Passive and Active Piezo Sensors

The piezoelectric measuring methods can be roughly divided in two groups, corresponding to the fact of whether the sensor works with a passive or an active principle. 

There are two types of sensors to be distinguished axial and bending sensors. In the case of an axial sensor the force works in the polarization direction, while for the bending sensor the force works perpendicularly to it. Concerning the latter, emerging tensile or pressure forces depend on the distance of the active material from the neutral fiber [91]. 

Independently from the material the following equations describe the sensor effect [84]  

If the electric field is zero and no thermal expansion is predominant above, the equation reduces to 

A mechanical tension vector T causes a dielectric displacement D that generates a charge q which is 

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