反射式GPR中地下异构介质的FDTD二维建模与仿真

在此利用地下表层介质物理特性具有高斯统计分布这一分布特性在传统的均匀空间加入高斯随机信号,在进行探测时这些背景信号就会影响GPR探测响应,从而得到相应的地质图像,建立．了各向异性地质模型,理论上通过这种建。,模方法可以创建任何复杂的地质模型,这将为研究地下介质提供更丰富的地质资料。在最后用反射式GPR对所建地质模型进行了FDTD的二维Matlab仿真,取得了预想的效果,仿真图像形象地证明了这一各向异性地质模型的可行性。     

Effectiveness of 2-D and 2.5-D FDTD Ground-Penetrating Radar Modeling for Bridge-Deck Deterioration Evaluated by 3-D FDTD

Computational modeling effectively analyzes the wave propagation and associated interaction within heterogeneous reinforced concrete bridge decks, providing valuable information for sensor selection and placement. It provides a good basis for the implementation of the inverse problem in defect detection and the reconstruction of subsurface properties, which is beneficial for defect diagnosis. The objective of this study is to evaluate the effectiveness of lower order models in the evaluation of bridge-deck subsurfaces modeled as layered media. The two lower order models considered are a 2-D model and a 2.5-D model that uses the 2-D geometry with a compressed coordinate system to capture wave behavior outside the cross-sectional plane. Both the 2- and 2.5-D models are compared to the results obtained from a full 3-D model. A filter that maps the 3-D excitation signal appropriately for 2- and 2.5-D simulations is presented. The 2.5-D model differs from the 2-D model in that it is capable of capturing 3-D wave behavior interacting with a 2-D geometry. The 2.5-D matches results from the corresponding 3-D model when there is no variation in the third dimension. Computational models for air-launched ground-penetrating radar with 1-GHz central frequency and bandwidth for the detection of bridge-deck delamination are implemented in 2-, 2.5-, and 3-D using FDTD simulations. In all cases, the defect is identifiable in the results. Thus, it is found that in layered media (such as bridge decks) 2- and 2.5-D models are good approximations for modeling bridge-deck deterioration, each with an order of magnitude reduction in computational time.      

An accurate 2-D hard-source model for FDTD

This letter describes an accurate two-dimensional (2-D) hard-source model for finite-difference time-domain (FDTD). The proposed model allows accurate control over the effective radius of a 2-D hard source. In addition, the TM version of the source model is directly applicable as a very accurate 2-D thin-wire model. The proposed model is verified in 2-D for both TM and TE case using a recently introduced method for finding the effective radius of a filamentary 2-D hard source     

一种新型探地雷达天线的FDTD分析

探地雷达系统一般采用超宽带短脉冲信号,因而其天线系统也必须为宽带的。该文给出一种新型的探地雷达天线,该天线为置于镜像面上且具有离散指数电阻加载的单偶极子。通过FDTD法对该天线辐射特性的仿真计算表明,选择合适的电阻加载方式,可以消除由于天线末端阻抗不匹配而引起的二次反射,使天线具有较好的辐射波形和一定的带宽,从而满足实际探地雷达系统的需要。文中还分析了收发天线不同组合方式对直耦信号和目标回波信号的影响。     

FDTD分析探地雷达天线的辐射特性

探地雷达系统一般采用超宽带短脉冲信号,因而其天线系统必须具有较好的宽带性能。只有几种类型的宽带天线能够用于探地雷达系统中,如电阻加载的蝶形天线、TEM喇叭天线及其变形形式。本文将给出一种新型的探地雷达天线,该天线为置于镜像面上且具有离散指数电阻加载的单偶极子。文中将采用FDTD计算和分析该天线在自由空间和有耗媒质上方时的辐射特性。结果表明,通过选择一定的电阻加载形式,可使天线具有较好的辐射波形,从而能够满足实际探地雷达的需要。最后,通过地下目标散射场的理论结果和实验结果说明了本文所采用方法的正确性。     

