Tetsu Shijo

The Modified Surface-Normal Vectors in the Physical Optics

Simple equivalent surface currents perturbed from the physical optics (PO) are proposed, which predict accurate scattering fields without using a special knowledge about the high frequency asymptotic theories such as the geometrical theory of diffraction (GTD). A novel and empirical concept named ldquomodified surface-normal vectorsrdquo is introduced in the classical definition of the PO current, which is defined in a way that the reflection law is satisfied at each point of interest in the integration region. This empirical and geometrical replacement of the surface-normal vectors drastically enhances the accuracy of the PO to a level of the GTD.

Large-Size Local-Domain Basis Functions with Phase Detour and Fresnel Zone Threshold for Sparse Reaction Matrix in the Method of Moments

Locality in high frequency diffraction is embodied in the Method of Moments (MoM) in view of the method of stationary phase. Local-domain basis functions accompanied with the phase detour, which are not entire domain but are much larger than the segment length in the usual MoM, are newly introduced to enhance the cancellation of mutual coupling over the local-domain; the off-diagonal elements in resultant reaction matrix evanesce rapidly. The Fresnel zone threshold is proposed for simple and effective truncation of the matrix into the sparse band matrix. Numerical examples for the 2-D strip and the 2-D corner reflector demonstrate the feasibility as well as difficulties of the concept; the way mitigating computational load of the MoM in high frequency problems is suggested.

Accuracy demonstration of physical optics with modified surface-normal vectors

In this paper, the simple equivalent surface currents, which are enhanced accuracy of the physical optics (PO) to the level of GTD, were obtained by introducing the modified surface-normal vectors in the PO currents. The effectiveness was numerically demonstrated to the scattering problems for the three-dimensional circular disc, the two-dimensional corner and parabola reflector. This concept is perfectly different from the fringe wave correction. The PO with the modified surface-normal vectors has high versatility owing to the free singularities in the GO boundaries, focus, and caustics

EMI reduction technology in 85 kHz band 44 kW wireless power transfer system for rapid contactless charging of electric bus

A 44 kW wireless power transfer (WPT) system is being developed for rapid contactless charging in an electric bus in the 85 kHz band, the candidate frequency for a wireless charging system for light-duty vehicles that is currently undergoing standardization. For field operation of this WPT system using the 85 kHz band in Japan, permission for use as industrial facilities emitting radio waves is required under the Radio Act. A two-channel WPT system with currents of opposite phase in the two transmit pads of the channels is introduced to reduce radiated emissions to within the Radio Act limits of electromagnetic radiation disturbance by cancelling the emission from each channel. Then, the diagonal placement of the transmit pads for the two channels is proposed to avoid the interference between the two channels where the interference couplings become null. Finally, the measured emission of the 44 kW WPT system in a 10 m anechoic chamber is shown.

Optimization of thickness and shape of core block in resonator for 7 kW-class wireless power transfer system for PHEV/EV charging

Transmitting and receiving resonators for 7 kW-class wireless power transfer/transmission (WPT) systems operating at 85 kHz have been developed for contactless Electric Vehicle (EV)/Plugin Hybrid EV (PHEV) charging. The light weight and small volume of the on-board receiving resonator to be mounted on the vehicle are required attributes. A thickness and a shape of the core in the resonance coil are optimized considering a coil weight, a core loss and a coupling coefficient between the resonators. The coupling coefficient and a coil loss included the core loss of the on-board prototype resonator with the core weight of 4.3 kg and a size of 600 mm by 400 mm are measured for 7 kW-class WPT system. Coil-to-coil power efficiency at the rated transfer power can be estimated with high accuracy by evaluating the core loss. The coil-to-coil efficiency of 93.8% at 160-mm air gap is achieved for the prototype resonator to be mounted on the vehicle.

Development of resonant coil for kW-class wireless power transfer system

We have developed resonant coils for kW-class wireless power transfer systems used in industrial applications such as EV/PHEVs. The characteristics requested for such coils are small size, lightweight and low loss. In this study we have simulated two test coils that have different arrangement of ferrite cores. Both coils have outline size of 50 cm square and thickness of about 3 cm. The proposed core arrangement reduced the core loss by 38% compared with the conventional type.

Design and development of 77-GHz pair-slot array antenna with single-mode post-wall waveguide for automotive radar

A 77-GHz slot array antenna with a single-mode post-wall waveguide is presented for automotive radars. First, transmission losses and fabrication costs of various transmission lines in millimeter-wave band are compared. The measured transmission loss in the 77-GHz post-wall waveguide integrated in a PTFE substrate at 77 GHz is shown 0.20 dB/cm, which is less than that of the microstrip line. Then, the design method of one-dimensional slot subarray with the single-mode post-wall waveguide is discussed. Finally, an antenna system composed of four subarrays has been fabricated. The measured gain of the antenna system is 24.4 dBi gain at the designed frequency of 76.5 GHz, and the efficiency for aperture size of 55 mm by 9.2 mm is 67%.

Geometrical optics terms calculated by a PO-MER line integration methodology

The purpose of this paper is to open the discussion, from the numerical point of view, on the direct equivalence between the physical optics (PO) surface integral and the modified edge representation (MER) line integrals. When the scattered field is composed by the diffracted field and the GO contributions the entity of MER line integration is not clear and the equivalence between the PO surface-to-MER line-integration has not been confirmed. In this paper, it is numerically demonstrated that MER line integration around the stationary phase point (SPP), which is the reflection or the intersection of the ray path between the source and the observer, gives the geometrical optics terms. The GO terms are understood as the reflected wave in the reflection region or the direct incident wave (with negative sign) in the shadow region. The general and important results derived are: the PO surface integral is decomposed into the GO and the diffraction terms via the MER line integrals.

Combined use of PO-MoM and Local-MoM for reducing MoM areas for wide angular observation points

PO-MoM is a hybrid method where Physical Optics Current Approximation is corrected by addition of the Fringe wave component (FW) obtained by Method of Moment (MoM). Authors have succeeded to define/localize the areas for the MoM on the scatterer by introducing the Fresnel zone number. Unfortunately, this area extends most of the scatterer surface for some specific combinations of the source and the observer and reduction of computational load fails. This paper introduces another high frequency concept of locality of diffraction, Local-MoM, proposed by the authors, for compensating this defect. Combined use of PO-MoM and Local-MoM realizes almost frequency independent number of unknowns.

Far Field Calculation of the Defocused Parabolic Reflector Antennas by the Modified Edge Representation Line Integrals

This article resumes the recent results in the scattering field calculation by the modified edge representation technique, in the sense of the high frequency approximation. The expression of the scattering geometrical optics field contributions by the use of the MER line integrals is taken into account. The MER is applied to the conductive sphere and the convergence of the MER line integration to the scattering geometrical optics is observed. The radiation pattern is calculated for the defocused parabolic reflector antenna, with special interest in the reflection region. The agreement with the physical optics surface integration is observed and discussed