
38 Fundamentals of Sensors for Engineering and Science
stretched diaphragm, a small air gap (∼0.001 in.), and a receiving plate. The
plate is connected through a circuit capacitor to an amplifier and through
a circuit resistor to a dc-voltage source that is biased to several hundred
volts. This bias voltage establishes a fixed charge on the sensor’s diaphragm
and receiving plate. The source cathode is connected to the amplifier’s other
input and its anode to the circuit resistor and the sensor housing.
The impingement of sound pressure waves on the sensor causes small
displacements of the diaphragm and, hence, relatively small variations in
the sensor’s ...