Aero-acoustics, a branch of acoustics which studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces, is a growing area and has received fresh emphasis due to advances in air, ground and space transportation. While tests of a real object are possible, the setup is usually complicated and the results are easily corrupted by the ambient noise. Consequently, testing in relatively tightly-controlled laboratory settings using scaled models with reduced dimensions is preferred. However, when the dimensions are reduced by a factor of M, the amplitude and the bandwidth of the corresponding acoustic waves are increased by 10logM in decibels and M, respectively. Therefore microphones with a bandwidth of several hundreds of kHz and a dynamic range...[ Read more ]

Aero-acoustics, a branch of acoustics which studies noise generation via either turbulent fluid motion or aerodynamic forces interacting with surfaces, is a growing area and has received fresh emphasis due to advances in air, ground and space transportation. While tests of a real object are possible, the setup is usually complicated and the results are easily corrupted by the ambient noise. Consequently, testing in relatively tightly-controlled laboratory settings using scaled models with reduced dimensions is preferred. However, when the dimensions are reduced by a factor of M, the amplitude and the bandwidth of the corresponding acoustic waves are increased by 10logM in decibels and M, respectively. Therefore microphones with a bandwidth of several hundreds of kHz and a dynamic range covering 40Pa to 4kPa are needed for aero-acoustic measurements.

Micro-Electro-Mechanical-system (MEMS) microphones have been investigated for more than twenty years, and recently, the semiconductor industry has put more and more concentration on this area. Compared with all other working principles, due to their scaling characteristic, piezoresistive type microphones can achieve a higher sensitivity bandwidth (SBW) product, and in turn they are well suited for aero-acoustic measurements. In this thesis, two metal-induced-lateral-crystallized (MILC) polycrystalline silicon (poly-Si) based piezoresistive type MEMS microphones are designed and fabricated using surface micromachining and bulk micromachining techniques, respectively. These microphones are calibrated using an electrical spark generated shockwave (N-wave) source. For the surface micromachined sample, the measured static sensitivity is 0.4μV/V/Pa, dynamic sensitivity is 0.033μV/V/Pa and the frequency range starts from 100kHz with a first mode resonant frequency of 400kHz. For the bulk micromachined sample, the measured static sensitivity is 0.28μV/V/Pa, dynamic sensitivity is 0.33μV/V/Pa and the frequency range starts from 6kHz with a first mode resonant frequency of 715kHz.