Analysis of electret sub-miniature microphones

Previously a method of evaluation of electret microphones with a flexible diaphragm has been presented. It was based on taking into account electrostatic forces between a membrane and a back plate in the field of electret. However this method is not appropriate for a sub-miniature microphone with a rigid diaphragm. Besides this use of a double-layer dielectric with different sizes and dielectric constants of the back plate and a diaphragm is also a reason for such inapplicability. Usually an estimation of the microphone sensitivity is based on an evaluation of the voltage that is generated by diaphragm oscillations. Thus an alternating of field in a gap between the diaphragm and the back plate is a general basis for all types of microphone's evaluation.