This paper deals with the scattering and diffraction of a plane wave by a randomly rough half-plane by three tools: the small perturbation method, the Wiener-Hopf technique and a group theoretic consideration based on the shift-invariance of a homogeneous random surface. For a slightly rough case, the scattered wavefield is obtained up to the second-order perturbation with respect to the small roughness parameter and represented by a sum of the Fresnel integrals with complex arguments, integrals along the steepest descent path and branch-cut integrals, which are evaluated numerically. For a Gaussian roughness spectrum, intensities of the coherent and incoherent waves are calculated in the region near the edge and illustrated in figures, in terms of which several characteristics of scattering and diffraction are discussed.

In this paper, we present an error concealment method to recover damaged blocks for block-based image coding schemes. Imperfect transmission of image data results in damaged blocks in the reconstructed images. Hence recovering damaged image blocks is needed for reliable image communications. To recover damaged blocks is to estimate damaged blocks from the correctly received or undamaged neighborhood information with a priori knowledge about natural images. The recovery problem considered in our method is to estimate a larger block, which consists of a damaged block and the undamaged neighborhood, from the undamaged neighborhood. To find an accurate estimate, a set of the feature vectors is introduced and an estimate is expressed as a linear combination of the feature vectors. The proposed method recoveres damaged blocks by projecting the undamaged neighborhood information onto the feature vectors. The sequential projections onto the feature vectors algorithm is proposed to find the projection coefficients of the feature vectors to minimize the squared difference of an estimate and the undamaged neighborhood information. We tested our algorithm through computer simulations. The experimental results showed the proposed method ourperforms the frequency domain prediction method in the PSNR values by 4.0-5.0dB. Tthe reconstructed images by the proposed method provide a good subjective quality as well as an objective one.

A new configuration of high gain circularly polarized microstrip antenna with a diagonal short and its analysis using boundary element method with a radiation load are presented. The center of a radiating patch is shorted with a 45-degree diagonal offset for not only obtaining a high gain but exciting a circular polarization. This configuration leads to achieving high gain with keeping a very low profile configuration. Boundary element method with radiation load which takes into account the effect of radiation loss is employed to analyze this complicated configuration. The radiation load, which is very important when boundary element method is applied to antenna analyses, can be obtained from radiation admittance using recurring technique, so that the accuracy of the antenna characteristic calculations can be improved. This antenna was designed and tested in the L-band and good characteristics, axial ratios and radiation patterns, have been verified.

The applicability of a boundary matching technique is presented for reconstructing the refractive-index profile of a circularly symmetric cylinder from the measurement of the scattered wave when the cylinder is illuminated by an H-polarized plane wave. The algorithm of reconstruction is based on an iterative procedure of matching the scattered wave calculated from a certain refractive-index distribution with the measured scattered-wave. The limits of reconstruction for strongly inhomogeneous lossless and lossy cylinders are numerically shown through computer simulations under noisy environment, and are compared with those in the E-wave case.

This paper is concerned with a point-oriented finite volume time domain (FVTD) method in the Cartesian coordinate system for analyzing electromagnetic wave scattering by arbitrary shaped metallic gratings. The perfectly matched layer (PML) is used for the absorbing boundary conditions (ABC's) in the directions corresponding to transmitted and reflected wave regions. An FVTD version of the Floquet's theorm is described to impose the periodic condition in the direction where conducting rods are located periodically. The boundary conditions for a conductor rod which is not well suited to the Cartesian coordinate system are satisfied in an average fashion by introducing image fields at image points. It is shown that the present method gives accurate numerical results. Numerical calculations are also carried out for thick conducting rods which seem difficult to deal with in an analytical way.

