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1.
The radiation directivity of a complicated conformal array of underwater acoustic transducers is presented based on the boundary "element method. It includes the element directivity of each transducer, the natural beam pattern and the controlled beam pattern of the transducer array. At first, the boundary element model of the conformal array is built up, and then the boundary condition is exerted on the model according to the design and environment in which the transducer array is used, and the radiation directivity of the conformal array is calculated. An experiment has been done to measure the directivity in an anechoic water tank. The calculated and the experimental results are compared and analyzed. They are consistent to each other. It is shown that the boundary element method together with the detailed calculations is successful to simulate and predict the radiation directivity of an underwater acoustic transducer array. 相似文献
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Emission of underwater acoustic orbital angular momentum(OAM) is studied as well as underwater acoustic communications with OAM multiplexing. Theoretical acoustic properties for circular phased array are analyzed based on point source theory. We optimize and design an array prototype based on cymbal transducer. The diameter of array prototype is 180 mm, the number of array elements is 10, and the working frequency is 25 k Hz. It emits acoustic OAM with topological charges-3 to 3. The favorable r... 相似文献
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Point Sources and Gaussian beams are used frequently as fundamental building blocks for developing ultrasonic beam models. Both these models have different weaknesses that limit their effectiveness. Here, we will show that one can develop a Gaussian Beam Equivalent Point Source (GBEPS) model that removes those weaknesses and combines the accuracy and versatility of the point source models with much of the speed and well-behaved nature of Gaussian beam models. We will demonstrate the efficiency and versatility of this new GBEPS model in simulating the beams generated from ultrasonic phased arrays, using as few as one Gaussian beam per element of the array. A single element GBEPS model will be shown to be as accurate as a point source model even when substantial beam focusing or steering is present in the array or where the array beam is transmitted through an interface. At the same time the GBEPS model will be shown to be several orders of magnitude faster than the point source model. 相似文献
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LIU Wangsheng LI Ya'an YU Hongpei 《声学学报:英文版》2011,(4):464-472
The sound field distribution of a broadband array is calculated using the acoustics FEM and BEM.The FEM-BEM model is established for a nine-element plane array and its numerical method of calculating mutual radiation impedance among the transducers is given. The changing law of mutual radiation impedance influencing acoustics performances is analyzed. The directivity and beam width of the plane array are calculated at three resonance frequencies.A broadband dense plane array with nine elements is developed using triply resonant transducers.The input impedance and directivity of the plane array are measured in anechoic water tank.Results show that it is reasonable to design the array according to the half wavelengh of the first resonance frequency of the array element.The numerical solution agrees with the measuring results well,which indicates the FEM-BEM method is feasible to calculate sound field distribution and analyze mutual impedances. 相似文献
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Sung-Jin Song YE Jing Hak-Joon Kim Suk-Chull Kang Sung-Sik Kang Kyungcho Kim Myung-Ho Song 《声学学报:英文版》2010,(3):209-219
Simulation of phased array beams in dovetail and austenitic welds is conducted to optimize the setup of phased array ultrasonic testing(PAUT).To simulate the beam in such material with complex geometry or with characteristic of anisotropy and inhomogeneity, firstly,linear phased multi-Gaussian beam(LPMGB) models are introduced and discussed. Then,in the case of dovetail,wedge is designed to maximize the stable amplitude of the beam along the steering path;in the case of austenitic weld,modified focal law are developed to solve the problem of beam screwing and defocusing due to the material properties.To verify the effectiveness of the modified focal law,beam fields are calculated using LPMGB model in austenitic welds. 相似文献
6.
The mutual radiation impedance ignored in conventional array directivity formula is introduced into the calculation of array radiation sound field,and a modified array directivity formula considering the mutual radiation impedance is gained according to the superposition principle.Results of computer simulation and experiments for a uniform linear array and a uniform planar array show superior performance on the present of the practical directivity pattern of the modified formula in this paper in comparison to the conventional one. 相似文献
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Understanding the effect of source-receiver geometry on sound propagation in surface ducts can improve the performance of near-surface sonar in deep water. The Lloyd-mirror and normal mode theories are used to analyze the features of surface-duct propagation in this paper. Firstly, according to the Lloyd-mirror theory, a shallow point source generates directional lobes, whose grazing angles are determined by the source depth and frequency. By assuming a part of the first lobe to be just trapped in the surface duct, a method to calculate the minimum cutoff frequency (MCF) is obtained. The presented method is source depth dependent and thus is helpful for determining the working depth for sonar. Secondly, it is found that under certain environments there exists a layer of low transmission loss (TL) in the surface duct, whose thickness is related to the source geometry and can be calculated by the Lloyd-mirror method. The receiver should be placed in this layer to minimize the TL. Finally, the arrival angle on a vertical linear array (VLA) in the surface duct is analyzed based on normal mode theory, which provides a priori knowledge of the beam direction of passive sonar. 相似文献
8.
