NASA's Langley Research Center, in collaboration with Michigan State University (MSU), has developed a microphone array that identifies the locations and strengths of acoustic sources using sensors that are “self-calibrated” with closed-loop feedback control. This results in an array that can be considered “self-matching.” Beamforming microphone arrays typically consist of tens to hundreds of microphones. The location of an acoustic source can be determined by exploiting the acoustic wave propagation delays from the source to each of the microphones. For the system to be accurate, each microphone must be calibrated to account for varying magnitude and phase frequency responses. Manual calibration is time-consuming and may need to be repeated regularly to take into account effects such as heat and humidity. The NASA Langley/MSU innovation removes such time-consuming calibration and provides more accurate results.

A microphone array in the Langley Jet Noise Laboratory.

This invention uses microphones that are self-calibrated using electrical actuation, and feedback control that self-matches the frequency response of each microphone in the array based on user specifications. NASA Langley and MSU have developed and tested a microphone prototype using a thin polyvinyledinefluoride (PVDF) film membrane, which allows for actuation in a feedback scheme. The feedback actively modifies such sensor parameters as membrane stiffness, resonant frequency, damping, and DC attenuation. A fiber-optic sensor was used to detect displacement of the membrane's center caused by acoustic pressure. The feedback response was verified as closely matching what was predicted.

Potential applications include aeroa-coustics research, jet noise research, military, and remote sensing.

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