Inverse scattering of dielectric cylindrical target using dynamic differential evolution and self‐adaptive dynamic differential evolution

The inverse problem under consideration is to reconstruct the characteristic of scatterer from the scattering E field. Dynamic differential evolution (DDE) and self‐adaptive dynamic differential evolution (SADDE) are stochastic‐type optimization approach that aims to minimize a cost function between measurements and computer‐simulated data. These algorithms are capable of retrieving the location, shape, and permittivity of the dielectric cylinder in a slab medium made of lossless materials. The finite‐difference time‐domain (FDTD) is employed for the analysis of the forward scattering. The comparison is carried out under the same conditions of initial population of candidate solutions and number of iterations. Numerical results indicate that SADDE outperforms the DDE a little in terms of reconstruction accuracy. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Solving time domain microwave imaging for two‐dimensional inhomogeneous dielectric cylinder

This article presents the studies of time domain inverse scattering for a two‐dimensional (2D) inhomogeneous dielectric cylinder buried in a slab medium by the asynchronous particle swarm optimization (APSO) and dynamic differential evolution (DDE) method. The method of finite‐difference time‐domain is employed for the analysis of the forward scattering part, while the inverse scattering problem is transformed into optimization one. The DDE algorithm and the APSO are applied to reconstruct the permittivities distribution of a 2D inhomogeneous dielectric cylinder. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise. Numerical results indicate that the APSO algorithm outperforms the DDE in terms of reconstruction accuracy and convergence speed. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:147–154, 2014.     

Electromagnetic imaging of buried perfectly conducting cylinder targets using the dynamic differential evolution

Dynamic differential evolution (DDE) for shape reconstruction of perfect conducting cylinder buried in a half‐space is presented. Assume that a conducting cylinder of unknown shape is buried in one half‐space and scatters the field incident from another half‐space where the scattered filed is measured. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. The inverse problem is resolved by an optimization approach, and the global searching scheme DDE is then used to search the parameter space. Numerical results demonstrate that even when the initial guess is far away from the exact one, good reconstruction can be obtained by using DDE both with and without the additive Gaussian noise. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Electromagnetic scattered field time series from finite difference time domain trained time delay neural network

This paper uses time delay neural network (TDNN) for predicting electromagnetic (EM) fields scattered from dielectric objects (cylinder, cylinder‐hemisphere, and cylinder‐cone) using: (a) FDTD generated initial field data for similar conducting objects and (b) Statistical information for the nature of fields. Statistical data indicated that the scattered field nature is close to deterministic. The TDNN structure determination uses statistical data for fixing the number of delays and tabular technique to obtain the number of hidden neurons. The TDNN training uses the Levenberg‐Marquardt (LM) algorithm. The model outputs follow standard FDTD results closely.     

An inverse scattering analysis without information of sources producing incident fields

An inverse scattering approach based on the field equivalence principle is developed for reconstructing the electrical parameters of a stratified medium using only electric field time‐domain data measured at two observation points in presence and absence of the medium. The magnetic field data at the observation points are calculated from the electric field data by solving two equivalent problems for the incident and scattered fields. By noting that the field of an equivalent problem for the total field in the interior region between two observation points is null in the exterior region, the functional of the electrical parameters is introduced. A genetic algorithm is applied for minimization of the functional to estimate the parameters. Numerical simulations demonstrate the effectiveness of the approach. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Implementation of convolutional perfectly matched layer for three‐dimensional hybrid implicit‐explicit finite‐difference time‐domain method

The hybrid implicit‐explicit (HIE) finite‐difference time‐domain (FDTD) method with the convolutional perfectly matched layer (CPML) is extended to a full three‐dimensional scheme in this article. To demonstrate the application of the CPML better, the entire derivation process is presented, in which the fine scale structure is changed from y‐direction to z‐direction of the propagation innovatively. The numerical examples are adopted to verify the efficiency and accuracy of the proposed method. Numerical results show that the HIE‐FDTD with CPML truncation has the similar relative reflection error with the FDTD with CPML method, but it is much better than the methods with Mur absorbing boundary. Although Courant‐Friedrich‐Levy number climbs to 8, the maximum relative error of the proposed HIE‐CPML remains more below than ?71 dB, and CPU time is nearly 72.1% less than the FDTD‐CPML. As an example, a low‐pass filter is simulated by using the FDTD‐CPML and HIE‐CPML methods. The curves obtained are highly fitted between two methods; the maximum errors are lower than ?79 dB. Furthermore, the CPU time saved much more, accounting for only 26.8% of the FDTD‐CPML method while the same example simulated.     

A new multilevels Huygens sub‐gridding finite difference time domain based on a tree structure and object oriented programming

In this article, an efficient sub‐gridding finite‐difference time‐domain is developed for the simulation of multiscaled electromagnetic problems. The proposed technique is based on using the Huygens surfaces for interfacing electromagnetic fields between different grids. The use of the Object Oriented Programming for modeling FDTD simulations facilitates the imbrication of multiple sub‐grids. That heightens the spatial ratio without affecting the accuracy and stability of the sub‐gridding technique. Spatiotemporal interpolation is used to evaluate the electromagnetic fields in Huygens surface location among the coarse grid. Results of numerical experiments prove that the use of imbricated sub‐grids and spatiotemporal interpolation in the Huygens sub‐gridding is more efficient than the use of a single sub‐grid with only spatial interpolation.     

