applications of piezoelectricity

APPLICATIO

PIEZOELECTRICITY

2015

Sakti Prasanna Muduli

APPLICATIONS OF

PIEZOELECTRICITY

2015

Sakti Prasanna Muduli

APPLICATIONS OF

Government College of Engineering, Keonjhar

Piezoelectricity is a concept of conversion of mechanical energy to electrical energy and vice versa, not by any electromagnetic principle but by the process of Polarization. Piezoelectric effect was first discovered in the year of 1880 but the applicatipiezoelectricity starts in 20materials are regarded as smart materials due to the amazing property. Including some natural occurring crystals (Quartz, Rochell’s salt, Topaz), artificial crystals and polymerproperty. Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation. Due to plenty availability of materials and wide ranges of appmotor, speaker, ultrasonic techniques, digital oscillator, this is a material concept for advance technologies. This not only provides a wide range of applications but also a large field of research for modern technologies such as piezo accelerometer, energy harvesting, in biomedical sensors ect. Piezoelectricity is not limited to advance technology but also in daily life equipments such as LPG gas lighter, general quartz clock, buzzers in alarm and loud spemicrophones.

APPLICATIONS OF PIEZOELECTRICITY


Sakti Pr. Muduli


Piezoelectricity is a concept of conversion of mechanical energy to electrical energy and vice versa, not by any electromagnetic principle but by the process of Polarization. Piezoelectric effect was first discovered in the year of 1880 but the applicatipiezoelectricity starts in 20th century. Now-a-days piezoelectric materials are regarded as smart materials due to the amazing property. Including some natural occurring crystals (Quartz, Rochell’s salt, Topaz), artificial crystals and polymers also show piezoelectric

Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation. Due to plenty availability of materials and wide ranges of applications in fields such as sensors, transducers, motor, speaker, ultrasonic techniques, digital oscillator, this is a material concept for advance technologies. This not only provides a wide range of applications but also a large field of research for

ern technologies such as piezo accelerometer, energy harvesting, in biomedical sensors ect. Piezoelectricity is not limited to advance technology but also in daily life equipments such as LPG gas lighter, general quartz clock, buzzers in alarm and loud spe

APPLICATIONS OF PIEZOELECTRICITY 2

ELECTRICITY


Piezoelectricity is a concept of conversion of mechanical energy to electrical energy and vice versa, not by any electromagnetic principle but by the process of Polarization. Piezoelectric effect was first discovered in the year of 1880 but the application regarding

days piezoelectric materials are regarded as smart materials due to the amazing property. Including some natural occurring crystals (Quartz, Rochell’s salt,

s also show piezoelectric Piezoelectricity is found in useful applications such as the

production and detection of sound, generation of high voltages, electronic frequency generation. Due to plenty availability of materials

lications in fields such as sensors, transducers, motor, speaker, ultrasonic techniques, digital oscillator, this is a material concept for advance technologies. This not only provides a wide range of applications but also a large field of research for

ern technologies such as piezo accelerometer, energy harvesting, in biomedical sensors ect. Piezoelectricity is not limited to advance technology but also in daily life equipments such as LPG gas lighter, general quartz clock, buzzers in alarm and loud speakers,


CONTENTS

1. Introduction to piezoelectricity

2. Cause of piezoelectricity

3. Discovery and History

4. Types of piezoelectric materials

5. Application fields

a) As a high voltage source

b) Sensors

c) Actuators

d) As frequency standard

e) Sonic and Ultrasonic applications

f) Motor

6. Mechanism of some applications

a) LPG lighter

b) Quartz clock and Crystal Oscillator

c) Piezoelectric trnasformer

d) Piezoelectric Accelerometer

e) Energy harvesting

7. Conclusion

8. References


INTRODUCTION TO PIEZOELECTRICITY

The conversion of mechanical energy into electrical one is generally achieved by means of electromagnetism (elecrto-magnetic induction). But there are other physical phenomena that can also convert mechanical energy into electricity directly, one of which is piezoelectricity.

Piezoelectric Effect is the ability of certain materials to generate an

electric charge in response to applied mechanical stress and reverse

process is also possible.

The word “piezoelectricity” is derived from a Greek word “pizo” or “piezein” which means to squeeze or press.

Hence the piezoelectric effect exists in two domains.

a) Direct piezoelectric effect: Converts mechanical stress to emf b) Reverse piezoelectric effect: Converts electrical energy to mechanical

compression or expansion

These two effects are described in the figure bellow

Figure 1


• First figure shows the direct piezoelectric effect; i.e when a piezoelectric material is subjected to mechanical stress, the voltmeter connected to its other two surface shows +ve deflection, hence electro motive force(emf) is generated.