Chaos game representation(CGR) is an iterative mapping technique that processes sequences of units,such as nucleotides in a DNA sequence or amino acids in a protein,in order to determine the coordinates of their positions in a continuous space.This distribution of positions has two features:one is unique,and the other is source sequence that can be recovered from the coordinates so that the distance between positions may serve as a measure of similarity between the corresponding sequences.A CGR-walk model is proposed based on CGR coordinates for the DNA sequences.The CGR coordinates are converted into a time series,and a long-memory ARFIMA(p,d,q) model,where ARFIMA stands for autoregressive fractionally integrated moving average,is introduced into the DNA sequence analysis.This model is applied to simulating real CGR-walk sequence data of ten genomic sequences.Remarkably long-range correlations are uncovered in the data,and the results from these models are reasonably fitted with those from the ARFIMA(p,d,q) model. 相似文献
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Laser-driven ultrafast X-ray sources are widely used for diagnostic radiography. However, there is a large divergence of fast electrons when they are generated by an intense short-pulse laser interacting with a foil target.We design a nanowire array target to achieve a more compact point X-ray source. Fast electrons are confined and guided by the nanowire array structure in order to generate a Kαsource with a small spot size. In our work, the smallest measured source size is comparable to the laser spot size, while the conversion efficiency can reach2.4 × 10-4. 相似文献
10.
We employ the target detection to improve the performance of the feature-based fusion of infrared and visible dynamic images, which forms a novel fusion scheme. First, the target detection is used to segment the source image sequences into target and background regions. Then, the dual-tree complex wavelet transform (DT-CWT) is proposed to decompose all the source image sequences. Different fusion rules are applied respectively in target and background regions to preserve the target information as much as possible. Real world infrared and visible image sequences are used to validate the performance of the proposed novel scheme. Compared with the previous fusion approaches of image sequences, the improvements of shift invariance, temporal stability and consistency, and computation cost are all ensured. 相似文献
11.
An aluminium hemicylindrical sample has been irradiated with an array of laser lines, with each line acting as a source of acoustic waves. Detection of the generated ultrasonic waves was performed using both a wide-band stabilized Michelson interferometer and a 20 MHz piezoelectric transducer. Experimental and theoretical results are presented which reveal that the use of a spatially modulated laser source produces significant narrow-banding of the detected ultrasound, compared with a single point or single line source case. Additionally, for a given line spacing, ultrasound of a particular frequency can be directed. Owing to the nature of the acoustic signals generated by each individual array element, superposition of several signals does not result in any energy directivity similar to that encountered in phase electromagnetic array antennas. While time or frequency feature enhancement may be obtained in a desired direction, in most cases the far field energy directivity pattern is simply the incoherent sum of the energy directivity of each array element. 相似文献
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The goal of this work was to develop an extended ultrasound transducer model that would optimize the trade-off between accuracy of the calculation and computational time. The derivations are presented for a generalized transducer model, that is center frequency, pulse duration and physical dimensions are all normalized. The paper presents a computationally efficient model for lens-focused, circular (axisymmetric) single element piezoelectric ultrasound transducer. Specifically, the goal of the model is to determine the lens effect on the electro-acoustic response, both on focusing and on matching acoustic properties. The effective focal distance depends on the lens geometry and refraction index, but also on the near field limit, i.e. wavelength and source radius, and on the spectrum bandwidth of the ultrasound source. The broadband (80%) source generated by the transducer was therefore considered in this work. A new model based on a longitudinal-wave assumption is presented and the error introduced by this assumption is discussed in terms of its maximum value (16%) and mean value (5.9%). The simplified model was based on an extension of the classical KLM model for transducer structures and on the related assumptions. The validity of the implemented extended KLM model was evaluated by comparison with finite element modeling, itself previously validated analytically for the one-dimensional