Modelling the electromechanical film (EMFi)

The porous EMFi electret film is modelled using a simplified one air gap structure. Linear models for the sensor and actuator thickness operation modes of the film are identical, which shows the reciprocity of the sensor and actuator models. Using the models with some experimental data the film's Young's modulus, sensitivity and charge density on the polypropylene/air void interfaces are determined. The effect of the charges near the surfaces seems to be negligible. The electromechanical transducer constant or the sensitivity values are higher using a pseudo-static actuator measurement compared to a dynamic sensor measurement associated with some static pressure. (C) 2000 Elsevier Science B.V. All rights reserved.