Preliminary results of a silicon condenser microphone with internal feedback

In order to overcome the problem of a too large bias voltage and to increase the bandwidth of silicon condenser microphones with small air gaps, an electrostatic feedback system is presented that will reduce the movement of the diaphragm of the microphone. It is shown that a 10-fold reduction of the movement of the diaphragm is possible for microphones with an air gap of 35 mu m. However, to get a reduction of about ten times over a wide range of frequencies, an actuator with a larger sensitivity is needed. This can be achieved by the use of a smaller air gap, which may also increase the sensor sensitivity.<>