We study the electromagnetic wave propagation in three-dimensional (3-D) dense random discrete media containing dielectric spheroidal scatterers. We employ a Monte Carlo method in conjunction with the Method of Moments to solve the volume integral equation for the electric field. We calculate the effective permittivity of the random medium through a coherent-field approach and compare our results with a classical mixing formula. A parametric study on the dependence of the effective permittivity on particle elongation and fractional volume is included.

This paper deals with the scattering problem of a layer where many spherical lossy particles of high dielectric constant are randomly distributed. A radiative transfer equation is used to calculate the scattering cross section of the layer. Four different multiple scattering methods are applied to determine the coefficients of the equation. The scattering cross sections of the four methods are compared by changing the incident angle and polarization of incident waves and the layer thickness. The comparison shows that the scattering cross section fairly depends on the multiple scattering methods and that we need to use an appropriate multiple scattering method for a scattering problem when using a radiative transfer equation.

An averaged intensity peak profile of light scattered from a random medium depends on a thickness of a sample as well as parameters such as a volume fraction and a size of particles composing the medium. We used this dependence to measure a depth profile varied in the random medium. We demonstrated the possible simultaneous measurement of a transport mean free path and a depth of an aqueous suspension of titanium particles.

To make clear numerically the scattering characteristics for a body embedded in a random medium, we need to analyze the bistatic cross-section (BCS). The scattering problem can be analyzed as a boundary value problem by using current generator method. The fourth moment of Green's functions in the random medium, which is necessary for the analysis, is obtained approximately by two-scale method. We analyze numerically the BCS of conducting circular cylinders in continuous random media, which are assumed to fluctuate about the dielectric constant of free space. The numerical results agree well with the law of energy conservation. The effects of random media on the BCS are also clarified numerically.

In this paper we report the results of a study regarding the backscattering from wind-roughened water surfaces. The reference profile data has been deducted by an experiment held at the University of Heidelberg circular wave tank facility. The scattering theory is based on a fractal description of the surface and a combined use of the Kirchhoff approximation and the small perturbation method (SPM). The scattering results are tested versus the ones obtained via the periodic-surface moment method. The study shows the reliability of the novel approach.

A program is developed to simulate the signal received by a bistatic pulse radar for a defined scenario. The signal collected at the receiving antenna is calculated as a function of time by taking into account the vectorial aspect of the electromagnetic waves and various elements operating in the radar radiolink. The radar radiolink is designed in a modular structure for a general configuration where the transmitter, the target and the receiver are moving. Modules such as elements characterizing the antennas radiation or defining the target scattering can be inserted in accordance with the desired radar scenario. Then the developed model permits to simulate a wide range of radar scenarios where returns from targets and clutter can be individually processed and their characteristics can be investigated in time or frequency. The interest of this model is great because it permits, for a defined scenario, to generate radar data which can be used in signal processing algorithms for target detection, clutter suppression or target classification. This paper shows the implementation of the simulation program considering a concrete radar scenario. The presented scenario deals with the simulation of the sea clutter occurring in a bistatic radar radiolink over the sea surface. In this application where the sea surface is considered as the target, the electric field scattered from the sea surface is calculated by assuming that the surface is described by two independent scales of roughness.

The finite volume time domain (FVTD) method is applied to electromagnetic wave scattering from random rough dielectric surfaces. In order to gain a better understanding of physics of backscattering of microwave from rough surface, this paper treats both horizontal and vertical polarizations especially at low- grazing angle. The results are compared with those obtained by the Integral equation method and the small perturbation method as well as with the experimental data. We have shown that the present method yields a reasonable solution even at LGA. It should be noted that the number of sampling points per wavelength for a rough surface problem should be increased when more accurate numerical results are required, which fact makes the computer simulation impossible at LGA for a stable result. However, when the extrapolation is used for calculating the scattered field, an accurate result can be estimated. If we want to obtain the ratio of backscattering between the horizontal and vertical polarization, we do not need the large number of sampling points.

The mean reflection and transmission coefficients of electromagnetic waves incident onto a two-dimensional slightly random dielectric surface are investigated by means of the stochastic functional approach. We discuss the shift of Brewster's scattering angle using the Wiener kernels and numerical calculations. It is also shown that the phase shift at the reflection into Brewster's angle for a flat surface does not depend on the rms height of the surface, but does on the correlation length of the surface.

The power coupling coefficients between cores of waveguide systems with random geometrical imperfections along the fiber axis are determined by comparing numerical solutions of the coupled mode equations with numerical solutions of the coupled power equations and the dependence of the power coupling coefficient on the correlation length with respect to the propagation constants of modes is clarified. When the correlation length D is small the power coupling coefficient is proportional to κ ² D where κ is the mean mode coupling coefficient and is independent of the fluctuation of the propagation constants. For sufficiently large D the power coupling coefficient d_c decreases in proportion to D^-1 with increasing D and when D , d_c 0. Then the dependence of the power coupling coefficient on the mode coupling coefficient and the fluctuation of the propagation constants δ β is expressed as a function of a single variable κ /δ β .

