Volume 125, Issue 6, June 2009
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Attenuation and dispersion of antiplane shear waves due to scattering by many two-dimensional cavities125(2009); http://dx.doi.org/10.1121/1.3124779View Description Hide Description
Propagation and scattering of antiplane shear waves within media with two-dimensional cavities are numerically simulated, and the attenuation and phase velocities are experimentally determined. The results are compared with the predictions by the Foldy theory and its three corrected versions. If the cavity concentrations are small such as 0.02, the differences among the theoretical predictions are insignificant, and every theory is consistent with the experimental results. For higher concentrations such as 0.1, the differences become significant, but there are no objective grounds to say that any of the corrected versions of the Foldy theory works better than the original. If the error tolerance is as high as 10%, the simple Foldy formula may remain useful for concentrations up to about 0.1.
125(2009); http://dx.doi.org/10.1121/1.3126943View Description Hide Description
A streak camera is used to measure the shape of sonoluminescence pulses from a cavitation bubble levitated stably in a sulfuric acid solution. The shape and response to an acoustic pressure field of the sonoluminescence pulse in 85% by weight sulfuric acid are qualitatively similar to those in water. However, the pulse width in sulfuric acid is wider than that in water by over one order of magnitude. The width of the sonoluminescence pulse is strongly dependent on the concentration of the sulfuric acid solution, while the skewed distribution of the shape remains unchanged.
125(2009); http://dx.doi.org/10.1121/1.3126525View Description Hide Description
It is widely accepted that diagnosticultrasound has the potential to elevate the temperature of tissue being scanned. Because both the maximum value of the temperature rise and the temporal profile of that rise are necessary to estimate the risk correctly, the temperature rise at an observation point for an exposure condition is presumed to have two components, that is, . The amplitude component is the maximum value of , and the exposure time component represents the time dependency of that . Ninety-six cases were investigated to obtain the proposed model at six frequencies, four source diameters, and four -numbers. Then, using the relative change in the rate of induction of a thermal effect due to ultrasound exposure that produces different from a threshold exposure, the safe use time (SUT) model was constructed. SUT informs the user of the maximum duration of exposure in a region at a particular output level that would be no more hazardous than scanning at the threshold exposure. Using the SUT model, high power ultrasound can be applied for a short time so that the user can improve imaging performance while staying within safe limits.
A Fabry–Pérot fiber-optic ultrasonic hydrophone for the simultaneous measurement of temperature and acoustic pressure125(2009); http://dx.doi.org/10.1121/1.3117437View Description Hide Description
A dual sensing fiber-optic hydrophone that can make simultaneous measurements of acoustic pressure and temperature at the same location has been developed for characterizing ultrasound fields and ultrasound-induced heating. The transduction mechanism is based on the detection of acoustically- and thermally-induced thickness changes in a polymer film Fabry–Pérot interferometer deposited at the tip of a single mode optical fiber. The sensor provides a peak noise-equivalent pressure of 15 kPa (at 5 MHz, over a 20 MHz measurement bandwidth), an acoustic bandwidth of 50 MHz, and an optically defined element size of . As well as measuringacoustic pressure,temperature changes up to can be measured, with a resolution of . To evaluate the thermal measurement capability of the sensor,measurements were made at the focus of a high-intensity focused ultrasound (HIFU) field in a tissue mimicking phantom. These showed that the sensor is not susceptible to viscous heating, is able to withstand high intensity fields, and can simultaneously acquire acoustic waveforms while monitoring induced temperature rises. These attributes, along with flexibility, small physical size , immunity to Electro-Magnetic Interference (EMI), and low sensor cost, suggest that this type of hydrophone may provide a practical alternative to piezoelectric based hydrophones.
125(2009); http://dx.doi.org/10.1121/1.3117441View Description Hide Description
The detection of localized defects such as cracks and corrosion in pipes using guided elastic waves is now an established non-destructive testing procedure. However, the prediction of guided wave excitation and scattering in pipes is a complex three-dimensional (3D) problem with many parameters that can generally only be solved using numerical methods. In many important industrial applications, the diameter of a pipe is much larger than wall thickness. In this case an approximate theory is applicable, when a pipe is considered as an unwrapped isotropic plate. In this paper, a technique for obtaining pipe mode amplitudes in terms of the solution to the forced 3D problem on a plate is presented. The same principle is extended to relate guided wave scattering from defects in plates to scattered circumferential modal amplitudes from defects in pipe. This is of practical benefit as the scattering of guided waves by defects in a plate is a much simpler problem than that in a pipe, and one that, in some cases, can be solved using analytical methods. Results are shown that illustrate the application of the method to reflection from through-thickness circumferential cracks in pipes.