The Technical Committee on Electromagnetic Theory of Institute of Electrical Engineers of Japan, has organized a special issue on “Recent Progress in Electromagnetic Theoryand its Application."The special issue is intended to include papers not only presented inour regular symposium, but also those which are not presented there, but are suitable for inclusion. This paper is intended to review the special issue and its papers(including review and original papers) selected for the present special issue.

View full abstract

For the analyses of the electromagnetic fields, the role of the numerical analysis methods has become more and more increased due to the remarkable development of the computer resources. In these methods, the iterative methods on the time domain have many advantages for the three-dimensional vector analyses because of their efficiency on both computation time and memory storage. The formulation of these methods are based on the spatial structure of the arrangement of field variables according to the Maxwell’s equations. In this review, the some models of these structures are explained, and it is presented that the treatment as the equivalent circuit has many merits as the generalized network for not only the electromagnetic field variables but also the vector potential variables with the gauge condition.

View full abstract

Analysis methods for modeling of photonic crystal fibers, such as the effective-index approach, basis-function expansion approach, and numerical approach, are reviewed. Using a full modal vector model, the dispersion and leakage properties of holey fibers and photonic band-gap fibers are investigated.

View full abstract

This paper presents that scattering by a body in a random medium consists of the following two issues; one is scattering of spatially partially coherent wave by the body and the other is coupling between incident and scattered waves through the random medium. Investigating separately each issue makes the scattering more understandable. The numerical analysis of scattered power by conducting cylinders leads to the radar cross-sections quite different from those in free space, under the condition that the radar cross-section of the random medium is negligibly small. The causes of the difference are explained on the basis of above separation of the scattering, and we emphasize that the spatial coherence length of incident wave is one of key parameters for estimating the cross sections.

View full abstract

Short-term earthquake prediction is still an urgent and important subject for seismo-active countries like Japan. There have been recently found a lot of convincing evidences on the presence of electromagnetic phenomena associated with earthquakes. One of the most promising candidates for short-term earthquake prediction is ultra-low-frequency (frequency less than 10Hz) (abbreviated as ULF) electromagnetic emission. We first review earlier observational facts, and then show our latest results, especially on the existence of such ULF emissions by means of sophisticated signal processing. Finally, we discuss the generation and propagation mechanisms of those seismo-ULF emissions.

View full abstract

This paper is a review on the properties of atmospheric gravity waves that are responsible for the transfer of tropospheric perturbation to the ionospheric altitudes. The generation mechanism of these waves by means of meteorological sources, earthquakes and by the processes of earthquake preparation (by precursors) is examined. We suggest an experimental program for the investigation of acoustic-gravity channel of a seismic effect upon the ionosphere.

View full abstract

An important problem in the theory of linear systems is the relationship between the frequency- and the time-domain characteristics. An interesting problem of this sort is to obtain the step response of a system when its amplitude function is given, which arises in the design of filters, the measurement of system characteristics, etc. Two conventional methods are (1) factorization method that uses the factorization of the amplitude function, and (2) ω- domain method that uses the Kramers-Kronig relation to get the phase function from the attenuation function. Both methods are poor as computer algorithms.
We introduced here a new algorithm that uses the Kramers-Kronig relation extended to complex frequency domain, and that can easily be carried out by a computer. As an application, we have analyzed the problem of negative group velocity, and showed that the group velocity of a wave packet is nothing but the phase velocity of the envelope.

View full abstract

Our recent studies related to the large-scale FDTD computation for computational electromagnetics are presented as an activity report. In this paper, high accuracy FDTD methods and the FDTD parallel computaion are described. These are applied to large-scale problems of electiromagnetic waves.

View full abstract

Scattering of a Gaussian beam by a dielectric cylinder is analyzed by using the moment methods combined with the multigrid method. The scattered fields can be obtained by the volume equivalent theorem. The integral equation is converted to the matrix form by the moment methods. As numerical examples, the scattering of a Gaussian beam by a circular dielectric cylinder is considered. The CPU time and residual norm are examined for the conventional multigrid cycle. Also, the modified multigrid cycle proposed here is compared with the conventional one. The scattered near fields are calculated and are compared with those obtained by the method of eigenfunction expansion.

