This paper proposes a novel metamaterial structure, which equivalently indicates negative permittivity, for the purpose of applying it to a near-field imaging and/or diagnostics of electromagnetic properties by using a surface plasmon in microwave frequency range. The proposed structure consists of a conducting wire lattice with conducting spheres embedded at the mid-point of the wire. It is shown that a spatial dispersion of the wire lattice can be reduced significantly by the sphere. It is also shown that this structure can successfully be applied to an excitation of the surface plasmon in the microwave frequency range by adequately cutting into a thin slab.

A numerical technique for improving the accuracy of a rectangular loop antenna based on the Finite Difference Time Domain (FDTD) method is proposed. In this technique, a quasi-static field behaviour is incorporated into the FDTD update equations, and the more accurate numerical technique can be obtained without the need of using fine cells. The simulation results of this proposed technique are compared with the Method of Moment to confirm the effectiveness of the technique.

This paper implements some new techniques to analyze the light beam scattering from a magneto-optical (MO) disk using the three-dimensional finite-difference time-domain (FDTD) method. The anisotropic FDTD update equations are implemented to calculate the propagation of a coherent monochromatic light in the MO material. An anisotropic absorbing boundary condition based on Berenger's perfectly matched layer (PML) concept is also developed. The Gaussian incident light beam is introduced into FDTD computation region exactly by using equivalent electric and magnetic currents. The scattering pattern of light beam from the MO disk is computed and in part compared with that obtained by using the boundary element method. The scattering patterns by the circular recording bit of different radius are calculated to indicate the optimum radius of the recording bit.

Recursive convolution (RC) approach and later piecewise linear recursive convolution (PLRC) approach which greatly improves the accuracy of the original RC approach, have been proposed for analyzing the electromagnetic propagation through linear dispersive materials using the finite difference time domain (FDTD) method. However, these methods can not be applied directly when the dispersion function has multi-order poles. In this paper the PLRC approach are extended to a rational function having the poles of multi-order.

The characteristics of transient electromagnetic responses between two dipole antennas are investigated theoretically and experimentally for the case where one dipole antenna is located above an interface of a lossy ground half-space and another is buried underground. First, an asymptotic expression for the refracted electric fields is derived based on the saddle point method when a horizontal dipole is buried in the lossy half-space. A suitable saddle point which differs from the conventional one is selected for evaluation when the observation point is located far enough away from the buried antenna. The resultant formula indicates that the refracted electric fields can be interpreted by the sum of two waves. When the observation point is very close to the interface, one of which is a direct wave which propagates from the buried antenna toward the interface point just beneath the observation point and the other a lateral wave which propagates from the buried antenna to the interface with an angle of total reflection and then propagates along the interface. Next, the transient reception voltages of the antenna over the ground surface are measured. It is shown that the experimental results agree very well with the theoretical results, confirming the validity of the theory.

This paper discusses on the methods and their numerical simulation results of the one-dimensional profiling of dielectric targets in the direction of electromagnetic wave incidence. Two different inverse profiling algorithms are proposed. First method is based on the Rayleigh approximation. The inverse profiling is carried out by performing the Fourier transformation of the backscattered field in frequency domain. In this method, the dielectric constant of the target is assumed as known beforehand. The second method is based on the extended physical optics (EPO) method. The EPO method was proposed for calculating the backscattering cross section for a conducting scatterer, however, we apply the EPO method to the inverse problem of the dielectric target whose dielectric constant is not known. The validity and limitation of each method are tested numerically for spherical and spheroidal targets.

A two-dimensional quasi-exact active imaging method for detecting the conducting objects buried in a dielectric half-space is proposed. In this imaging method, an image function which is a projection of buried object to an arbitrary direction, is introduced exactly by taking account of the presence of the planar boundary. The image function is synthesized from the scattering fields which are measured by moving a transmitting antenna (a current source) and a receiving antenna (an observation point) simultaneously along the ground surface. The scattering field is generated by the physical optics current assumed on the surface of buried object. Because the effectiveness of physical optics approximation has been confirmed for this problem, this is a quasi-exact active imaging method. The validity of this imaging method is confirmed by some numerical simulations and an experiment.

This paper analyzes the effective radiation efficiency of a ground-penetrating radar (GPR) consisting of two resistor-loaded bow-tie antennas covered with a ferrite-coated conducting cavity by using finite-difference time-domain (FDTD) method. The GPR is located above a lossless or lossy ground surface. The relation between the radiation powers into the ground and air, dissipated powers at the loaded resistors and ferrite absorber, and the reflected power due to impedance mismatching, is clarified numerically.

This paper discusses the fully three-dimensional finite difference time domain (FDTD) method to analyze a monopole antenna mounted on a rectangular conducting box covered with a layer of dielectric. The effects of the conductivity and the permittivity of the dielectric layer are investigated. It is shown that all calculation results agree very well with the measured data.

