共查询到20条相似文献,搜索用时 296 毫秒
1.
Karbeyaz BU Miller EL Cleveland RO 《The Journal of the Acoustical Society of America》2007,121(2):1226-1237
Conventional ultrasound transducers used for medical diagnosis generally consist of linearly aligned rectangular apertures with elements that are focused in one plane. While traditional beamforming is easily accomplished with such transducers, the development of quantitative, physics-based imaging methods, such as tomography, requires an accurate, and computationally efficient, model of the field radiated by the transducer. The field can be expressed in terms of the Helmholtz-Kirchhoff integral; however, its direct numerical evaluation is a computationally intensive task. Here, a fast semianalytical method based on Stepanishen's spatial impulse response formulation [J. Acoust. Soc. Am. 49, 1627-1638 (1971)] is developed to compute the acoustic field of a rectangular element of cylindrically concave transducers in a homogeneous medium. The pressure field, for, lossless and attenuating media, is expressed as a superposition of Bessel functions, which can be evaluated rapidly. In particular, the coefficients of the Bessel series are frequency independent and need only be evaluated once for a given transducer. A speed up of two orders of magnitude is obtained compared to an optimized direct numerical integration. The numerical results are compared with Field II and the Fresnel approximation. 相似文献
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This article develops a model for the study of the transient ultrasonic waves radiated by a transducer in a liquid and transmitted into a solid through a plane interface. The method is an extension to the transient case, of the angular spectrum method previously developed for the monochromatic case. It is based on the decomposition of the ultrasonic field, in impulse plane waves. The radiated waveform is calculated at any point in the field by a simple summation of these impulse plane waves, where the propagation delay and the refraction have been taken into account. These plane waves are, first of all, delayed by an amount of time corresponding to the travel time up to the considered field point. The transmission through the plane interface is taken into account by using Snell refraction laws and transmission coefficients. In the obtained results all the waves previously described by other authors are highlighted: direct wave, edge waves, head waves as well as subsurface waves with a clear resolution between compression and shear waves. 相似文献
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A nonparaxial multi-Gaussian beam model based on the rectangular aperture is proposed in order to overcome the limitation of paraxial Gaussian beam model which losing accuracy in off-axis beam fields. With the method, acoustical field generated by an ultrasonic linear phased array transducer is calculated and compared with the corresponding field obtained by Rayleigh-Sommerfeld integral, paraxial multi-Gaussian beam model, and Fraunhoffer approximation method. Simulation examples show that nonparaxial multi-Gaussian beam model is not limited by the paraxial approximation condition and can predict efficiently and accurately the acoustical field radiated by a linear phased array transducer over a wide range of steering angles. 相似文献
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References: 《声学学报:英文版》2008,27(1):65-74
The ultrasonic transient field of horizontally polarized shear wave radiated by a 2/2 piezoelectric composite normal probe was analyzed. The analytic field solutions for two different surface force sources were deduced and the transient displacement field distribution on the central cross-section was plotted by numerical calculations. Direct wave and edge wave as well as head wave were observed distinctly in the plots. The experimental results of time domain waveform conformed with the theoretical predictions, which supported the theoretical and numerical results about the transient field of the transducer. 相似文献
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A model is proposed to assess the transient ultrasonic field radiated by a planar transducer and scattered by a target with a known dimension and geometry. The approach is based on the hypothesis of linear acoustics for a perfectly rigid reflector immersed in an isotropic, homogeneous and lossless fluid. The detected acoustic pressure is explained in terms of the plane and edge waves. In order to determine the boundary effects on the detected pressure, targets of different sizes were used in our simulations. An experimental verification of the proposed model is presented for the case of circular planar targets with different radii made of duralumin and immersed in distilled water. In general, the theoretically predicted results are in good agreement with the experimentally measured results. 相似文献
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F. Obermeier 《Journal of sound and vibration》1980,72(1):39-49
The mechanisms of sound generation by unsteady, subsonic flows in the presence of solid boundaries are investigated. For this purpose an alternative integral representation for the radiated pressure field is applied which is different from the generally used integral representation introduced by Lighthill and Curle. The main advantage of the method is that there is a linear dependence of the integrand on the time derivative of the vorticity fluctuations in the hydrodynamic near field; instead of the ordinary Green function a “vector Green function” is used. This vector Green function can be chosen for a given flow field in such a way that surface integrals do not appear. Finally, the theory is illustrated by two- and three-dimensional model flows. Analytical solutions are determined by applying the method of matched asymptotic expansions. 相似文献
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M.S. Howe 《Journal of sound and vibration》1975,43(1):77-86
This paper describes a technique for determining the mean square asymptotic properties of the radiation fields of uniformly convecting multipole source distributions which avoids the usual asymptotic far field analysis of the integral representation of the wave field. The method is based on the principle of conservation of energy and is illustrated here by a consideration of the acoustic field radiated by convected sources located in free space and within a semi-infinite jet flow. 相似文献
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A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly. 相似文献
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Ultrasonic non-destructive testing of pieces of complex geometry with a flexible phased array transducer 总被引:1,自引:0,他引:1
Ultrasonic non-destructive testing of components of complex geometry in the nuclear industry faces several difficulties: sensitivity variations due to unmatched contact, inaccurate localization of defects due to variations of transducer orientation, and uncovered area of the component. To improve the performances of such testing and defect characterization, we propose a new concept of ultrasonic contact phased array transducer. The phased array transducer has a flexible radiating surface able to fit the actual surface of the piece to optimize the contact and thus the sensitivity of the test. To control the transmitted field, and therefore to improve the defect characterization, a delay law optimizing algorithm is developed. To assess the capability of such a transducer, the Champ-Sons model, developed at the French Atomic Energy Commission for predicting field radiated by arbitrary transducers into pieces, has to be extended to sources directly in contact with pieces of complex geometry. The good behavior of this new type of probe predicted by computations is experimentally validated with a jointed transducer positioned on pieces of various profiles. 相似文献
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M. A. Lyalinov 《Russian Journal of Mathematical Physics》2009,16(2):277-286
The work deals with the far field asymptotics of the classical solution for the problem of diffraction by an impedance cone.
