We examine the relationship between 116 VHF sensor events recorded by the VHF sensor on the Maido-1 satellite and lightning strokes detected by the World Wide Lightning Location Network (WWLLN) to show that most of the VHF sensor events were caused by lightning discharges. For each VHF sensor event, the WWLLN events within 1400 km from the subsatellite point and within 1 sec, 30 sec, and 300 sec of the VHF sensor trigger time are analyzed. We find that the coincidence rates in the North and South American continents, and in Southeast/East Asia and the Australian continent are greater than 0.90. Those in the African and European continents, and in the Pacific and Atlantic Oceans are less than 0.61. These high enough coincidence rates indicate that the VHF sensor events were emitted from lightning, although the coincidence rates in the other regions are quite low because of the low detection efficiency of the WWLLN in the regions. We also focus on 6 coincident events measured by both the VHF sensor and the WWLLN. The incidence angles of the EM waves for the VHF sensor are estimated from the group delay characteristics of the recorded EM waveforms. Compared with the WWLLN lightning locations, the two incidence angles are temporally and spatially coincident. These results indicate that a large fraction of the VHF sensor events are emitted by lightning discharges.

The cause-and-effect relation between plasmon-resonance absorption and surface wave in a sinusoidal metal grating is investigated. By introducing an equivalent impedance model, similar to an equivalent circuit on an electric circuit, which is an impedance boundary value problem on the fictitious surface over the grating, we estimate the surface wave from the eigen field of the model by using the resonance property of the scattered field. Through numerical examples, we illustrate that the absorption in the grating occurs in the condition of exciting the surface wave along the model, and the real part of the surface impedance is negative on about half part of the fictitious surface in the condition.

An inverse scattering problem of estimating the reflection coefficient and the surface impedance from two sets of absolute values of the near field with periodic change is investigated. The problem is formulated in terms of a nonlinear simultaneous equations which is derived from the relation between the two sets of absolute values and the field defined by a finite summation of the modal functions by applying the Fourier analysis. The reflection coefficient is estimated by solving the equations by Newton's method through the successive algorithm with the increment of the number of truncation in the summation one after another. Numerical examples are given and the accuracy of the estimation is discussed.

An inverse scattering problem of estimating the surface impedance for an inhomogeneous half-space is investigated. By virtue of the fact that the far field representation contains the spectral function of the scattered field, complex values of the function are estimated from a set of absolute values of the far field. An approximate function for the spectral function is reconstructed from the estimated complex values by the least-squares sense. The surface impedance is estimated through calculating the field on the surface of the half-space expressed by the inverse Fourier transform. Numerical examples are given and the accuracy of the estimation is discussed.

The electromagnetic scattering of a plane wave by an inhomogeneous plane whose surface impedance changes locally on the plane is treated. A boundary-value problem is formulated to describe the scattering phenomenon, in which the boundary condition depends on the surface impedance of the plane. Application of the Fourier transform derives an integral equation, which is approximately solved by the method of least-squares. From the solution of the equation, the scattered field is obtained by the inverse Fourier transform. By the use of the incomplete Lipschitz-Hankel integral for the computation of the field, numerical examples are given and the scattering phenomenon is discussed.

The transient phenomenon of electromagnetic waves caused by a time dependent resistive screen in a waveguide is treated. A boundary-value problem is formulated to describe the phenomena, in which the resistivity of the screen varies from one steady state to another in dependence on time. Application of Fourier analysis derives an integral equation, which is approximately solved by the method of least-squares. From the solution of the equation, the transient field is obtained by the inverse Fourier transform. By the use of the incomplete Lipschitz-Hankel integral for the computation of the field, numerical examples showing typical transient phenomenon are attached.

The transient phenomenon of electromagnetic waves caused by a time dependent resistive screen in a waveguide is treated by using Wiener-Hopf technique. A boundary-value problem is formulated to describe the phenomenon, in which the resistivity of screen varies from infinite to zero in dependence on time. Application of the Fourier transformation with respect to time derives a Wiener-Hopf equation, which is solved by a commonly known decomposition procedure. The transient field is derived from the solution of the equation in terms of the Fourier inverse transform. By using the incomplete Lipschitz-Hankel integral for the computation of the field, numerical examples are given and the transient phenomenon is discussed.

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.

For plasma simulations, we developed a one-dimensional (1d) Object-Oriented Particle-in-Cell code for X11-based Unix workstations (XOOPIC) by modifying the current two-dimensional version which was originally developed by PTSG (Plasma theory and simulation group) in the University of California at Berkeley. We implemented a simplified field solve and current deposition in the code. We retained three components of particle velocity, although the spatial variation for particle position and field components is limited to one dimension. To verify the function of the 1d code, we perform simulations with typical models such as the Child-Langmuir current model and electromagnetic wave propagation in plasma. In both cases, the simulation results quantitatively agree with the theory.

The problem of transient scattering caused by abrupt extinction of a terminative conducting screen in a waveguide is considered. First, a boundary-value problem is formulated to describe the transient phenomena, the problem in which the boundary condition depends on time. Then, application of the Fourier transformation with respect to time derives a Wiener-Hopf-type equation, which is solved by a commonly known decomposition procedure. The transient fields are obtained through the deformation of the integration path for the inverse transformation and the results are represented in terms of the incomplete Lipschitz-Hankel integrals. Numerical examples showing typical transient phenomena are attached.

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.

The characteristics of an open-boundary Cherenkov laser for an electromagnetic wave with a continuous frequency spectrum are numerically analyzed. A given power spectral density for the input wave is found to get concentrated around the frequency where the spatial growth rate is maximum, as it grows along the electron beam. In addition, the frequency for the maximum growth rate is found to shift gradually to higher values. Furthermore, by gradually increasing the permittivity of the dielectric waveguide along it, we can always get the maximum power spectral density at the frequency where the spatial growth rate initially becomes maximum at the input.