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 applicati
piezoelectricity starts in 20
materials are regarded as smart materials due to the amazing property.
Including some natural occurring crystals (Quartz, Rochell’s salt,
Topaz), artificial crystals and polymer
property. 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 app
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
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 spe
microphones.
APPLICATIONS OF PIEZOELECTRICITY
Sakti Pr. Muduli
discovered in the year of 1880 but the applicati
piezoelectricity starts in 20th
century. Now-a-days piezoelectric
Topaz), artificial crystals and polymers also show piezoelectric
Piezoelectricity is found in useful applications such as the
and wide ranges of applications in fields such as sensors, transducers,
ern technologies such as piezo accelerometer, energy harvesting,
general quartz clock, buzzers in alarm and loud spe
APPLICATIONS OF PIEZOELECTRICITY 2
ELECTRICITY
discovered in the year of 1880 but the application regarding
days piezoelectric
s also show piezoelectric
Piezoelectricity is found in useful applications such as the
lications in fields such as sensors, transducers,
ern technologies such as piezo accelerometer, energy harvesting,
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 t
polarization, one end is more negatively charged
positively charged, and is called a dipole. This is a result of the atoms that
make up the molecule and
axis 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 re
have 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,
. To understand the whole mechanism we have to first know
about the centre of symmetry. To explain this, we have to look at
individual 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 dipoles
direction. The crystal is said to be symmetrical because if you were to
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
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
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 piezoelectricit
of domestic, industrial, aut
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 w
described.
1. Mechanism of LPG Stove lighter
There is a wide range of applications of piezoelectricit
domestic, industrial, automobile, biomedical, laboratory, aerospace
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
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 vibrate in a
constant frequency that is 32,768Hz = 215
Hz. 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 (Liquid 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 system:
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

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