• Second one shows the reverse piezoelectric effect; i.e when voltage is applied on two opposite surfaces of a piezoelectric material that shows expansion.

Polarity of emf according to type of force:

The polarity emf generated across to surfaces of a piezoelectric material depends upon the type of force it is subjected to; i.e force is compressive or tensile. The following figures explain detail about it.

Figure 2 Figure 3

In figure 2 shown above, when a compressive force(squeezed) is applied to a piezo electric material, emf produced is +ve in nature. Remaining the connection same if the material is subjected to a tensile force(stretched) then the polarity will be opposite.

Recent technlogies are all based upon automation and automation is incomplete without sensors, tranducers and actuarors. Many pressure sensors, microphones are using this piezoelectricity as the basis. Hence this is animportant topic to discuss about the applications of pizoelectricity.

CAUSE OF PIEZOELECTRICITY

Piezoelectric effect is formed in crystal having no centre of symmetry. To understand the whole about the centre of symmetry. individual molecules that make up tpolarization, one end is more negatively chargedpositively charged, and is called a dipole. This is a result of the atoms that make up the molecule andaxis is an imaginary line that runs through t

• In a mono-crystal direction. The crystal is said to be cut the crystal at any point, the resultant polar axes of the two pieces would lie in the same direction

• In a poly-crystal, there are different rehave a different polar axis. It is concept. Figure 5

Fig.4 Symmetric polar axis Fig.5 Asymmetric polar axis

Mechanism:

1) Normally, the charges in a piezoelectric crystal are exactly balanced, even if they're not symmetrically arranged.

2) The effects of the charges exactly cancel out, leaving no net charge on the crystal faces.

3) If crystal is squeezed,



Piezoelectric effect is formed in crystal having no centre of . To understand the whole mechanism we have to first know

about the centre of symmetry. To explain this, we have to look atindividual molecules that make up the crystal. Each molecule has polarization, one end is more negatively charged and the other end is

and is called a dipole. This is a result of the atoms that make up the molecule and the way the molecules are shaped. The polar axis is an imaginary line that runs through the centre of those dipoles

the polar axes of all of the dipolesdirection. The crystal is said to be symmetrical because if you were to cut the crystal at any point, the resultant polar axes of the two pieces would lie in the same direction as the original. Figure 4

, there are different regions within the material that have a different polar axis. It is asymmetrical. Figure


the charges in a piezoelectric crystal are exactly balanced, even if they're not symmetrically arranged. The effects of the charges exactly cancel out, leaving no net charge

the crystal faces. If crystal is squeezed, the charges are forced to be out



Piezoelectric effect is formed in crystal having no centre of mechanism we have to first know

To explain this, we have to look at the he crystal. Each molecule has

and the other end is and is called a dipole. This is a result of the atoms that

the way the molecules are shaped. The polar he centre of those dipoles.

the polar axes of all of the dipoles lie in one because if you were to

cut the crystal at any point, the resultant polar axes of the two pieces

gions within the material that . Figure illustrates this


the charges in a piezoelectric crystal are exactly balanced,

The effects of the charges exactly cancel out, leaving no net charge

out of balance.


4) Now the effects of the charges (their dipole moments) no longer cancel one another out and net positive and negative charges appear on opposite crystal faces. By squeezing the crystal, a voltage is produced across its opposite faces—and that's piezoelectric effect.

The above four processes are shown in the figures bellow;

Figure. 6,7,8,9

• If the material is compressed, then a voltage of the same polarity as the poling voltage appears between the electrodes. If stretched, a voltage of opposite polarity appears.

• Conversely, if a voltage is applied the material deforms. A voltage with the opposite polarity as the poling voltage causes the material to expand, and a voltage with the same polarity causes the material to compress.

• If an AC signal is applied then the material will vibrate at the same frequency as the signal.


DSCOVERY AND HISTROY

Piezoelectric effect was first proven in 1880 by the French Physicist brothers Pierre and Jacques Curie . They combine their knowledge of Pyroelectric effect and the crystal structure of respective materials. Pyroelectric effect describes the generation of electric potential in response to temperature change. Among the materials showing Pyroelectricity, Quartz, Rochell’s salt, Tourmaline, Topaz shows the piezoelectricity most.

Fig. 10 Pierre Curie Fig. 11 Jacques Curie

Curies did not predict the converse or reverse piezoelectric effect . In 1881 Gabriel Lippmann mathematically deduced this concept and Curie brother confirmed it.

