A one-dimensional material model of lead magnesium niobate (PMN) is presented. The model includes saturation phenomenology, but excludes hysteresis and dispersion. (Constant temperature is assumed.) It is shown that the strain can be taken to respond as an exactly quadratic function in the electric displacement D throughout the saturation region and yet still deduce the full observed response of the material, including flattening of the curve, when the strain is expressed as a function of electric field E. The model developed here is shown to be compatible with experimental measurements previously acquired by other researchers.
The problem of driving a transducer in such a way as to produce a tone burst of steady-state sound radiation in the surrounding fluid medium is considered. The goal is to determine the driving voltage waveform to apply to a transducer to produce an acoustic pressure waveform in the fluid that is a segment of a steady-state sine wave, beginning and ending at zero crossings of the sine, i.e., the usual turnon and turnoff transients are suppressed. The theoretical driving voltage waveform for a spherical transducer is shown to consist of a sum of a pedestal voltage, a ramp voltage, and a sinusoidal voltage that is phase shifted with respect to the sinusoid appearing in the fluid. Both theoretical and numerical calculations are given here. The following paper presents results of experimental measurements. The measurements were carried out on several spherical transducers (one of which was selected for presentation) and on an array of piezoelectric tubes. These experiments confirm the validity of the theory.
Results of experiments that were conducted to investigate the validity of the theory presented in the preceding paper are given. The method was applied to a number of spherical piezoelectric sources, one of which was selected for presentation here, and to a source consisting of an array of piezoelectric tubes. A high degree of transient suppression was realized.
In the article, "Acoustical Doppler effect analysis--Is it a valid method?" [ J. Acoust. Soc. Am. 83, 1223-1230 (1988) ], Censor considers the problem of scattering in the presence of moving objects under conditions of space-and time-dependent moving media. He considers this situation in the context of a generalized linear wave equation. This equation predicts the generation of Doppler-type spectral components at frequencies that are equal to (i) the sum of the frequencies of the primary waves, (ii) the difference of the frequencies of the primary waves, and (iii) harmonics of these sum-and-difference frequencies. However, since the nonlinear wave equation also predicts scattered spectral components at these same frequencies, and since those predicted by the nonlinear theory are usually much stronger than those predicted by Censor's theory, the generalized linear wave equation used by Censor is generally inadequate for accurately predicting the amplitudes of the spectral components of interest.However, a limited regime is identified in which the spectral components predicted by Censor's theory can dominate those predicted by nonlinear theory. PACS numbers: 43.20.Bi, 43.25.Gf, 43.25.Jh, 43.25.Cb Controversy concerning the proper theoretical treatment of the scattering of sound in the presence of moving boundaries dates back to an article published by Censor • in 1972. Since then, there has been an exchange of several articles. 2-7 In an attempt to resolve the issues raised by our earlier objections, Censor has published Ref. 8. In Ref. 8, Censor sets the stage for his theoretical treatment by first offering an interpretation of the objections we have raised regarding his theory. He states, 8 "Essentially the objections were concerned with the facts that a linear model has been assumed, and that the motion imparted to the medium by the mooing scatterers has been ignored." [Emphasis added. ] However, a careful reading of our articles will show that our concerns only regard the failure of Censor's theory to properly account for the nonlinearities involved in the problems he has solved. Thus, the arguments used in Ref. 8, which address only the question of medium motion, fail to address the objections we have raised. Censor's article does not address the questions we have raised concerning the inherent nonlinearities involved in the problems he has solved. It is well known that the linear wave equation is not exact in acoustics and there is a vast body of Please also see article in this issue: D. Censor, "Acoustical Doppler effect analysis--Is it a valid method?," J. Acoust. Soc. Am. 83, 1223-1230 (1988). literature 9 in existence regarding the theoretical foundation, and the experimental confirmation, of the subject of nonlinear acoustics. We cannot understand the use of the linear wave equation (although in a generalized form) as the basis of the theoretical arguments in Ref. 8 when it is the very use of the linear wave equation for the problems considered in Refs. 1 and 4 that we have called into question. The star...
Several methods for improving conventional panel measurement methodology are described. Methods for reducing the low-frequency cutoff of conventional echo-reduction tests, and for simulating impulse-response testing are presented. The new methods are demonstrated to reduce the low-frequency cutoff for conventional echo-reduction tests by an octave ͑to 5 kHz͒, and evidence is provided that suggests that lowering by another octave is feasible. The simulated impulse-response testing was achieved by radiating, through the use of exact transient-suppression methods, broadband interrogating waves, centered on 10 kHz, of single-cycle and half-cycle duration. A new, approximate method of staged transient suppression that permits significantly enhanced projector output relative to that achieved with exact transient suppression is described. The staged transient-suppression method is applicable to the improvement of insertion-loss tests. Finally, a new method for correcting edge-diffraction-contaminated insertion-loss measurements of panels fabricated of decoupling materials is presented. The new method was demonstrated in the frequency range of 500-11 000 Hz, and utilizes staged transient suppression in its implementation.
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