Small Piezoresistive Silicon Microphones Specially Designed for the Characterization of Turbulent Gas Flows

Piezoresistive microphones have been designed and fabricated using surface micromachining technology. The acoustic sensors, which are specially designed for turbulence gas flow measurements, are fabricated with the very small diaphragm side lengths of 100 and 300 um. An expression for the dynamic pressure sensitivity is derived where the diaphragm bending forces, the tensile built-in stain force, as well as the fluid compressibility forces are considered. The acoustic sensitivity’s, which are in the range 0.3-0.9 u V/Pa for a supply voltage of 10 V, are compared with the calculated values, showing good agreement. The frequency response is falt up to 10 kHz within -+ 2dB. The ability to measure the smallest pressure eddies in a turbulent boundary layer is verified and compared for different diaphragm sizes