The first application of piezoelectricity was SONAR, i.e ultrasonic submarine detector. That technology used transducers having quartz crystal. This was the time of first-world war. After the success of SONAR, record player, ultrasonic transducers for measurement of viscosity and elasticity were used. During second-world war United-states, Russia, Japan discovered a new class of synthetic materials those having better


piezoelectric effect than naturally occurring materials such as quartz. Then ceramic piezoelectric materials were produced and developed.

One significant example of the use of piezoelectric crystals was developed by Bell Telephone Laboratories. Following first-world war, Frederick R. Lack developed the “AT cut ” crystal, a crystal that operated through a wide range of temperatures. Lack's crystal didn't need the heavy accessories previous crystal used, facilitating its use on aircraft. This development allowed Allied air forces.

TYPES OF PIEZOELECTRIC MATERIAL

The interesting thing about Piezoelectricity is both natural and synthetic materials are available. Here is the list of piezoelectric materials given bellow.

Naturally occurring materials:

Non-biological Biological material 1) Quartz(SiO2) 2) Berlinite (AlPO4) 3) Sucrose (table sugar) 4) Rochelle salt 5) Topaz(Al2SiO4(F,OH)2) 6) Tourmaline-group minerals 7) Lead titanate (PbTiO3)

1) Dry Bone 2) Tendon 3) Silk 4) Wood 5) Enamel 6) Dentin 7) DNA

Synthetic materials:

A) Synthetic Crystals 1) Gallium orthophosphate (GaPO4) 2) Langasite (La3Ga5SiO14)

B) Synthetic Ceramics C) Lead-free Ceramics


1) Barium titanate (BaTiO3) 2) Lead zirconate titanate 3) Potassium niobate (KNbO3) 4) Lithium niobate (LiNbO3) 5) Lithium tantalate (LiTaO3) 6) Sodium tungstate 7) Zinc oxide (ZnO)

1) Sodium potassium niobate ((K,Na)NbO3)

2) Bismuth ferrite (BiFeO3)

3) Sodium niobate (NaNbO3) 4) Bismuth titanate(Bi4Ti3O12) 5) Sodium bismuth titanate

• Some nano-structured semiconductor crystal having non central symmetry (such as the Group III-V and II-VI materials, due to polarization of ions under applied stress and strain e.g GaN, InN, AlN and ZnO). ZnO is the most used material in the recent field of piezoelectricity.

• Some Polymers (PVDF- Polyvinylidene fluoride) and some organic nano structures also show this property.

• Barium titanate was the first piezoelectric ceramic discovered. • Lead zirconate titanate is the most common piezoelectric ceramic in

use today.

APPLICATION FIELDS

Due to the intrinsic characteristics of piezoelectric materials, there is a wide range of applications such as sensors, actuators, crystal oscillator, ultrasonic application, piezo-motor ect. Sensors and actuators have great importance in instrumentation and automotive sectors. Crystal oscillator is used in almost all microprocessor based systems. Before 2010 demand of piezo electric devices was very high but material productions are not significant. Now piezoelectronics is experiencing the fastest growth. Here some of the applications fields and respective examples are explained. Some of the examples are explained later in detail.

1. As High Voltage Power Source:

Some piezoelectric substances like quartz can generate potential differences of thousand volts, during sufficient mechanical stress is applied. This high voltage pulse can be used to generate spark, micro scale energy


harvesting, piezoelectric transformer. Following are some examples of uses-

I. LPG stove Lighter and Cigarette lighter II. Energy harvesting in micro scale (New concept) III. Piezoelectric transformer (New concept)

From the above uses Lighter Mechanism and Energy harvesting are explained later in detail.

Advantages:- a) This method of creating spark doesn’t require any power source like

battery. b) High voltage pulse can be generated without any electrical

instrument.

Disadvantages:-

Only the disadvantage is that voltages only can be produce in form of pulses.

2. Sensors and Actuators:

Piezoelectric materials can be used to convert pressure, acceleration, temperature, strain or force direct to electrical emf. Hence the above parameters can be sensed or measured by means of such materials. Piezoelectric sensors are versatile tools for the measurement of various processes. They are used for quality assurance, process control and for research development in many industries. Generally after 1950 piezoelectric effect was started to be used as sensors and transducers. Some of the examples of piezo sensors are given below-

I. High precision piezoelectric microphones II. Electric guitar pickup III. Piezoelectric micro balance (very sensitive chemical and biological

sensors) IV. Strain gauge V. Electronic drum pad VI. Pressure sensors

VII. Accelerometer (New concept)


VIII. In automobile Engine Management Systems(Knock sensor, Vibration sensor)

An actuator is the mechanism by which a control system acts upon an environment. Actuator operated by a source of energy typically electric current, hydraulic fluid pressure or pneumatic pressure and converts that energy to motion. In piezoelectric actuators converse effect is used. By applying voltage the material changes its shape and this concept can be used to provide pressure in micro scale at very high precision than hydraulic and pneumatic pressure. We can use this technology to control operating of small nozzles (ink jet printer), micro scale movement. The advance version of piezoelectric actuator is amplified piezoelectric actuator. These don’t require any lubricants. Some examples-

