A Microphone Array on a Chip for High Spatial Resolution Measurements of Turbulence

Abstract

A microelectromechanical systems-based microphone array on a chip has been developed and applied to aeroacoustic measurements. The array is designed to measure the fluctuating pressures present under a turbulent boundary layer (TBL). Each chip measures 1 cm 2 and contains 64 individually addressable capacitively sensed microphones, with a center to center pitch of ∼1.25 mm. Surface topology, including the packaging, is kept to less than 0.13 mm. Element-to-element sensitivity variation in the array is less than ±2.5 dB from least to most sensitive, and phase variation is less than ±6.5°( at 1 kHz). The microphone 3-dB bandwidth is 700 Hz to 200 kHz, and the microphones are linear to better than 0.3% at sound pressure levels up to 150-dB SPL. A unique switched architecture system electronics and packaging method are employed to reduce data acquisition channel count requirements, and to maintain a low surface roughness. The array has been applied to the measurement of single point turbulence spectra under a flat plate TBL in a flow duct at Mach numbers up to 0.6 and Reynolds numbers based on plate length of 10 7 .

A Flush-Mount Sensor Package for a Mems Piezoelectric Microphone With Through-Silicon-Vias for Aircraft Fuselage Arrays

“…TSVs were formulated into the fabrication to eliminate the use of front side wire bonds. The packaged sensor demonstrates an overall flushness to within 10 µm, showing an order of magnitude improvement from recently reported efforts in similar endeavors [2]. Preliminary characterization shows a comparable sensitivity (13.1 µV/Pa) and significantly higher resonant frequency (194 kHz) than the most recent piezoelectric aeroacoustic microphone [1].…”

“…Previously developed MEMS aeroacoustic microphones [1][2][3][4][5][6][7][8][9][10] have failed to address the need for a sensor that can be packaged and installed with a hydraulically smooth front surface to be used for boundary layer measurements in a fuselage array. Protrusions from the surface must be within the viscous sublayer, or smaller than 5 viscous wall units, in order for the flow to see an essentially flat surface [11].…”

“…Protrusions from the surface must be within the viscous sublayer, or smaller than 5 viscous wall units, in order for the flow to see an essentially flat surface [11]. The surface topography of the sensor and associated package that utilizes wire bonds alone is locally limited to ~130 μm [2], and a required protective encapsulant adds to the surface roughness. Additionally, through-silicon via (TSV) transducer implementation has largely been limited to under-bump metallization attachment techniques [12,13] where sensor flushness is not a priority.…”