Acoustic Sensing Technologies

Prof. Miao Yu Director, Sensors and Actuators Laboratory

Department of Mechanical Engineering University of Maryland, College Park, MD, USA

mmyu@umd.edu

IMECE International Mechanical Engineering Congress & ExpositionPhoenix, AZ, USA

November 11 – 17, 2016

Outline

Introduction

Overview of current acoustic sensor technologies

Fundamental constraints of acoustic sensing

Research efforts on the use of emerging materials and bio-inspiration to create new acoustic sensing concepts and technologies

Introduction: Sound Waves

Sound waves can be considered as longitudinal pressure waves.

As the pressure wave propagates, the pressure along the direction of the propagation changes.

Acoustic waves have the following fundamental properties: amplitude, frequency, wavelength, and speed of propagation.

Frequency range is from 0 to over 1 GHz Audible range: 20 Hz to 20 kHz

Ultrasound: 20 kHz and up

Infrasound: 0 to 20 Hz

Kinsler, Frey, Coppens, and Sanders, Fundamentals of Acoustics, 1999.

Introduction: Sound Pressure

Sound pressure is the local pressure deviation from the ambient (average, or equilibrium) pressure caused by a sound wave.

Sound pressure level (SPL) is a logarithmic measure of the effective sound pressure relative to a reference value. It is measured in decibels (dB) above a standard reference level.

where Pref is the reference sound pressure and Prms is the rms sound pressure being measured Pref = 20 Pa

2

10 10210log ( ) 20logrms rms

ref ref

P PSPL dBP P

Introduction: Sound Pressure

0 dB2×10−5 Pa (RMS)Auditory threshold at 1 kHz10 dB6.32×10−5 PaLight leaf rustling, calm breathing

20 – 30 dB2×10−4 – 6.32×10−4 PaVery calm room40 – 60 dB2×10−3 – 2×10−2 PaNormal conversation at 1 m

approx. 60 dB2×10−2 PaTV (set at home level) at 1 m60 – 80 dB2×10−2 – 2×10−1 PaPassenger car at 10 m

78 dB0.356 PaHearing damage (over long-term exposure, need not be continuous)

80 – 90 dB2×10−1 – 6.32×10−1 PaTraffic on a busy roadway at 10 m110 – 140 dB6.32 – 200 PaJet at 100 m

approx. 120 dB20 PaHearing damage (possible)150 dB632 PaJet engine at 30 m168 dB5,023 PaM1 Garand rifle being fired at 1 m

171 dB (peak)7,265 Pa.30-06 rifle being fired 1 m to shooter's side

dB re 20 μPapascalSound in airSPLSound pressureSource of sound

0 dB2×10−5 Pa (RMS)Auditory threshold at 1 kHz10 dB6.32×10−5 PaLight leaf rustling, calm breathing

20 – 30 dB2×10−4 – 6.32×10−4 PaVery calm room40 – 60 dB2×10−3 – 2×10−2 PaNormal conversation at 1 m

approx. 60 dB2×10−2 PaTV (set at home level) at 1 m60 – 80 dB2×10−2 – 2×10−1 PaPassenger car at 10 m

78 dB0.356 PaHearing damage (over long-term exposure, need not be continuous)

80 – 90 dB2×10−1 – 6.32×10−1 PaTraffic on a busy roadway at 10 m110 – 140 dB6.32 – 200 PaJet at 100 m

approx. 120 dB20 PaHearing damage (possible)150 dB632 PaJet engine at 30 m168 dB5,023 PaM1 Garand rifle being fired at 1 m

171 dB (peak)7,265 Pa.30-06 rifle being fired 1 m to shooter's side

dB re 20 μPapascalSound in airSPLSound pressureSource of sound

Source: https://en.wikipedia.org/wiki/Sound_pressure

Airborne acoustic sensors: Acoustic pressure measurements:

• Capacitive (condenser microphones)• Resistance microphones• Magnetic microphones• Piezoelectric microphones • Fiber optic microphones

Directional microphones and microphone arrays

Introduction: Acoustic Sensors

Sound pressure can be measured by using a microphone in air and a hydrophone in water

Condenser Microphones

Sound pressure moves a plate or a flexible diaphragm in a capacitor which induces a change in capacitance

Operation principle:

Electret: a ferroelectric material that has been permanently charged or polarized

C = Ad , C = QV

dV QA

Health care: hearing aids, medical ultrasonic imaging

Defense and safety: sonar systems, acoustic surveillance

Industry: non-destructive detection, metrology, consumer electronics (telephones, TVs and radios, smart phones)

Acoustic Sensor Applications

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Confined space and weight constraint MAV: size less than 15 cm Hearing aid: cosmetically

acceptable Consumer electronics

Reduction of the perturbation of the primary sound field by the sensor

Near field measurements without complex algorithms to compensate for the wave front curvature

Why Miniaturization?

