Xiao-Bang Xu

MICROWAVE IMAGING OF BURIED INHOMOGENEOUS OBJECTS USING PARALLEL GENETIC ALGORITHM COMBINED WITH FDTD METHOD

Microwave imaging of buried objects has been widely used in sensing and remote-sensing applications. It can be formulated and solved as inverse scattering problems. In this paper, we propose a hybrid numerical technique based on the parallel genetic algorithm (GA) and the finite-difference time-domain (FDTD) method for determining the location and dimensions of two-dimensional inhomogeneous objects buried in a lossy earth. The GA, a robust stochastic optimization procedure, is employed to recast the inverse scattering problem to a global optimization problem for its solution. To reduce its heavy computation burden, the GA-based inverse computation is parallelized and run on a multiprocessor cluster system. The FDTD method is selected for the forward calculation of the scattered field by the buried inhomogeneous object because it can effectively model an inhomogeneous object of arbitrary shape. Sample numerical results are presented and analyzed. The analysis of the numerical results shows that the proposed hybrid numerical technique is able to determine the location and dimension of a 2D buried inhomogeneous object, and the parallel computation can effectively reduce the required computation time. 284 Chen, Huang, and Xu

Scattering of TM excitation by coupled and partially buried cylinders at the interface between two media

An analysis of scattering from coupled conducting cylinders near the planar interface between two semi-infinite, homogeneous halfspaces of different electromagnetic properties and from partially buried conducting cylinders is presented. The perfectly conducting cylinders of general cross sections are of infinite extent and the excitation is transverse magnetic to the cylinder axes. Coupled integral equations for the unknown current induced on the cylinders are derived and a numerical method for solving them is described. In addition, a simple technique is employed to determine the far-zone scattered field from knowledge of the cylinder current. Data displaying the distribution of the induced current and the scattered field patterns for cylinders of interest are presented and discussed.

Current induced by TE excitation on a conducting cylinder located near the planar interface between two semi-infinite half-spaces

An analysis is presented for determining the current induced by a known transverse electric excitation on a perfectly conducting cylinder located near the planar interface separating two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The conducting cylinder of general cross section is of infinite extent and the excitation is transverse electric to the cylinder axis. Two types of integral equations, the magnetic field integral equation and the electric field integral equation, are formulated, and the Greens functions for the integral equations are derived in an appendix. Numerical solution methods for solving the integral and integrodifferential equations are presented. For a strip parallel or perpendicular to the interface, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters, including the case of a cylinder resting on the interface.

Measurement/computation of effective permittivity of dilute solution in saponification reaction

For better application of microwaves in chemistry, the interaction between microwaves and the chemical reaction needs further study. Since the reactants form a complicated mixture, which changes with time, an effective permittivity can be used to describe the molecular polarization of the mixture in the reaction. The effective permittivity is expected to change with microwave frequency, temperature and reaction time. However, in many cases, the change of effective permittivity in a saponification reaction is too small to be detected using traditional methods. In this paper, we present a hybrid experimental/computational method for determining the effective permittivity in a saponification reaction. We use a resonant coaxial sensor to measure the reflection coefficients. To predict its performance, the electromagnetic-field distribution near the sensor and the reflection coefficient are calculated employing a frequency-dependent finite-difference time-domain method. Next, we develop a genetic-algorithm-based inverse-calculation technique and employ it to determine the complex permittivity of pure water from the measured reflection coefficient and compare the results with those obtained from Debyes equation. Finally, the hybrid experimental/computational method is employed to determine the effective permittivity of a dilute solution in a typical saponification reaction. Results are presented and discussed.

Automated design of a three-dimensional fishbone antenna using parallel genetic algorithm and NEC

A new antenna configuration, named the three-dimensional fishbone antenna (3DFA), as an improvement of the conventional fishbone antenna, is presented in this letter. It consists of dipoles that may be of nonuniform lengths with unequal spacing and are allowed to tilt in haphazard directions. To achieve a high endfire gain and good impedance match, the structural parameters of the 3DFA are optimized in an automated design, making use of the genetic algorithm (GA) in conjunction with numerical electromagnetic codes (NEC) and cluster parallel computation. The design results are presented and discussed. A prototype of such designed 3DFA has been fabricated and tested. The measured radiation pattern and the return loss of the antenna are compared with the computational results, and a good agreement is observed. Another such designed 3DFA has achieved an endfire gain up to 16.72 dBi, which surpass the maximum gain of a conventional Yagi-Uda antenna with the same number of elements by 87%.

