6-2.

Figure 6-2: A view of the outlet channels from the main channel comparing the quality of a

laser printer (left) to a bromide transparency printed by Type Tamer (right).

Next the mask is exposed onto a pre-sensitised board using photolithography. A pre-

sensitised board consists of three main layers: a top layer of photo-resist, a conductive layer

(typically copper) and an insulating layer. The boards used for this project were Kinsten®

2OZGD1530, which have a copper thickness measured as 2 ounces rolled out over 1 square

foot. This is equivalent to a thickness of 71.12 �m. These boards were cut into 75 x 80 mm

pieces using a guillotine in the School of Electrical, Electronic and Computer Engineering.

The mask is placed on top of the photo-resist and placed into a Kinsten® KVB-30D light

box. The areas of photo-resist that are not covered by the mask are exposed to ultraviolet

(UV) light for 90 seconds. The board is then removed from the light box and placed into a

developer solution (10 g/L solution of sodium hydroxide and water). This removes the areas

of photo-resist that were exposed to UV light revealing the copper layer beneath.

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Once all of the exposed photo-resist has been removed the board is placed into a Kinsten®

ET-10 etching tank. The tank contains an etchant solution (200 g/L solution of ammonium

persulphate and water) that is heated to between 50°C and 60°C and aerated using an air

pump. This process removes all of the copper that was exposed in the developer solution.

Finally the remaining photo-resist can be removed by wiping the board with acetone. A

completed PCB mould is shown in Figure 6-3.

Figure 6-3: A completed PCB mould.

6.1.2 Device Fabrication

The completed PCBs were used as moulds to imprint the designs into PMMA sheets.

Imprinting was achieved using a Carver Inc® 3889 automatic hydraulic press to hot emboss

the moulds into the PMMA. The hydraulic press required a ‘recipe’ to be input which

defined temperatures, dwell times and pressures. The recipe used for this project was

developed by Professor Keating, Dr. Harris and Christopher Godfrey and is illustrated in

Figure 6-4. Forced convection, produced by two 5 inch DC fans, was used to decrease the

time required for the equipment, mould and PMMA to cool.

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Figure 6-4: Hot embossing recipe (temperatures, dwell times and pressures) used and the

effect of forced convection (Godfrey, 2010).

The PMMA sheets used were 50 x 50 x 1.5 mm. The PMMA sheet and PCB mould were

cleaned with isopropanol to remove any surface contaminants prior to imprinting. The

PMMA sheet is then placed on top of the PCB mould, put in between the two platens of the

hydraulic press and the recipe is initiated.

The next step to fabricate the devices is to drill holes for the inlets and outlets. These were

drilled using a Global Machinery Company® (GMC) LSR13DP drill press and a 1.5 mm

diameter drill bit.

Once the holes were drilled the channels had to be sealed. The sealing process was

developed by Dr. Harris and Christopher Godfrey. A 250 µm thick sheet of PMMA was

bonded to the 1.5 mm thick PMMA to seal the channels. The bonding solution consists of 2

parts ethanol to 1 part acetone. Acetone is the active bonding agent and Harris and Godfrey

found that increasing the acetone concentration degraded the PMMA channels while

decreasing the acetone resulted in excessively long bonding time. 4-5 drops (approximately

200 �L) of the bonding solution was applied to the thin PMMA and then the imprinted

PMMA was placed onto the thin piece and lightly held down. Using a syringe and the drilled

inlet and outlet holes, air was blown through the main channel and the gratings to remove any

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excess bonding solution. Once all of the excess bonding solution was removed a 3 kg weight

was applied for 20 minutes. The device was checked periodically over this compression

stage to ensure no excess bonding solution had been pushed into the channels and if any was

observed it was removed with the syringe. Finally the bonding was inspected under a

microscope and if poor bonding was observed the process was repeated.

The final step to fabricate the devices was to attach the inlet and outlet tubing. The tubing

used was Microtube Extensions® PIV12797, which has an outer diameter of 1.27 mm and an

inner diameter of 0.97 mm. The tube ends were cut at a slight angle to prevent a seal being

formed against the bottom of the channel and thus restricting fluid flow. The tubes were then

attached using an epoxy adhesive.

A finished device is shown in Figure 6-5.

Figure 6-5: Photographs of the top (left) and bottom (right) of one of the finished devices.

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Appendix C: Device Measurement

Appendix C.1 Investigation Into Printing Tolerances

Figure 6-6: Scale bar printed at Type Tamer, with line widths varying from 10 micrometres

to 10 mm

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Figure 6-7: The deviation between design and measured dimensions of fluid channels on

Type Tamer masks shown as a histogram and overlaid normal distribution curve.

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Figure 6-8: Measurements from the scale bar printed at Type Tamer compared to the

nominal line lengths. The excellent linear relationship indicates that the offset observed is

fixed, not a function of feature size.

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Appendix C.2 Calibration Pieces

Figure 6-9: A) Calibration piece 1, used at 5× magnification.

B) Calibration piece 2, used at 20× magnification.

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Appendix C.3 Identified Design Issues

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Figure 6-10: A typical resonator design, with the undesired line fill of the top 7 gratings

removed

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Appendix D: Automation Software

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Appendix D.2 User Parameter Definitions

Parameter Type Min Max Units

1) Lab

Equipment

Connections

Function

Generator

Address

String Valid VISA Address

Oscilloscope

Address

String Valid VISA Address

2) User-Defined

Parameters

Start Frequency Integer 0 200 000 000 Hz

End Frequency Integer Start

Frequency

200 000 000 Hz

Frequency Step Integer 1 200 000 000 Hz


Delay Integer 0 MAX_INT ms

3) Oscilloscope

Scaling

Conditions

Frequency Integer 0 200 000 000 Hz


Time Integer 0 MAX_INT ms

Table 6: Input parameter definitions

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Appendix D.3 Comparison With Manual Tests

Figure 6-11: Comparison between manual and automatic test resolution. The test

shows the measured output voltage through a 20mm length of PMMA.

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Appendix E: Transmission Tests

Appendix E.1 Equivalent Electrical Circuit

Figure 6-12: Equivalent circuit model of a piezoelectric transducer. Cp and Rp represent the

internal parallel capacitance and resistance of the sensor, and Cc is the capacitance due to

external cabling (Karki, 2000)

A 1 M� resistor (Rp in Figure 6-12) was placed in parallel with a 100�F capacitor (CP) to

approximate the electrical properties of a PZ27 transducer at its 2 MHz resonance (Ferroperm

Piezoceramics: A/S ®, 2011). The cables leading to the circuit were cut so that their length

matched that of the receiver transducer as closely as possible (Cc).

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Appendix G: Attenuation Tests

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Appendix G.1 PMMA Sample Dimensions

Nominal

Length

(mm)

5 10 15 20 25 30 35 40 45 50

Measured

Length

(mm)

4.7 10.12 14.74 19.9 24.92 30.48 34.84 40.13 45.01 50.13

% Error -6 1.2 -1.7 -0.5 -0.32 1.6 -0.46 0.33 0.02 0.26

Table 11: Comparison between the specified and measured lengths of the PMMA segments

cut at the mechanical and materials engineering workshop at UWA.

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acoustic properties of pmma: towards bragg gratings in ......acoustic properties of pmma: towards...

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