I. Loud speaker (voltage causes the vibration of piezoelectric polymer film)

II. In high precision microscope for movement of lenses III. Inkjet printer (to drive the ejection of ink towards paper) IV. Diesel engines (Fuel injector) V. X ray shutter VI. Camera lens movement

Advantages:

a) Accuracy is very high than other sensors. b) Construction is easy. c) Actuators don’t need lubricants due to absence of moving parts.

Disadvantages:

a) The actuators may require voltages of 100v range. b) Only micro scale movement is possible.

3. As Frequency standard:

Some piezoelectric crystals like quartz vibrate in a defined natural frequency when pulse is applied. They use both direct and reverse piezoelectric effect. As the result of vibration they provide reverse pulse. The mechanism can be used to mark the time and hence can be used as frequency standard.


I. General quartz clock II. Crystal oscillator to provide reference clock pulse to microprocessor

based devices.

Mechanism of quartz clock is explained latter.

4. Sonic and ultrasonic applications : By providing voltage pulse of high frequency to a piezoelectric material film it vibrates in frequency providing sonic and ultrasonic sound wave which can be used for

I. Underwater submarine detection II. Ultrasound in medical technology III. Metal fault detection For receiving that ultrasonic wave piezoelectric transducers are used too. 5. Piezoelectric motor:

Although piezoelectricity was a known concept “Ultrasonic piezoelectric motor” was a completely new concept during 21st century. A piezoelectric motor or piezo motor is a type of electric motor based upon the change in shape of a piezoelectric material when an electric field is applied. Piezoelectric motors make use of the converse piezoelectric effect whereby the material produces acoustic or ultrasonic vibrations in order to produce a linear or rotary motion due to friction. Different types of motors such as Speed and precision motor, Stepper motor, low speed and high torque motor have respective different designs and principle of operation but basic mechanism is same as described above. These motors are very small in size as shown in the figure


Figure 12 Figure 13

Figure 12 shows a very small size rotary piezo motor figure 13 is of a valve control motor; it is also very small in size.

Piezoelectric motors are used in sigh precision rotation and linear movement such as

I. Movement of camera lens II. Rotation of radar III. Very small scale valve control IV. Laser movement in case of biomedical modern operations

Advantages:

a) Negligible effect from external magnetic or radioactive fields, and also no generation of these fields

b) High resolution and high accuracy c) Rapid response, dynamic range of 4kHz d) Wide range of angular steps and angular velocities e) Scalable customizable design

Disadvantages:

a) Necessity for a high frequency power supply b) Large scale devices are impossible

MECHANISM OF SOME APPLICATIONS

There is a wide range of applications of piezoelectricitof domestic, industrial, autengineering ect. Some of the applications are categorised and listed above but in this section mechanism of some common applications and some emerging new technologies wdescribed.

1. Mechanism of LPG Stove lighter



There is a wide range of applications of piezoelectricitdomestic, industrial, automobile, biomedical, laboratory, aerospace

engineering ect. Some of the applications are categorised and listed above but in this section mechanism of some common applications and some emerging new technologies which are going to be developed in future are

Mechanism of LPG Stove lighter

Fig. 14



There is a wide range of applications of piezoelectricity in the fields omobile, biomedical, laboratory, aerospace

engineering ect. Some of the applications are categorised and listed above but in this section mechanism of some common applications and some

hich are going to be developed in future are


Many years ago Neanderthal man used stones to get spark and then used spark to light fire and cook his hunting. It was the first step towards man’s progress and prosperity. In present days we are using LPG stoves in our kitchen. Even wonder that a small force of thumb can produce a spark easily to light the fire on stove. Even we don’t require a match box which may have the possibility of limited stick, weather condition and not the spark but a fire comes, which may be dangerous near LPG. So we use a simple lighter. There are also electric lighters which use battery power for spark generation; but battery has limited power so we get limited times of spark and we need to change the battery within certain periods. Hence all the battery lighters are replaced by piezoelectric lighters.

� Outside of gas lighter there is a bottom and that bottom is attached to a hammer & spring . On the other end of the lighter there is a Piezo-ceramic crystal .

