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921.
Numerical simulation of the ultrasonic waves generated by ring-shaped laser illumination patterns 总被引:1,自引:0,他引:1
Jianfei Guan Zhonghua Shen Xiaowu Ni Jian Lu Jijun Wang Baiqiang Xu 《Optics & Laser Technology》2007,39(6):1281-1287
The generation of ultrasound in aluminum plate subjected to ring-shaped laser beam illumination has been studied quantitatively by using the finite element method. The superposition effects of surface acoustic waves on the top surface and the bulk ultrasonic waves on the rear surface of specimen have been obtained in a single simulation. The typical displacement profiles of the bulk ultrasonic wave at various depths along the central axis of the ring are obtained for three different radii, and the effect of the ring radius on the focal depths of the compression and shear mode are determined. The numerical results confirm that the focal depth of a bulk acoustic mode is determined by the directivity patterns of the acoustic mode generated by point-like laser sources via a thermoelastic mechanism, which depends on the physical constants of elastic medium. 相似文献
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In the present paper, we have theoretically calculated the non linear elastic constants of single crystalline Ni NWs at very broad temperature range 20–300 K validating simple interaction potential model. The temperature dependent ultrasonic attenuation and other related properties are determined using their second and third order elastic constants (SOECs/TOECs). Where possible, the results are compared with experiments from literature. There is a correlation between the thermal conductivity and ultrasonic attenuation in the temperature range 100–300 K. Also, a correlation between the resistivity and ultrasonic attenuation in the temperature range 40–100 K has been established validating the theoretical approach. 相似文献
926.
J.Y. Zhang W.J. XuJ. Carlier X.M. Ji B. NongaillardS. Queste Y.P. Huang 《Ultrasonics》2012,52(1):47-53
Background
High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge.Objective and method
Here we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100 MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance.Results
For a 100 MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86 μm at the focal depth. When decreasing from half wavelength in silicon (42 μm) to half wavelength in water (7.5 μm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42 μm to 7.5 μm. The crosstalk between adjacent elements at the central frequency is, respectively, −95 dB, −39.4 dB, and −60.5 dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4 kΩ, 26.4 kΩ, and 24.2 kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model.Conclusion
These results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging. 相似文献927.
In this paper, based on the fundamental formulae of the first-order and second-order Kirchhoff approx-imation and with consideration of the shadowing effect, the backscattering enhancement of the one-dimensional veryrough fractal sea surface with Pierson-Moskowitz spectrum is studied under the second-order Kirchhoff approximationat microwave frequency. The numerical results are compared with those of the first-order Kirchhoff approximation andintegral equation method. The dependencies of the bistatic scattering cross section and the backscattering enhancementon the incident angle, fractal dimension, and windspeed over the sea surface are analyzed in detail. 相似文献
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Effect of ultrasonic pretreatment on kinetics of gelatin hydrolysis by collagenase and its mechanism
Gelatin is a mixture of soluble proteins prepared by partial hydrolysis of native collagen. Gelatin can be enzymatically hydrolyzed to produce bioactive hydrolysates. However, the preparation of gelatin peptide with expected activity is usually a time-consuming process. The production efficiency of gelatin hydrolysates needs to be improved. In present work, effect of ultrasonic pretreatment on kinetic parameters of gelatin hydrolysis by collagenase was investigated based on an established kinetic model. With ultrasonic pretreatment, reaction rate constant and enzyme inactivation constant were increased by 27.5% and 27.8%, respectively. Meanwhile, hydrolysis activation energy and enzyme inactivation energy were reduced by 36.3% and 43.0%, respectively. In order to explore its possible mechanism, influence of sonication on structural properties of gelatin was determined using atomic force microscopy, particle size analyzer, fluorescence spectroscopy, protein solubility test and Fourier transform infrared spectroscopy. Moreover, hydrogen peroxide was used as a positive control for potential sonochemical effect. It was found that reduction of gelatin particle size was mainly caused by physical effect of ultrasound. Increased solubility and variation in β-sheet and random coil elements of gelatin were due to sonochemical effect. Both physical and chemical effects of sonication contributed to the change in α-helix and β-turn structures. The current results suggest that ultrasound can be potentially applied to stimulate the production efficiency of gelatin peptides, mainly due to its effects on modification of protein structures. 相似文献
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