Capacitive Silicon Sensors for Ultrasound
The simulation, implementation, and experimental study of ultrasonic sensors made with micromachining techniques on silicon wafers is discussed. The theoretical model of the sensor is based on a lumped-element equivalent circuit and takes into consideration the customary components of a condenser microphone including stiffness and friction of the air gap. The simulation results show the effect of the frictional damping on the frequency response: In general, the microphones have two frequency ranges of constant sensitivity, controlled by the tension of the membrane and by the air gap stiffness, respectively, and separated by a resistive drop-off region. Depending on the amount of resistive damping, either of the restoring forces can control the resonance frequency. An implementation of the microphone consists of a membrane chip with a Si3N4 membrane and a backplate chip with holes or slits bonded to the membrane chip. Experimental results for the sensitivity and frequency response of a two-chip silicon microphone are presented. The microphone shows an almost constant sensitivity of about 1.6 mV/Pa in the frequency range up to 180 kHz. Finally, the micromechanical processing steps of a new single-chip, ultrasonic sensor not yet implemented are discussed.
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Document Type: Research Article
Publication date: 1997-07-01
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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