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Journal of the Acoustical Society of America

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Feb 2002

Volume 111, Issue 2, pp. 643-1128

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Research into an integrated intelligent structure— A new actuator combining piezoelectric ceramic and electrorheological fluid

Li Quanlu

J. Acoust. Soc. Am. Volume 111, Issue 2, pp. 856-860 (2002); (5 pages)

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The design, preparation, and application of high-performance piezoelectric ceramics, e.g., FD3–PZT and FD4–PZT, then preparation, performance measurement, and applications of composite electrorheological fluids have been studied, respectively. The integrated intelligent structure (i.e., a new actuator) combining the piezoelectric ceramic and the electrorheological fluids, and their applications have been investigated, and emphasis was given to the applications in acoustics and vibration control, etc. as may be noted. © 2002 Acoustical Society of America.
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43.38.Ar Transducing principles, materials, and structures: general
43.38.Fx Piezoelectric and ferroelectric transducers

Noise in miniature microphones

Stephen C. Thompson, Janice L. LoPresti, Eugene M. Ring, Henry G. Nepomuceno, John J. Beard, William J. Ballad, and Elmer V. Carlson

J. Acoust. Soc. Am. Volume 111, Issue 2, pp. 861-866 (2002); (6 pages) | Cited 8 times

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The internal noise spectrum in miniature electret microphones of the type used in the manufacture of hearing aids is measured. An analogous circuit model of the microphone is empirically fit to the measured data and used to determine the important sources of noise within the microphone. The dominant noise source is found to depend on the frequency. Below 40 Hz and above 9 kHz, the dominant source is electrical noise from the amplifier circuit needed to buffer the electrical signal from the microphone diaphragm. Between approximately 40 Hz and 1 kHz, the dominant source is thermal noise originating in the acoustic flow resistance of the small hole pierced in the diaphragm to equalize barometric pressure. Between approximately 1 kHz and 9 kHz, the noise originates in the acoustic flow resistances of sound entering the microphone and propagating to the diaphragm. To further reduce the microphone internal noise in the audio band requires attacking these sources. A prototype microphone having reduced acoustical noise is measured and discussed. © 2002 Acoustical Society of America.
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43.38.Bs Electrostatic transducers

Acoustic radiation impedance of rectangular pistons on prolate spheroids

Jeffrey E. Boisvert and A. L. Van Buren

J. Acoust. Soc. Am. Volume 111, Issue 2, pp. 867-874 (2002); (8 pages) | Cited 4 times

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The self and mutual radiation impedances for rectangular piston(s) arbitrarily located on a rigid prolate spheroidal baffle are formulated. The pistons are assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wave functions are obtained using computer programs that have been recently developed to provide accurate values of the wave functions at high frequencies. Results for the normalized self and mutual radiation resistance and reactance are presented over a wide frequency range for different piston sizes and spheroid shapes. © 2002 Acoustical Society of America.
Show PACS
43.38.Hz Transducer arrays, acoustic interaction effects in arrays
43.20.Rz Steady-state radiation from sources, impedance, radiation patterns, boundary element methods
43.30.Jx Radiation from objects vibrating under water, acoustic and mechanical impedance
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