Piezoelectric effect
A piezoelectric substance is a crystalline mineral which responds to a mechanical force by generating an electric charge.
The substance may be considered as a lattice of electric dipoles, which together form a polarized field. When the field undergoes mechanical stress, the field changes its polarization, either through a physical reconfiguration of the dipole lattice or a re-orientation of the dipole moments under stress. This is the piezoelectric effect.
Piezoelectric material (1) before poling, (2) after poling. Adapted from source: http://www.physikinstrumente.com/tutorial/4_15.html
The piezoelectric effect is reciprocal, meaning: A) a piezoelectric substance will respond to a mechanical force by generating an electric charge, and; B) it will respond to an electric field by generating a mechanical response. This latter response is called the inverse piezoelectric effect.
The piezoelectric effect and its inverse are also proportional. The voltage generated by the piezoelectric effect is proportional to: A) the amount of force applied, and; B) the type of force applied (i.e. tension and compression produce opposite polarities). Likewise, the mechanical response of the inverse piezoelectric effect is proportional to: A) the field's strength, and; B) the field’s polarity.
The piezoelectric effect is passive, and requires no additional power other than the mechanical or electric stimulus.
Direct and inverse piezoelectric effects. Source: http://resources.edb.gov.hk/physics/articleIE/smartmaterials/SmartMaterials_e.htm
Piezo sensors
Used for quality assurance, process controll and for research and development i.e. medical, aerospace, nuclear instrumentation and tilt sensors. Piezo technology is insensitive to electromagnetic fields and radiation, which enable measurements in harsh conditions. Down-side of the Piezo sensor is that they cannot be used for truly static measurement. This happens because a static force will have continous effect to the sensor.
Piezo actuators
These piezo components have high power density, high positioning accuracy, high reliability and low powers losses. So by actuators it is great way to create aerospace applications. Different application for the actuators are valves, door locks, and energy harvesting.
Piezo transducers
Transducers provide high efficiency and inherently broadband performance.
They are used for i.e Proximity Sensing, Fluid Level Detection and Solid/liquid Separation.
Single-layer Piezoelectric Generators
The main point is to create very quickly, very high voltage and very low current. Following applications are working this way, cigarette lighters and some grills. By pressing a button causes a spring-loaded hammer to apply a mechanical force. By the result of piezoelectric effect it produces a voltage that passes across a small gap and ignite the gas.
Multilayer Piezoelectric Generators
Consist of a stack of very thin piezoelectric ceramics with electrodes.
with piezoelectic effect it generates low voltage with high current.
Excellent for solid-state batteries for electronic circuits and in sensors i.e. which monitor tire pressure in cars.
Piezoelectric ceramics
Frequently used in this capacity to ignite a fuel source in lighters, gas stoves and welding equipment. [5.]
An example how the Piezoelectric Element works. Adapted from source: http://global.kyocera.com/fcworld/charact/elect/piezo.html
Piezoelectric materials
Nowadays for the Piezoelectric sensing is mostly used ceramics. The earliest one was Titanate. The three most popular piezoelectric materials are Zinc oxide, Aluminum nitride and lead-zirconite-titanium oxides what is known as PZT.
Piezoelectric materials are usually sensitive to temperature changes. For example quartz looses sensitivity if the temperature drops with a slope of -0,016%/Celsius. With PVCF films and materials the sensitivity changes when the temperature is on the higher or lower side of 40 Celsius.
Piezoelectric materials are usually generated from high-purity metal oxides in form of fine powder (lead oxide, titanium oxide etc.).The powder is calcinated and mixed in a right proportion. Then it is mixed with solid and/or liquid organic binders to make a so called "cake" and heated in a controlled temperature. The material is covered with contact electrodes and poled. After this the piezoelectric material is shaped to its final shape. [8.]
New materials
- Single Crystals:
- magnesium niobate / lead titanate (PMN-PT)
- lead zirconate niobate / lead titanate (PZN-PT)
- lithium niobate (LiNbO3)
- lithium niobate with dopants
- lithium tetraborate (Li2B4O7)
- quartz
- barium titanate (BaTiO3)
- Relaxors:
- lead magnesium niobate
- lead magnesium niobate / lanthanum
- lead nickel niobate [4.]
Modeling piezoelectric sensing
As earlier we determined how piezoelectric will work and here is explanation how to determine a g-coefficent:
Determining the coefficent a voltage gradient:
Determining other coefficent which h is determined:
Piezoelectrical phenomenon is said in other words that it changes mechanical energy into electrical energy
It can be determined as the following:
coupling coefficents kmn is:
The capacitance of piezoelectric can be determined by using the formula as below:
where a is area and l is the crystal thickness
At last the output voltage can be calculated such as:
References
- http://www.piceramic.com/piezo_effect.phphttps://www.americanpiezo.com/knowledge-center/piezo-theory/piezoelectricity.htm
- http://en.wikipedia.org/wiki/Piezoelectricity
- https://www.americanpiezo.com/piezo-theory/ceramics.html
- https://www.americanpiezo.com/knowledge-center/piezo-theory/new-materials.html
- https://www.americanpiezo.com/piezo-theory/generators.html
- http://en.wikipedia.org/wiki/Amplified_piezoelectric_actuator#Applications
- http://www.matsysinc.com/products/transducers/examples.php
- Jacob Fraden: Handbook of Modern Sensors (Physics, Designs and Applications), Fourth Edition, Springer