PhD Thesis Presentation
High Frequency MEMS Sensor for Aero-acoustic Measurements

by Mr Zhijian ZHOU

 :  21 Jan 2013 (Mon)
 :  5pm
Venue  :  Library Learning Common, Tutorial Space A-C, HKUST

Examination Committee
Prof David E COOK, ECON/HKUST (Chairman)
Prof Man WONG, ECE/HKUST (Thesis Supervisor)
Prof Libor RUFER, TIMA/University of Grenoble (Thesis Supervisor)
Prof Philippe BLANC-BENON, LMFA/Ecole Centrale de Lyon (External Examiner)
Prof Philippe COMBETTE, MITEA/Universite Montpellier II (External Examiner)
Prof Wenjing YE, MECH/HKUST
Prof Skandar BASROUR, TIMA/University of Grenoble
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 decibel 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 industry has put more and more concentrations on this area. Compared with all other working principles, due to its 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 microphone are designed and fabricated using surface micromachining and bulk micromachining techniques, respectively. These microphones are calibrated using 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.

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