This paper is concerned with a point-oriented finite volume time domain (FVTD) method in the Cartesian coordinate system and its application to the analysis of electro-magnetic wave propagation in a bended waveguide as well as radiation from and receiving by a horn antenna with a flange of arbitrary angle. The perfectly matched layer (PML) is used for the absorbing boundary conditions (ABC's). The boundary conditions for a perfect conductor not well suited to the Cartesian coordinate system are also proposed. According to this algorithm, the boundary conditions are satisfied in an average fashion at the conductor surface without changing the computational scheme. In this sense, numerical computations based on the present method are simple but flexible. Numerical results show good convergence.

This paper is concerned with the perfectly matched layer (PML) for a lossy medium in terms of a finite volume time domain (FVTD) method based only on the Cartesian coordinate system. In this point-oriented FVTD method, there are no spatial differences between electric and magnetic fields. We can take account of the inhomogenity of the lossy medium by considering averaged material constants in each rectangular cell. Numerical examples are given for the electromagnetic wave propagation in two-dimensional tunnels with bends and branches.

In this paper, we present an analysis of microstrip line with a trapezoidal dielectric ridge in multilayered media. The method employed in this characterization is called partial-boundary element method (p-BEM) which provides an efficient technique to the analysis of the structures with multilayered media. To improve the convergence of the Green's function used in the analysis with the P-BEM, we employ a technique based on a combination of the Fourier series expansion and the method of images. Treatment on convergence for the boundary integrals is also described. After this treatment, it requires typically one tenth or one hundredth of Fourier terms to obtain the same accuracy compared with the original Green's function. Numerical results are presented for two microstrip lines that have a trapezoidal dielectric ridge placed on a one-layered substrate and a two-layered substrate. These numerical results demonstrate the effects on the characteristics of the microstrip line due to the existence of the dielectric ridge as well as the second layer between the ridge and the fundamental substrate.

A method for the recognition of handprinted Thai characters input using an image scanner is presented. We use methods of edge detection and boundary contour tracing algorithms to extract loop structures from input characters. The number of loops and their locations are detected and used as information for rough classification. For fine classification, local feature analysis of Thai characters is presented to discriminate an output character from a group of similar characters. In this paper, four parts of the recognition system are presented: Preprocessing, single-character segmentation, loop structure extraction and character identification. Preprocessing consists of pattern binarization, noise reduction and slant normalization based on geometrical transformation for the forward (backward) slanted word. The method of single-character segmentation is applied during the recognition phase. Each character from an input word including the character line level information is subjected to the processes of edge detection, contour tracing and thinning to detect loop structures and to extract topological properties of strokes. The decision trees are constructed based on the obtained information about loops, end points of strokes and some local characteristics of Thai characters. The proposed system is implemented on a personal computer, and a high recognition rate is obtained for 1000 samples of handprinted Thai words from 20 subjects.

The ultraclean sputtering process (UC-process) was newly introduced in the fabrication of Co62.5Ni30Cr7.5 and Co85.5Cr10.5Ta4 thin film media to establish a new concept in controlling microstructure. UC-process enables the realization of high coercive force Hc up to 2.7-3 kOe in both CoNiCr and CoCrTa media (15/50 nm magnetic/Cr thicknesses) without the decrement of saturation magnetization. The purification of the atmosphere during sputtering and the removal of the adsorbed oxygen impurity on the substrate surface play important roles in obtaining high Hc by applying the UC-process. This high Hc is mainly due to the realization of large magnetocrystalline anisotropy field of grains Hkgrain and low intergranular exchange coupling. UC-process realizes the adequate separation of grains by segregated grain boundaries even in media with thin Cr thickness of 2.5 nm, and enables grain size reduction without the remarkable increment in intergranular exchange coupling. In these media, the reduction of the grain size is most effective for the improvement of readback signal to media noise ratio S/Nm. In the media with grains sufficiently separated by segregated grain boundaries fabricated by the UC-process, control of grain size reduction and further increase in Hc/Hkgrain value through the decrement in intergranular magnetostatic coupling are required to obtain higher S/Nm value.

In the paper a problem of wave scattering from a local penetrable inhomogeneity inside a planar dielectric waveguide is studied. The surface potentials method is applied for the problem and the set of systems of BIE is obtained and analyzed from the view-point of their numerical solution. The effective numerical algorithm based on the Nyström method is proposed. The equations for a scattering diagram and mode conversion coefficients are derived.

