Piezoelectricity and its

applicationsMughees Khan (BEE-FA13-124)

Haseeb Rehman (BEE-FA13-057)

Uzair (BEE-FA13-030)

Usama Khalid (BEE-FA13-073)

What is piezoelectricity?Piezoelectricity is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure.

The piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect (the internal generation of electrical charge resulting from an applied mechanical force) also exhibit the reverse piezoelectric effect (the internal generation of a mechanical strain resulting from an applied electrical field). For example, lead zirconate titanate crystals will generate measurable piezoelectricity when their static structure is deformed by about 0.1% of the original dimension. Piezoelectricity is found in useful applications such as the production and detection of sound, generation of high voltages, electronic frequency generation, microbalances, to drive an ultrasonic nozzle, and ultrafine focusing of optical assemblies. Examples of such materials will be described later.

Mechanism of Piezoelectricity

The nature of the piezoelectric effect is closely related to the occurrence of electric dipole moments in solids. The latter may either be induced for ions on crystal lattice sites with asymmetric charge surroundings (as in BaTiO3 and PZTs) or may directly be carried by molecular groups (as in cane sugar). The dipole density or polarization (dimensionality [Cm/m3] )may easily be calculated for crystals by summing up the dipole moments per volume of the crystallographic unit cell. As every dipole is a vector, the dipole density P is a vector field. Dipoles near each other tend to be aligned in regions called Weiss domains. The domains are usually randomly oriented, but can be aligned using the process of poling (not the same as magnetic poling), a process by which a strong electric field is applied across the material, usually at elevated temperatures. Not all piezoelectric materials can be poled.

• Piezoelectricity is the combined effect of the electrical behaviour of the material

D= εE

• where D is the electric charge density displacement, ε is permittivity and E is electric field strength.

• Output Power from PiezoElectric Materials

The output voltage obtained from a single piezoelectric crystal is in millivolt(mV) range, which is different for different crystals.

• And the wattage is in microwatt(mW)

• In order to produce higher voltages, the piezoelectric materials can be arranged in series.

• It is used to power backup supplies or to power low-power microprocessors

Materials Many materials, both natural and synthetic, exhibit piezoelectricity:

• Naturally Occuring Quartz Sucrose Topaz

Lead Titanate (PbtiO3)

• Synthetic Ceramics Barium titanate(BaTiO3)(first piezoelectric ceramic) Zinc Oxide:

Polycrystalline (ceramic) ZnO with randomly oriented grains exhibits no piezoelectric effect.Ceramics and polycrystalline thin films of ZnO may exhibit macroscopic piezoelectricity only if they are textured (grains are preferentially oriented), such that the piezoelectric responses of all individual grains do not cancel. This is readily accomplished in polycrystalline thin films.

Piezoelectric SensorsA piezoelectric sensor is a device that uses the piezoelectric

effect, to measure changes in pressure, acceleration, temperature, strain or force by converting them to an electrical charge. The prefix piezo- is Greek for 'press' or 'squeeze'.

• One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements.

Sensor designBased on piezoelectric technology various physical quantities can

be measured; the most common are pressure and acceleration. For pressure sensors, a thin membrane and a massive base is used, ensuring that an applied pressure specifically loads the elements in one direction.

Various sensor application include :• Piezoelectric elements are also used in the detection and generation of

sonar waves• Power monitoring in high power applications (e.g. medical

treatment, sonochemistry and industrial processing)• Piezoelectric microbalances are used as very sensitive chemical and

biological sensors

• Reduction of vibrations and noise

Different teams of researchers have been investigating ways to reduce vibrations in materials by attaching piezo elements to the material. When the material is bent by a vibration in one direction, the vibration-reduction system responds to the bend and sends electric power to the piezo element to bend in the other direction. Future applications of this technology are expected in cars and houses to reduce noise. Further applications to flexible structures, such as shells and plates, have also been studied for nearly three decades.

• SurgeryA recent application of piezoelectric ultrasound sources is piezoelectric surgery, also known as piezosurgery. Piezosurgery is a minimally invasive technique that aims to cut a target tissue with little damage to neighboring tissues. For example, its use in hand surgery for the cutting of bone, using frequencies in the range 25–29 kHz, causing microvibrations of 60–210 μm. It has the ability to cut mineralized tissue without cutting neurovascular tissue and other soft tissue, thereby maintaining a blood-free operating area, better visibility and greater precision.

• Floor Mats And People Powered Dance Clubs

• Series of crystal can be laid below the floor mats,tiles and carpets.

• One footstep can only provide enough electrical current to light two 60-watt bulbs for one second.

• When mob uses the dance floor, an enormous voltage is generated.

• This energy is used to power the equipment of nightclubs.

• Mobile Keypads And Keyboards

• Crystals laid down under the keys of mobile unit and keyboard.

• For every key pressed vibrations are created.

• These vibrations can be used for charging purposes.

• Gyms and workplaces

• Vibrations caused from machines in the gym.

• At workplaces, piezoelectric crystal are laid in the chairs for storing energy.

• Utilizing the vibrations in vehicle like clutches, gears etc.

Advantages and disadvantages of Piezoelectricity

Advantages •Unaffected by external electromagnetics fields.

•Pollution free.

•Low maintenance.

•Easy replacement of equipment.

Disadvantages• They cannot be used for

truly statics measurements.

• Can pick up stray voltages in connecting wires.

• Crystal is prone to crack if overstressed.

• May get affected by long use at high temperatures.

• Conclusion

• Flexible piezoelectric materials are attractive for power harvesting apllications because of their ability to withstand large amount of strain.

• Convert the ambient vibration energy surrounding them into electrical energy.

• Electrical energy can then be used to power other devices or stored for later use.