View full abstract

A very efficient and accurate method to characterize electromagnetic scattering by multilayered periodic arrays of circular cylinders is presented, using the lattice sums technique, the aggregate T-matrix algorithm, and the generalized reflection and transmission matrices for a layered system. The method is quite general and applies to various configurations of two-dimensional or three-dimensional periodic arrays. The unit cell of array can contain two or more cylinders, which may be dielectric, conductor, gyrotropic medium, or their mixture with different sizes. The periodic spacing of cylinders along each array plane should be same over all layers, otherwise the cylinders in different layers may be different in material properties and dimensions.

View full abstract

Diffraction of electromagnetic plane waves by the multielements periodic grating consisting of dielectric coaxial cylinders with different radii and location per unit cell is analyzed. Using the additional theorem for the cylindrical functions and the projection method, an infinite system of linear equations for the unknown coefficients of the multipole spectra is obtained. This system of equations is solved by the reduction method, and the analytical expressions for both transmission and reflection coefficients are derived by using the relationship between the diffracted spectra and the multipole spectra. The numerical examples for the two-elements grating demonstrate the effects of the internal multiple scatterings within a unit cell on the frequency response in the transmission coefficient.

View full abstract

In this paper, we numerically analyze the transient response of pulse propagation in a multi-layered printed circuit board with a via and a bump. FDTD method is used for our models. It is found from numerical results that; (1) Even if the lengths of the striplines are equal, pulse waveforms passed through a via and a bump are different according to the direction of the striplines. (2) The propagating pulses are influenced by the pad size connecting the bump rather than the bump size. (3) For the model consisted of a via and a bump pulse distortion of responses are substantially improved, if the smaller bump part (including pads) can be designed.

View full abstract

To realize wider viewing angle for a liquid-crystal display (LCD), particular attention is being paid to the in-plane switching (IPS) mode of LCD, where pixel electrodes and common (opposite) electrodes are arranged on the same array substrate and liquid crystal is made respond by an electric field generated in parallel to the substrate. So far, two types of array electrode structures are proposed in IPS-LCD. One is the array structure with two electrode layers where pixel electrodes and common electrodes are formed on different conductive layers. In the other array structure they are formed on one conductive layer. Although both electrode structures of IPS-LCD have problems dependent on the process conditions, light leakage observed only in the former structure along the edge of the common electrodes at zero bias is an essentially serious problem. By studying light wave propagation in the IPS-LCD using a two-dimensional finite-difference time-domain method we have found that the light leakage is caused by the tapered side surfaces of the common electrodes.

View full abstract

The following two kinds of researches are conducted in my laboratory: (A) electromagnetic (EM) wave theory with application to sensing, imaging and material estimate, and (B) high data rate satellite communications systems. Each research has five subjects and this paper addresses four subjects, which are (A-1) Effective parameters of a medium containing many particles, (A-2) Radar characteristics of a body surrounded by a random medium, (A-3) Statistical methods for measuring ocean waves in satellite altimetry, and (B-4) Atmospheric turbulence effects on high data rate satellite communications. Here A and B in parentheses indicate above two researches, respectively. To solve these subjects the author has proposed fundamental and original methods and thereby obtained many interesting results to scientists and engineers. General remarks are made on the results in this paper.

View full abstract

We observed ground clutter from cultivated land in a range interval 31.9 to 37.5 nmi (59.1 to 69.5 km), over an azimuth interval of 90.57° to 113.43°, using an L-band long-range air-route surveillance radar (ARSR) having a frequency 1.33 GHz, a beamwidth 1.23°, a pulsewidth 3.0 μs. Weather conditions were clear and the wind velocity was 2 to 10 knots (1.0 to 5.1 m/s). Recorded data has been processed by single and double canceller moving target indicator (MTI) processors. To determine the amplitude statistics of ground clutter after single and double canceller MTI processing, we introduced the Akaike Information Criterion (AIC), which is more rigorous fit of the distribution to the data than the least squares method. We have found that the ground clutter after single canceller MTI obeys the log-Weibull distribution with the shape parameter of c=6.55 for entire data, and the Weibull, log-Weibull and K-distributions with the shape parameters of 1.79 ≤ c ≤ 1.95, 7.27 ≤ c ≤ 7.45 and 5.53 ≤ ν ≤ 20.39, respectively, for data within the beam width of an antenna. And the ground clutter after double canceller MTI obeys the K-distribution with the shape parameter of ν=4.00 for entire data, and the Weibull and K-distributions with shape parameters of 1.67 ≤ c ≤ 1.94 and 3.18 ≤ ν ≤ 25.75, respectively, for data within the beam width of an antenna.