planar geometry considered. The pressure field was then propagated using the adequate formulation of the Rayleigh integral for both the extended KLM and finite element results. The simplified approach based on the KLM model delivered the focused response with good accuracy, and hundred-fold lower calculation time in comparison with a mode comprehensive FEM method. The trade-off between precision and time thus becomes compatible with an iterative procedure, used here for the optimization of the acoustic impedance of the lens for the chosen configuration. An experimental comparison was performed and found to be in good agreement with such an extension of the KLM model. The experiments confirm the accuracy of such a model in a validity domain up to −12 dB on the pulse-echo voltage within a relative error of 9% between experiment and modeling. This extended KLM model can advantageously be used for other transducer geometries satisfying the assumption of a predominantly longitudinal vibration or in an optimization procedure involving an adequate criteria for a particular application. 相似文献
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The use of non-contact laser techniques for the generation of ultrasound has extended the limits of the application of traditional ultrasonic techniques. This paper focusses on the use of one such non-contact laser technique, known as ‘optical fibre array’, to generate shear and surface waves. The shear wave experimental directivity pattern results are presented and compared with the theoretical results of a single source and an array source. The experimental directivity results for the surface wave are also presented, and compared with the theoretical results. The data show that the array enhances signal generation in the forward direction for both shear and surface waves. The array gain is also discussed. The receiver for the directivity measurements was a contact piezoelectric transducer. 相似文献
16.
This paper investigates the scattering characteristics of the fundamental anti-symmetric (A(0)) Lamb wave at through holes in composite laminates. Three-dimensional (3D) finite element (FE) simulations and experimental measurements are used to study the physical phenomenon. Unidirectional, bidirectional, and quasi-isotropic composite laminates are considered in the study. The influence of different hole diameter to wavelength aspect ratios and different stacking sequences on wave scattering characteristics are investigated. The results show that amplitudes and directivity distribution of the scattered Lamb wave depend on these parameters. In the case of quasi-isotropic composite laminates, the scattering directivity patterns are dominated by the fiber orientation of the outer layers and are quite different for composite laminates with the same number of laminae but different stacking sequence. The study provides improved physical insight into the scattering phenomena at through holes in composite laminates, which is essential to develop, validate, and optimize guided wave damage detection and characterization techniques. 相似文献
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此处所介绍的厅堂声学计算机模型计算了房间和多功能厅的声学响应。这个模型是以房厅的三维表示为基础的。每个墙面都赋予一个吸声系数,并且分成更小的单元。首先计算了单元间影响系数所组成的矩阵。对于给定的声源,可以计算每个单元收到的能量,并由此定出房厅内任一点的声级,这样又能够算出(a)随距离变化的衰减,(b)在任一平面上的声照度,和(c)任一点所收到声能的接收指向性.可以算出房厅内任一被选定点的回波图,作为接收器所在地接收指向性随时间的演变;这么一个特点使得有可能核对目视图象和声图象之间的可能不符。这个软件能够设法任意修改房间的形状,以最优化房间的声学特征.本文列举了一个厅堂声学的研究例,是关于沙特拉伯首都Riyadh的 Ahura主厅的。 相似文献
19.
Conventional near-field acoustical holography (NAH) is generally based on the free-field assumption, which can cause errors when interfering sources are present in practical environments. To cope with this problem, previous research suggested a combined pressure-velocity approach for NAH that provides certain advantages to rejection of interferences. This paper revisits this idea in a broader context of optimal array design and examines the feasibility of using unidirectional microphones in each channel of the array such that the robustness of inverse reconstruction is enhanced against interfering sources. As indicated in the simulation, the numerical noise in finite difference estimation of particle velocity can nullify the advantage of the well-conditioned velocity-based reconstruction. In the proposed approach, the characteristics of each array channel consisting of two microphones are tailored by taking into account not only the directivity, but also the robustness against self-noise. An objective function based on directivity index and white noise gain is exploited in a linear quadratic optimization of a two-element end-fire array. The proposed optimal array is validated in conjunction with the equivalent source model (ESM) -based NAH through numerical simulations, with an interfering source positioned behind the array. The results have shown the directive optimal array has yielded improved quality of images in comparison with conventional approaches in the presence of an interfering source and sensor noise. 相似文献