PIEZOELECTRIC EFFECT              

Piezoelectric Effect

  Piezoelectric Effect or Piezoelectric property of a material refers to the ability to induce opposite charges at two faces (correspondingly, to exhibit a voltage difference between the faces) of the material as a result of the strain due to mechanical force (either tension or compression) applied across the surfaces. This process is also reversible in the sense that a mechanical strain would be experienced in the material when subjected to opposite electric charging at the two faces by means of an applied potential.

 In the event of such an applied voltage being alternating, the material specimen will experience vibrations. Likewise, an applied vibration on the specimen would induce an alternating potential change between the two faces. The most commonly known materials that exhibit piezoelectric properties are natural materials like quartz and a number of crystalline and polycrystalline compounds.

 The strain versus the electric phenomenon perceived in piezoelectric materials is dictated by a coefficient that has components referred to a set of orthogonal coordinate axes (which are correlated to standard crystallographic axes). For example, denoting the piezoelectric coefficient (ratio between piezoelectric strain component to applied electric field component at constant mechanical stress or vice versa) as dmn, the subscript n (1 to 3) refers to the three euclidian orthogonal axes, and m = 1 to 6 specifies the mechanical stress-strain components. The unit for dmn is meter/volt which is the same as coulomb/newton. In the piezoelectric phenomenon, there is an electromechanical synergism expressed as a coupling factor K defined by K2, which quantifies the ratio of mechanical energy converted into electric charges to the mechanical energy impressed on the material. Being a reversible process, a relevant inverse ratio is also applicable.