Yoichi Okuno

Introduction to Yasuura’s Method of Modal Expansion with Application to Grating Problems

In this chapter we introduce the theory of the Yasuura’s method based on modal expansion and explain the methods of numerical computation in detail for several grating problems. After a sample problem we discuss the methods for solving two types of problems that require additional knowledge and steps, that is, scattering by a dielectric cylinder and diffraction by a grating. Some numerical results are shown to give an evidence of an experimental rule for the number of linear equations in formulating the least-squares problem that determines the modal coefficients. After confirming the rule we show a couple of examples of practical interest, i.e., scattering by a relatively deep metal grating, plasmon surface waves on a metal grating placed in conical mounting, scattering by a metal surface modulated in two directions, and scattering by periodically located dielectric spheres. To provide supplementary explanations of particular problems, four appendices are given; H-wave scattering from a cylinder, the normal equation and related topics, conical diffraction by a dielectric grating, and comparison of modal functions and the algorithm of the smoothing procedures.

Plasmon excitation on a thin metal-film grating: Profile effect and applications

We investigate plasmon excitation on the surfaces of a thin metal-film grating, which are sinusoidally modulated with a common period and different initial phases. Employing Yasuuras method of modal expansion, we numerically find the resonance angle, field distribution, power flow in the vicinity of the grating surfaces, and efficiency of propagating orders. By setting the amplitude of the metal-film grating and the phase difference between the top and the bottom surface, we can examine the profile effect on plasmon excitation. In addition we show some results for a grating in conical mounting.

A novel compact Printed Inverted-F MIMO antenna operating at 5.8GHz for WiFi applications

In this paper, we propose a novel compact Printed Inverted-F MIMO Antenna operating at 5.8 GHz for WiFi applications. A fractal shape patch shorted at one end is used, which works to reduce the size of antenna. To further reduce the size of antenna, we extend an edge of patch towards the ground. In order to obtain high isolation, we use a PIFA with a ground plane. The simulation results show that the proposed antenna has good performance for WiFi applications.

Resolution of a grating-based plasmon index sensor with efficiency-alone interrogation

High-resolution measurement of refractive index has a wide range of application and employment of the plasmon resonance absorption combined with phase detection is a promising way to achieve 8-digit resolution. However, because the phase detection in light-wave frequency is not simple, we would like to report on a method of refractive-index measurement by using efficiency-alone interrogation. The basic idea comes from the fact that the TM-wave diffraction efficiency of a metal grating placed in conical mounting can be extremely small at the resonance angle (the polar angle of incidence at which the resonance absorption occurs). We have found in our previous works that (1) there is an appropriate azimuth (a parameter of the conical mounting) determined by a rough value of the index; (2) the TM efficiency at the resonance angle can be 10-8 or less. Hence, if we use a rotating stage with an instrumental resolution of 1/4000 degrees in finding the resonance angle, the expected resolution in refractive index would be a little less than 7-digit.

A UHF RFID reader antenna with near field inductive wireless power transfer feature

An RFID reader antenna with truncated segmented coupling elliptical loop is proposed to operate at UHF band. The segmented coupling rings are used to achieve inductive wireless power transfer (WPT) while communication. The proposed UHF reader antenna has an input impedance matching bandwidth (S11 <; -10 dB) of 60 MHz (890-950 MHz) with the highest gain reaching 3.8 dB at 915 MHz. The WPT feature during communication makes the proposed antenna desirable for some special RFID applications such as implantable medical device without battery.