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DelFly Micro(theworld'ssmallestcamera‐carryingMAV)

Miniature microphones: MEMS and fiber optic microphones

MEMS Microphones

(Source: Tutorial for MEMS microphones, STMicroelectronics)

MEMS microphones are fabricated on semiconductor production lines using silicon wafers and highly automated processes.

Layers of different materials are deposited on top of a silicon wafer and the unwanted material is then etched away, creating a moveable membrane and a fixed backplate over a cavity in the base wafer.

MEMS Microphones

The market is expected to reach $1.65B by 2019(Report, MEMS microphone 2014, Yole Developpment)

Fiber Optic Microphones

A fiber optic microphone converts acoustic waves into electrical signals by sensing changes in light intensity or phase

Fiber optic microphones are free of electro-magnetic interference (EMI) and can have superior performance compared to their electrical counterparts.

They have proven to be particularly useful in medical applications, such as inside the MRI suites as well as in remote control rooms, and high temperature environment

Optical fiberMembrane

Fiber Optic Microphones

Fiber optic Mic. compared to Brüel and Kjær 4134 Mic (3 times larger).

Fabry-Perot sensor

I2I1

I0

(Yu and Balachandran, 2003)

Fiber Optic Microphones

(Chen et al. 2010)

(Bucaro et al. 2005)

(Stief, 2012)

Performance of Acoustic Sensors

Performance parameters Sensitivity Bandwidth Signal to noise ratio Directionality Resolution: minimum detectable signal

Fundamental constraints in acoustic sensing Acoustic pressure sensors: minimum detectable pressure

Directional microphones (or microphone arrays): minimum detectable directional cues

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d

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Fundamental Constraints in Acoustic Sensing

Acoustic pressure sensors

Sensitivity

1 2 2

2.952 (1 )

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Bandwidth

Trade off between sensitivity and bandwidth !

MDP poses a fundamental challenge to the development of miniature acoustic pressure sensors.

Small sensors suffer from poor minimum detectable pressure (MDP) determined by the noise floor of the system

Fundamental Constraints in Acoustic Sensing

The size constraint poses a fundamental challenge to the development of miniature directional microphones or microphone arrays

d

L

Sound source

sindtime differenceof arrivalc

As d→0, both time and intensity difference approach 0.

Size constraint in directional acoustic sensing

1020log left

right

AA

Intensity difference

The engineered sound localization systems face the size constraint.

New Acoustic Sensing Concepts and Technologies Based on Emerging Materials

and Bio-inspiration

High Sensitivity, Ultra-Miniature Fiber Optic Acoustic Sensor Based on Graphene Diaphragm

• Thickness of 0.34 nm for a monolayer graphene, the Young’s modulus 1 TPa

• Strongest material ever tested • Using few-layer graphene to achieve high bandwidth

and high sensitivity• Miniature graphene-based acoustic sensor (overall

diameter 320 m)

2 4

3

3 116M

d

aSE h

1 2 2

2.952 (1 )

dh Efa v

High Sensitivity, Ultra-Miniature Fiber Optic Acoustic Sensor Based on Graphene Diaphragm

R. Ganye, Y. Chen, H. Liu, and M. Yu, Applied Physics Letters 108, 261906, 4pp., doi: 10.1063/1.4955058.

Size: 320 m; 40 times smaller than the reference mic

Metamaterial Enhanced Acoustic Sensing

Y. Chen, H. Liu, M. Reilly, H. Bae, and M. Yu, “Enhanced Acoustic Sensing through Wave Compression and Pressure Amplification in Metamaterials”, Nature Communications 5, Article number: 5247, 2014

Metamaterials Enhanced Acoustic Sensing System

All natural acoustic materials have refractive indices N<1 (N=cair/cmedium)

Using anisotropic metamaterial to achieve high refractive index

Wave compression and amplification happen in high-index metamaterials

Amplification of pressure field

Metamaterial enhanced acoustic sensing system

Acoustic Metamaterials: High Index and Graded Index

(a)

Gradual increase of refractive index along the wave propagation

Effective coupling of the acoustic wave into the material

Having similar wave compression and amplification effect as high-index materials

Low dimensional GRIN metamaterial good for sensing

Graded-index (GRIN) acoustic metamaterials

Bulk GRIN metamaterial

Low dimensional GRIN metamaterial

Metamaterial Enhanced Acoustic Sensing: Experimental Arrangement

• Metamaterial device: Array of 100 stainless plates spaced by air gaps, air gap distance 1.4 mm,array periodicity 3.4 mm, thicknessof plates 2 mm, and width of plate increases from 0.5 mm to 50 mm with a step of 0.5 mm.