� When the bottom is pressed, first the hammer is moved away from the crystal and the spring gets charged . When the bottom is pressed beyond a limit, the spring is discharged with releasing the hammer.

� Soon the hammer hits the piezo-ceramic crystal and a high voltage of about 800v is generated across the crystal.

� One wire from one crystal end and a metallic rod connected on the other end. There is a small gap between the rod end and open terminal of wire.

� Due to high voltage, air breakdown occurs and spark is produced. That lights up the gas coming outside from the tank.

� The ceramic, used, is PTZ (Lead Zirconate Titanate) , which has very low cost and high sensitive.


Figure 15 Piezoelectric spark producers are small devices (1 inch), used both in LPG lighters and cigarette lighters. In cigarette lighters a single switch works for both spark production and gas release and as the result fire glows. Spark occurs once but fire exists till the switch is pressed. Following is the different parts of a cigarette lighter and a piezoelectric spark producer:


Fig. 16 Fig. 17 The internal structure of the small spark generator is shown in fig. 15. Now automatic LPG cooking stoves are also available in which spark generator is already present. Advantages:

• Very safe to use • Doesn’t require any battery or stone • It is reliable. • Works for many years

2. Mechanism of Quartz clock:


Fig. 18

Time is the only dimension that controls everything in this world. There is no start and end point of time scale. But we have assumed or marked the years, months and days. For us sunrise, sunset, movement of moon ect are time scales. But in a day we need a clock to track the time accurately. From starting days of civilisation man try to track time with many concepts such as sun clock, sands of time (hour glass). Then comes mechanical clock and pendulum clock; but they shows many problems. Then quartz clock came. We know that quartz is a piezoelectric material. Before the mechanism of quartz clock we should know about the history of quartz clock-

• 1927 – First quartz clock was built by Warren Marrison & J W Horton at Bell Telephone laboratory.

• 1967 – First European Quartz clock for consumers by “Astrochone” • 1969 – First Quartz wrist watch by “Calibrer”, Japan • During 1980 due to development of solid state digital electronics it

was possible to make compact and inexpensive quartz clock.

Present days all the clocks, we are using, that may be digital, analog, wrist watch, wall clock, are quartz clocks.

Here is the figure showing internal parts of a quartz wrist watch.


Fig. 19

1. Battery 2. Electric stepping motor 3. Microchip 4. Circuit connects microchip to other components 5. Quartz crystal oscillator 6. Crown screw for setting time 7. Gears turn hour, minute, and second hands at different speeds 8. Tiny central shaft holds hands in place

Mechanism :

Chemically, quartz is a compound called silicon dioxide (SiO2), and is a piezoelectric material. Clocks use Quartz crystal oscillator , which looks like a simple circuit component as capacitor or resistor but its internal structure is somewhat different as shown in the figure 20 and 21.


Fig. 20 Fig. 21

Quartz crystal inside the oscillator is bifurcated like a tuning fork. The amazing cause that why quartz, not other piezoelectric crystal, is used in clock is – when an electric pulse is applied, the crystal vibr ate in a constant frequency that is 32,768Hz = 2 15Hz. Because of reverse piezoelectric effect it also generates electric pulse of same frequency. As the frequency is the power of two, that can be easily converted to 1Hz frequency digitally. 1Hz frequency is required to drive the second hand of a clock. Overall mechanism is as described below

� Battery provides current to input microchip circuit � Input microchip circuit makes quartz crystal (precisely cut and shaped

like a tuning fork) oscillate (vibrate) 32768 times per second . � Output microchip circuit detects the crystal's oscillations and turns

them into regular electric pulses, one per second . � Electric pulses drive miniature electric stepping motor. This converts

electrical energy into mechanical power. � Electric stepping motor turns gears. � Gears sweep hands around the clock-face to keep time.

The above is the mechanism of how an analog watch works. But mechanism digital clock is not different. In digital clock the output of second


micro chip is given to seven segment display and counters are used for minute and hour calculation.

A question may arise in our mind that why the clock gain or lose time . Quartz crystal has a constant vibration frequency of 32,768Hz, but this may vary up to 0.06Hz due to temperature change. Due to this reason clock gains or lose small time.

Clock is not the only application of crystal oscillator, but all most every digital system requires a frequency standard to run hence they also use crystal oscillator of different size and different frequency rating. Some of them and the internal structure is shown below

Fig. 22 Fig. 23


3. Piezoelectric transformer:

We all are acquainted with the term “Transformer”, which is a static piece of device that step up, down or keep same value of voltage or current keeping the frequency constant by the principle of electromagnetic induction. Generally there are two windings in a common transformer named primary & secondary and their no of turns are according to our requirement. Both windings are electrically isolated but connected magnetically through the core.

