Micromachined reconfigurable microphone array for wind tunnel testing

A surface micromachined, front-vented, 64 channel (8×8), capacitively sensed microphone array-on-a-chip devices for aeroacoustic testing is described. The arrays are fabricated using the MEMSCAP PolyMUMPs polysilicon surface micromachining process, with a Parylene-C passivation layer. The devices are packaged with low profile interconnects, presenting a maximum of 100 μm of surface topology. The array electronics allow the microphone outputs to be redirected to one of two channels, allowing dynamic reconfiguration of the effective transducer shape in software. Measured microphone sensitivity is 0.15 mV/Pa for an individual microphone and 8.7 mV/Pa for the entire array, in close agreement with model predictions. The microphones and electronics operate over the 200–40 000 Hz band. The dynamic range extends from 60 dB SPL in a 1 Hz band to greater than 150 dB SPL. Element variability is ±0.05 mV/Pa in sensitivity with an array yield of 95%. Off-chip electronics provide 80 dB off isolation. Preliminary wind tunnel testing at flow rates of up to 23 m/s indicates that the devices continue to operate in flow without damage, and can be successfully reconfigured on the fly. Analysis of measured boundary layer pressure spectra at six flow rates from 5 to 23 m/s is underway.