• Optical detection system: Graphene based fiber optic acoustic probe

Metamaterial Enhanced Acoustic Sensing: Experimental Results

12-fold pressure field amplification!

• Wave compression and amplification demonstrated

• Experimental results compare well with simulations

Metamaterial Enhanced Acoustic Sensing: Experimental Results

Recovery of signal overwhelmed by noise

SNR<1

20 dB enhancement on SNR

Acoustic sensing can greatly benefit from bio-inspired ideas

520m

Directional hearing in nature Hearing animals rely on two ears to receive

directional cues• Interaural time difference (ITD)• Interaural intensity difference (IID)

Sound source localization facilitates communication, finding prey, and escape from predators

Diversity of auditory systems Interaural separation: sub-milimeters to

~100s mm• Human: ~170 mm• Insects: millimeters or less:

Directional Hearing in Animals

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Acoustic communication in elephants

Parasitic fly Ormia Ochracea Attracted to the 5 kHz calling song of male crickets

(Cade, 1975) Distance between auditory organs: ~520 m ITD < 1.5 s, IID < 1 dB ~70 receptor cells Fly ear: Size constraint AND signal processing

constraint Superior directional hearing (Robert et al., 1992, 1996)

mITD: 50 s, mIID: 10 dB Directional resolution: 2

Mechanism Mechanical coupling between eardrums Two vibration modes of the ear

Flyoncricket

http://hoylab.corn

ell.edu

Fly ear and 2-DOF model (Miles et al, 1995)

Rocking mode Bending mode

Superior Directional Hearing of the Fly Ormia

Fly’s localization/lateralization scheme (Mason et al., 2001)

Localization in the azimuth range of || ~20-30• Accurately pinpoint the sound source location

Lateralization in the range of || > ~20-30:• Only make a left/right decision with a constant turn size

Localization

Lateralization Lateralization

Are the structural parameters, the calling song frequency of the crickets, and the sound source localization scheme related?

Superior Directional Hearing of Fly Ormia

Mason A, Oshinsky M, Hoy R, Nature 410, 686-690, 2001.

Use modal analysis to determine directional cues at the mechanical response

Revisit 2-DOF model with a different approach (Liu et al., 2013): modal analysis

Unraveling the Bio-Physics of Fly Ear: Revisit 2DOF Model

1 32

2k km

11

km

Performance parameters NEVER been investigated: Mechanical interaural phase difference mIPD: directional cue

independent of sound source frequency

Directional sensitivity DS: mIPDDS

In the vicinity of midline (- , = 30), define Average directional sensitivity (ADS)

Nonlinearity (NL)

mIPD mIPD0 ADS

NL 1ADS

12

mIPD mIPD

2

d

The fly ear represents a natural optimal structure that can simultaneously achieve the maximum ADS and the minimum NL at 5 kHz.

Unraveling the Bio-Physics of Fly Ear: Dual Optimality

Achieving dual optimality at different working frequencies

Design Space Optimization

One can create optimal synthetic devices to mimic the fly ear, which can be tailored to work at any frequency.

0 5 10 15 20 25 300

0.5

1

1.5

Frequency (kHz)

ADS

Fly ear dual optimality at 5kHz

0 5 10 15 20 25 300

0.05

0.1

0.15

NL

NL

ADS

0 5 10 15 20 25 300

0.5

1

1.5

Frequency (kHz)

ADS

Fly ear dual optimality at 5kHz

0 5 10 15 20 25 300

0.05

0.1

0.15

NL

NL

ADS

MEMS sensor device with dual optimality

Fly-Ear Inspired Sensors

520m

Ormia’s ear

OurMEMSsensor

MEMSdevicedualoptimality

at8kHz

(Luke et al., 2009, Liu et al., 2013)

Interaural phase difference (IPD) versus azimuth (8 kHz, the working frequency)

• Directionalsensitivityatthemidline:1.69deg/deg (Initial:0.167deg/deg)• Performanceequivalenttoaconventionalmicrophonepairwitha

separationof10timeslarger

10 times amplification of IPD

10 times amplification of DS

Fly-Ear Inspired Sensors

Biology-Inspired Miniature Directional Microphone Array

Fly ear

Biology-inspired microphone

Large sound localization system

Miniature sound localization device

Müller, P., and Robert, D., J. Exp. Biol. 204, 1039–1052, 2001.(Lisiewski et al., 2011)

Miniature acoustic sensors Dr. Haijun Liu Dr. Hyungdae Bae Mr. Felix Stief

Acoustic metamaterials Dr. Yongyao Chen Dr. Haijun Liu Mr. Randy Ganye

Fly ear inspired sensors Dr. Haijun Liu Mr. Andrew Lisiewski Dr. Laith Sawaqed

Collaborators Dr. Luke Currano and Danny Gee from ARL Dr. Doug Olson from NIST

Support received from NSF, AFOSR, ARL&DARPA, ONR DURIP, NIST, and University of Maryland, College Park

Acknowledgements

List of References

R. Ganye, Y. Chen, H. Liu, and M. Yu, Characterization of wave physics in acoustic metamaterials using a fiber optic point detector, Applied Physics Letters 108, 261906, 4pp., doi: 10.1063/1.4955058.

