84 research outputs found

    Comparison of Particle Swarm Optimization and Self-Adaptive Dynamic Differential Evolution for the Imaging of a Periodic Conductor

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    [[abstract]]The application of two techniques to reconstruct the shape of a two-dimensional periodic perfect conductor from mimic the measurement data is presented. A periodic conducting cylinder of unknown periodic length and shape scatters the incident wave in half-space and the scattered field is recorded outside. After an integral formulation, the microwave imaging is recast as a nonlinear optimization problem; a cost functional is defined by the norm of a difference between the measured scattered electric fields and the calculated scattered fields for an estimated shape of a conductor. Thus, the shape of conductor can be obtained by minimizing the cost function. In order to solve this inverse scattering problem, transverse magnetic (TM) waves are incident upon the objects and two techniques are employed to solve these problems. The first is based on an particle swarm optimization (PSO) and the second is a self-adaptive dynamic differential evolution (SADDE). Both techniques have been tested in the case of simulated mimic the measurement data contaminated by additive white Gaussian noise. Numerical results indicate that the SADDE algorithm is better than the PSO in reconstructed accuracy and convergence speed.[[notice]]補正完畢[[incitationindex]]SC

    Electromagnetic scattering of metallic cylinders of arbitrary shape by using asynchronous particle swarm optimization and non-uniform steady state genetic algorithm

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    [[abstract]]Two techniques for the shape reconstruction of multiple metallic cylinders from scattered fields are investigated in this paper, in which two-dimensional configurations are involved. After an integral formulation, the method of moment (MoM) is applied to solve it numerically. Two separate perfect-conducting cylinders of unknown shapes are buried in one half-space and illuminated by the transverse magnetic (TM) plane wave from the other half space. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equation is derived and the imaging problem is reformulated into optimization problem. The non-uniform steady state genetic algorithm (NU-SSGA) and asynchronous particle swarm optimization (APSO) are employed to find out the global extreme solution of the object function. Numerical results demonstrate even when the initial guesses are far away from the exact shapes, and the multiple scattered fields between two conductors are serious, good reconstruction can be obtained. In addition, the effect of Gaussian noise on the reconstruction results is investigated and the numerical simulation shows that the reconstruction results are good and acceptable, as long as the SNR is greater than 20 dB.[[incitationindex]]SCI[[booktype]]電子版[[booktype]]紙

    Comparison of Particle Swarm Optimization and Asynchronous Particle Swarm Optimization for Inverse Scattering of a Two- Dimensional Perfectly Conducting Cylinder

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    [[abstract]]This paper reports a two dimensional time domain inverse scattering algorithm based upon the finite-difference time domain method for determining the shape of perfectly conducting cylinder. Finite difference time domain method (FDTD) is used to solve the scattering electromagnetic wave of a perfectly conducting cylinder. The inverse problem is resolved by an optimization approach and the global searching scheme asynchronous particle swarm optimization (APSO) is then employed to search the parameter space. By properly processing the scattered field, some EM properties can be reconstructed. One is the location of the conducting cylinder, the others is the shape of the perfectly conducting cylinder. This method is tested by several numerical examples; numerical results indicate that the APSO outperforms the PSO in terms of reconstruction accuracy and convergence speed. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

    Microwave imaging of a partially immersed non-uniform conducting cylinder

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    [[abstract]]In this paper, we investigate the imaging problem to determine both the shape and the conductivity of a partially immersed non-uniform conducting cylinder from the knowledge of scattered far-field pattern of TM waves by solving the ill-posed nonlinear equation. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived and the inverse problem is reformulated into an optimization one. The steady-state genetic algorithm is then employed to find out the global extreme solution of the object function. As a result, the shape and the conductivity of the conductor can be obtained. Numerical results are given to demonstrate that even in the presence of noise, good reconstruction can be obtained.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]電子

    Inverse Scattering of Dielectric Cylindrical Target Using Dynamic Differential Evolution and Self-Adaptive Dynamic Differential Evolution

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    [[abstract]]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.[[notice]]補正完畢[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

    Self-adapting control parameters in dynamic differential evolution on inverse scattering problems: SADDE for inverse scattering