View full abstract

In this study, we shall examine a high-frequency electromagnetic scattered field by a conducting strip. The high-frequency scattered field by the conducting strip can be represented by applying the UTD (uniform GTD (Geometrical Theory of Diffraction)) solution for a conducting half-plane solved as a canonical problem. Then we shall derive from the UTD the two versions of the Keller’s GTD without applying the “trick" introduced in the paper by Keller: the first version is expressed by using the geometrical optics field, if any, and the edge diffracted rays and the second version is expressed by using only the edge diffracted rays. The first version (the second version) is applicable in the region close to (far away from) the conducting strip. We also derive the novel criterion for applying the GTD. We will show that, as the observation point moves far away from the strip in the illuminated region, the geometrical ray appeared in the UTD will be cancelled by the portions of the edge diffracted rays, thereby validating the second version of Keller’s GTD, which does not include the geometrical ray term. The validity and applicable range of the GTD and the UTD are confirmed by comparing with the reference solution calculated numerically from the method of moments.

View full abstract

Power bus noise prediction in multilayer printed circuit boards requires an accurate estimation of the power bus impedance. We have previously developed a fast algorithm for efficiently and accurately calculating the impedance of a rectangular power bus structure, based on a cavity mode model. In this paper, we show that the fast algorithm can also be easily utilized for a right-angled triangular power bus structure. Together with a segmentation method, the fast algorithm can then be extended to calculate the impedances of more complicated power bus structures whose patterns consist of several segments of rectangles and/or right-angled triangles. Fast computation of the S-parameters and good agreement between the calculated results and measurements for various boards demonstrated the efficiency and accuracy of using the fast algorithm together with the segmentation method as a powerful technique to estimate the power bus impedance.

View full abstract

The introduction of extremely low frequency electric fields with human body has become an increasingly important subject since potential health hazards due to the electric fields emitted by extremely high-voltage power lines. The health effect of the weak current induced in the human body as a result of the interaction between human body and power frequency electric fields has been investigated. In this paper, the finite element method is applied to the analysis of the current density distributions in the human model which stands with erect position on the conductive ground layer in the uniform electric field, and the characteristics of such internal current density distributions are clarified.

View full abstract

Abstract Nano-meter wave waveguide is a basic element of Nano-meter wave devices, which will be important in nano-technologies, bio-engineering, cell membrane, genetics, and so on. Until now, the nano-meter wave waveguide characteristics have hardly been examined and effective nano-meter wave waveguides have not been developed. We have investigated photonic crystal with a lattice constant of the same order as the wavelength of nano-meter waves.
In the nano-meter wave region, the refractive index of a material becomes smaller than 1, and it has the characteristics depending on the frequency of the incident electromagnetic wave. We have calculated photonic band structures for two-dimensional C and Mo arrays with plane wave expansion method. Although complete bandgaps in these matters do not exist, we have found the existence of local bandgaps.

View full abstract

The space formed by the ground and ionosphere is known to act as a resonator for extremely low frequency (ELF) waves. Lightning discharges trigger this global resonance, which is known as Schumann resonance. Even though the inhomogeneity (like day-night asymmetry, local perturbation etc.) is important for such a subionospheric ELF propagation, the previous analyses have been always made by some approximations because the problem is too complicated to be analyzed by any exact full-wave analysis. This paper presents the application of the conventional numerical FDTD (finite difference time domain) method to such a subionospheric ELF wave propagation, in which any kinds of inhomogeneities can be included in this analysis. The present paper is intended to demonstrate the workability of this method for a realistic waveguide (with day-night asymmetry), by comparing the results from this method with those by the corresponding analytical method.

View full abstract

We present an algorithm for accelerating the convergence of the time domain formal solution constructed for the natural electromagnetic pulses propagating in the Earth-ionosphere cavity. Such pulses originate from vertical lightning discharges and travel around the globe at extremely low frequencies (ELF). A compact formula is found for horizontal magnetic field component. Results of computations are demonstrated for a set of the source-observer distances and properties of time domain solution are discussed.