Piezoelectric transformers are an alternative to wire wound magnetic transformers. They behave differently and have a number of advantages, e.g., they are lighter and smaller, and they have excellent electrical isolation and no magnetic stray flux. For these reasons they have been used as high voltage generators in CCFL (Cold Cathode Fluorescent Lamp) backlighting inverters for LCD (L iquid Crystal Display) of Laptop computers as the crystal units don’t have light itself. Piezoelectric transformers also can be step up and step down. The design of piezoelectric transformer was first given by Dr. Rosen in 1950 . Generally in this purpose the material used is barium titanate-based ceramics. There are different modes of piezo effect as shown

Fig. 24 Fig. 25

Fig 24 Longitudinal mode piezoelectric element . The direction of the operating stress, T, is parallel to the polarization direction.


Fig.25 Transverse mode piezoelectric element . The direction of the operating stress, T, is perpendicular to the polarization direction

Mechanism:

Unlike magnetic transformers that based on electromagnetic energy transfer, piezoelectric transformers exchange electric potential with mechanical force. A typical multi-layer PZT(Piezoelectric transformer) with “longitudinal-mode” geometry is shown in Figure 26.

Fig. 26

Above figure shows a typical longitudinal mode of piezoelectric transformer for the use of CCFL application. Vin is connected across primary piezo layers and Vout is connected across both primary and secondary materials in transverse.

� An ac voltage is applied to the VIN electrodes, causing mechanical expansion and compression in the thickness direction.

� This displacement on the primary is transferred as a force in the longitudinal or length direction.


� Mechanical resonance occurs Due to transverse and longitudinal vibration.

� Voltage gain is a function of the PZT is given by

�� =��ℎ × ��

ℎ��× �(�)

Where • g(ω) = piezoelectric material coefficient which is a function of

vibrational frequency. • Layer is the no of primary piezo layers • Length refers to overall length

Variation of mechanical displacement and stress with respect to overall length are shown in the same figure.

• At an instance mechanical stress is +ve in primary side as voltage is applied longitudinal to the layers of piezo material where as that is negative in rest part because current is drawn in transverse direction.

• We know that longitudinal compression causes transverse expansion. That’s why mechanical displacement is +ve in the middle.

We can draw the electrical equivalent circuit for piezoelectric transformer as shown

Fig. 27 Capacitances Cinput and Coutput are due to the ceramic crystal. Cinput is much greater than Coutput, because input crystal is layered. Series LRC circuit is due to the mechanical resonance.


This is an example of step up transformer. Using same concept step down transformer also can be designed. Piezoelectric Transformer can be further modified to be used in DC-DC converter and electronic ballasts for fluorescent lamps. Advantages of piezoelectric transformer are explained as the comparison with electromagnetic transformer.

Piezoelectric transformer Electromagnetic Transformer

� Use electro-mechanical principle

� Smaller in size � More efficiency � Lower cost � Lighter due to no metallic part

� No heating effect � Lower electromagnetic noise

and stray � Operating voltage is limited

and large scale is impossible � Only sinusoidal smooth wave

is suitable for operation

� Use electro-magnetic principle

� Comparatively larger � Less efficiency � Higher cost � Heavier due to all metallic

parts � Heating effect is present � Higher electromagnetic

noise and stray losses � Can be used in both small

and large scale � Any alternating wave can be

treated


4. Piezoelectric accelerometer:

Accelerometer is a device that measures acceleration i.e rate of change of velocity. We can say accelerometer is a sensor that senses motion of body to which it is attached. Accelerometers have multiple applications in industry and science. Highly sensitive accelerometers are components of initial navigation system for aircraft and missiles. Followings are the fields where accelerometers are used

• In navigation systems of rockets, aeroplanes, ships ect • Automobile airbag system • Seismometer • Gradiometer (two accelerometers are combined to detect planner

surface) • Smart phones, tablet pc, computer, mp3 players(orientation sensors

and for gaming) • Modern washing machines • And a lot of industrial applications

An accelerometer developed by Honeywell in the 1980s for use on the space shuttle. Due to such vast applications of accelerometer, it works as a very important sensor.

Concept behind accelerometer:

Acceleration is the time rate of change of velocity. An accelerometer is based on Newton’s second law of motion . That describes that acceleration is caused by the force on the body which is in the same direction of acceleration. Can be represented by

�� = �� × ��

Accelerometer works on this formula not on the time rate of change of velocity. It can be understood from the following example. We feel ourselves thumping backward when our driver accelerates suddenly. We experience a backward force and taking our mass into consideration we


can calculate acceleration. Every accelerometer works in broadly the same way. There are many types of accelerometers such as

Mechanical, capacitive, laser, magnetic induction, optical ect

Before going to our topic piezoelectric accelerometer we have to understand the mechanism of a simple accelerometer. Here mechanisms of mechanical and capacitive accelerometer are explained bellow.

