Hitoshi Shimasaki

Magnetically tunable superconductor filters using yttrium iron garnet films

Magnetically tunable superconducting single-resonator filters using YIG films have been demonstrated experimentally. Tunability of 400 MHz at a center frequency of 6 GHz was achieved for a half wavelength microstrip comprising a YIG-YBCO-MgO composite structure. The reason why the quality factor of the filter is relatively low is possibly due to an increase of the magnetic linewidth /spl Delta/H at liquid nitrogen temperature. The theory on dispersion relation of the filter is also presented.

Experimental study on the radiation beam scan of a waveguide slot array antenna filled with a ferrite

This paper describes a millimeter wave slot array antenna whose beam direction can be scanned by a bias magnetic field. A rectangular waveguide with radiating slots on the side wall is partially filled with a ferrite slab. The propagation characteristic changes by applying a dc bias magnetic field parallel to the ferrite, so the radiation direction of the leaky waves from the slot array can be scanned. The radiation pattern of a prototype antenna has been measured at 40 GHz. The main beam direction changes from 10 to 3 degree by the bias magnetic field of 0.73 T.

Signal interference analysis model in near-field coupling communication

Near-field coupling communication (NFCC) is a technology that uses the surface of the human body as a transmission path. To suppress the radiation signal from the human body, NFCC devices use a carrier frequency of less than 10 MHz. Because the radiation signal has the potential to disturb the other NFCC links, the radiation signal from other devices needs to be suppressed to ensure stable NFCC links. This paper describes our investigation of the interfering mechanism in NFCC systems to put the systems into practical use, such as at a ticket gate in the train station. We measured interference signal losses depending on the distance between two phantoms, regarded as human bodies. Based on the experimental and simulated results, an equivalent circuit of the signal interference was proposed. From the interference analytical model, we identified the capacitance that caused the interference problem and found that weakening the effects of this capacitance was important to achieve a stable NFCC link.

Measurement of a slot antenna backed by a textile cavity with post-walls of conductive threads

A flexible cavity-backed slot antenna has been improved by using a post-wall structure. Arrays of conductive threads as vias between two conductive sheets of textiles are forming post-walls of the rectangular cavity. The reflection and radiation characteristics of the slot antenna have been measured for the flat case and the case of being bent. This type of antenna is flexible and wearable, so it is useful in applications of wearable electrical systems.

Measurement of the surface resistance of conductive textiles at microwave frequency

Textile samples which consist of conductive threads are characterized in a microwave frequency range. The configurations of the threads used in this study are traditional ones which have no metallic wires or filaments and have been used in decoration in clothing for hundred years. A half-wavelength microstrip line resonator is fabricated and the Q factors are measured for a copper strip line and for the strip of sample textile from the frequency responses. Difference of Q factors in the two cases leads to the relationship between the surface resistances of the sample and a copper sheet. Then the surface resistances of the samples as conductive sheets are listed and compared. It is found that the relative resistivity is less than four for some textiles. These conductive textiles using a traditional technology are expected to use in wearable electrical systems.

Influence of the coupling between a cavity and a transmission line on the measurement of complex permittivity by the resonant cavity perturbation method

The real part of permittivity can be evaluated at 2.247 GHz by the resonant cavity perturbation method in strong coupling state up to -3.7 dB of coupling that has not been investigated. The imaginary part of the permittivity can be evaluated reliably up to -14 dB of coupling. In the resonant cavity perturbation method, the influence of the coupling on blank and sample loaded cavity are compensated up to -14 dB of |S21|. The possibility of measuring high loss materials was shown by the measurement of Au coated ceramic rod.

Efficient optical control of millimeter waves in a slot line on semiconductor plasma substrate

Efficient control of millimeter-waves in a slot line on an Si and GaAs substrate is discussed both theoretically and experimentally. The spectral-domain method is used to estimate the propagation and the attenuation constants in the slot line with the density of the optically induced plasma as a parameter. Experiments in the millimeter-wave range of 35-50 GHz are carried out using high-resistivity Si and GaAs wafers with the dimension of 15 mm/spl times/30 mm/spl times/600 /spl mu/m. The slot-width could be varied from 0.5 to 2 mm. The attenuation of millimeter waves by over 20 dB can be controlled by optical means using light-emitting diodes with 870 nm wavelength and 68 mW optical power. The experimental results agree considerably well with the theory. The response of millimeter waves with pulsed optical illumination is also examined using a high-power laser diode of 20 W optical power and a pulsewidth less than 100 ns. High-speed response due to optically induced plasma is confirmed for the slot line on GaAs substrate.

Coil design guidelines for high efficiency of wireless power transfer (WPT)

Efficient operation of a wireless power transfer (WPT) system is a major design challenge in many WPT applications. This paper presents a method for designing a high efficiency WPT system when restrictions are imposed on receiver coil (Rx) size. The optimum pitch of the transmitter (Tx) and Rx coils is evaluated by analyzing the coil quality factor and coupling coefficient. Empirical formulae are proposed to derive generalized design guidelines for a given Rx size. The proposed empirical approach can be directly used for the design of a WPT with miniaturized Rx coils without using time consuming optimization algorithms. The proposed empirical expressions are validated with experimental results.

Numerical analysis of nonlinear magnetostatic wave propagation by finite element method

In this paper, we have formulated and solved the nonlinear dispersion relation for magnetostatic surface wave modes propagating along a ferrite film with the help of FEM.

Microstrip line tunable filters using yttrium iron garnet film substrate

Microstrip line tunable filters with a longitudinally magnetized yttrium iron garnet film have been investigated experimentally and theoretically. A half wavelength microstrip line resonator with L-shaped stubs, longer side of which is parallel to the center strip, has been proposed so that attenuation poles are tunable with applied magnetic bias fields and synchronized with the passband, and the experimental results axe compared with the numerical calculation. In addition, we have proposed the composite structure of the above-mentioned resonator and another microstrip line with the same substrate connected in cascade to suppress the unexpected passband due to magnetostatic waves.