PIEZOELECTRIC PROPERTIES OF NONUNIFORM ELECTRETS

It is generally well known that the piezoelectric effect in solids is tightly connected with the molecular structure of a solid dielectric. However, an analysis of a simple model of this phenomenon provides a conclusion that piezoelectricity can also appear in materials containing the fixed space charge and spatially dependent elasticity. In such a situation the changes of the space charge distribution under the external stress will not follow the changes in the molecular structure. The resulting changes in the effective surface charge densities on both electrodes are the source of a piezo-signal. To demonstrate a simple model supporting the above hypothesis, a thin double-layer electret was prepared. The layers were made of polymers with significantly different mechanical properties (coefficients of elasticity). The most interesting results of this work offer, as is believed, the possibilities of the preparation of the technologically new high-sensitive and low-cost piezoelements, and the more widespread use of materials suitable for the production of a wide variety of sensors. © 1995.