Mechanical:-

� They have something like a mass attached to a spring suspended inside an outer casing.

� When they accelerate, the casing will move off immediately. But the mass will lag behind and the spring will stretch with a force that corresponds to the acceleration.

� The distance the spring stretches (which is proportional to the stretching force) can be used to measure the force and the acceleration in a variety of different ways.

� Seismometers (used to measure earthquakes) work in broadly this way, using pens on heavy masses attached to springs to register earthquake forces. When an earthquake strikes, it shakes the seismometer cabinet but the pen (attached to a mass) takes longer to move, so it leaves a jerky trace on a paper chart.

Fig. 28

Here red ball is a heavy mass, connected to the cashing by a spring, and the cashing is attached to the body of which acceleration is to be measured. A pen is connected to the heavy ball which traces on a paper.


Capacitive:-

The mechanism is same but there is a spring in the opposite side of the spring. When cashing accelerates, the heavy mass lags and presses the plate of the capacitor. Change in capacitance can be sensed by ac bridges and converted to acceleration. Figure3 is as shown below-

Fig. 29

Now we are very much clear about the mechanism of accelerometer.

Piezoelectric accelerometer:-

This is very simple if we replace the capacitor by a piezoelectric material, it is squeezed when cashing accelerates. The advantage is that it directly provides electric signal which can be converted to acceleration directly.

Fig. 30

More advance piezoelectric accelerometers can be designed using two piezoelectric materials on two sides of the heavy mass, that is called


differential accelerometer. Now some industries and gadget companies like apple are using piezoelectric accelerometer.

Advantages:-

1. Piezoelectric accelerometers are smaller in size in comparison to mechanical and capacitive accelerometers.

2. They don’t require any bridge circuit or displacement sensor for conversion

3. These are more sensitive

4. Energy harvesting using Piezoelectric material: Human civilisation needs development of technology and development of technology needs more energy production. The country is regarded as more developed which has more energy (electrical energy) production. There are many ways of electrical energy production that may be from renewable or non-renewable energy sources. Renewable energy sources are now being encouraged by govt because they are pollution free. Some of them are solar, tidal, wind ect. These can be generated either in large or in small scale. When we go for small scale energy generation battery comes first, but battery is chemical powered and causes harm to our environment. Although we can’t get rid of batteries but we can make its use limited. Hence rechargeable batteries are being used. Batteries require charging, replacement and other maintenance efforts. For example, in the applications such as villages, border areas, forests, hilly areas, where generally remote controlled devices are used, continuous charging of the microcells is not possible by conventional charging methods .So, some alternative methods needs to be developed to keep the batteries full time charged and to avoid the need of any consumable external energy source to charge the batteries. To resolve such problems, Energy harvesting technique is proposed as the best alternative. There exists variety of energy harvesting techniques but mechanical energy harvesting happens to be the most


prominent. This technique utilizes piezoelectric components where deformations produced by different means are directly converted to electrical charge via piezoelectric effect. Subsequently the electrical energy can be regulated or stored for further use. The proposed work in this research recommends Piezoelectricity as an alternate energy source. The motive is to obtain a pollution-free energy source and to utilize and optimize the energy being wasted.

� We know that when stress is applied on a piezoelectric material, electrical emf is produced.

� The output voltage obtained from a single piezoelectric crystal is in milli volt range, which is different for different crystals. And the wattage is in microwatt range.

� So in order to achieve higher voltages, the piezoelectric crystals can be arranged in cascading manner, that is, in series. The energy thus obtained is stored in lithium batteries or capacitors. This is the working principle behind piezoelectric energy harvesting system.

At first we have to find out the sources of vibration at which we can put piezoelectric material for electricity production. Followings are some of sources of vibration

A. Power Generating Sidewalk

The piezoelectric crystal arrays are arranged underneath pavements, sidewalks and other high traffic areas like highways, speed breakers for maximum voltage generation. The voltage thus generated from the array can be used to charge the chargeable Lithium batteries, capacitors etc. These batteries can be used as per the requirement.

B. Railway Track

We all must have seen the vibrating rails when train goes on it. This is one of the best examples of source of vibration. Hence there we can use the piezoelectric energy harvesting concept at stations.

