A new piezoelectric microphone with divided electrodes

Abstract

A new type of piezoelectric ceramic microphone is proposed. Its merits are as follows. (1) High output, high efficiency—A high output voltage was obtained by dividing the piezoelectric ceramic electrodes and connecting them in series. The output voltge is proportional to the number of divisions. However, since the impedance is high, an FET circuit is required to decrease output impedance. At the same time, an improvement of the signal-to-noise ratio was also realized. (2) Reduction of diaphragm mechanical impedance—To improve the matching to the impedance of air, a mechanical transformer was introduced. The center of the diaphragm was lightened and its rigidity was increased by combining a dome-type diaphragm and ring-shaped piezoelectric ceramic. This made it easy to control the frequency response. (3) Stability—The diaphragm consists of a Y2O3⋅PSZ ceramic thin film formed into a dome shape and laminated to a ring-shaped ceramic. This structure showed a higher temperature stability and noticeably lower aging change than the conventional flat-type diaphragm. The specifications of the prototype microphone are the following: diameter, 1 in. (23.8 mm), nondirectional; sensitivity, −59 dB/uμbar at FET source output; frequency response, 20 Hz–12.5 kHz −+ 1.5 dB; S/N ratio, 59 dB A-weighted.