Chi-Hsien Sun

Comparison of Dynamic Differential Evolution and Self-Adaptive Dynamic Differential Evolution for Buried Metallic Cylinder

The application of two techniques for the reconstruction of shape reconstruction of a metallic cylinder from scattered field measurements is studied in this paper. These techniques are applied to two-dimensional configurations, for which the method of moment (MoM) is applied to solve the integral equations. Considering that the microwave imaging is recast as a nonlinear optimization problem, an objective function is defined by the norm of the difference between the measured scattered electric fields and those calculated for each estimated metallic cylinder. Thus, the shape of a metallic cylinder can be obtained by minimizing the objective function. In order to solve this inverse scattering problem, two techniques are employed. The first one is based on dynamic differential evolution (DDE) algorithm, while the second one is an improved version of the DDE algorithm with self-adaptive control parameters, called SADDE. Both techniques are tested for the simulated data contaminated by additive white Gaussian noise. Numerical results indicate that SADDE algorithm outperforms DDE algorithm in terms of reconstruction accuracy and convergence speed.

Design and applications of radio-over-fiber schemes to indoor wireless coverage and highspeed rails

A low-cost radio-over-fiber (RoF) based integrated transmission of long term evolution (LTE) and worldwide interoperability for microwave access (WiMAX) signals is proposed to solve the shadowing effect of building envelopes and the complexity of transmitting system in wireless access network services. This scheme is also applied to solve the problems of required fast handover and poor signal penetration in tunnels for high-speed rail mobile connections. We design and demonstrate experimentally a multi-service WiMAX/LTE RoF system that can extend the indoor signal coverage, with an emphasis on the power conversion efficiency and optoelectronic component selections. The designed RoF transceivers and switches are being deployed in both the campus buildings and the tunnels of Taiwan High-Speed Rail system to allow mobile connections.

Image reconstruction for buried inhomogeneous dielectric cylinders by evolutionary algorithms

This paper presents the studies of time domain inverse scattering for a two dimensional inhomogeneous dielectric cylinder buried in a half-space by the finite difference time domain (FDTD) method and evolutionary algorithms (EAs). For forward scattering, the FDTD method is employed to calculate the scattered E fields, while for the inverse scattering the evolutionary algorithms are utilized to determine the permittivity of the buried cylindrical scatterer with arbitrary cross section. The results obtained for different examples show that the dynamic differential evolution (DDE) algorithms outperform the non-uniform steady state genetic algorithm (NU-SSGA) variants in terms of finding best optima. The suitability and efficiency of applying these two methods for microwave imaging of 2-D inhomogeneous dielectric cylinders are examined.

Estimation of the Two-Dimensional Homogenous Dielectric Scatterer in a Slab Medium Using Particle Swarm Optimization and Asynchronous Particle Swarm Optimization

A microwave imaging technique based on particle swarm optimization (PSO) and asynchronous particle swarm optimization (APSO) are proposed for the electromagnetic inverse scattering. In this article, the finite-difference time-domain (FDTD) method is employed for the analysis of the forward scattering part, while PSO and/or APSO schemes (combining with FDTD) are applied to tackle the inverse scattering part. These two schemes aim for the simultaneous reconstruction of the location, shape, and permittivity of the dielectric scatterer in a slab medium. The reconstruction is based on the minimization of a cost functional, which evaluates the difference between measured and estimated values of the electric field. These two schemes are tested by several numerical examples, and the numerical results indicate that APSO outperforms 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.

Microwave imaging of buried dielectric cylinders by asynchronous particle swarm optimization

This paper presents the studies of time domain inverse scattering for a two dimensional inhomogeneous dielectric cylinder buried in a slab medium by the finite difference time domain (FDTD) method and the asynchronous particle swarm optimization (APSO) method. The APSO is applied to reconstruct permittivity of the two-dimensional inhomogeneous dielectric cylinder. Numerical result shows that APSO is able to yield good reconstructed quality.

Electromagnetic imaging of buried perfectly conducting cylinders targets using APSO

We present a computational approach to the imaging of a two-dimensional (2-D) embedded perfectly conducting cylinder by the asynchronous particle swarm optimization (APSO). An embedded conducting cylinder of unknown shape scatters the incident transverse magnetic (TM) wave in a half space while the scattered field is recorded outside. 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 solved by an optimization approach and the global searching scheme the asynchronous particle swarm optimization is then employed to search the parameter space. Numerical simulations show that even when the measured scattered fields are contaminated with Gussian noise, the quality of the reconstructed results obtained by the APSO algorithm is very good.

Inverse scattering for a buried 2D homogeneous dielectric cylinder using by SSGA

This paper presents an image reconstruction approach for a buried homogeneous cylinder with arbitrary cross section in half 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 subsurface 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.