A directional acoustic array using silicon micromachined piezoresistive microphones

Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida, United States
The Journal of the Acoustical Society of America (Impact Factor: 1.5). 02/2003; 113(1):289-98. DOI: 10.1121/1.1527960
Source: PubMed


The need for noise source localization and characterization has driven the development of advanced sound field measurement techniques using microphone arrays. Unfortunately, the cost and complexity of these systems currently limit their widespread use. Directional acoustic arrays are commonly used in wind tunnel studies of aeroacoustic sources and may consist of hundreds of condenser microphones. A microelectromechanical system (MEMS)-based directional acoustic array system is presented to demonstrate key technologies to reduce the cost, increase the mobility, and improve the data processing efficiency versus conventional systems. The system uses 16 hybrid-packaged MEMS silicon piezoresistive microphones that are mounted to a printed circuit board. In addition, a high-speed signal processing system was employed to generate the array response in near real time. Dynamic calibrations of the microphone sensor modules indicate an average sensitivity of 831 microV/Pa with matched magnitude (+/-0.6 dB) and phase (+/-1 degree) responses between devices. The array system was characterized in an anechoic chamber using a monopole source as a function of frequency, sound pressure level, and source location. The performance of the MEMS-based array is comparable to conventional array systems and also benefits from significant cost savings.

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    • "Many microelectromechanical systems (MEMS) based electroacoustic devices, such as microphones, utilize composite plates [1] [2] [3]. The plate's mechanical response to acoustic pressure oscillations is important in determining the sensitivity, bandwidth, and dynamic range of the electroacoustic device. "
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    ABSTRACT: Many micromachined electroacoustic devices use thin plates in conjunction with electrical components to measure acoustic signals. Composite layers are needed for electrical passivation, moisture barriers, etc. The layers often contain residual stresses introduced during the fabrication process. Accurate models of the composite plate mechanics are crucial for predicting and optimizing device performance. In this paper, the von Kármán plate theory is implemented for a transversely isotropic, axisymmetric plate with in-plane tensile stress and uniform transverse pressure loading. A numerical solution of the coupled force-displacement nonlinear differential equations is found using an iterative technique. The results are verified using finite element analysis. This paper contains a study of the effects of tensile residual stresses on the displacement field and examines the transition between linear and nonlinear behavior. The results demonstrate that stress stiffening in the composite plate delays the onset of nonlinear deflections and decreases the mechanical sensitivity. In addition, under high stress the plate behavior transitions to that of a membrane and becomes insensitive to the composite nature of the plate. The results suggest a tradeoff between mechanical sensitivity and linearity.
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    • "Furthermore, unlike small diaphragms made via traditional means, the MEMS diaphragms can be well controlled in terms of dimensions and stress [6]. Batch fabrication can be leveraged to produce microphones with closely matched specifications, which is beneficial for microphone arrays [7]. Additionally, the cost of a MEMS microphone has the potential to be lower than traditional microphones, provided there is sufficient volume [8]. "
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    ABSTRACT: This paper presents the development of a micro-machined dual-backplate capacitive microphone for aeroacoustic measurements. The device theory, fabrication, and characterization are discussed. The microphone is fabricated using the five-layer planarized-polysilicon SUMMiT V process at Sandia National Laboratories. The microphone consists of a 0.46-mm-diameter 2.25-mum-thick circular diaphragm and two circular backplates. The diaphragm is separated from each backplate by a 2-mum air gap. Experimental characterization of the microphone shows a sensitivity of 390 muV/Pa. The dynamic range of the microphone interfaced with a charge amplifier extends from the noise floor of 41 dB/ radicHz up to 164 dB and the resonant frequency is 178 kHz.
    Full-text · Article · Jan 2008 · Journal of Microelectromechanical Systems
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