Index of content:
Volume 104, Issue 5, November 1998
- STRUCTURAL ACOUSTICS AND VIBRATION 
Modeling and measurement of nonlinear dynamic behavior in piezoelectric ceramics with application to 1-3 composites104(1998); http://dx.doi.org/10.1121/1.423866View Description Hide Description
The nonlinear vibratory behavior of a 1-3 piezoceramic composite is characterized theoretically and experimentally. The developed theoretical model for the electroelastic behavior of the 1-3 composite follows conventional assumptions made by prior investigators but includes nonlinear terms to account for hysteresis in the embedded PZT phase. Experimental measurements of the quasistatic and dynamic mechanical response of the 1-3 with embedded PZT-4 or PZT-5H phases to harmonic electrical excitation over a range of excitation frequencies and two different mechanical loading conditions quantify the nature and level of nonlinearity and illustrate its dependence on the type of PZT material and the mechanical coupling conditions of the 1-3 to its surroundings. Good agreement exists between theoretical predictions and experimental measurements.
Active control of sound transmission through a double-leaf partition by volume velocity cancellation104(1998); http://dx.doi.org/10.1121/1.423899View Description Hide Description
The paper considers the active control of harmonic sound transmitted through a double-leaf partition by cancelling the volume velocity of the radiating panel. The double-leaf partition consists of a pair of small plates, separated by a 100-mm air-gap. The panel volume velocity can be sensed by a single shaped film of piezoelectric PVDF material attached to the plate. Cancellation of volume velocity using a single point force is compared with the result using a matched, distributed actuator which applies a uniform force to the plate and does not give rise to control spillover. Comparison with earlier work in which the volume velocity of a single plate was cancelled [Johnson and Elliott, J. Acoust. Soc. Am. 98, 2174–2186 (1995)] shows that substantial reductions in the transmitted sound power are only possible up to around 350 Hz, as opposed to 600 Hz in the single panel case. A radiation mode analysis of the panels shows that the double-leaf construction provides good passive attenuation of the first radiation mode at high frequencies, so that inefficiently radiating even modes of the radiating panel make a dominant contribution to the radiated sound power. Thus there is no advantage in controlling volume velocity in this frequency range.
104(1998); http://dx.doi.org/10.1121/1.423867View Description Hide Description
The scattering of acoustic waves by an elastic sphere embedded in an elastic isotropic medium is investigated. Expressions for the scatteredwaves are given in terms of monostatic and bistatic scattering cross sections. The resonances of the solid sphere were determined numerically in the individual normal mode amplitudes; dispersion curves for the phase velocities of the circumferential waves were also obtained. Computations and experimental results for an aluminum sphere embedded in Plexiglas were in good agreement.
104(1998); http://dx.doi.org/10.1121/1.423868View Description Hide Description
The concept of supersonic acoustic intensity was developed in 1995 out of a need to locate the sources of radiation on an internally excited, submerged cylindrical shell. Supersonic intensity is obtained through signal processing of near-field holographic data to remove the subsonic part of the helical or plane wave spectrum, leaving only the radiating components. This eliminates the out-of-plane circulation of the acoustic intensity vector which results from evanescent waves. The resulting supersonic intensity on the surface is generally only positive, representing outgoing power flow from the surface. Since negative intensity regions of a vibrator are removed, sources of radiation are readily located on the surface of the vibrator. Since the earlier work concentrated on a cylindrical geometry, the theory is presented here for a planar geometry. In many ways the theory for the planar case is simpler and more straightforward. Numerical examples are given for simply supported, baffled plates. It is shown how the supersonic intensity reconstructions, and resulting location of radiating source regions are consistent with the popular theories of corner and edge mode radiation from plates.