You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 13 Next »

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.

 

 

Applications (Aleksi)

http://www.youtube.com/watch?v=fHp95e-CwWQ

 

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.


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

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.php

https://www.americanpiezo.com/knowledge-center/piezo-theory/piezoelectricity.html

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

Jacob Fraden: Handbook of Modern Sensors (Physics, Designs and Applications), Fourth Edition, Springer

 

  • No labels
You must log in to comment.