Hitoshi Hayashi

Tandem Lange 3-dB 90° hybrid implemented on FR4 substrate

This paper presents a tandem Lange 3-dB 90° hybrid. The hybrid consists of two 8.34-dB Lange couplers connected in tandem and is implemented on a 4-layer flame resistant laminate, composed of woven fiberglass cloth with an epoxy resin binder (FR4) substrate, by using inner-layer crossovers, instead of conventional bonded crossovers. Owing to its optimized tandem structure and inner-layer crossovers, for operating characteristics within the frequency range 440-760 MHz, the hybrid exhibits a power coupling of 3.5 ± 0.6 dB and return losses greater than 23 dB. Furthermore, isolation and phase difference between the output ports is greater than 29 dB and 90° ± 1°, respectively.

Novel Encoding Method for Non-contact IC Card or RFID Systems

We propose a novel encoding method for non-contact IC card or RFID systems. The Manchester code that is currently used for non-contact IC card or RFID systems requires a phase-locked loop (PLL) because intervals of the state transition change. In our novel encoding system, state transitions occur periodically at the center of a waveform through the use of an encoding method involving three waveforms.

Miniaturized broadband three-way power divider

This paper presents a miniaturized broadband three-way power divider. The divider is developed by using a cascade connection of 90° Lange couplers and is implemented on an FR4 substrate. For the frequency range of 460-710 MHz, which corresponds to the relative bandwidth of more than 42%, the divider exhibits power splits of -5.1 ± 0.6 dB, return losses greater than 20 dB, and isolation between output ports greater than 23 dB. The measurement results reveal the feasibility of the proposed power divider configuration for broadband circuit applications with the output ports located well away from each other.

Spontaneous room-temperature formation of broccoli-like Ag–GeTe nanostructures assisting filamentary resistive switching

We report on a novel fabrication of nanostructures of silver (Ag) germanium telluride (GeTe) at room temperature and the control of resistive switching using them. We systematically fabricated Ag seed nanoparticles of various sizes by thermal annealing and demonstrated that deposition of GeTe by RF sputtering onto the Ag seed nanoparticles spontaneously produced nanostructures including broccoli-like, hollow nanostructures comprised predominantly of nanocrystalline grains of Ag, Ag3Ge, Ag2Te, and Ag5Te3. The nanostructure shape and the constituent crystalline phases depend on the amount of Ag used for the seeds. The nanostructure formation followed nanoscale phase separation and crystallization into an unexpected phase from the phase diagram, including a metastable state. The structural changes were characteristic of the Ag nanoparticles; no significant structural changes occurred for GeTe deposition onto Ag films. As an application of the spontaneously formed nanostructures, we demonstrated a control resistive switching when a voltage was applied with a lateral Ag electrode pair deposited onto the top. We found that the Ag amount used for the seed formation determined the polarity of resistive switching and the SET/RESET voltages. By increasing the Ag amount, the resistive switching turned from the clockwise direction to the counter-clockwise direction, and the SET/RESET voltages were lowered.

High-speed start-up and low-power decoding circuit for body-centric communications

We present a high-speed start-up and low-power decoding circuit for body-centric communications. The Manchester code that is currently used for Ethernet (10BASE-T), noncontact IC cards, and RFID systems, requires a phase-locked loop because intervals of the state transition change. In the proposed circuit, state transitions occur periodically at the center of a waveform owing to the use of an encoding method involving several waveforms.

Security requirements for smart grid services in Japan

Security is one of the most important factors for success of smart grid services. This paper presents the security requirements for smart grid services in Japan. We consult two major documents for smart grid security in the U.S. and EU, “NISTIR 7628” and CENs “the Smart Grid Information Security”, and discuss the results of the security requirements extracted from these documents.

Miniaturized broadband three-way power divider with 120° phase differences between output ports

This paper presents a miniaturized broadband three-way power divider with 120° phase differences between output ports. The divider is developed by using a cascade connection of 90° Lange couplers and is implemented on an FR4 substrate. For the frequency range of 440-770 MHz, which corresponds to a relative bandwidth of more than 54%, the divider exhibits power splits of -5.3 ± 0.6 dB, return losses greater than 20 dB, and isolation between output ports greater than 19 dB. Furthermore, for the frequency range of 560-580 MHz, the divider exhibits errors in the desired relative phase difference between output ports of less than 4°. The measurement results reveal the feasibility of the proposed power divider configuration for broadband circuit applications with the output ports located well away from each other.

High-speed start-up and low-power decoding circuit for wireless sensor networks

A high-speed start-up and low-power decoding circuit for wireless sensor networks is presented. The Manchester code that is currently used for Ethernet (10BASE-T), noncontact IC cards, and RFID systems requires a phase-locked loop because the intervals of the state transition change. In the proposed circuit, state transitions occur periodically at the center of a waveform owing to the use of an encoding method involving several waveforms.

Miniaturized broadband rat-race hybrid for UHF biomedical and healthcare applications and TV white space systems

This paper presents the simulated and measured results for a miniaturized broadband rat-race hybrid for UHF biomedical and healthcare applications and TV white space systems. The hybrid was implemented on an FR4 substrate using spiral inductors and chip capacitors. For the frequency range of 430-710 MHz, which corresponds to the relative bandwidth of more than 49%, the rat-race hybrid exhibits power splits of -3.5 ± 0.7 dB, return losses greater than 14 dB, isolation between output ports greater than 21 dB, and errors in the desired relative-phase difference between output ports less than 4°.

Optimization of Power-Efficient Wireless Mesh Networks in Outdoor Environment in Japan

This paper proposes the optimization of power-efficient wireless mesh networks in outdoor environment, particularly for gas metering in Japan. We investigate the effect on the total power consumption by changing the output power and allocated frequency band of the gas metering system. From the simulation results, we show that these changes are effective in achieving low power consumption.