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    [[abstract]]The application of two techniques for the reconstruction of shape reconstruction of the perfectly conducting cylinder from scattered field measurements is studied in the present paper. These approaches are applied to two-dimensional configurations. After an integral formulation, a discretization using the method of moment (MoM) is applied. The inverse scattering problems are transformed into optimization problems. Considering that the microwave imaging is recast as a nonlinear optimization problem, an objective function is defined by the norm of a difference between the measured scattered electric field and that calculated for an estimated the shape of the perfectly conducting cylinder. Thus, the shape of metallic cylinder can be obtained by minimizing the objective function. In order to solve this inverse scattering problem, two techniques are employed. The first is based on a dynamic differential evolution (DDE). The second is a new version of the DDE algorithm with self-adaptive control parameters (SADDE). Numerical results indicate that the self-adaptive dynamic differential evolution algorithm (SADDE) outperforms the DDE in terms of reconstruction accuracy.[[conferencetype]]國際[[conferencedate]]20110926~20110930[[conferencelocation]]Seoul, Kore

    Comparative Study of Some Population-based Optimization Algorithms on Inverse Scattering of a Two-Dimensional Perfectly Conducting Cylinder in Slab Medium

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    [[abstract]]The application of four techniques for the shape reconstruction of a 2-D metallic cylinder buried in dielectric slab medium by measured the cattered fields outside is studied in the paper. The finite-difference time-domain (FDTD) technique is employed for electromagnetic analyses for both the forward and inverse scattering problems, while the shape reconstruction problem is transformed into optimization one during the course of inverse scattering. Then, four techniques including asynchronous particle swarm optimization (APSO), PSO, dynamic differential evolution (DDE) and self-adaptive DDE (SADDE) are applied to reconstruct the location and shape of the 2-Dmetallic cylinder for comparative purposes. The statistical performances of these algorithms are compared. The results show that SADDE outperforms PSO, APSO and DDE in terms of the ability of exploring the optima. However, these results are considered to be indicative and do not generally apply to all optimization problems in electromagnetics.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[booktype]]電子

    Nondestructive Evaluation of Buried Dielectric Cylinders by Asynchronous Particle Swarm Optimization

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    [[abstract]]This paper presents the study of time domain inverse scattering for a two-dimensional inhomogeneous dielectric cylinder buried in a slab medium via the finite difference time domain (FDTD) method and the asynchronous particle swarm optimization (APSO) method. For the forward scattering part, the FDTD method was employed to calculate the scattered E fields. Base on the scattering fields, these inverse scattering problems were transformed into optimization problems. The APSO method was applied to reconstruct the permittivity of the two-dimensional inhomogeneous dielectric cylinder. In addition, the effects of Gaussian noise on the reconstruction results were investigated. Numerical results show that even when the measured scattered fields were contaminated with Gaussian noise, APSO was able to yield good reconstructed quality.[[notice]]補正完畢[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]電子

    Time Domain Microwave Imaging for a Buried Dielectric Cylinder by Dynamic Differential Evolution

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    [[abstract]]This paper presents the studies of time domain inverse scattering for a two dimensional homogeneous dielectric cylinder buried in a half-space which are based on the finite difference time domain (FDTD) method and the dynamic differential evolution (DDE). For the forward scattering, the FDTD method is employed to calculate the scattered E fields, while for the inverse scattering the DDE scheme is utilized to determine the shape, location and the permittivity of the buried cylindrical scatterer with arbitrary cross section. The subgirdding technique is implemented for the FDTD code in order to model the shape of the cylinder more smoothly. In additions, in order to describe an unknown cylinder with arbitrary cross section more effectively during the course of searching, the closed cubic-spline expansion is adopted to represent the scatterer contour instead of the frequently used trigonometric series. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered fields are contaminated with Gaussian noise, DDE is able to yield good reconstructed quality.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

    Image Reconstruction for 2D Homogeneous Dielectric Cylinder Using FDTD Method and SSGA

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    [[abstract]]This paper presents an image reconstruction approach for a 2-D homogeneous cylinder with arbitrary cross section in free space. The computational method combines the finite difference time domain (FDTD) method and non-uniform steady state genetic algorithm (NU-SSGA) to determine the shape and location of the scatterer with arbitrary shape. The subgirdding technique is implemented for modeling the shape of the cylinder more closely. The inverse problem is reformulated into an optimization problem and the global searching scheme NU-SSGA with closed cubic-spline is then employed to search the parameter space. A set of representative numerical results is presented for demonstrating that the proposed approach is able to efficiently reconstruct the electromagnetic properties of homogeneous dielectric scatterer even when the initial guess is far away from the exact one. In addition, the effects of Gaussian noises on imaging reconstruction are also investigated.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙
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