A numerical scheme to analyze a three-dimensional perfectly conducting body that has edges and corners is presented. The geometry of the body can be arbitrary. A new formulation using boundary element method has been developed. This formulation allows that a scatterer has edges and corners, where the behavior of the electromagnetic fields become singular.

In this paper, we presented an analysis of single and coupled microstrip lines covered with protective dielectric film which is usually used in the microwave integrated circuits. The method employed in the characterization is called partial-boundary element method (p-BEM). The p-BEM provides an efficient means to the analysis of the structures with multilayered media or covered with protective dielectric film. The numerical results show that by changing the thickness of the protective dielectric films such as SiO2, Si and Polyimide covered on these lines on a GaAs substrate, the coupled microstrip lines vary within 10% on the characteristic impedance and within 25% on the effective dielectric constant for the odd mode of coupled microstrip line, respectively, in comparison with the structures without the protective dielectric film. In contrast, the single microstrip lines vary within 4% on the characteristic impedance and within 8% on the effective dielectric constant, respectively. The protective dielectric film affects the odd mode of the coupled lines more strongly than the even mode and the characteristics of the single microstrip lines.

Closed-form solutions of the characteristic initial value problem for electric and magnetic fields propagating as nonsinusoidal plane TEM-waves in lossy unbounded media are calculated with Riemann's method and discussed in detail. As an application, the reflection and transmission of waves on a planar boundary is examined, when one semi-infinite medium is lossy.

A parallel blower system is quite familiar in hydraulic machine systems and quite often employed in many process industries. It is dynamically dual to the fundamental functional element of digital computer, that is, the flip-flop circuit, which was extensively studied by Moser. Although the global dynamic behaviour of such systems has significant bearing upon system operation, no substantial study reports have hitherto been presented. Extensive research concern has primarily been concentrated upon the local stability of the equilibrium point. In the paper, a piecewise linear model is used to analytically and numerically investigate its manifold global dynamic behaviour. To do this, first the Poincar map is defined as a composition boundary map, each of which is defined as the point transformation from the entry point to the end point of any trajectory on some boundary planes. It was already shown that, in some parameter region, the system exhibits the so-called chaotic states. The chaos generating process is investigated using the above Poincar map and it is shown that the map contains the contracting, stretching and folding operations which, as we often see in many cases particularly in horse shoe map, produce the chaotic states. Considering the one dimensional motions of the orbits by such Poincar map, that is, the stretching and folding operations, a one dimensional approximation of the Poincar map is introduced to more closely and exactly study manifold bifurcation processes and some illustrative bifurcation diagrams in relation to system parameters are presented. Thus it is shown how many types of bifurcations like the Hopf, period doubling, saddle node, and homoclinic bifurcations come to exist in the system.

We have investigated the Josephson microwave self-radiation and the linewidth from different types of YBa2Cu3Oy(YBCO) grain boundary junctions: natural grain boundary junctions, step-edge junctions and bicrystal junctions. The Josephson self-rediation was directly observed using a total power radiometer receiver with receiving frequencies fREC=1.7-72 GHz. All junctions exhibited microwave self-radiation peaks with intensity of order of 10-12-10-14 W. For step-edge and bicrystal junction, they appeared at a voltage related to the Josephson frequency-voltage relation, V=n(h/2e)f, while for natural grain boundary junctions, the above relation did not hold, suggesting a Josephson medium property. For all types of junctions the observed Josephson linewidth deviated from the theoretical RSJ values due to the extra noise source in the grain boundary junction. The Josephson linewidth decreased with increasing the receiving frequency for all type of junctions. The reduction of Josephson linewidth at higher frequencies indicates that the critical current fluctuations due to a critical current spread at small bias voltages and a crystalline disorientation at the junction boundary generate an additional noise in grain boundary junctions.