In this paper, the electromagnetic scattering from a cylinder with a computer-generated random rough surface is analyzed by a numerical simulation method. The validity of the proposed numerical method is confirmed by comparing the present numerical results with those calculated by the perturbation method to second order and its Pade approximation. It is shown that the present proposed method can be applied to the case where the surface roughness becomes relatively large.

This paper deals with a quantitative inversion algorithm for reconstructing the permittivity and conductivity profiles of bounded inhomogeneous buried objects from measured multifrequency and multiincidence backscattered field data. An Edge-Preserving regularization scheme is applied leading to a significant enhancement in the profiles reconstructions. The applications concern civil engineering and geophysics as well as mine detection and localization. The performance of the reconstructions are illustrated with different synthetic data.

A method for determination of the location, shape, and material properties of a 3D object from measurements of the scattered field, when the object is successively illuminated by a number of incident fields is presented. This work extends the method previously developed for reconstructions of 2D permittivity and conductivity from electromagnetic measurements to the more complicated full-vector 3D electromagnetic inversion. Furthermore, a frequency hopping strategy to improve the resolution of the unknown objects when the frequency is raised, is underlined. Results of numerical experiments are presented to illustrate both strengths and weaknesses of the method.

An inverse scattering problem in three dimensional two layered media is investigated. The shape and the location of the acoustic scatterer buried in one half-space are determined. With some a priori information, it becomes possible to solve this problem in three dimensions. Using the moment method, the scattered field is obtained for the estimated scatterer. An iterative procedure based on the Newton's method for the nonlinear least square problem is able to solve the inverse scattering problem. Some numerical results are presented.

Borehole radar is known as a powerful technique for monitoring of subsurface structures such as water flow. However, conventional borehole radar systems are operated in the frequency range lower than 100 MHz and the resolution is poor to measure a surface roughness and an inner structure of subsurface fractures directly. In order to monitor the water flow, these characteristics of subsurface fractures are important. We developed a polarimetric borehole radar system using dipole antennas and axial slot antennas and have found that this system can provide more information than conventional borehole radar. However, the relationship between the characteristic of subsurface fracture and the measured polarimetric radar information has not been clear. In this paper, we simulate electromagnetic wave scattering from subsurface fractures having a rough surface by Finite-Difference Time-Domain (FDTD) technique and discuss the relationship between a surface roughness of subsurface fracture and the polarimetric information. It is found that the subsurface fracture having strong cross-polarized components can be estimated to be rough surface fracture. The full polarimetric single-hole radar measurement was carried out at the Mirror Lake site, NH, USA. In this experiment, we found that subsurface fractures can be classified into some groups by an energy scattering matrix, and found that the subsurface fracture estimated to have a rough surface corresponds to that has higher water permeability.

A two-dimensional algorithm, which combines the well-known Synthetic Aperture Radar (SAR) imaging and the recently developed effective inversion method, is presented and applied to a three-dimensional configuration. During the first stage a two-dimensional image of a realistic three-dimensional buried object is obtained. In the second stage the average permittivity of the object is estimated using a two-dimensional effective inversion scheme where the geometrical information retrieved from the SAR image is employed. The algorithm is applicable in real time.

In Synthetic Aperture Radar Interferometry (InSAR), phase unwrapping holds the key to accurate inversion of digital elevation data. Two new techniques are introduced in this paper that can perform automatic phase unwrapping. The first one is an "optimal" branch-cut algorithm and the second one a hybrid branch-cut/least-square technique, in which pole locations form the weighting basis for the weighted least-square approach. Application of both techniques to ERS-1 data indicates that the height inversion errors are comparable and offer over fifty percent reduction in root mean square (rms) height error compared to the straight least squares method and over thirty-five percent reduction in rms height error compared to the weighted least squares method based on coherence data weighting schemes. The hybrid technique is especially appealing due to its computational efficiency and robustness when compared to traditional branch-cut algorithms.

A signal processing approach is discussed which has the potential for imaging strongly scattering objects from a series of scattering experiments. The method is based on a linear spectral estimation technique to replace the filtered backpropagation for limited discrete data and a subsequent nonlinear signal processing step to remove the contribution of multiple scattering my means of homomorphic filtering. Details of this approach are discussed and illustrated by applying the imaging algorithm to both simulated and real data.