The finite difference time domain (FDTD) method has been developed in tandem with the progress of computer technology since K. S. Yee applied it to the analysis of an electromagnetic problem in 1966. The FDTD method is widely recognized as a powerful computational tool for analyzing electromagnetic problems involving complex geometries, such as antennas, microwave and optical waveguides and interaction between antennas and the human body. The commercial electromagnetic simulators based on the FDTD are also being developed very actively because users are able to trace temporal electromagnetic behaviors and to easily obtain a practical level of accuracy. However, the user must understand the principle of the method in order to use the simulator efficiently. In this paper, the basic concept and the principle of the FDTD method are reviewed for beginners, including graduate course students, rather than specialists in this discipline. Several recent topics concerning electromagnetic and antenna problems are also introduced.

The antennas for subsurface radar are usually covered with a conducting cavity to prevent the radiation field from affecting the electromagnetic environment and to protect the received field from external noises. Furthermore, radiowave absorber is attached to the interior wall of the cavity in order to suppress the multiple reflections in the cavity. In this paper, the characteristics of the two-dimensional cavity-backed antenna having the absorber and the over-all properties of this subsurface radar due to buried objects are numerically analyzed by the Finite-Difference Time-Domain method. It is shown that the pulse propagation in the ground is confined to the narrow region due to the cavity. It is also shown that the multiple reflections in the cavity are effectively suppressed by choosing the suitable absorber, and so that the distinctive pulse echo can be obtained.

In this paper, the surface impedance boundary condition (SIBC) for a dispersive lossy medium backed by a perfect conductor is implemented in computation of electromagnetic (EM) scattering using the finite difference time domain (FDTD) method. The dispersion of the surface impedance is incorporated into FDTD update equations by using the piecewise linear recursive convolution (PLRC) approach. The validity of the proposed method is confirmed numerically.

This paper proposes a low-profile unidirectional supergain antenna applicable to wireless communication devices such as mobile terminals, the Internet of Things and so on. The antennas used for such systems are required to be not only electrically low-profile but also unsusceptible to surrounding objects such as human body and/or electrical equipment. The proposed antenna achieves both requirements due to its supergain property using planar elements and a closely placed planar reflector. The primary antenna is an asymmetric dipole type, and consists of a monopole element mounted on an edge of a rectangular conducting plane. Both elements are placed on a dielectric substrate backed by the planar reflector. It is numerically and experimentally shown that the supergain property is achieved by optimizing the geometrical parameters of the antenna. It is also shown that the impedance characteristics can be successfully adjusted by changing the lengths of the ground plane element and the monopole element. Thus, no additional impedance matching circuit is necessary. Furthermore, it is shown that surrounding objects have insignificant impact on the antenna performance.

A high accuracy numerical technique based on the Finite Difference Time Domain (FDTD) method for a long dipole antenna analysis is presented. An improvement of the accuracy can be achieved without reducing the cell size by incorporating a quasi-static field behavior into the FDTD update equations. A closed form of the quasi-static field is obtained from a low frequency limit of a sinusoidal current distribution. The validity of the proposed algorithm is confirmed even when the length of dipole antenna is longer than half wavelength by comparing the results with the Method of Moment.

A band diagram is fundamental for investigating the electromagnetic properties of periodic structures such as photonic and/or electromagnetic crystals and electromagnetic bandgap structures. In this paper, computer resources and the accuracy of the Finite Difference Frequency Domain and the Finite Difference Time Domain methods are studied. The periodic structure treated here consists of two-dimensional dielectric cylinders.

The advantages of the use of directional antennas for portable telephones are demonstrated. They contribute to (1) reduction of power absorption into a head, (2) reduction of multi-path interference, and (3) power saving and increase of a battery life time. This paper compares directional and omni-directional antennas existing near the head of operator, in terms of radiation patterns with a head and the power absorbed into a head. It is pointed out that radiation patterns with a head are more or less directive for both types of antennas, while the power absorbed into a head is much smaller for directional antennas.

In this paper, the influence of surface waves on the characteristics of on-glass antennas is clarified to enable appropriates design of C-band automotive on-glass antennas. Composite glasses are used in automotive windshields. These automotive composite glasses are composed of three layers. First, the surface wave properties of composite glass are investigated. Next, the effects of surface waves on the reflection coefficient characteristics of on-glass antennas are investigated. Finally, the antenna placement to reduce surface wave effect will be presented. Electromagnetic field analysis of a dipole antenna placed at the center of a 300mm × 300mm square flat composite glass showed that the electric field strength in the glass had ripples with the half wavelength period of the surface waves. Therefore, it was confirmed that standing waves are generated because of these surface waves. In addition, it is confirmed that ripples occur in the reflection coefficient at frequencies. Glass size is divisible by each of those guide wavelengths. Furthermore, it was clarified that the reflection coefficient fluctuates with respect to the distance between the antenna and a metal frame, which is attached to the end face in the direction perpendicular to the thickness of the glass because of the influence of standing waves caused by the surface waves; additionally, the reflection coefficient gets worse when the distance between the antenna and the metal frame is an integral multiple of one half wavelength. A similar tendency was observed in an electric field analysis using a model that was shaped like the actual windshield shape. Because radiation patterns also change as a result of the influence of surface waves and metal frames, the results imply that it is necessary to consider the actual device size and the metal frames when designing automotive on-glass antennas.