AIR-PRESSURE-CHANGE DETECTOR

摘要

PURPOSE: To detect a weak and extremely low frequency nonaudible sound wave correctly at high accuracy by a structure wherein a cantilever strip piezoelectric element of specified thickness responds to the oscillation of the air at the through hole part of a substrate. CONSTITUTION: A strip piezoelectric element 2 of 300μm thick or less has a cantilever end 2a at the through hole part of a substrate 1 and the other end 2b located in the through hole. In response even to a weak pneumatic pressure transmitting from a vent 5b through a case 5, the piezoelectric element oscillates at the end 2b thereof to induce an output voltage. It is delivered through an impedance conversion circuit 8 and the weak and extremely low frequency sound wave is detected correctly at high accuracy. The piezoelectric element 2 and the impedance conversion circuit 8 are encased 5 in order to reduce external noise due to electrode induction.