A Novel Planar Slot Array Antenna With Omnidirectional Pattern

A novel planar slot array antenna with omnidirectional radiation pattern in the horizontal plane is proposed. The antenna has a simple structure based on a stripline. Its fabrication employs a low-cost and accurate planar printed technique. A series of rectangular-shaped loop slots are etched on two parallel ground planes, and act as radiators. The basic principle of operation of the antenna is discussed in this study. An antenna with eight back-to-back slots is designed by employing the genetic algorithm (GA) implemented on a cluster system to achieve good omnidirectional radiation characteristics. A prototype antenna is fabricated and measured. The measurement results agree with the simulation data and show that this antenna possesses encouraging features. For example, at the working frequency of 5.8 GHz, it has a well-formed omnidirectional pattern with maximum gain variation less than 0.5 dB in the horizontal plane, a high gain level of 10 dBi, side lobes 10 dB below the main lobe and no beam squint. Meanwhile, this antenna achieves an impedance bandwidth of 4.6% of the center frequency (5.68-5.95 GHz) for S11 <; -10 dB and exhibits stable omnidirectional performance over the impedance bandwidth.

TE scattering by partially buried and coupled cylinders at the interface between two media

The scattering of transverse electric (TE) illumination by partially buried conducting cylinders and by coupled conducting cylinders in two media is studied. The conducting cylinders are of general cross section and of infinite extent. Data depicting far-zone scattered fields for various cylinders and media parameters of interest are presented, and the highly lobate patterns which differ significantly from those due to cylinders in homogeneous space are discussed and explained. >

A Two-Step Numerical Solution of Magnetic Field Produced by ELF Sources within a Steel Pipe

A buoyant water massage device for use in a swimming pool, the device having a body support structure capable of supporting a persons body at the surface of the water, where the body support structure has an opening through which pressurized fluid streams are directed against the back of the user reclining on the device by a fluid dispersal structure. The fluid dispersal structure is connected to a pressurized water source and an air entrainment apparatus and the fluid dispersal structure is disposed a distance below the body support structure such that the fluid dispersal structure does not contact the users body. Preferably the fluid dispersal structure is adjustable longitudinally relative to the body support structure.

Analysis of Temperature Effect on p-i-n Diode Circuits by a Multiphysics and Circuit Cosimulation Algorithm

A novel cosimulation algorithm that combines physical-model-based multiphysics simulation with equivalent-model-based circuit simulation is proposed. In the algorithm, multiphysics simulation couples multiple physical equations (e.g., the electromagnetic, semiconductor transport, thermodynamics equations, etc.) to be solved numerically by an iterative approach. The multiphysics simulation is for modeling the electrothermal behavior of semiconductor devices, and then, it is incorporated into the circuit simulation to extend the simulation from semiconductor devices to circuits. Employing the proposed algorithm, sample numerical results for the temperature effect on circuits comprising commercial p-type-intrinsic-n-type diodes with a model number of mot_bal99lt1 are obtained and compared to measurement data. The comparison shows a good agreement between these two sets of data, which validates the feasibility and accuracy of the proposed algorithm. Moreover, the proposed algorithm can provide a useful physical mechanism for understanding temperature effect on semiconductor devices and circuits.

A Fast Algorithm to Simulate 2-D Electromagnetic Field for Objects With Gradually Time-Varying Dielectric Permittivity

In some cases such as heating objects by microwave power, variation of the temperature in objects changes their dielectric permittivity and then leads to variation of the electromagnetic (EM) field. The commonly adopted method of simulation for the heating procedure is to repeatedly execute the full-wave simulation for each small time intervals, which results in a heavy computation burden. A fast algorithm for simulating 2-D sceneries is proposed for the first time. It starts with a full-wave simulation to get an initial EM field, and then corrects the EM field in an efficient way rather than repeating the full-wave simulation when the objects permittivity has slightly changed. A few sample numerical results are presented and analyzed, which verifies the accuracy, robustness, and effectiveness of the proposed fast algorithm.