A novel hybrid algorithm based on FDTD and WCS‐FDTD methods

In this article, a hybrid algorithm based on traditional finite‐difference time‐domain (FDTD) and weakly conditionally stable finite‐difference time‐domain (WCS‐FDTD) algorithm is proposed. In this algorithm, the calculation domain is divided into fine‐grid region and coarse‐grid region. The traditional FDTD method is used to calculate the field value in the coarse‐grid region, while the WCS‐FDTD method is used in the fine‐grid region. The spatial interpolation scheme is applied to the interface of the coarse grid region and fine grid region to insure the stability and precision of the presented hybrid algorithm. As a result, a relatively large time step size, which is only determined by the spatial cell sizes in the coarse grid region, is applied to the entire calculation domain. This scheme yields a significant reduction both of computation time and memory requirement in comparison with the conventional FDTD method and WCS‐FDTD method, which are validated by using numerical results.     

An FDTD‐based waveguide filter simulator: Calibration against analytical models

A three‐dimensional (3D) finite‐difference time‐domain (FDTD) simulator is developed for the investigation of network (S‐) parameters of rectangular cross‐section waveguide filters. The simulator is calibrated against analytical LC equivalent models. Any number of horizontal or vertical windows can be located to act as capacitive or inductive irises, respectively, and two‐port filter characteristics can be obtained automatically. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Electromagnetic modeling of 2D electronic mode‐stirred reverberating chambers for electromagnetic compatibility and interference analysis and design

This research concentrates on developing a complete theoretical tool to analyze the electronic mode‐stirred reverberating chamber. A 2D modeling of the EM fields is performed, which can then readily be extended to a 3D analysis of the cavity. The finite‐difference time‐domain (FDTD) method is implemented to discretize the Maxwell's equations. With our newly proposed method, the electromagnetic‐field characteristics can be easily studied inside the reverberating chamber under a realistic circumstance, thus opening doors to the analysis of a large spectrum of problems related to both commercial and military applications. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

A new FDTD stencil for reduced numerical anisotropy in the computer modeling of wave phenomena

An isotropic finite difference scheme is utilized for the development of a new stencil for the finite‐difference time‐domain (FDTD) modeling of electromagnetic wave propagation. The key attribute of the new stencil is the improved isotropy of the numerical phase velocity at fairly moderate spatial sampling of the fields. More specifically, for a given phase velocity anisotropy error, the new stencil requires a much coarser grid than the one required by the standard, second‐order accurate FDTD stencil. This, in turn, amounts to gains in computational resources when transient electromagnetic interactions in electrically‐large domains are being modeled. The numerical attributes of the proposed stencil, namely, its dispersion, anisotropy and stability, are presented in the context of its application to the numerical simulation of two‐dimensional transient electromagnetic wave propagation. Through a series of numerical studies, the enhanced isotropy provided by the proposed scheme is demonstrated and contrasted in a quantitative manner to that of the standard FDTD stencil. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

FDTD analysis of photoconducting antennas for millimeter‐wave generation

In this paper, a hybrid numerical technique is presented for modeling a photoconducting antenna structure designed for optoelectronic generation of millimeter waves. The technique interfaces the solid‐state device model with the three‐dimensional (3D) finite‐difference time‐domain (FDTD) method to achieve the active antenna modeling effectiveness and efficiency. The FDTD algorithm is applied to simulate the passive part of the antenna structure, whereas the numerical device simulation is employed to model the photoconductor that is illuminated by lasers. Physical performance of the photoconductor and response of the antenna are analyzed. Numerical results show good correlation with the experimental result and consequently demonstrate the feasibility of the full‐wave modeling. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 213–220, 2000.     

Implementation and optimization of GPU‐based parallel one‐step leapfrog ADI‐FDTD for far‐field scattering problems

The one‐step leapfrog alternative‐direction‐implicit finite‐difference time‐domain (ADI‐FDTD), free from the Courant‐Friedrichs‐Lewy (CFL) stability condition and sub‐step computations, is efficient when dealing with fine grid problems. However, solution of the numerous tridiagonal systems still imposes a great computational burden and makes the method hard to execute in parallel. In this paper, we proposed an efficient graphic processing unit (GPU)‐based parallel implementation of the one‐step leapfrog ADI‐FDTD for the far‐field EM scattering simulation of objects, in which we present and analyze the manners of calculation area division and thread allocation and a data layout transformation of z components is proposed to achieve better memory access mode, which is a key factor affecting GPU execution efficiency. The simulation experiment is carried out to verify the accuracy and efficiency of the GPU‐based implementation. The simulation results show that there is a good agreement between the proposed one‐step leapfrog ADI‐FDTD method and Yee's FDTD in solving the far‐field scattering problem and huge benefits in performance were encountered when the method was accelerated using GPU technology.     

