共查询到20条相似文献,搜索用时 359 毫秒
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Acoustical Physics - The article investigates the possibility of reconstructing a reflector image using the compressive sensing (CS) method based on an incomplete set of echo signals measured by an... 相似文献
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D. A. Marakasov 《Russian Physics Journal》2009,52(12):1271-1280
The problem of reconstructing the wind velocity profile from the spatiotemporal statistics of turbulent reflected optical
radiation intensity fluctuations is considered in the article. Expressions for the spatiotemporal correlation function and
the spectrum of weak intensity fluctuations of the wave scattered on a diffusive screen are derived. An algorithm for reconstructing
the wind velocity profile from the spatiotemporal spectra of the intensity of a reflected spherical wave in the turbulent
atmosphere is suggested. The results of closed numerical experiments are presented that confirm the efficiency of the suggested
algorithm. 相似文献
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Excitation of a Stoneley wave in a single fluid-filled crack of small wave size in a borehole under an external seismic wave incident on it at an arbitrary angle is considered. On the basis of the solution obtained, the feasibility of solving the inverse problem of reconstructing the crack orientation from the data of vertical seismoacoustic profiling by hydrophones with the use of minimal input data is demonstrated. 相似文献
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G. M. Makhonin 《Acoustical Physics》2014,60(5):588-596
The paper considers the problem of reconstructing the shape of echo-sounded objects under conditions when the well-known methods, e.g., the Boyarskii method, are inapplicable or inefficient. A variant of the method is proposed for reconstructing the shape of an object using the function from the Gaussian curvature of the surface. As well, it is shown that the main information on this function is carried by the initial region of the echo signal and that the results of reconstructing the shape depend on the correlation duration of probing signals. When ultra-wideband probing signals are applied, this method is fundamentally suitable for reconstructing the shape of silt-covered objects. Formally, the method is applicable only for convex surfaces, but it can be expanded to more complex surfaces under certain conditions. 相似文献
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已有的反射式terahertz(THz)波层析研究都是针对平行界面进行,开展了样品内非平行界面的反射式THz波层析成像的数值模拟研究.根据物理模型给出了重构算法,并编制了相应的重构软件,数值计算结果表明非平行界面的重构是可行的.分析表明,重构误差主要来源于计算中的近似处理和累积误差.讨论了曲线轮廓界面的近似处理方法,提出当曲线轮廓各点的曲率半径都比较大时,可以把曲线分割成多段直线处理.最后分析了影响纵向分辨率的因素.结果表明,输入脉冲的脉宽越大则纵向分辨率越低,一般情况下纵向分辨率可达到亚毫米量级.
关键词:
terahertz波
反射式层析成像 相似文献
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E. G. Bazulin 《Acoustical Physics》2013,59(2):210-227
We have studied the possibility of solving the inverse scattering problem in the Born approximation, i.e., the reconstruction of scatterer images from the measured set of echo signals. We have considered generalization of the classical combined SAFT (C-SAFT) algorithm to the case of multiple reflections from uneven boundaries of the tested object taking into account the transformation of the wave type for several positions of the antenna grid, which makes it possible to obtain high-quality scatterer images. Representation of the direct problem in matrix form makes it possible to switch to solving the inverse problem, which can be solved using the Tikhonov regularization procedure, because it is an ill-posed. We have considered the possibility of using the entropy of the image estimate as the stabilizing functional that forms the essence of the maximum entropy method (MEM). The advantage of the MEM over the conventionally used linear C-SAFT method has been shown. The ray model taking into account reflections of rays from the boundaries of the tested object with uneven boundaries has been used for constructing the function estimate. We have demonstrated the ability of the MEM to obtain the scatterer images with superresolution and to suppress the “side lobes” of the function of the point scattering on the collapsed set of echo signals. The use of echo signals reflected from the boundaries of the tested object makes it possible to reconstruct the scatterer shape more exactly. Examples of images reconstructed by the MEM on echo signals obtained in the numerical and model experiments have been presented. 相似文献
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Technical Physics - The interaction of a plane shock wave (M = 5) with an ionized plasma region formed before the arrival of a shock wave by a low-current glow gas discharge is considered... 相似文献
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Vasiljevic M Kundu T Grill W Twerdowski E 《The Journal of the Acoustical Society of America》2008,123(5):2591-2597
Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper. 相似文献
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建立检测系统的数学模型,可以更好地理解超声检测的物理本质。分析了超声波从产生、介质中传播、缺陷耦合以及接收的全过程,将缺陷回波表示为探头响应函数与缺陷响应的时域卷积。利用空间脉冲响应和基尔霍夫近似建立了超声波与平面型缺陷的耦合模型,用大平面试块底面回波和大平面响应进行反卷积求得了探头的响应函数,并详细分析了探头在不同偏置位置时不同大小缺陷响应的特点,发现缺陷回波由直达回波和边缘回波组成,直达回波和边缘回波极性相反,且直达回波的幅值远远大于边缘回波。 相似文献
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Simulating the response of multiple microphones to a single acoustic source in a reverberant room 总被引:2,自引:0,他引:2
P M Peterson 《The Journal of the Acoustical Society of America》1986,80(5):1527-1529
A method is presented for simulating the impulse response between an acoustic source and multiple microphones in a reverberant room. The method is similar to the image method described by Allen and Berkley [J. Acoust. Soc. Am. 65, 943-950 (1979)] but includes modifications to simulate received echo arrival time accurately. The essential modification is to represent each received echo as a low-pass-filtered impulse at the correct arrival time. Using this "low-pass impulse" method, reverberant rooms can be simulated with sufficient accuracy to investigate multiple-microphone systems that are sensitive to interchannel phase. 相似文献
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M. I. Kulish V. B. Mintsev S. V. Dudin A. E. Ushnurtsev V. E. Fortov 《JETP Letters》2011,94(2):101-105
The processes associated with the arrival of a strong shock wave at the surface of a metal have been considered. It has been
experimentally revealed that the withdrawal of the wave from a shock-loaded sample under release is accompanied by the formation
of not only a dusty flow, but also a metal plasma. The temperature of the plasma component, which is about 1 eV, has been
determined from the relation of the line intensities using the spectral diagnostics of the plasma. 相似文献
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The possibility of the aberration-free reconstruction of a synthesized hologram-Fresnel projector in the case when the angles
of incidence of the reconstructing plane wave exceed the angle of incidence of the plane reference wave during hologram synthesis
is shown. The character of the dependence of admissible angles of incidence of the reconstructing wave on the parameters of
the synthesis of hologram projectors is revealed and described mathematically. The results of an experimental study that confirms
the possibility of the aberration-free reconstruction of hologram projectors at angles of incidence of the reconstructing
plane wave that exceed the angle of incidence of the reference wave of the plane are presented. The results of the successful
implementation of the projection photolithography process using a synthesized relief-phase reflection hologram-Fresnel projector
are demonstrated. 相似文献
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W Lindemann 《The Journal of the Acoustical Society of America》1986,80(6):1623-1630
This paper explains the "law of the first wave front" and related binaural phenomena on the basis of the model presented in the previous paper [Lindemann, J. Acoust. Soc. Am. 80, 1608-1622 (1986)] in which a contralateral inhibition mechanism was added to the well-known model of binaural cross correlation. In order to verify the predictions of the extended model, psychoacoustic experiments were performed with pairs of narrow-band impulses which were presented through headphones. The test signals consisted of a diotic primary sound and an "echo" with an interaural arrival-time difference. Lateralization was measured as a function of the time delay between primary sound and echo. For delays below the echo threshold, summing localization and the law of the first wave front were simulated; for delays above the echo threshold, the model predicts an influence of the primary sound on the lateralization of the echo. 相似文献
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为了研究激光激发出的超声波在带过渡圆角的金属平板上的传播规律和检测表面缺陷的方法,采用有限元法模拟了该类平板中的激光超声现象,分析了表面波在圆角区域的传播规律和与表面缺陷的作用过程。数值结果表明:激光激发出纵波、横波和Rayleigh波等,其中Rayleigh波主要存在于表面mm量级,并且在过渡圆角处发生模式转换生成了直达波R′和模式转换波RR等多种表面波;经过过渡区域后的声波在表面缺陷处发生了反射和透射现象,通过B扫图可以检测缺陷的位置。随着缺陷深度的增加,表面波的透射系数不断减小,且透射波Rt和Rst存在0.5 μs左右的到达时间差,该时间差与缺陷深度近似成线性正相关。数值结果为激光超声检测带过渡圆角的平板表面缺陷提供了有价值的参考。 相似文献
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传统超声检测多使用直达波进行检测,但在各向异性、非均匀的复杂结构检测中存在诸多限制。将超声波在此类多重散射介质中的传播近似为扩散过程,探索采用超声扩散场信号进行复合材料表面缺陷的检测定位。在此过程中形成的扩散场能对介质密集采样,对缺陷的出现高度敏感。针对铺层结构为[0°/90°]12的碳纤维增强环氧树脂基复合材料板,基于Locadiff方法建立表面缺陷定位的理论模型,开展缺陷出现前后波形的理论不相关性计算。结合实验求解扩散系数,开展检测信号的不相关性分析。最后利用反演计算的模型给出缺陷的定位结果。结果表明,当缺陷直径为10 mm时,定位误差为6.99%;当缺陷直径为5 mm时,定位误差为9.29%,可以实现复合材料表面缺陷的定位。 相似文献
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The collisionless Boltzmann equation is solved by an iterative characteristic method to calculate temporal and spatial plasma wave echoes of arbitrary order neglecting self-consistent fields. Using this model the measured spatial echo amplitude dependence from the transmitter separation is explained. 相似文献