C. Power Generating Boots or Shoes

In United States Defense Advance Research Project Agency (DARPA) initiated a innovative project on Energy harvesting which attempts to power battlefield equipment by piezoelectric generators embedded in


soldiers' boots. However, these energy harvesting sources put an impact on the body. DARPA's effort to harness 1-2 watts from continuous shoe impact while walking were abandoned due to the discomfort from the additional energy expended by a person wearing the shoes.

D. Gyms and Workplaces

Researchers are also working on the idea of utilizing the vibrations caused from the machines in the gym. At workplaces, while sitting on the chair, energy can be stored in the batteries by laying piezoelectric crystals in the chair. Also, the studies are being carried out to utilize the vibrations in a vehicle, like at clutches, gears, seats, shock-ups, foot rests.

E. Mobile Keypad and Keyboards

The piezoelectric crystals can be laid down under the keys of a mobile unit and keyboards. With the press of every key, the vibrations created can be used for piezoelectric crystal and hence can be used for charging purpose. Now smart phones are coming with touch screens but it can be applied to computer keyboards.

F. Floor Mats, Tiles and Carpets

A series of crystals can be laid below the floor mats, tiles and carpets which are frequently used at public places, dance clubs. When a bulk of people use this dance floor, enormous amount of voltage is generated which can be used to power the equipments of the night club.

In Netherlands, Rotterdam’s new club WATT has a floor that harnesses the energy created by dancer’s steps. Designed by Dutch company called the Sustainable Dance club, the floor is based on the piezoelectric effect. As club goers dance on floor, the floor is compressed by less than half an inch. It makes contact with the piezoelectric material under it and generates around 2-20 watts of electricity which is being used to lighten up the decorated floor LEDs.


Output stages of piezoelectric energy harvesting sy stem:

� The output of a piezoelectric crystal is alternating signal. In order to use this voltage for low power consuming electronic devices, it has to be first converted into digital signal.

� This is done with the help of AC to DC converter as shown in Fig.31. It shows a simple diode rectifier to convert AC to DC. This is followed by a capacitor, which gets charged by the rectifier up to a pre-decided voltage, at which the switch closes and the capacitor discharges through the device. In this way, the energy can be stored in the capacitor, and can be discharged when required.

Fig. 31

But the energy harvesting capacity of this circuit is not appreciable. Hence, a DC to DC converter is used after bridge rectifier stage, which has been demonstrated in Fig. 32.


Fig. 32

The addition of DC-DC converter has shown an improvement in energy harvesting.

Cost effectiveness :

The assembly developed using series and parallel combination of piezo-crystals is very cost effective. A single crystal costs around 23 – 25 Rupees, and hence the cost of whole assembly is very less. It is very encouraging to get a good voltage and current at such a low cost at the same time utilizing the waste energy. And piezoelectric ceramics can be produced in required amounts now.

Use of piezoelectric crystals has being started and positive results are obtained. With further advancement in field of electronics, better synthesized piezoelectric crystals and better selection of place of installations, more electricity can be generated and it can be viewed as a next promising source of generating electricity. It may be in micro scale but we can save electrical energy which is enough for floor LEDs, mobile phone battery charging, blue-tooth sensor activation ect. At most it is not polluting our environment and not consuming any non-renewable source like fossil fuel .


CONCLUSION

Piezoelectricity is not a new concept in engineering but it is a revolutionary concept in the field of sensors and transducers. Now we can find the use of piezoelectricity not only in every individual houses but in many industries, aeronautics, automobiles ect. There are also some of the concepts those need to be developed such as piezoelectric accelerometer, motor, underwater acoustic transducers, piezoelectric transformers ect. As piezoelectricity is a simple concept and materials are easy to produce, Indian industries should take a step towards it. This is not only related to electrical and electronics but also very much related to mechanical engineering. Mechanical strain gauges, micro scale displacement sensors, small valve switches, sensitive balance are possible only due to piezoelectricity. There are some lead free piezoelectric materials which can replace those materials having lead and hence it will be eco-friendly.


REFERENCES

BOOKS

1) J.P. Bentley, Principles of Measurement Systems, Pearson Education 2) , William D. Callister, David G. Rethwisch, Material Science and Engineering an introduction, Wiley Publication 3) How it works, The clock, A CBT Publication 4) K. Krishna Murty, How things work?, Pustak Mahal

WEB

1) https://en.wikipedia.org/wiki/Piezoelectricity 2) http://www.explainthatstuff.com/quartzclockwatch.html 3) http://www.mmech.com/transformers 4) https://en.wikipedia.org/wiki/Piezoelectric_accelerometer 5) http://www.explainthatstuff.com/accelerometers.html 6) https://en.wikipedia.org/wiki/Piezoelectric_motor

applications of piezoelectricity

Technology