5.4.1 Direct Piezoelectric Effect
Direct effect occurs when an applied stress to a material gives rise to a change in the polarization density which in turn can be detected as electric field or potential across the sample. Here, the polarization is directly proportional to the stress applied, as described by the equation.
where P is polarization, σ is applied stress and d is piezoelectric coefficient (actually a third rank tensor).
5.4.2 Reverse or Converse Piezoelectric Effect
The reverse is true is when an electric field is applied to the material and as a result, a strain is induced expressed as
where ε is the strain induced, d is the piezoelectric coefficient and E is the applied electric field.
| Figure 5.20 Direct and Converse Piezoelectric Effects |
The direct piezoelectric effect is used as the basis for force, pressure, vibration and acceleration sensors while converse effect is used as a basis for actuator and displacement devices.
|
