Volume 108, Issue 2, August 2000
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
On the applicability of Kramers–Krönig relations for ultrasonic attenuation obeying a frequency power law108(2000); http://dx.doi.org/10.1121/1.429586View Description Hide Description
In the recent literature concern has been raised regarding the validity of Kramers–Krönig relations for media with ultrasonic attenuation obeying a frequency power law. It is demonstrated, however, that the Kramers–Krönig dispersion relations for application to these types of media are available. The developed dispersion relations are compared with measurements on several liquids, and agreement is found to better than 1 m/s over the experimentally available bandwidth. A discussion regarding the validity of these dispersion relations, in particular how the dispersion relations relate to the so-called Paley–Wiener conditions, forms the conclusion.
108(2000); http://dx.doi.org/10.1121/1.429587View Description Hide Description
The loss and phase advance due to diffraction are experimentally observed by measuring the amplitude and phase of radio frequency (rf) tone burst signals in the VHF range, in an ultrasonic transmission line consisting of a buffer rod with an ultrasonic transducer on one end, a couplant of water, and a solid specimen of synthetic silica glass. The measured results agree well with the calculated results from the exact integral expression of diffraction. The diffractioneffects on the velocity and attenuationmeasured in this frequency range and their corrections are investigated to realize more accurate measurements. It is shown that attenuationmeasurements are influenced by diffraction losses and can be corrected by numerical calculations, and that velocity measurements are affected by the phase advance caused by diffraction. This investigation demonstrates that, in complex-mode velocity measurements, in which the velocity is determined from the measured phase of the signals, the true velocity at each frequency can be obtained by correction using the numerical calculation of diffraction. Based on this result, a new correction method in amplitude-mode velocity measurements is also proposed. In this new method, the velocity is determined from the intervals of interference output obtained by sweeping the ultrasonic frequency for the superposed signals generated by the double-pulse method. Velocity may be measured accurately at frequencies in the Fresnel region, and diffraction correction is essential to obtain highly accurate values with five significant figures or more.
108(2000); http://dx.doi.org/10.1121/1.429588View Description Hide Description
The five independent second-order elastic constants of a transversely isotropic aluminum/alumina fiber composite have been measured for the first time using a resonantultrasound spectroscopy technique. These data were used to deduce the elastic constants and engineering moduli for off-axis loading conditions.
108(2000); http://dx.doi.org/10.1121/1.429589View Description Hide Description
The scattering-inducedattenuation coefficient of a beam of longitudinal waves propagating through an austenitic steel plate is measured as a function of the texture angle. The experimental data were obtained by mapping the incident and the transmitted ultrasonic field, and by evaluating the energy loss experienced by each plane wave component of the beam. Contrary to the behavior of data obtained by means of conventional techniques, that of the data reported in this work agrees qualitatively with the theoretical predictions. The reasons for the disagreement between theory and data obtained by means of conventional techniques are also discussed.
108(2000); http://dx.doi.org/10.1121/1.429590View Description Hide Description
The earliest known reference to the mode-locking, or entrainment, of two maintained oscillators is Christiaan Huygens’ description of two pendulum clocks “falling into synchrony” when hung on the same wall. We describe an analogous phenomenon in acoustics—the mode-locking of two thermoacoustic engines which have their cases rigidly welded together, but which are otherwise uncoupled. This “mass-coupling” might compete with acoustic coupling when the latter is used to enforce antiphase mode-locking in such engines, for vibration cancellation. A simple theory relating the phase difference between the engines in the locked state to the corresponding ratio of their pressure amplitudes is in excellent agreement with theory and numerical simulations. The theory’s prediction relating the phase difference to the engines’ natural frequency difference is qualitatively confirmed by experiment, despite larger experimental uncertainties. The mass coupling is relatively weak compared to the aforementioned acoustic coupling, and in general occurs in antiphase, so we conclude that mass coupling will not interfere with vibration cancellation by acoustic coupling in most circumstances.