Volume 115, Issue 6, June 2004
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Temperature dependence of ultrasonic propagation speed and attenuation in excised canine liver tissue measured using transmitted and reflected pulses115(2004); http://dx.doi.org/10.1121/1.1738453View Description Hide Description
Previous reported data from our laboratory demonstrated the temperature dependence of propagation speed and attenuation of canine tissue in vitro at discrete temperatures ranging from 25 to However, concerns were raised regarding heating the same tissue specimen over the entire temperature range, a process that may introduce irreversible and, presumably, cumulative tissue degradation. In this paper propagation speed and attenuation vs temperature are measured using multiple groups of samples, each group heated to a different temperature. Sample thicknesses are measured directly using a technique that uses both transmitted and reflected ultrasound pulses. Results obtained using 3 and 5 MHz center frequencies demonstrate a propagation speed elevation of around 20 m/s in the range, and a decrease of 15 m/s in the range, in agreement with previous results where the same specimens were subjected to the entire temperature range. However, sound speed results reported here are slightly higher than those reported previously, probably due to more accurate measurements of sample thickness in the present experiments. Results also demonstrate that while the propagation speed varies with temperature, it is not a function of tissue coagulation. In contrast, the attenuation coefficient depends on both tissue coagulation effects and temperature elevation.
115(2004); http://dx.doi.org/10.1121/1.1710501View Description Hide Description
This paper presents and demonstrates a noncontact method for measuring the Lamb wave dispersion spectrum of a plate. Noncontact air-coupled source and receive transducers are used with line-focus mirrors and 50–700 kHz broadband apparatus for simultaneous measurement over a broad spectrum of refractive angles and multiple guided modes. Broadband, wide-angle wave forms are measured as a function of position. The Fourier transform of these wave forms from the domain to the domain gives an approximate spectrum of the dispersion relation. We measure the dispersion spectra of Lucite™, aluminum, balsa wood, and a carbon fiber epoxy laminate, and show that the measured spectra agree well with the dispersion relation calculated from Lamb wave theory.
115(2004); http://dx.doi.org/10.1121/1.1710503View Description Hide Description
Measurements are made of the heat transferred between two identical parallel-plate heat exchangers under conditions of oscillating flow over a range of frequencies and amplitudes. The results are analyzed and summarized in terms of heat-exchanger effectiveness, the ratio of the actual heat transfer rate to the maximum possible heat transfer rate. Measured results are compared to the DELTAE model that is often used in the design of conventional thermoacoustic devices, and possible improvements to the model are offered.
115(2004); http://dx.doi.org/10.1121/1.1707091View Description Hide Description
Thermal effects due to high ultrasound absorption in bone pose an ongoing safety issue. Of considerable concern is the heating of the soft tissue adjacent to the bone surface. Mathematical models can be useful in predicting the transient temperature near the interface during insonation. This paper develops a model that provides the temperature field in terms of simple expressions that convey the functional dependence of the material properties, and are easily incorporated into standards and ultrasound machine software, yet are able to incorporate the material properties of both bone and soft tissue. The model contains an asymptotic theory based upon a “high-attenuation” assumption: the distance diffused by heat over the time of interest is large compared to the ultrasound attenuation length. Model predictions of temperature rise and location of maximum temperature were in close agreement with finite-element calculations, using parameters appropriate for radiation-force imaging and focused-ultrasound surgery.
Amplitude and phase calibration of hydrophones up to 70 MHz using broadband pulse excitation and an optical reference hydrophone115(2004); http://dx.doi.org/10.1121/1.1707087View Description Hide Description
A substitution calibration technique for piezoelectricultrasonichydrophones is presented that uses an optical multilayerhydrophone as the reference receiver. Broadband nonlinearly distorted focused pulses are first measured with the reference hydrophone and then with the hydrophone to be calibrated. By Fourier transformation of the time wave forms and division of the frequency spectra, the complex-valued frequency response of the hydrophone under test is obtained in a broad frequency range in a very fast and efficient way and with high frequency resolution. The results obtained for a membrane hydrophone and a needle-type hydrophone are compared with those obtained by independent calibration techniques such as primary calibration using optical interferometry and secondary calibration using time-delay spectrometry, and good agreement is found. The calibration data obtained are apt to improve the results of ultrasound exposure measurements using broadband voltage-to-pressure conversion. This is demonstrated for standard pulse parameter determination from exemplar exposure measurements on a commercial diagnostic ultrasound machine. For the membrane hydrophone, the evaluation method commonly used leads to an overestimation of the positive peak pressure by up to 50%, an underestimation of the rarefactional peak pressure by up to 11%, and an overestimation of the pulse intensity integral by up to 28%.