Application of MEMS Microphone Array Technology to Airframe Noise Measurements

Abstract

Current generation microphone directional array instrumentation is capable of extracting accurate noise source location and directivity data on a variety of aircraft components, resulting in significant gains in test productivity. However, with this gain in productivity has come the desire to install larger and more complex arrays in a variety of ground test facilities, creating new challenges for the designers of array systems. To overcome these challenges, a research study was initiated to identify and develop hardware and fabrication technologies which could be used to construct an array system exhibiting acceptable measurement performance but at much lower cost and with much simpler installation requirements. This paper describes an effort to fabricate a 128-sensor array using commercially available Micro-Electro-Mechanical System (MEMS) microphones. The MEMS array was used to acquire noise data for an isolated 26%-scale high-fidelity Boeing 777 landing gear in the Virginia Polytechnic Institute and State University Stability Tunnel across a range of Mach numbers. The overall performance of the array was excellent, and major noise sources were successfully identified from the measurements.

Noise Spectra and Directivity for a Scale-Model Landing Gear

“…Such a finding is consistent with previous aeroacoustic studies performed on similar models. 9,10,19,20 The oleo / strut noise appears most dominant in the non-door, sideline view. This noise region is less well defined for the door sideline view, perhaps due to the strut orientation and partial obscuration by the door.…”

“…10 Detailed testing of the same model, both in baseline and noise treated configurations, was conducted in a hard-walled wind tunnel in 2004. 19,20 However, these tests did not include extensive directivity measurements. The most complete full-scale directivity measurements reported to date have been those of Pott-Pollenske et al acquired on an Airbus A319 aircraft.…”

Three-Dimensional Applications of DAMAS Methodology for Aeroacoustic Noise Source Definition

“…VT Landing Gear Test. An aeroacoustic noise test 6 was conducted for a 26%-scale, high-fidelity Boeing 777 main landing gear (LG) model in the Stability Wind Tunnel at the Virginia Polytechnic Institute and State University (Virginia Tech, VT). The model was previously tested at VT 7 and at NASA Ames Research Center 8 .…”

“…The model was previously tested at VT 7 and at NASA Ames Research Center 8 . A portion of the VT measurements was conducted by NASA LaRC with the primary purpose of demonstrating the use of an array using Micro-Electro-Mechanical System (MEMS) sensors 6 .…”

Quick and easy binary to dB conversion

“…One such application is the collection of acoustic data using an array of MEMS microphones [7][8][9]. To monitor this process, it is desirable to provide an indication in decibels (dB) of the amplitudes of the analog inputs.…”