Kuniyuki Motojima

Electromagnetic scattering by the Luneberg lens with reflecting cap

The near-field distribution in the case of the normal incidence to the Luneberg lens reflector is numerically obtained by using the modal expansion technique and point-matching method. As a model of the Luneberg lens, six different homogeneous media is used. A microwave experiment was also performed.

Scattering of Gaussian beam from a hemispherical boss on a conducting plane

A new expression of a Gaussian beam derived by using a spectral domain method is applied to the scattering problem from a hemispherical boss on a conducting plane. On the method of images, the original problem is reduced to that of the scattering of two Gaussian beams by a full sphere. The scattered fields are expressed in simple closed forms which are valid when the diameter of the boss is comparable to or less than the Gaussian beamwidth. The difference between the bistatic radar cross section of a Gaussian beam and that of a plane wave is discussed.

System of equations describing charges of multiple conductors immersed in electrostatic fields

Problems of electrostatic fields involving multiple conductors arise in various scientific fields. It is known that the relation between the electric potentials and the charges of multiple conductors can be expressed by a system of linear equations. However, the well-known system of equations holds true only when no other charge exists external to the conductors. In this paper, we derive an extended system of equations that is valid even if the conductors are immersed in electrostatic fields due to external charges.

Scattering and Focusing Effect of Stepped Index Luneberg Lens

Focusing effect of the Luneberg lens for wide bandwidth is studied with emphasis on experiment. A model experiment was performed using a stepped index (six-layer) spherical lens. The total electric field amplitude along the propagation axis has the maximum value (focal point) on the surface of the lens. As the size parameter ka (k: wave number, a: radius of the sphere) is larger, the electric field amplitude at the focal point becomes larger. These results correspond with the power of convergence (focusing effect) by the Luneberg lens. The experimental values are in a good agreement with theoretical ones that are calculated using homogeneous multilayered approximate method. They are also in a good agreement with the results using exact solutions for the inhomogeneous dielectric sphere (the ideal Luneberg lens). Therefore, it is found that the six-layer spherical lens has the optimum variation of dielectric constants for the Luneberg lens and maintains focusing effect for wide bandwidth.

Electromagnetic scattering by the Luneberg lens reflector

A Luneberg lens with a metallic reflector is considered, for which the permittivity is a parabolic function of the radius. The electromagnetic scattering is considered and numerically evaluated by using the point matching method (PMM). The convergence of the total cross-section versus the number of sampling points has been examined. Near electric field distributions in space are presented and scattering patterns are also illustrated. It is found that the scattering pattern does not depend on the conical viewing angle for the reflector. A microwave experiment was also performed by six homogeneous layered media and also compared with theoretical values.

Equivalent-Circuit Expression of Environmental Noise Electric Fields in Intrabody Communication Channels

In the development of intrabody communication systems, the most challenging goal is to protect against noise due to other electronic devices. In this paper, the equivalent-circuit expression of environmental noise electric fields (the so-called radiated noise) in intrabody communication channels are derived based on the theory of electrostatic fields. In addition, numerical examples are shown by means of electrostatic analysis based on the method of moments, and the results agree with those by full-wave analysis based on the finite-difference time-domain method and those by measurements. Therefore, it is concluded that the proposed circuit model can properly express the contribution of environmental noise electric fields.

A note on signal paths in intrabody communication channels

In this study, the signal paths in intrabody communication channels are discussed by evaluating the electric fluxes between conductors and the earth ground. This study is based on the equivalent circuit model of which parameters are obtained via an electrostatic analysis. The obtained results clarified the electric flux flows in the communication channels, and they quantitatively support the previous study reported by one of the authors.

A hybrid technique combining FDTD and series solution for near-to-far-field transformation

A new near-to-far-field transformation that combines the FDTD and the series solution is presented. In this method, near-field data is calculated by FDTD and far-field data is also expressed by series solution. The boundary condition is applied to a virtual surface, which encloses arbitrarily shaped scatterers. In order to verify this method, scattering patterns from this transformation are compared with scattering patterns from exact solution. Numerical results show that errors in the far-field data from this method is less than surface equivalence theorem. Thus, this method is valid for obtaining the far-field data.

Technique for calculation of the propagation constant in an optical planar waveguide with a Gaussian profile

We performed analysis of a planar waveguide with arbitrary index variations. We obtained numerical results for the propagation coefficient by using first-order Langer and Liouville transformations. The accuracy of the numerical results is confirmed by a comparison with those obtained by other methods.

Estimation of wave source position by using spherical wave function

Estimation of wave source position is important technique for searching unknown noise source in EMI and EMC measurement. In this paper a new estimation technique for searching the position of wave source is proposed by using spherical vector wave function and point matching method. In our method a few virtual boundaries are placed on surrounding space encompassed the unknown wave source. Then, applying the boundary condition on the virtual boundaries, the unknown coefficients in the spherical vector wave function can be obtained. In order to verify the validity of this method, numerical experiments are carried out. As the result of them, position of unknown wave source can be estimated accurately by using our method.