Characterization of Aeroacoustic, Silicon Micromachined Microphones for Aircraft Fuselage Arrays

Thispaperdescribesthedesignandcharacterization ofamicromachined microphoneforaircraft fuselagearrays utilized by aeroacousticians to help identify aircraft noise sources and/or assess the effectiveness of noise-reduction technologies. The developed microphone utilizes piezoelectric transduction via an integrated aluminum nitride layer in a thin-film composite diaphragm fabricated using a combination of surface and bulk micromachining. The experimental characterization of several microphones is presented. Measured performance was in line with the Boeing Company specifications for the fuselage array application, including sensitivities of 32:1 � V=Pa to 43:7 � V=Pa,minimumdetectablepressuresaslowas40dB(1Hzbinat1kHz),confirmedbandwidthsupto20kHz, >100 kHz resonant frequencies, and 3% distortion limits between 160 and 172 dB sound pressure level. With this performance, in addition to the small sizes, these microphones are shown to be a viable enabling technology for low-cost, high-resolution fuselage array measurements.