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DESIGN AND PRELIMINARY TESTING OF A MEMS MICROPHONE PHASED ARRAY

In recent years, electret and MEMS (micro-electrical mechanical systems) microphones have been used as low-cost alternatives to more costly condenser microphones for use in phased arrays. In aeroacoustic testing, phased arrays are ideal for their ability to locate and quantify noise sources. Research into the design, fabrication, and implementation of a lowcost, electronically simple phased array will increase its potential as a common research tool. This paper discusses the design and preliminary testing of a simplified MEMS microphone array for use in aeroacoustic testing. The primary intent of the array design was to improve the signal-to-noise ratio of aeroacoustic sources as opposed to locating them accurately, particularly in a wind tunnel with a square cross section of 152.4 mm x 152.4 mm. Using a number of beamforming algorithms, the design of the phased array was modeled numerically. The phased array was constructed on a single, two-layer PCB (printed circuit board) and composed of 27 MEMS microphones each with built-in amplification and RF protection. The Underbrink equal area aperture array layout was used in the design with 9 spirals each consisting of 3 microphones. Further design and manufacturing details are presented. The array was calibrated and used successfully in preliminary testing using the conventional beamforming technique to locate noise sources within the expected margin of error.