In many designs of capacitive microphones or pressure sensors the electrode size is chosen to be equal to the diaphragm size. In this paper it will be discussed whether an electrode size or shape that differs from that of the diaphragm is attractive for obtaining a maximum value for the sensor sensitivity and the signal-to-noise ratio. A theoretical analysis will be given for circular diaphragms and electrodes, from which it can be shown that for maximum sensitivity the electrode should be located at the centre of the diaphragm, with a radius depending on the value of the amplifier input capacitance.
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