View full abstract

The problem of radio wave propagation allowing for a 3D localized lower ionospheric irregularity appears in accordance with the necessity of the theoretical interpretation of VLF remote sensing data. The various processes in the Earth’s crust and in the terrestial environment (earthquakes, magnetic storms, sporadic E-layers, lightning-induced electron precipitations, rocket launches, artificial ionosphere heating, nuclear explosions, etc.) may cause ionospheric perturbations with different intensity and size. This paper presents a full-wave numerical-analytical method for the 3D radio wave propagation problem. We consider the VLF field by a vertical electric dipole in the Earth-ionosphere waveguide with an irregularity in the lower ionosphere as an example. The impedance non-uniform waveguide model is constructed. In the scalar approximation, the problem is reduced to the surface integral equation for Hertz’s vector component. Using an asymptotic (kr>> 1) integration along the transverse direction to the propagation path, we transform this equation to the one-dimensional integral equation taking into account the field scattered by the irregularity. This last one is solved by combining the semi-inversion method and the subsequent iterations. The proposed technique is useful for the study of both small- and large-scale irregularities. Numerical results of VLF point source field diffraction from a truncated highly conducting cylinder are presented.

View full abstract

The extremely low frequency propagation associated with Schumann resonance phenomena are calculated numerically by the frequency-domain finite difference method, and distribution of source lightnings is identified by solving an inverse problem using the computed spectra as a set of basis functions. The finite difference equations are formulated in terms of discretized magnetic fields in the Cartesian coordinates adopting a cylindrical shell cavity for simplicity. The most reliable electron and neutral density models in the atmosphere and the ionosphere can be used to take into consideration propagation losses. The inverse problem already developed is applied to the measured data to reconstruct lightning activity distribution as a function of distance from the observation point. The reconstructed data successfully show the lightning active season, time, and distance, which are reasonable in comparison with the earlier reports.

View full abstract

The authors have been developing a new type of lightning location and monitoring system based on a technique of “VHF broadband digital interferometry". This paper summarizes this VHF broadband digital interferometer (DITF), together with new observations. As a first step of the development, the experimental system is installed and lightning observations are conducted. In these observations, imaging of lightning progression is obtainable in two- and/or three-dimensions. The effectiveness of our results has been confirmed by the comparisons with the results of previous studies and other observations. The evaluation of the system is discussed to improve its accuracy, and the advanced system is completed. At present, the advanced system has been completed and the first result is obtained. It is concluded that the function of the system works well, and the VHF broadband DITF for lightning monitoring is accomplished with high accuracy from the aspects of time and space resolutions.

View full abstract

We calculate by the Full Wave method the ionospheric penetration of the electromagnetic field radiated from a dipole source on the ground. The results show a clear difference in day and night wave propagation. The French Space agency has developed a plan for a micro-satellite called “DEMETER" for the observation of the electromagnetic waves from natural geophysical phenomena such as earthquakes and volcanic eruptions. We examine the possibility to directly detect onboard a satellite the electromagnetic wave radiated by an earthquake.

View full abstract

An effective method is developed to identify and eliminate signals originated from external magnetic variations in the frequency range of 0.001 to 1 Hz in the geoelectric potential data. It is based on the interstation transfer function (ISTF) approach with the use of wavelet transform. Good performance has been found for the data at Kiyosumi station using Kakioka station as a reference, which means that almost whole of the inductive field could be eliminated successfully and other signals could be recognized with keeping their waveform. The detectability of simulated seismic electric signals (SES) has also been examined, and the result shows the successful discrimination of SES. These experimental facts indicate the effectiveness of our proposed signal reduction method.

View full abstract

This paper investigates the SAR induced in an inhomogeneous model of human body for exposure to EM waves from a dipole antenna at 400 MHz. The antenna is attached to the human body behind the neck. In particular, we compare the results obtained with the homogeneous and inhomogeneous models. For a main result, a large difference in the SAR distributions is observed between two models. Additionally, the peak SARs averaged over 10-g of tissue in the homogeneous model are overestimated as compared with those in the inhomogeneous model, only when the antenna-model distance is small.

View full abstract

In order to explain the propagation of VHF radio waves for TV broadcasting transmitted from Southeast Asia associated with equatorial plasma bubbles, we have examined ray paths of the radio waves scattered by field-aligned irregularities in equatorial plasma bubbles. In determining the ray paths of the radio waves, a ray tracing calculation combined with a model of the scattering by field-aligned irregularities is used. It is found that VHF radio waves transmitted from Philippines can propagate to Japan due to scattering by field-aligned irregularities located above the East China Sea.

View full abstract