We propose an adaptive complex-amplitude texture classifier that takes into consideration height as well as reflection statistics of interferometric synthetic aperture radar (SAR) images. The classifier utilizes the phase information to segment the images. The system consists of a two-stage preprocessor and a complex-valued SOFM. The preprocessor extracts a complex-valued feature vectors corresponding to height and reflectance statistics of blocks in the image. The following SOFM generates a set of templates (references) adaptively and classifies a block into one of the classes represented by the templates. Experiment demonstrates that the system segments an interferometric SAR image successfully into a lake, a mountain, and so on. The performance is better than that of a conventional system dealing only with the amplitude information.

Nonlinear characteristics of a DBR (Distributed Bragg Reflector) Cherenkov laser are investigated with the aid of particle simulation, allowing for the nonlinear properties of the electron beam. Numerical results show that the EM power extracted from the cavity is considerably suppressed by the nonlinear effect of the electron beam. Additionally, the extracted EM power is found to be critically dependent on the reflection coefficient of the DBR at the output end. Thus the DBRs at both ends of the cavity should be carefully designed in order to extract the EM power from the cavity efficiently.

Several types of coplanar waveguide (CPW) resonator are analyzed by use of the field decay method based on the FDTD algorithm in this paper. Quality (Q) factors of a CPW resonator, including radiation Q, conductor Q, dielectric Q and unloaded Q, are investigated thoroughly. A new procedure to calculate conductor Q is proposed. Some CPW resonators are fabricated and measured in order to validate the analysis method. It is shown that radiation from a CPW resonator can be reduced by means of the stepped impedance technique. It is also seen that miniaturization of CPW resonators can be realized if the stepped impedance structure is adopted.

To extract extrinsic resistances, conventional cold-FET methods require additional DC measurements or channel technological parameters. Additionally, the methods need at least two sets of cold-FET S-parameters measured at different cold-FET bias conditions in order to completely determine gate and drain pad capacitance as well as extrinsic gate, source and drain inductance and their resistances. One set of S-parameters handles the extraction of extrinsic inductances, and the other set extracts the gate and drain pad capacitance. To be free from additional DC measurement or channel technological parameters and reduce the number of sets of cold-FET S-parameters, we propose a cold-FET method that can extract all the extrinsic elements including the gate and drain capacitance, using only one set of cold-FET S-parameters. The method has shown excellent agreement between modeled and measured S-parameters up to 62 GHz at 56 different normal operating bias points.

The micro positioning systems using magnetic suspension technique, which is one of precision actuating method, have been suggested. Utilizing the various potentials such as the exclusion of a mechanical friction, they are being applied broadly to multi degrees of freedom (d.o.f) system requesting high accuracy or hybrid system requesting to be controlled position and force simultaneously. This paper presents the entire development procedure of a novel six d.o.f micro positioning system using mag-netic levitation, with a repulsive force mechanism covering the all d.o.f. First, the interactions between magnetic elements are modeled and the system design flow by an optimal location of the elements is given. A kinematic relationship between the measuring instruments and the levitated object is derived, and dynamic characteristics are identified by the narrow gap principles. And the main issues for control are discussed.

Precise simulation of non-quasi-static (NQS) characteristics is crucial for the analog application of MOS transistors. This paper presents the small signal admittance model of four-terminal NQS MOS transistors by solving the differential equation derived from the primary principle. The model contains the bulk-charge effect, the mobility reduction, and the velocity saturation. The results are compared with those for the conventional quasi-static model, the BSIM3v3 NQS model, and the 2-D device simulation.

The subject of this study is to propose a new structure that can realize simultaneously high breakdown voltage and high packing density for both Nch low side switch and Pch high side switch in 200 V class rating. As the conventional techniques for the electric field relaxation, the structure of field plate, field ring and RESURF are well known, but these techniques are inadequate for the high packing density because they are the techniques in surface region. In order to conquer this subject, it is necessary to relax the electric field in the deep region. The electric field relaxation was investigated by device simulation. In the Nch low side switch the electric field is relaxed by buried oxide film in SOI structure. However, electric field relaxation cannot be realized only by adapting the SOI structure for Pch high side switch. Then we tried to insert an intrinsic layer between P-drift layer and the buried oxide film in order to spread the depletion layer in the deep region. This spread depletion layer by intrinsic layer and the depletion layer by field plate connect vertically, and the dosage of the ion implantation for drift layer can be set to two times higher than the case without intrinsic layer. As the results, it was revealed that the SOI structure with intrinsic layer is effective to achieve this subject. Furthermore, by fabricating both Nch low side switch and Pch high side switch on intrinsic SOI substrate, breakdown voltage more than 250 V were achieved.

The authors have demonstrated AlGaN/GaN HEMTs with lightly-doped buried p-layers under the channel for the first time. A 1.5-µm-gate device showed good pinch-off characteristics, g_m of 25 mS/mm, and breakdown voltage of 70-90 V. Carrier confinement by the p-n junction was confirmed by capacitance-voltage measurements. These results indicate the potential of p-layer insertion into GaN-based FETs.