Volume 115, Issue 3, March 2004
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
115(2004); http://dx.doi.org/10.1121/1.1645247View Description Hide Description
Acoustic transmission coefficient and phase velocity of a Lucite slab with circular cylindrical pores with a nonrigid pore frame were experimentally and theoretically investigated. For theoretical investigation a new phenomenological model, the modified Biot-Attenborough (MBA) model, was proposed. The MBA model takes into account both the first kind and the second kind of waves introduced by Biot. It also separately considers viscous and thermal effects with three new phenomenological parameters: boundary, phase velocity, and impedance parameters. The theoretical estimation with three phenomenological parameters shows reasonably good agreement with the experimental data. The physical characteristics of porous medium such as porosity and pore size can be inversely analyzed in terms of the acoustic data such as the transmission coefficient and phase velocity as the functions of porosity and frequency. This makes acoustic diagnosis possible for noninvasively investigating physical characteristics of porous media such as bones and ocean sediments.
115(2004); http://dx.doi.org/10.1121/1.1639332View Description Hide Description
In this paper, constitutive relations are solved in the Fourier domain using a finite-element-based commercial software. The dynamic responses of viscoelastic bars or plates to either thermal or mechanical loads are predicted by considering complex moduli (Young, Poisson, stiffness moduli) as input data. These moduli are measured in the same frequency domain as that which is chosen for modeling the wave propagation. This approach is simpler since it suppresses the necessity of establishing a rheological model. Specific output processing then allows the numerical predictions to be compared to analytical solutions, in the absence of scatterers. The performances of this technique and its potential for simulating more complicated problems like diffraction of waves or for solving inverse problems are finally discussed.
115(2004); http://dx.doi.org/10.1121/1.1649333View Description Hide Description
An acoustic field spontaneously induced in a thermoacoustic prime mover consisting of a looped tube and resonator is determined through simultaneously measurements of pressure P and velocity U. A thermal efficiency of the thermoacoustic prime mover of this type has been reported to reach 30%. The measurements of the acoustic field in the present system revealed that a phase lead of U relative to P takes a negative value of about −20° in the regenerator where the output power of the prime mover is generated. It was concluded that the possession of a negative phase lead at this position is taken as a clue in a significant increase in the output power. Moreover, the analysis in the thermoacoustic mechanism shows that a precise position for the location of a second regenerator acting as a heat pump exists in the looped tube. Indeed, by locating the second regenerator at the position, a thermoacoustic cooler was constructed. The thermoacoustic cooler could generate a low temperature of −25 °C without involving any moving parts.
115(2004); http://dx.doi.org/10.1121/1.1643367View Description Hide Description
The optoacoustic generation of a helicoidal ultrasonic beam is demonstrated. Such an ultrasonic “doughnut” beam has a pressure amplitude minimum in the center along its entire longitudinal extension, and it carries orbital angular momentum. It is produced by illuminating a specially structured absorbing surface in a water tank with pulsed laser light. The absorbing surface has a profile with a screw dislocation, similar to the transverse cross-sectional surface of a helix. Upon illumination with modulated light, a correspondingly prepared absorber generates an ultrasonicwave with the desired phase discontinuity in its wave front, which propagates through the water tank and is detected with spatial resolution using a scanning needle hydrophone. This situation can be viewed as the optoacoustic realization of a diffractive acoustical element. The method can be extended to tailor optoacoustically generated ultrasonicwaves in a customized way.