共查询到20条相似文献,搜索用时 62 毫秒
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Resistively loaded Vee dipoles are considered for use in a short-pulse ground penetrating radar (GPR) used to detect buried antipersonnel land mines. First, a study is made to select a short pulse to radiate that is most appropriate for the problem. A simple one-dimensional (1-D) analysis of some representative soils and a land mine is used to select a radiated pulse similar in shape to a differentiated Gaussian pulse with a spectral peak at 4 GHz. Based on previous studies, the conductivity of the arms of the Vee dipole is linearly tapered from the feed to the open ends. A fully three-dimensional (3-D) finite-difference time domain (FDTD) model is developed and used to simulate the GPR land mine detection problem. Using this model, a resistively loaded Vee dipole is selected and evaluated. Parametric studies related to the problem are conducted including: varying the height of the Vee above the ground, varying the position of the land mine both laterally and in depth, and examining the effects of the geometry of the land mine on the received signal. Environmental conditions are examined including signal returns from rocks and variations in the shape of the surface of the ground. The FDTD results are validated by comparisons with experimental data. These studies demonstrate that resistively loaded Vee dipoles can greatly reduce clutter related to the antenna, making the task of distinguishing land mines (targets) much easier 相似文献
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The three-dimensional (3D), wideband, bistatic ground penetrating radar (GPR) scatter response of rough, realistic ground is efficiently and accurately simulated using a hybrid high resolution 3D and large area two-dimensional (2D) finite difference time domain (FDTD) model. The 3D computation carefully models the transmitting and receiving antennas, while the 2D FDTD models wave propagation between the antennas and the scattering by the soil below them. The FDTD soil model considers realistic frequency dependent (dispersive) soil with Gaussian height variations. The modeling results are compared to experiments performed with the Geo-Centers, Inc., Newton, MA, commercially available GPR system used for mine detection. Despite the simplicity of the 2D model, the results of the simulation and the experiment agree quite well 相似文献
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A fully three-dimensional simulation of a ground-penetrating radar:FDTD theory compared with experiment 总被引:13,自引:0,他引:13
A fully three-dimensional, finite-difference time-domain (FDTD) model of a ground-penetrating radar is described. The FDTD simulation completely models the transmitting and receiving antennas, the antenna feeds, the dispersive Earth, and the buried object. Results of scattering from three different buried cylindrical pipes are compared to previously measured results for a one-third size scale model of an actual radar and are shown to be in good agreement 相似文献
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In some electromagnetic (EM) systems proposed for the detection of buried objects, such as landmines, the transducers (antennas) are located very close to the surface of the Earth. The coupling of energy into the Earth is then by the near field of the transducers, or, more precisely, by evanescent waves as well as propagating waves in the spectrum for the radiation from the transducers. Evanescent waves also contribute to the coupling of the scattered field from the shallowly buried object to the transducers. In this paper, we use simple models based on a plane-wave spectral analysis to perform a preliminary examination of the role that evanescent waves can play in the detection and identification of the buried object. The degree to which features in the image of the object can be resolved is of particular interest, since the features can be used to distinguish the object from clutter (such as rocks). The effect of loss in the soil on imaging is also of interest 相似文献
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Yan Qing Zeng Qing Huo Liu 《Geoscience and Remote Sensing, IEEE Transactions on》2001,39(6):1165-1173
Acoustic waves can be a viable tool for the detection and identification of land mines, unexplored ordnance (UXO), and other buried objects. Design of acoustic instruments and interpretation and processing of acoustic measurements call for accurate numerical models to simulate acoustic wave propagation in a heterogeneous soil with buried objects. Compared with the traditional seismic exploration, high attenuation is unfortunately ubiquitous for shallow surface acoustic measurements because of the loose soil and the fluid in its pore space. To adequately model such acoustic attenuation, we propose a comprehensive multidimensional finite-difference time-domain (FDTD) model to simulate the acoustic wave interactions with land mines and soils based on the Biot theory for poroelastic media. For the truncation of the computational domain, we use the perfectly matched layer (PML). The method is validated by comparison with analytical solutions. Unlike the pure elastic wave model, this efficient PML-FDTD model for poroelastic media incorporates the interactions of waves and the fluid-saturated pore space. Several typical land mine detection measurements are simulated to illustrate the application 相似文献
