Yoshinobu Okano

Development and characteristics of a biological tissue-equivalent phantom for microwaves

Various phantoms (simulated biological bodies) have been proposed as a biological model for studies of electromagnetic effects on the human body. This paper reports the characteristics of the phantom developed by the authors that realized electrical characteristics equivalent to the biological body. Examples of its communication and clinical applications are presented. The present phantom is made of agar, polyethylene powder, sodium chloride, TX-151, preservative, and deionized water and simulates the relative permittivity and conductivity of a high-water-content tissue. In the present phantom, electrical characteristics almost equal to those in the biological tissue are realized with a single composition ratio over the frequency range of 300 MHz to 2.5 GHz. It is also possible to simulate the electrical characteristics of an arbitrary high-water-content tissue by adjustment of the composition. No special equipment is needed for fabrication and the preservation is easy. Further, as examples of applications of this phantom to the human body, the SAR measurement examples are presented in the COST 244 human head model and coaxial-slot antenna for hyperthermia. The present phantom is useful as a human model to study the mutual effects of the human body and electromagnetic waves.

The SAR evaluation method by a combination of thermographic experiments and biological tissue-equivalent phantoms

Many different phantoms have been proposed as human head models for experimental estimation of the electromagnetic energy field induced in the human head caused by the use of an RF device. Here, a biotic tissue-equivalent solid phantom is introduced as the human head model realizing the same relative dielectric constant and conductivity as brain tissue and skull layer. This brain-equivalent solid phantom and skull-equivalent phantom make it possible to accomplish highly reliable and precise estimation of specific absorption rate (SAR) in the human head. The phantom models of cube, sphere, and realistic human heads are fabricated. Measurements are performed to estimate the SAR in the human head models exposed to microwave sources by using the thermographic method.

A simple shape broadband planar antenna adaptable to RFID-tag

This paper presents a simple shape planar antenna with high adaptability to an Radio Frequency IDentification tag. The feed point of this antenna consists of two adjacent electrodes in the plane which can be matched to the intrinsic impedance of a coaxial cable (50-/spl Omega/) without using parasitic elements or balun. Specifically, the aperture shape inside the loop antenna is modified without deforming the antenna element outline. Control of the input impedance becomes possible and bandwidth for S11/spl les/-10 dB can reach about 49% of the central frequency. The proposed antenna demonstrates a steady gain (3.5-4.2 dBi) within a wide frequency range. An investigation of antenna-element miniaturization showed the sectional area of the antenna element could be compressed by about 50% while maintaining wide bandwidth.

Accurate measurement of small input resistances using a conventional network analyzer

Precise and accurate measurement of input resistance is essential to characterize small antennas whose input resistance is very small. However, this is very difficult because uncertainty, which includes imprecision and inaccuracy, sometimes exceeds the resistance being measured. A method for precise measurement of small input resistance using a conventional network analyzer is presented. Inaccuracy, which includes an actual conductor loss of the antenna under test (AUT), manufacturing error, and the residual systematic errors is then estimated. The former two sources of inaccuracy are obtained by comparing a radiation efficiency measurement of a small loop antenna using the Wheeler cap method with a calculated radiation efficiency. Using these values in the calculation of the input resistance, a true input resistance is acquired. Finally, the actual value of the residual systematic errors for each instrument is estimated by comparison between the true input resistance and the measurement.

Analysis of terahertz oscillator using negative differential resistance dual-channel transistor and integrated antenna

The terahertz (THz) band ranges from 100 GHz to 10 THz generally. For easy available of the applications, for example, an imaging system and an indoor wireless communication system using this band, an ultrahigh-frequency oscillator device as a wave source with a frequency of one or a few hundred GHz using the negative differential resistance dual-channel transistor (NDR-DCT) proposed by National Institute of Advanced Industrial Science and Technology (AIST) has been studied. The equivalent circuit model of NDR-DCT was based on the measured device properties and analogy with resonant tunnelling diodes (RTDs). It was shown that an antenna on an wafer, which consists of the electrodes of the transistor, could be realized with the slit reflector by numerical analysis. In this study, we simulated and confirmed the validity of our design of the antenna at any frequencies up to a few hundred GHz. The oscillation frequency of this device was analyzed at 150 GHz and more mainly by specifying the dependence of NDR-DCT characteristics on the gate length for the first time. Improvements in the characteristics of the oscillation device using the optimum gate length were shown.

A study on solid phantoms for estimation of interaction between human body and electromagnetic waves

An experimental evaluation for the specific absorption rate (SAR) is necessary to estimate the interaction between the human body and electromagnetic waves. This paper presents measurements for the SAR of modeled human heads using the tissue-equivalent solid phantoms. The phantoms developed have almost the same complex dielectric constant as homogeneous tissue in the microwave region.

A tissue-equivalent solid phantom for estimation of interaction between human head and handset antenna

In this paper, accurate measurements for the SAR of modeled human heads using the brain equivalent phantom are presented. First, SARs of cubic and spherical phantoms in the vicinity of a dipole antenna are measured and compared with calculation. Secondly, a monopole antenna in a metal box, which simulates a mobile phone, is used. The operating frequency is considered only at 900 MHz. To enhance the accuracy of the experiments, the ingredients for the head model were carefully conditioned complying with COST 244 (1994).

Growth of InGaAsP solar cells and their application to triple-junction top cells used in smart stack multijunction solar cells

The authors report on high-quality InGaAsP (1.61–1.65 eV) solar cells grown on a GaAs substrate; their study is the first to grow these using solid-source molecular beam epitaxy (SS-MBE). A temperature of 430 °C was found to be suitable for the growth of the InGaAsP solar cells. The properties of these InGaAsP solar cells were found to be better than those of AlGaAs solar cells that had the same bandgap energy, and it was found to be suitable for use as the second cell in a triple-junction top cell used in a smart stack multijunction solar cell. The authors also developed an InGaP/InGaAsP/GaAs solar cell and found that it had an impressive open-circuit voltage of 3.16 V. This result indicates that high-performance InGaP/InGaAsP/GaAs triple-junction solar cells can be fabricated using SS-MBE.

Novel Hybrid Antenna for Broadcasting Satellite and Terrestrial HD-TV

High-definition television (HD-TV) is available via satellite broadcast and terrestrial HD-TV services. However, antennas that can receive HD-TV signals using different carrier waves (i.e., X band and UHF band) have not yet been designed. Therefore, in an effort to realize such an antenna, we created a slot aperture in the reflector of a typical Broadcasting Satellite (BS) antenna, and investigated its possible use as a UHF-band antenna element. Furthermore, a practical hybrid antenna for BS and terrestrial HD-TV was developed by implementing omnidirectional radiation in a parabolic reflector with a slot. This hybrid antenna exhibited excellent practical performance in a field test.

Development of tabular broadband antenna for UHF‐TV

A tabular loop antenna is proposed that can be matched to the characteristic impedance of a coaxial cable without using complex parasitic elements or expensive matching elements while maintaining the broadband character and superior gain of the loop antenna. Specifically, modification of the aperture shape inside the loop is attempted without changing the external shape. In this way, the control of the input impedance becomes possible and the bandwidth for VSWR ≤ 2 can reach about 40% at the center frequency of 620 MHz for UHF-band TV. An antenna with a unidirectional radiation pattern with a reflector was fabricated for trial and was studied both by experiments and by FDTD analysis. It was confirmed that the bandwidth for VSWR ≤ 2 reaches about 50% at 620 MHz. Further, with regard to the dynamic gain, a stable gain of 7.6 to 8.2 dBi was attained for the entire UHF band. This antenna will be useful for ground wave digital broadcasting.