Analysis for scattering of conductive objects covered with anisotropic magnetized plasma by trapezoidal recursive convolution finite‐difference time‐domain method

The finite‐difference time‐domain method (FDTD) is extended to three‐dimensional (3D) anisotropic magnetized plasma based on the trapezoidal recursive convolution (TRC) technology. The TRC technique requires single convolution integral in the formulation as in the recursive convolution (RC) method, while maintaining the accuracy comparable to the piecewise linear recursive convolution (PLRC) method with two convolution integrals. In this article, the numerical results indicate that the TRC‐FDTD method not only improves accuracy over the RC‐FDTD with the same computational efficiency but also spends less computational time than the PLRC‐FDTD based on the same accuracy. The 3D TRC‐FDTD formula is provided and the bistatic radar scattering sections of conductive targets covered with anisotropic magnetized plasma are calculated. The results show that magnetized plasma cover layer can greatly reduce echo energy of radar targets, and the anisotropic magnetized plasma cover has better absorption effect than nonmagnetized. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Applications of anisotropic one‐step leapfrog HIE‐FDTD method in microwave circuit and antenna

To verify the effect of artificial anisotropy parameters in one‐step leapfrog hybrid implicit‐explicit finite‐difference time‐domain (FDTD) method, we calculated several microwave components with different characteristics. Introduced auxiliary field variable can reduce the program difficulty and improve the computational efficiency without additional computational time and memory cost. Analyses of the numerical results are proved that the calculation time is reduced to about one‐sixth compared to the traditional FDTD method for the same example simulated. The memory cost and relative error are remained at a good level. The numerical experiments for microwave circuit and antenna have been well demonstrated the method available.     

Comparison of image reconstruction by using near‐field and far‐field data for an imperfect conductor

Image reconstruction by using near‐field and far‐field data for an imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity scatters the incident wave in free space and the scattered near and far fields are measured. By using measured fields, the imaging problem is reformulated into an optimization problem and solved by the genetic algorithm. Numerical results show that the convergence speed and final reconstructed results by using near‐field data are better than those obtained by using far‐field data. This work provides both comparative and quantitative information. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 69–73, 2001.     

Maximum likelihood ratio detection of abrupt state change for MIMO linear systems based on frequency domain data

This paper is devoted to the detection of abrupt changes for multiple‐input, multiple‐output (MIMO) linear systems based on frequency domain data. The real discrete‐time Fourier transform is used to map the measured inputs and outputs from the time domain to the frequency domain. Under the hypothesis that the state change occurrence time is k, the system is split up into two systems at the time instant k. One of them describes the frequency dynamics before the hypothetical state change occurs, whereas the other describes the frequency dynamics after the hypothetical occurrence. Thus, the latent state change is modeled as an initial state disturbance to be estimated on the basis of frequency domain samples. Furthermore, the occurrence time is estimated by maximizing a likelihood ratio function. Finally, a numerical example is presented to show the performance. Copyright © 2012 John Wiley & Sons, Ltd.     

A one‐step leapfrog HIE‐FDTD method for rotationally symmetric structures

In this work, they propose a one‐step leapfrog hybrid implicit‐explicit finite‐difference time‐domain (HIE‐FDTD) method for body‐of‐revolution (BOR). Meanwhile, its Convolutional Perfect Matched Layer (CPML) absorbing boundary condition is implemented. In this method, the implicit difference is applied in the angular direction. All the resultant updating equations are still explicit. However, the stability condition of the proposed method is relaxed. The analytical analysis shows that its time step is only determined by the smaller one of spatial increments Δρ and Δz. A scattering example is provided to demonstrate the new algorithm. At the same time, the relative of reflection error of the CPML is given with comparisons of Mur.     

A novel approach for electromagnetic inverse scattering of a two‐dimensional perfect electric conductor object

A two‐dimensional shape determination technique for a perfect electric conductor target using electromagnetic inverse scattering is presented. The proposed algorithm uses the scattered field pattern and an inverse scattering technique derived from Green's function to retrieve the geometry of an unknown target. This method uses the scattering field data over a band of observation points, which is synthesized using frequency domain “method of moment” computational technique. We have verified this algorithm with four different types of numerical examples.     

Extinction of carbon–fiber powder calculated by the FDTD and turning bands methods at 35 GHz

The finite‐difference time‐domain (FDTD) method is used to calculate the specific extinction cross‐section (SECS) of the carbon–fiber powder at 35 GHz. The digitized models with a random process using the turning bands method are simulated for the carbon–fiber powder. The digitized models of the carbon–fiber powder having 12,500–5,832,000 cubical particles with cell sizes in the range of 7–100 μm. It is found that the numerical result of SECS obtained by using the diameter of a cylindrical carbon–fiber particle as the cubical cell size for simulations makes good agreement with the measurement data. It is also found that the SECS is directly proportional to the particle number at 35 GHz. It is also found that the maximum extinction occurs at a resonant particle size. Using curve fitting technique together with Newton's Iteration method, the resonant particle size may be expressed by δ₀ = 3408 × n μm, where n_p is the number of particles. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.