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基于时域有限差分方法和传输线方程,结合高效网格建模技术,文中提出了一种高效的时域建模算
法,它能有效解决微带线的电磁耦合建模问题,实现空间电磁场与微带线瞬态响应的同步计算。首先,结合经验公
式,计算得到微带线的单位长度分布参数,构建适用于微带线电磁耦合分析的传输线方程。然后,采用时域有限差
分(Finite-Difference Time-Domain, FDTD)方法,结合非均匀网格技术和自动网格生成技术,仿真得到微带线激励场,
并在每个时间步进上引入传输线方程获得等效分布源项。最后,对传输线方程使用FDTD 的中心差分格式进行离
散,实现微带线及其端接电路上瞬态响应的迭代求解。为了验证时域建模算法的正确性和高效性,通过自由空间和
屏蔽腔内PCB 上微带线电磁耦合的数值模拟,从计算精度和耗时两方面与传统FDTD 方法的计算结果进行了对比。 相似文献
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We address the problem of detecting low-dielectric contrast cavities buried deep in a lossy ground by using the finite-difference time-domain (FDTD) method in conjunction with signal processing techniques for extrapolation and object identification. It is well known that very low frequency probing is needed for deep penetration into the lossy ground, owing to a rapid decay of electromagnetic (EM) waves at higher frequencies. It is also recognized that numerical modeling using the FDTD method becomes very difficult, if not impossible, when the operating frequency becomes as low as 1 Hz. To circumvent this difficulty, we propose a hybrid approach in this paper that combines the FDTD method with signal processing techniques, e.g., rational function approximation and neural networks (NNs). Apart from the forward problem of modeling buried cavities, we also study the inverse scattering problem-that of estimating the depth of a buried object from the measured field values at the surface of the Earth or above. Numerical results for a buried prism are given to illustrate the application of the proposed technique 相似文献
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Chaos UWB Radar for Through-the-Wall Imaging 总被引:1,自引:0,他引:1
《IEEE transactions on image processing》2009,18(6):1255-1265
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The plane-wave spectrum technique is used to analyze the coupling between a pair of antennas separated by a planar interface. Multiple reflections between the antennas or between either antenna and the interface are included in the formulation. The formulation is used to model detection of buried objects, and a low-frequency metal detector example is analyzed in detail. For a transmitting loop and a buried oblate spheroid, the plane wave spectrum technique is shown to agree with well-known quasi-static approximations. Some experimental results from a 3-kHz metal detector are also shown. 相似文献
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Schroder C.T. Scott W.R. Jr. Larson G.D. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(6):1405-1415
A three-dimensional (3-D) finite-difference model for elastic waves in the ground has been developed and implemented. The model has been created to supplement the development of a sensor that uses elastic waves to detect buried land mines. The model is used to investigate the propagation characteristics of elastic waves in the ground and to explore the interaction of elastic waves with buried land mines. When elastic waves interact with a buried mine, a strong resonance occurs at the mine location. The resonance can be used to enhance the mine's signature and to distinguish the mine from clutter. Results presented in this paper explain the features of elastic wave propagation in the ground and show the interaction of elastic waves with both an anti-personnel mine and an anti-tank mine. 相似文献
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The versatility of the three-dimensional (3D) finite-difference time-domain (FDTD) method to model arbitrarily inhomogeneous geometries is exploited to simulate realistic ground-penetrating radar (GPR) scenarios for the purpose of assisting the subsequent designs of high-performance GPR hardware and software. The buried targets are modeled by conducting and dielectric prisms and disks. The ground model is implemented as lossy with surface roughness, and containing numerous inhomogeneities of arbitrary permittivities, conductivities, sizes, and locations. The impact of such an inhomogeneous ground model on the GPR signal is demonstrated. A simple detection algorithm is introduced and used to process these GPR signals. In addition to the transmitting and receiving antennas, the GPR unit is modeled with conducting and absorbing shield walls, which are employed to reduce the direct coupling to the receiver. Perfectly matched layer absorbing boundary condition is used for both simulating the physical absorbers inside the FDTD computational domain and terminating the lossy and layered background medium at the borders 相似文献
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Experimental model for a seismic landmine detection system 总被引:1,自引:0,他引:1
Scott W.R. Jr. Martin J.S. Larison G.D. 《Geoscience and Remote Sensing, IEEE Transactions on》2001,39(6):1155-1164
A laboratory-scale experimental model has been developed and tested for a system that uses artificially generated high-frequency seismic waves in conjunction with a radar-based noncontact displacement sensor to detect buried landmines. The principle of operation of the system is to measure the transient displacement field very close to a mine location. In this way, the absorption and the geometrical spreading of the seismic waves have not reduced the effects of the mine. By using a seismic excitation, the system exploits the large difference between the elastic properties of a mine and the surrounding soil. This difference causes seismic wave interactions in the vicinity of a mine to be quite distinctive and provides a method for imaging mines and distinguishing them from typical buried clutter. Images of a variety of simulated and inert anti-tank and anti-personnel mines have been formed using this system. Burial scenarios involving natural clutter (rocks and sticks), light surface vegetation, localized burial effects, and multiple mines in close proximity have been studied. None of these scenarios appears to pose serious problems for detection performance 相似文献
