Piezoelectricity

Chapter 6
Piezoelectric
Define Piezoelectricity. Why iron is useless for
piezoelectric purposes? What is the most well-known
piezoelectric material used in electronic devices?

• Piezoelectricity is the process of using crystals to

convert mechanical energy into electrical energy, or
vice versa.
• Most crystals, such as iron have a symmetrical unit
cell, the atoms in their unit cells are distributed
symmetrically around a central point. But some
crystalline materials don't possess a center of
symmetry making them candidates for
piezoelectricity.
 Piezoelectric

• Piezoelectric materials: The structure in

these crystals aren’t symmetrical but they
still exist in an electrically neutral balance.
• If you apply mechanical pressure to a
piezoelectric crystal, the structure
deforms, atoms get pushed around, and
suddenly you have a crystal that can
conduct an electrical current.
• If you take the same piezoelectric crystal
and apply an electric current to it, the
crystal will expand and contract,
converting electrical energy into
mechanical energy.
Types of
Piezoelectric
Materials
• There are a variety of
piezoelectric: both man-made
and natural.
• The most well-known (first
piezoelectric material) is the
quartz crystal.
• Other naturally occurring
piezoelectric materials include
cane sugar, Rochelle salt, topaz,
tourmaline, and even bone.
Types of Piezoelectric Materials
• Man-made piezoelectric materials include:
- PZT: is made from lead zirconate titanate and can produce more voltage
than quartz with the same amount of mechanical pressure.
- Barium Titanate: is a ceramic piezoelectric material is known for its long-
lasting durability, discovered during World War II
- Lithium Niobate: is a material that combines oxygen, lithium, and niobium
together in a ceramic material that performs similarly to barium titanate.

Lithium niobate. Barium Titanate

 How Piezoelectricity Works
Applying mechanical energy to a crystal is called a direct piezoelectric effect
and works like this:
1. A piezoelectric crystal is placed
between two metal plates (material in
perfect balance and does not conduct
an electric current)
2. Mechanical pressure is then applied to
the material by the metal plates, which
forces the electric charges within the
crystal out of balance. Excess negative
and positive charges appear on
opposite sides of the crystal face.
3. The metal plate collects these charges,
which can be used to produce a voltage
and send an electrical current through
a circuit.
 How Piezoelectricity Works
Applying an electrical signal to a material as an inverse piezoelectric effect. It
works like this:
1. We have a piezoelectric crystal placed
between two metal plates. The crystal’s
structure is in perfect balance.
2. Electrical energy is then applied to the
crystal, which shrinks and expands the
crystal’s structure.
3. As the crystal’s structure expands and
contracts, it converts the received
electrical energy and releases mechanical
energy in the form of a sound wave.
 • In today’s world of electronics piezoelectricity is
used everywhere.
• Uses piezoelectricity in the microphone. There’s
even a subway in Tokyo that uses the power of
human footsteps to power piezoelectric structures
Piezoelectricity in the ground.
Applications • Piezoelectricity Applications
o Actuators
o Speakers & Buzzers
o Drivers
o Sensors
o Power Generator
o Motors
Actuators
Actuators use piezoelectricity to power devices
like knitting and braille machinery, video
cameras, and smartphones.

In this system, a metal plate and an actuator

device sandwiches together a piezoelectric
material.

Voltage is then applied to the piezoelectric

material, which expands and contracts it. This
movement causes the actuator to move as well.
Speakers & Buzzers

Speakers use piezoelectricity to power

devices like alarm clocks and other small
mechanical devices that require high
quality audio capabilities.
These systems take advantage of the
inverse piezoelectric effect by converting
an audio voltage signal into mechanical
energy as sound waves.
Drivers

• Drivers convert a low voltage battery

into a higher voltage which can then
be used to drive a piezo device.

• This amplification process begins with

an oscillator which outputs smaller
sine waves. These sine waves are then
amplified with a piezo amplifier.
 Sensors

• Sensors are used in a variety of applications

such as microphones, amplified guitars, and
medical imaging equipment.

• A piezoelectric microphone is used in these

devices to detect pressure variations in sound
waves, which can then be converted to an
electrical signal for processing.
Power Generator
• One of the simplest applications for
piezoelectricity is the electric cigarette lighter.
• Pressing the button of the lighter releases a
spring-loaded hammer into a piezoelectric
crystal. This produces an electrical current
that crosses a spark gap to heat and ignite gas.
• This same piezoelectric power system is used
in larger gas burners and oven ranges.
 • Piezoelectric crystals are perfect for applications
that require precise accuracy, such as the
Motors movement of a motor.
• Piezoelectric material receives an electric signal,
which is then converted into mechanical energy to
force a ceramic plate to move.
 Review Questions
1- Define Piezoelectricity. Why iron is useless for piezoelectric purposes? What is
the most well-known piezoelectric material used in electronic devices?
2- Describe the behavior of piezoelectric material when applying mechanical
pressure on it, and when applying an electric current to it.
3- What is the main property of PZT Lead Zirconate Titanate, and Barium
Titanate?
4- How direct piezoelectric effect works?
5- How inverse piezoelectric effect works?
6- State and explain some piezoelectric applications.
• Equations to calculate the static voltage and static displacement of
piezoelectric elements:
• The commonly used elements are the plate and the disk. The applied
force is assumed to be vertical.
piezoelectric voltage coefficient
Example (1)

1- For a piezoelectric material if g33 equals 26.5*10-3 Vm/N, and d33 = 290*10-12 m/V. if a disk
of such material of outer diameter 20 mm and thickness 0.05 mm is suffering from a vertical
force 1 N, calculate the generated static voltage across the disk faces. (4.2 mV)
• Solution:
g33 = 26.5*10-3 Vm/N
d33 = 290.10-12 m/V
D = 20 mm
H = 0.05 mm
F= 1 N

𝟐𝟐𝟐𝟐. 𝟓𝟓 × 𝟏𝟏 × 𝟎𝟎. 𝟎𝟎𝟎𝟎

𝑽𝑽 = 𝟐𝟐
= 𝟒𝟒. 𝟐𝟐 𝒎𝒎𝒎𝒎
𝝅𝝅 × 𝟏𝟏𝟏𝟏
Example (2)

2- For the same material and disk if 20 V is applied across the disk faces, calculate the
change in its thickness. (0.0058 μm)

• Solution:
d33 = 290x10-12 m/V
V = 20V
H = ??

∆𝒉𝒉 = (𝟐𝟐𝟐𝟐𝟐𝟐 × 𝟏𝟏𝟏𝟏−𝟏𝟏𝟏𝟏 ) × 𝟐𝟐𝟐𝟐 = 𝟓𝟓. 𝟖𝟖 × 𝟏𝟏𝟏𝟏−𝟗𝟗 𝒎𝒎 = 𝟎𝟎. 𝟎𝟎𝟎𝟎𝟎𝟎𝟎𝟎 𝝁𝝁𝝁𝝁