The theory of a piezoelectric plastic film transducer for earphones

Abstract

The author is concerned with the theory of a domed piezoelectric plastic film which can be used as a combined diaphragm and transducer element in an earphone. In his model the diaphragm is held in a dome shape by a pressure, P, applied to one side. It is shown that the centre of the dome is displaced from the perimeter plane by a distance which varies as P1/3 at high pressures. At low pressures the displacement depends on the state of the diaphragm before pressure is applied. An electric field applied across the film thickness changes the dome displacement through the piezoelectric effect. For large P and small electric fields the change of displacement is linearly proportional to the field and varies as P-1/3. As P to 0 the behaviour is more complicated.