This paper presents a new numerical procedure for solving the scattering wave by the moving surface. Recently, the author and her colleagues have proposed a novel numerical procedure of grid generation having a coordinate line coincident with an arbitrarily shaped moving boundary. The time dependent curvilinear coordinate system which coincides with a contour of moving boundary in a physical region is transformed into fixed rectangular coordinate system. The simple form for the transformation is made possible to choose the function between the physical region and the rectangular computational region. The FD-TD algorithm is exactly solved in this fixed rectangular coordinate system. In this paper, for the application of the FD-TD algorithm to the body fitted grid generation with moving boundary, the stability criterion of FD-TD algorithm for the body fitted grid generation with moving boundary in three dimensions is derived. The stability criterion is shown an upper bound for time step assuring stable numerical solutions. The study of scattering of electromagnetic and acoustic wave from a moving or a rotating body is very important for electromagnetic probing of moving body. The problem has been investigated in the past by numerous authors. One of them is solved by FD-TD method, where the linear interpolation is introduced for the movement. By using the presented transformation technique where time component is added to the grid generation, the time depending coordinate system can be transformed into fixed rectangular coordinate system. Then the problems are directly solved by FD-TD method in the transformed coordinate system. To verify this numemical technique, scattered field is evaluated in the case when a plane wave is normally incident on a moving perfectly conducting flat plate. The numerical results are compared with the exact ones and excellent agreement between them is obtained.

A new simple formulation of absorbing boundary conditions with higher order approximation is proposed for the solution of Maxwell's equations with the finite-difference time-domain (FD-TD) method. Although this higher order approximation is based on the third order approximation of the one-way wave equations, we have succeeded in reducing it to an equation in a form quite similar to the second order appoximation. Numerical tests exhibit smaller reflection errors than the prevalent second order approximation.

We present a novel algorithm to reconstruct the refractive-index profile of a circularly symmetric object from measurements of the electromagnetic field scattered when the object is illuminated by a plane wave. The reconstruction algorithm is besed on an iterative procedure of matching the scattered field calculated from a certain refractive-index distribution with the measured scattered field on the boundary of the object. In order to estimate the convergence of the reconstruction, the mean square error between the calculated and measured scattered fields is introduced. It is shown through reconstructing several examples of lossy dielectric cylinders that the algorithm is quite stable and is applicable to high-contrasty models in situations where the Born approximation is not valid.

The electric or electronic circuits have many contact devices such as relay and switch. The contact between two nominally conducting flat surface has a lot of micro contact spots. The constriction resistance of the contact is known to determine the sum of the parallel resistance of the micro contacts and the interaction of them. The constriction resistance of two circular conducting spots was approximately formulated by Greenwood. This formulation shows that the interacted resistance of two circular spots is in inverse proportion to the distance between two conducting spots. It was known that this effect is introduced by the interaction between two conducting spots. However, the condition of interaction in the spots is not clear. Calculating the current density distribution in the spots is important to clarify the condition of interaction. The numerical analysis is very suitable to calculate the current density in the spots. In the fundamental case of the computation of the current density the boundary element method (BEM) is more efficient and accurate than that of the finite element method (FEM) because the boundary condition at the infinite is naturally satisfied and is not required a great number of the element in a wide space. In this paper the current density in the square spots is computed by the BEM. As the distance between two conducting spots becomes small, the current density in the two spots decreases. It becomes clear that the constriction resistance of conducting spots is increased by this effect. The decrease of current density by interaction is not uniformly, that at the near location to the opposite spot is larger than that at the far location in the same spot. In this paper the constriction resistance of two conducting spots is also considered. It was known that the constriction resistance of one conducting spot is not influenced by the form of spot very much. However, that of two conducting spots is not clear. The constriction resistance of two square spots is also computed by the BEM. The computed values of the constriction resistance of two square spots are compared with that of two circular spots by Greenwood's formulation and other results. As the result, it is clear that they have the considerable discrepancy. However, the trend of the variations is almost agree each other.