基于FDTD的1—D和2—D PGB结构的研究

用FDTD数值方法研究了用于微带传输线的1－D和2－D的PBG（Photonic Band-Gap）光子带隙结构，并且制作了不同PGB结构的电路用于实验，以比较计算结果和实验结果，详细分析了PGB结构的周期的大小和个数、单元的尺寸和形状等方面对其形成的阻带的影响，并给出了结论。     

3-D FDTD method with weakly conditional stability

A novel 3-D FDTD method with weakly conditional stability is presented. The time step in this method is only determined by one space discretisation. Compared with the ADI-FDTD method, this method has better accuracy and higher computation efficiency. CPU time for this weakly conditionally stable FDTD method can be reduced to about 3/4 of that for the ADI-FDTD scheme     

二维时域有限差分法对接地板宽度有限的共面波导的特性参数分析

本文利用二维时域有限差分（FDTD）法分析接地板宽度有限的共面波导（FGCPW）在高达1THZ频段内的频变特性。将计算结果与三维FDTD法分析结果相比较发现，其一致性较好，且大大提高了仿真的效率，通过比较拉地板宽度对FGCPW的色散和衰减特性的影响，说明设计共面波导的关键在于对几何尺寸参数的正确选择。文中还引出各参数间的一般约束关系。     

2-D FDTD method for exact attenuation constant extraction of lossy transmission lines

The two-dimensional finite-difference time-domain (2-D FDTD) method is undeniably efficient for full-wave analysis of uniform transmission lines. However, conventional 2-D FDTD method ignores the spatial attenuation along the propagation direction and yields approximate results. We propose a new 2-D FDTD method for extracting exact attenuation constants of lossy transmission lines. In the proposed method, we take the variation of field components with the propagation direction into consideration and describe an iterative process for finding exact attenuation constants. Numerical experiments show that, compared with the conventional 2-D FDTD method, results given by the iterative process agree much better with analytical solutions or measured data.     

Current-mode background suppression for 2-D LWIR applications

A new readout circuit involving two-step current-mode background suppression is studied for two-dimensional long wavelength infrared (2D LWIR) focal plane arrays. The simple pixel circuit has a very small skimming error of less than 0.3%, low noise characteristics for an adequate calibration range, and a long integration time of 2 ms.     

A frequency-dependent FDTD method for biological applications

A frequency-dependent finite-difference time-domain (FD)² TD method for calculating the response of pulses in plasma or water has recently been described. This method is an advance over the traditional finite-difference time-domain (FDTD) method in that it allows for the frequency dependence of these two media. The modification of the (FD)²TD method to obtain broadband frequency information in 3D biological applications is discussed. The implementation of this method is described, and its accuracy is verified by comparison with analytic solutions using the Bessel function expansion. The use of this method is illustrated by an example of the 3D simulation of a hyperthermia treatment using two applicators over a frequency range of 40 to 200 MHz     

Calculation of losses in 2-D photonic Crystal membrane waveguides using the 3-D FDTD method

The three-dimensional finite-difference time-domain method is used to obtain loss per unit length in a two-dimensional photonic crystal membrane waveguide by simulating three different length guides. Results are shown for propagation both above and below the light line. The results are compared with a Fourier expansion method and good agreement is obtained above and below the light line.     

Time-based pixel-level ADC with wide dynamic range for 2-D LWIR applications

A readout circuit involving a time-based pixel-level ADC is studied for two-dimensional long wavelength infrared focal plane arrays (2-D LWIR FPAs). The integration time of each pixel can be optimised individually and automatically. Using a time-based pixel-level ADC with two-step background suppression, the signal-to-noise ratio and dynamic range can be improved to 88.8 and 95.1 dB, respectively.     