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The effectiveness of infrared thermography applied to the detection of abandoned land mines is not yet acceptable. It can probably be improved, however, by computerized processing of the thermal images. This requires reference data, which must be provided mainly by experiments. A method is presented here, by which the heating and cooling cycles of a soil with a buried land mine can be replicated with reduced size and duration. The reference data acquired in the laboratory can be associated to realistic on-field tests by simply stretching the space and time scales. This will permit to reproduce indoors, quickly and effortlessly, the outdoor conditions of any place where the detection of buried land mines must be performed. In this paper, the general thermal problem is described, and the proposed method is comprehensively explained. The results of computer simulations and some laboratory tests are finally reported for validation. 相似文献
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Arunachalam K Maccarini PF Stauffer PR 《IEEE transactions on bio-medical engineering》2008,55(10):2397-2406
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Geogakopoulos S.V. Balanis C.A. Birtcher C.R. 《Antennas and Propagation, IEEE Transactions on》1999,47(6):978-985
Transmission line antennas are widely used elements. Analytical formulations for the coupling between transmission line antennas, e.g., loops and inverted-Ls, are developed. Furthermore, corrected current distributions that exhibit nonzero input current at the antiresonances of such elements are derived. The analytical results are compared with finite-difference time-domain (FDTD) calculations and measurements. Also, the physics of coupling is discussed. Finally, an FDTD technique that efficiently computes the two-port network parameters of a system of two antennas is developed based on a source with an internal resistance 相似文献
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Huang Z. Demarest K.R. Plumb R.G. 《Geoscience and Remote Sensing, IEEE Transactions on》1999,37(6):2692-2698
Calculating the current distribution and radiation patterns for ground-penetrating radar antennas is a challenging problem because of the complex interaction between the antenna, the ground, and any buried scatterer. Typically, numerical techniques that are well suited for modeling the antennas themselves are not well suited for modeling the heterogeneous grounds, and visa versa. For example the finite-difference time-domain (FDTD) technique is well suited for modeling fields in heterogeneous media, whereas the method of moments (MoM) is well suited for modeling complex antennas in free space. This paper describes a hybrid technique, based upon the equivalence principle, for calculating an antenna's current distribution radiation pattern when the antenna is located near an air-ground interface. The original problem is decomposed into two coupled equivalent problems: one for the antenna geometry and the other for the ground geometry, with field information passing between them via a rapidly converging iterative procedure. The fields in each region may be modeled using numerical techniques best suited to them. Results for several test cases are presented, using FDTD to model the ground problem and MoM for the antenna problem, that demonstrate the accuracy of this hybrid technique 相似文献
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Parallel particle swarm optimization and finite- difference time-domain (PSO/FDTD) algorithm for multiband and wide-band patch antenna designs 总被引:6,自引:0,他引:6
This paper presents a novel evolutionary optimization methodology for multiband and wide-band patch antenna designs. The particle swarm optimization (PSO) and the finite-difference time-domain (FDTD) are combined to achieve the optimum antenna satisfying a certain design criterion. The antenna geometric parameters are extracted to be optimized by PSO, and a fitness function is evaluated by FDTD simulations to represent the performance of each candidate design. The optimization process is implemented on parallel clusters to reduce the computational time introduced by full-wave analysis. Two examples are investigated in the paper: first, the design of rectangular patch antennas is presented as a test of the parallel PSO/FDTD algorithm. The optimizer is then applied to design E-shaped patch antennas. It is observed that by using different fitness functions, both dual-frequency and wide-band antennas with desired performance are obtained by the optimization. The optimized E-shaped patch antennas are analyzed, fabricated, and measured to validate the robustness of the algorithm. The measured less than - 18 dB return loss (for dual-frequency antenna) and 30.5% bandwidth (for wide-band antenna) exhibit the prospect of the parallel PSO/FDTD algorithm in practical patch antenna designs. 相似文献