Katsumi Furuya

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.

Novel Ring Waveguide Device in a 2D Photonic Crystal Slab –Transmittance Simulated by Finit-Difference Time-Domain Analysis–

We propose a novel ring waveguide device in a two-dimensional (2D) photonic crystal (PhC) slab with a hexagonal lattice of air holes in a semiconductor (Si/GaAs). The device consists of a single line-defect ring waveguide and other parts. We simulated the propagation of a 1 ps pulse in the device. We analyzed the device using the 2D finite-difference time-domain (FDTD) method. The 1 ps pulse is transmitted well through sharp 60 degree bends in the ring waveguide. We designed and examined four-port directional couplers (DC) as input/output (I/O) components for the ring device. Coupling between the I/O waveguides and the ring waveguide in the device can be achieved by the four-port DC. We adopted a defect pattern formed with a straight waveguide and a waveguide with bends as the DC structure. This pattern realizes the coupling length based on the coupled mode theory. Our DC with the new multistep-like waveguides improved both the directivity and coupling factor across most of the frequency band where there are practical guided-wave modes in the photonic band gap (PBG). The propagation loss of a 1 ps pulse in the ring waveguide is low, so the transmission property of the ring device depends mainly on the I/O parts. In this study, we confirmed that the ring device would be sufficient for such applications as delay lines.

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.

Basic Study of Coupling on Three-Dimensional Crossing of Si Photonic Wire Waveguide for Optical Interconnection on Inter or Inner Chip

For speeding up of transmission and energy saving on inter or inner chips of semiconductors, hydrogenated amorphous silicon (a-Si:H), unlike conventional crystal Si (c-Si), promises optical multilevel wiring on a Si IC. For three-dimensional (3D) crossing of Si/a-Si:H photonic wire waveguides, the loss and crosstalk as S-parameters of the two propagation modes are evaluated by numerical analysis at the C-band when the waveguide core is 200 ×400 nm2. Whether the crosstalk can be suppressed to -50 dB or less is to be a criterion. Even at the crossing angle of 30°, when the distance between the waveguides of the crossing is 1 µm or less, the crosstalk is suppressed sufficiently, while the radiation loss is also small if a TE-like mode propagates. These quantitative results are derived for the first time and show that the photonic 3D crossing can rival the present electric multilevel wiring from the viewpoint of device height. An important index for the 3D waveguide crossing fabrication is obtained.

Fine thickness control of amorphous silicon by wet-etching for low loss wire waveguide

Isotropic wet-etching without surface roughening was applied to an a-Si:H film with nanometer-scale thickness controllability. Record ∼1.2 dB/cm low propagation loss was obtained in an etched wire waveguide, being comparable to those of SOI waveguides.

An Analysis of THz Oscillator using Negative Differential Resistance Dual Channel Transistor (NDR-DCT) and Integrated Antenna

Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan Phone: +81-29-861-5501 E-mail: k-furuya@aist.go.jp Graduate School of Engineering, Shibaura Institute of Technology, 3-9-14 Shibaura, Minato-ku, Tokyo 108-8548, Japan Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan

An Analysis of Antenna Integrated THz Oscillator Using a Negative Differential Resistance Transistor

As THz wave has the advantages of enough resolution and penetration to materials, it has been examined to be used for the imaging system. The propagation distance of THz wave is limited to be short. That is also the advantage for application to the indoor wireless communication etc. For the achievement of the ultra-high frequency oscillator (and concurrently transmitter) device, the properties of small, electronic excitation, the antenna constructed and being on the wafer are important. For the purpose, the Negative differential resistance Dual channel transistor (NDR-DCT) proposed by AIST is utilized. In this paper, as an initial theoretical analysis, we simulated the oscillation frequency of this device at about 100GHz-1THz within the Terahertz band on which the abovee applications was expected. The equivalent circuit model of NDR-DCT was shown based on the analogy with the resonant tunnelling diode (RTDs), and the antenna as the resonance circuit part was designed by the numerical analysis. The possibility of the THz oscillation of this device was confirmed. The slit reflector that we proposed can realize the slot antenna on the device effectively and is suitable for three terminal structure semiconductor. its manufacturing is relatively easy.