Cellular Polypropylene electret Material Electromechanical Properties;Doctoral thesis

摘要

The cellular polypropylene (PP) film is soft and elastic and it encloses multiple polymer-gas interfaces between thin non-cellular surface layers. With a high enough corona voltage it is possible to achieve a high space charge density on the internal interfaces. The cellular charged structure forms an effective electret material that has an electromechanical transducer coefficient d33, typically around 200 Pcn(sup -1) for the 70 micrometers thick film. The sensor and actuator operations in thickness mode are reciprocal according to electromechanical models for simplified multiple and single layer structures. The direct d(sub 33) coefficient related to sensor operation in units of CN(sup -1) equals the indirect d(sub 33) coefficient related to the actuator operation in units of MV(sup -1). Dynamical measurements seem to give a lower transducer coefficient compared to quasi static measurements.