Y. Chen, H. Liu, M. Reilly, H. Bae, and M. Yu, “Enhanced Acoustic Sensing through Wave Compression and Pressure Amplification in Metamaterials”, Nature Communications 5, Article number: 5247, 2014.

H. Liu, L. Currano, D. Gee, T. Helms, and M. Yu, Understanding and mimicking the dual optimality of the fly ear, Scientific Reports, 3, Article number 2489, 2013.

L. Sawaqed, H. Liu, and M. Yu, Robotic sound source localization using bio-inspired acoustic sensors, Proceedings of IMECE2012: ASME 2012 International Mechanical Engineering Congress and Exposition, Houston, Texas, Nov 9-Nov 15, 2012

F. Stief, Miniature Low-Coherence Fiber Optic Acoustic Sensor With Thin-Film UV Polymer Diaphragm, Master’s thesis. A.P. Lisiewski, H. Liu, M. Yu, L. Currano, and D. Gee, Fly-ear inspired micro-sensor for sound source localization in two

dimensions, Journal of the Acoustical Society of America Express Letters, 129(5): EL166-EL171, 2011 H. Liu and M. Yu, Effects of air cavity on fly-ear inspired directional microphones: a numerical study, Proc. SPIE 7981

(SPIE Smart Materials/NDE): 79811V, 2011 A.P. Lisiewski, H. Liu, and M. Yu, Fly ear inspired miniature sound source localization sensor: localization in two

dimensions, Proceedings of IMECE2010: 2010 ASME International Mechanical Engineering Congress and Exposition, Vancouver, British Columbia, Nov 12-Nov 18, 2010

H. Liu and M. Yu, A new approach to tackle noise issue in miniature directional microphones: bio-inspired mechanical coupling, Proc. SPIE 7647 (SPIE Smart Materials/NDE): 76470P , 2010

L. H. Chen, C. C. Chan, W. Yuan, S. K. Goh, and J. Sun, High performance chitosan diaphragm-based fiber-optic acoustic sensor, Sensors & Actuators: A. Physical 163, 42-47, 2010.

H. Liu, M. Yu, L.J. Currano, and D. Gee, Fly-ear inspired miniature directional microphones: modeling and experimental study, Proceedings of IMECE2009: 2009 ASME International Mechanical Engineering Congress and Exposition, Lake Buena, FL, Nov 13-Nov 19, 2009

H. Liu, M. Yu, and X.M. Zhang, Understanding fly-ear inspired directional microphones, Proc. SPIE 7292 (SPIE Smart Materials/NDE): 72922M , 2009

List of References

L.J. Currano, H. Liu, B. Yang, M. Yu, and D. Gee, Microscale implementation of a bio-inspired acoustic localization device, Proc. SPIE 7321, 73210B, 2009

H. Liu, M. Yu, and X.M. Zhang, Biomimetic optical directional microphone with structurally coupled diaphragms, Applied Physics Letters 93(24): 243902, 2008.

H. Liu, Z. Chen, and M. Yu, Biology-inspired acoustic sensors for sound source localization, Proc. SPIE 6932(SPIE Smart Materials/NDE): 69322Y, 2008

J. A. Bucaro, N. Lagakos, and B. H. Houston, Miniature, high performance, low-cost fiber optic microphone, Journal of the Acoustical Society of America 118, 1406-1413, 2005.

M. Yu and B. Balachandran, Acoustic measurements using a fiber optic sensor system, Journal of Intelligent Material Systems and Structures, Vol. 14(7), pp. 409-414, 2003.

P. Müller and D. Robert, A shot in the dark: the silent quest of a free-flying phonotactic fly, J. Exp. Biol. 204, 1039–1052, 2001.

L.E. Kinsler, A.R. Frey, A. B. Coppens, J. V. Sanders, Fundamental of Acoustics 4th Edition, Wiley, 1999. R. Miles, D. Robert, and R. Hoy, Mechanically coupled ears for directional hearing in the parasitoid fly Ormia ochracea,

JASA A 98, 3059-3070, 1995. D. Robert, J. Amoroso, and R. Hoy, The Evolutionary Convergence of Hearing in a Parasitoid Fly and Its Cricket Host,

Science 258, 1135-1137, 1992. W. Cade, Acoustically Orienting Parasitoids: Fly Phonotaxis to Cricket Song, Science 190: 1312-1313, 1975.