Capacitance Microphone Dynamic Membrane Deflections

Abstract

In order to describe the operation of capacitance microphones accurately, it is necessary to have solutions for both the static and dynamic deflections of the moving electrode. The authors have previously presented numerical solution approaches to the static deflections caused by the electrical biasing of the microphone. The present paper describes an application of finite difference methods to the differential equations describing the dynamic membrane motion due to the acoustic excitation. The solutions include the effects of the static deflections and the motion of the thin air film between the microphone's electrodes. The numerical results are compared with published results for simplified stationary electrode geometries and with experimental data on more complicated geometries at different tension levels. The predicted mode shapes and resonant frequencies change greatly depending upon the magnitudes of the membrane tensions and the back chamber volume.