Novel current-mode background suppression for 2-D LWIR applications

A new readout circuit involving two-step current-mode background suppression is studied for two-dimensional long-wavelength infrared focal plane arrays (2-D LWIR FPAs). Buffered direct injection (BDI) and a feedback amplifier are used for the input circuit and background suppression circuit, respectively. The readout circuit has been fabricated using a 0.6-/spl mu/m 2-poly 3-metal CMOS process for a 64/spl times/64 LWIR HgCdTe IR array with a pixel size of 50 /spl mu/m/spl times/50 /spl mu/m. The simple pixel circuit has a very small skimming error of less than 0.3% and low noise characteristics for an adequate calibration range and integration time.     

Adaptive wire bow-tie antenna for GPR applications

In this paper, the basic design of an adaptive ground penetrating radar antenna is introduced. The antenna is able to adapt its input impedance to a variation in the antenna elevation and soil type to keep reflections at the antenna's terminal minimum. As a result, energy transfer from the generator to the antenna is maximized, which in turn maximizes the energy radiated by the antenna into the ground for different antenna elevations and soil types. The antenna is based on a wire bow-tie structure with variable flare angle for adjusting the antenna's input impedance. The flare angle variation is realized by short-circuiting the gaps separating the wires from the feed point of the antenna, for which electronic switching devices such as PIN diodes could be used to allow fast and convenient control of the antenna's flare angle.     

二维非正交坐标系下FDTD方法的数值色散特性

本文详细讨论了二维非正交坐标系下FDTD方法的色散特性，导出了其数值色散方程。理论计算结果表明，非正交FDTD方法的空间色散与网络尺寸、网络内角、波传播方向有密切关系。同时指出，在应用非正交FDTD方法解决有关时域电磁问题时，网格的部分应分量选取网格边长相接近，夹角接近90的情况以减少此方法的数值色散。     

A new 2-D FDTD method applied to scattering by infinite objects with oblique incidence

A new two-dimensional (2-D) finite-difference time domain (FDTD) method applied to scattering by infinite objects with oblique incidence is proposed. 2-D Maxwell's equations, differential equations, and perfectly matched layer (PML) absorbing boundary conditions (ABC) are derived. The incident wave, computed by the 1-D FDTD method, is set on the connecting boundary. The accuracy and the efficiency of the proposed method have been verified by comparing the results of the split-field periodic FDTD method, the sine-cosine method, and the transmission line theory method with the proposed method.     

Domain-overriding and digital filtering for 3-D FDTD subgridded simulations

We report on an extension of finite-difference time-domain (FDTD) subgridding (SG) algorithms incorporating digital filters and domain-overriding to three-dimensional (3-D) simulations and to problems involving materials traversing the SG interfaces. We show that significant improvements in accuracy can be obtained for these cases as well.     

Determination of the direction that has maximum phase-velocity for the 2-D and 3-D FDTD methods based on Yee's algorithm

To easily evaluate the performance of the numerical dispersion of the FDTD method, a simple and efficient manner to theoretically determine the special direction that has the maximum phase-velocity for arbitrarily shaped two-dimensional (2-D) and three-dimensional (3-D) Yee's cells is proposed. It is found that the wave propagating along the special direction obeys the following physical rule: the time that the wave takes to traverse the spatial step sizes along each of the main axes of the cell is identical. It is demonstrated that this special direction is closely related to the aspect ratio(s) of the cells, rather than the diagonals of the cells. Moreover, the mathematical expressions for the maximum phase-velocity of the 2-D and 3-D cells with arbitrary aspect ratios are derived for the first time.     

CAS-CAS transform for 2-D signals: A few applications

A few applications of a separable Hartley-like (CAS-CAS) transform in two-dimensional (2-D) signal processing is presented. The applications discussed include (i) the interpolation of signals, (ii) the computation of Hilbert transform, and (iii) the complex cepstrum computation. The computational advantage of the proposed methods over the algorithms using 2-D FFT are discussed.