Atsuhiro Nishikata

Characteristics of Leaky Surface Acoustic Waves Propagating on LiNbO3 and LiTaO3 Substrates.

Two types of leaky waves are obtained in this paper. They are the first leaky wave, whose phase velocity is between those of slow and fast shear waves, and the second leaky waves, whose phase velocity is greater than that of the fast shear wave. The characteristics of leaky waves propagating on LiNbO3 and LiTaO3 substrates are theoretically investigated by changing cut angles and propagating directions. Propagation loss of the first leaky wave for an electrically open surface becomes almost zero at =20, 40, 80, 100, 140 and 160° on ( , 90°, 0°)-cut LiNbO3 substrate, and K2 is 16.2% at these cuts. Phase velocities of the second leaky waves propagating on (90°, 90°, ψ )-cut LiTaO3 and LiNbO3 substrates are twice as fast as those of Rayleigh waves, and electromechanical coupling coefficient (K2) of 2.14% is obtained at ψ=31° on the LiTaO3 substrate. Propagation losses of both electrically open and short surfaces are almost zero at ψ=164° on the LiTaO3 substrate. K2 of as high as 12.9% is obtained at ψ=36° on the LiNbO3 substrate. Propagation losses of both electrically open and short surfaces are almost zero at ψ=163° on the LiNbO3 substrate.

Analysis for electromagnetic leakage through a plane shield with an arbitrarily-oriented dipole source

The shielding performance of an infinitely large plane shield of uniform and isotropic material is investigated theoretically. An infinitesimal electric or magnetic dipole is taken for a radiating source assuming that its location and orientation are arbitrary. To correctly use the conventional transmission theory for near-field shielding problems, a plane wave expansion is performed to describe all the fields involved. As a result, general formulae for the leakage fields are derived in an integral form for every configuration of the source and observation points. They are expressed in terms of the transmission coefficients of the evanescent waves and the ordinary plane waves. The validity of the formulae is verified by comparison of the computational results with the previously reported experimental results. It is found that the formulae can be applied to a very wide range of frequencies and distances. >

A Swept-Frequency Measurement of Complex Permittivity and Complex Permeability of a Columnar Specimen Inserted in a Rectangular Waveguide

This paper proposes a new method for the swept-frequency measurement of a solid materials complex permittivity and complex permeability. The proposed method utilizes a columnar specimen inserted in a rectangular waveguide, and the two-port S-parameters of the specimen are measured. In the analysis, the S-parameters are rigorously formulated in which the waveguides fundamental mode, as well as the higher order modes are taken into account. Measurement was performed by using a standard waveguide and three types of materials as specimens. Results were compared with the conventional transmission-line method using the same rectangular waveguide. It is confirmed that the complex permittivity and complex permeability measured by the proposed method agrees very well with those measured by the conventional transmission-line method.

Correction factors for normalized site attenuation

EMI standards require test sites to be validated by measuring the normalized site attenuation (NSA) instead of the classical site attenuation (CSA). Theoretical investigations are, therefore, carried out on the general formulation of NSA and CSA, where chain matrices are introduced to account for the effects of antenna circuits. It is found that the theoretical NSA values given by the standards are based on three assumptions inappropriate to measurements using tuned dipole antennas. Thus, correction is considered requisite for every NSA measurement when tuned dipoles are used. In this connection, new correction factors are proposed for various measurement configurations at 3-, 10-, and 30-m test sites. In addition, numerical evaluations are made on the correction factors applicable to the NSA measurements with antenna factors calibrated at 2 or 3 m above a metal plane. >

Resonance suppression of a spherical electromagnetic shielding enclosure by using conductive dielectrics

The resonance suppression for the electromagnetic shielding enclosure is theoretically investigated. A simple model of a double-layered spherical shell with a plane-wave illumination is assumed. When a spherical shell made of conductive dielectrics is covered with a thin metal layer, the conductivity of the dielectrics has an optimum value which minimizes the Q-factor at the fundamental resonant frequency. The optimum conductivity is shown to be a function of the resonant frequency and the thickness of the dielectric layer. The improvement of the shielding effectiveness by introducing the optimum conductivity is shown.

Complex permittivity measurement at millimetre-wave frequencies during the fermentation process of Japanese sake

Various chemical reactions occur simultaneously in barrels during the fermentation processes of alcoholic beverages. Chemical analyses are employed to monitor the change in chemical components, such as glucose and ethyl alcohol. The tests are carried out with extracted specimens, are costly and require time. We have developed a permittivity measurement system for liquid specimens in the frequency range from 2.6 to 50 GHz, and applied the system to fermentation monitoring. Experimental results proved that the observed change in complex permittivity suggests a decrease in the amount of glucose and an increase in alcohol content, which are the key chemical components during the fermentation process.

Feasibility study for reconstruction of information from near field observations of the magnetic field of laser printer

We measured leaked electromagnetic radiation that came from a laser printer. Using the measured data, we were able to easily reconstruct the printed image. To avoid unwanted monitoring, we have to prevent the printed image data from being reconstructed. In this paper, we first measured the magnetic field at a near field point and then reconstructed the image. Then, using the Sommerfeld integration model, we calculated the magnetic field shielding required to reduce the emitted radiation to a level where the image could not be constructed. From the calculation results, we found that we can easily attenuate the electromagnetic wave by using a thin shielding sheet and we can not remake the image if the distance from the noise source to observation point is more than 30 mm

Scattering Analysis for Layered Cylindrical Object Perpendicularly Piercing the Wider Walls of a Rectangular Waveguide and Its Application to

This paper describes a novel analysis for the scattering problem of a layered cylindrical object that pierces a rectangular waveguide through a pair of holes made at the center of the wider walls. In this analysis, the S-parameters are rigorously formulated in terms of the modal scattering coefficients of the cylindrical object. Here, the modal scattering coefficients are expressed as solutions to a set of linear equations of infinite extent. The layered object is represented by the admittance function, which can readily be calculated for an arbitrary number of layers, using a recurrence formula. To show the applicability of the presented formulas, two types of dielectric samples (polytetrafluoroethylene and polyacetar) and a ferrite sample were measured, and reasonable values were obtained. In addition, the complex permittivity of water was determined by using a glass capillary tube as a liquid container, and an excellent agreement was shown with the value predicted by Debyes formula.

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We have been developing an electromagnetic field intensity measurement system using an absorption screen made of dielectric material. In this developed system, a very small change of temperature on an absorption screen illuminated by the electromagnetic wave is measured using an infrared camera with 2-D lock-in processing technique.

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A free space method is in wide spread use for the reflectivity measurement of electromagnetic wave absorbers (EMA) in the VHF and UHF ranges. In the free space method, the reflection levels from both the EMA and a metal plate of the same size are measured, and the reflectivity is calculated by their ratio. The incident angle, such as normal or oblique, must be specified, and the polarization of the electromagnetic wave must also be specified as TE, TM, or circularly-polarized mode. A method using only a parallel beam made by placing a dielectric lens in front of a horn antenna in the millimeter wave band is studied experimentally. Electromagnetic wave absorption was measured for normal or oblique incidence using this parallel beam. The following effects are expected: the measurement system is compact because the wave plane becomes equiphase after shorter range running than for no lens use; it is made possible because the scattered wave can hardly enter the receiving part; it is possible to enlarge the incident angles to large degrees when measuring at oblique incidence.