The incident acoustic plane wave completely illuminates the semi-infinite conical surface. The scattered field contains different
components in the asymptotics, namely, the spherical wave from the vertex of the cone, the reflected waves, and, under some
conditions, also the surface waves of Rayleigh type. We give integral representations for the scattering diagram of the spherical
wave. The uniform (with respect to the observation direction) asymptotic expression for the wave field is also addressed and
described by the parabolic cylinder ansatz.
Dedicated to the memory of Vladimir Borovikov 相似文献
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The measured characteristics (efficiency and sensitivity) of two air-coupled transducers allow for the prediction of the absolute values of the pressure of the bulk waves generated in air and for the measurement of the pressure of the field radiated in air by guided waves propagating in a structure. With finite element software, the pressure field generated by an air-coupled transducer is simulated by introducing a right-hand side member in the Helmholtz equation, which is used for computing the propagation from the transducer to a plate. The simulated source is rotated in order to impose an angle of incidence with respect to the normal of the plate and generate the corresponding guided mode. Inside the plate, the propagation is simulated with the dynamic equations of equilibrium and a complex stiffness tensor to take into account the viscoelastic anisotropy of the material. For modeling the three-dimensional fields of the guided modes propagating in a two-dimensional non-symmetry plane, a 2.5 dimensional model is introduced. The model computes the value of the pressure field radiated in air by the plates for any guided modes and can predict the detectability of the system for a known defect in a structure. A test bed incorporating two air-coupled transducers is used to generate and receive various guided modes. Two plates made of Perspex and carbon-epoxy composite are tested. The pressure measured by the receiver at various positions is compared to the results of the model to validate it. 相似文献
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I. V. Andronov 《Acoustical Physics》2016,62(4):399-404
The problem of diffraction by an absolutely soft segment is considered in the high-frequency approximation. The asymptotic field decomposition is obtained, which makes it possible to trace the transition from classical asymptotics valid for grazing incidence to geometrical optics asymptotics, which describes scattering at a finite (not small) angle. 相似文献
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The method of nonlinear moments, when used to solve the Boltzmann equation, necessitates the calculation of collision integral
matrix elements. The matrix elements are hard to calculate numerically, especially at large indices. The asymptotics of the
matrix elements are constructed. In terms of the model of pseudopower particle interaction, a formula free of summation is
derived. This makes it possible to find the asymptotic behavior of linear and nonlinear elements when two indices are large.
For an arbitrary interaction cross section, asymptotic expansions of linear and nonlinear matrix elements in one index are
obtained. For Maxwellian molecules, asymptotic formulas are derived for three large indices. 相似文献
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非近轴近似多元高斯模型克服了近轴近似条件的限制,能保证较大偏转角度下模拟声场的精确度和效率。根据双层介质的瑞利积分模型和单层介质的非近轴近似多元高斯模型,推导出双层介质中基于非近轴近似多元高斯模型的单阵元辐射声场计算模型。并在得到各阵元声束偏转聚焦的延迟时间基础上,累加得到基于非近轴近似高斯模型的超声相控阵横波检测辐射声场计算模型。模拟计算带丙烯酸树脂楔块的超声相控阵探头在钢中横波检测的声束偏转与偏转聚焦辐射声场,并与近轴近似多元高斯模型的横波检测声束的偏转聚焦辐射声场进行比较分析。对比分析结果表明非近轴近似多元高斯模型计算速度更快,用时约为近轴近似多元高斯模型的1/13。此外,非近轴近似高斯模型方法横波检测的聚焦声束覆盖区域更大,能量更集中,更适于远场区域检测。 相似文献