Index of content:
Volume 111, Issue 2, February 2002
- TRANSDUCTION 
Research into an integrated intelligent structure— A new actuator combining piezoelectric ceramic and electrorheological fluid111(2002); http://dx.doi.org/10.1121/1.1421343View Description Hide Description
The design, preparation, and application of high-performance piezoelectricceramics, e.g., and 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 piezoelectricceramic 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.
111(2002); http://dx.doi.org/10.1121/1.1436072View Description Hide Description
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.
111(2002); http://dx.doi.org/10.1121/1.1420384View Description Hide Description
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.