Shuichi Obayashi

A body-shadowing model for indoor radio communication environments

Deterministic propagation prediction methods proposed for indoor radio are useful for estimating the average propagation loss in real environments, which usually have complicated geometries. On the other hand, these methods generally fail to accommodate human body shadowing, which is a significant propagation effect in indoor picocells. Several empirical models to describe body shadowing have been reported. However, to our knowledge, no appropriate model that can be used in combination with deterministic propagation prediction methods has been provided in the literature. In this paper, a new practical model is introduced, which provides a way to estimate body-shadowing effects deterministically with the existing ray-determination methods. The detailed procedure to combine our body-shadowing model with the ray-determination methods is described. Several examples are shown applying the procedure to a simple office layout.

Efficiency improvement of wireless power transfer via magnetic resonance using transmission coil array

The transfer efficiency between a transmission coil and a reception coil for wireless power transfer via magnetic resonance is a function of the orientation between the coils. When two coils share a single axis, the transfer efficiency is maximal, but otherwise the efficiency becomes lower. In this paper, a wireless power transfer system via magnetic resonance using a transmission coil array is proposed to improve the transfer efficiency. The transmission coils of the array are excited with appropriate phase weights by transmission circuit, according to the orientation among the transmission coils and the receiving coil. The effect of the proposed system is confirmed by simulation by a method of moment and measurement using a vector network analyzer.

A voltage ratio-based efficiency control method for 3 kW wireless power transmission

This paper presents a novel control method for wireless power transmission (WPT). The proposed method can maximize the power efficiency only by controlling the voltage ratio between the primary and the secondary side. Experimental measurement results of the prototype system with 3 kW power transmission show the efficiency difference between the proposed control method and the available maximum value is less than 0.3 % even with a large variation of coil-to-coil distance and load voltage. The automatic controller for the proposed method provides the load-following operation, maintaining both constant power and high efficiency, using a WLAN connection.

High-efficiency monolithic GaAs power MESFET amplifier operating with a single low voltage supply for 1.9-GHz digital mobile communication applications

A monolithic GaAs power amplifier IC using refractory WN/sub xW self-aligned gate power MESFETs has been developed for 1.9-GHz digital mobile communication systems, such as the Japanese personal handy phone system. The power amplifier operates with high efficiency and low distortion with a single low voltage supply of 2.7-3.0 V, by virtue of small drain knee voltage, high transconductance and sufficient breakdown voltage of the power MESFET. An output power of 23.7 dBm and a high power-added efficiency of 24.2% were attained at 3 V for 1.9-GHz /spl pi4-shifted QPSK (quadrature phase shift keying) modulated input when adjacent channel leakage power was -58 dBc at 600 kHz apart.<<ETX>>

A study of efficiency improvement of wireless power transfer by impedance matching

In wireless electric power transmission employing magnetic resonant coils, objects or debris in the vicinity of the coil cause impedance mismatching. The mismatching will decrease the transmission efficiency at the frequency for performing electric power transmission. We have investigated the efficiency improvement by impedance matching adjustment using variable lumped capacitors. In the present work, a loop is employed to excite the resonance coil, and a set of variable capacitors are added to the loop on the power transmission side to adjust the matching. For the test against a small object, a small aluminum plate was put close to the transmission coil, and the input impedance of the coil on the transmission side was adjusted by the variable capacitors. The test measurement showed that the adjustment of the input impedance substantially improved the efficiency at the power transfer frequency.

Bonding wire loop antenna built into standard BGA package for 60 GHz short-range wireless communication

The unlicensed 60 GHz frequency band is suitable for high-speed wireless systems with transmission rates of 1 Gbps or more. In this paper, we propose a bonding wire antenna built into a BGA package for 60 GHz short-range wireless communication. This antenna utilizes two bonding wires and a metal plate on an interposer in a BGA package and has a loop shape. The proposed antenna is built into a standard BGA package without special modification, so that it can be fabricated at low cost by conventional BGA package fabrication process. The first and unique evaluation of the antenna fully sealed by encapsulation resin was done by measurement. We describe the operation mechanism of the proposed antenna, the design procedure and the measurement results.

An adaptive array for high speed wireless local loops steered by local signal phase shifters

We propose an adaptive array steered by local signal phase shifters for high-speed wireless local loops. An adaptive array used as a radio receiver usually requires one or more frequency conversion sections to achieve acceptable sensitivity performance. The phase shift and the frequency shift of the signal from each antenna element can be accomplished simultaneously at the down-conversion stage by phase-controlled local signals. The configuration can avoid the additional loss or noise in the received signal due to the phase shifter itself, and ordinary commercial quadrature modulator ICs for mobile communications can be utilized for the CW local phase shifter. The adaptive array does not require high speed digital signal processing sections with fast AD converters for all of the array elements. In this paper, we describe the practical configuration of the array as well as pattern measurements in the S-band for a prototype including the essential elements.

Low profile double resonance frequency tunable antenna using RF MEMS variable capacitor for digital terrestrial broadcasting reception

It is difficult to realize the built-in antenna for wideband systems, because a frequency bandwidth of the low profile antenna is narrow. A frequency tunable antenna is a technique for wideband characteristics. In this paper a low profile double resonance frequency tunable antenna using MEMS variable capacitors is presented. It has high efficiency over a wide frequency band. Through both resonant portions from 465 to 665 MHz, the efficiency of more than −4 dB and the VSWR of less than 3 are observed in the measurement using the variable capacitor of 0.4–0.9 pF.

EMI reduction technology in 85 kHz band 44 kW wireless power transfer system for rapid contactless charging of electric bus

A 44 kW wireless power transfer (WPT) system is being developed for rapid contactless charging in an electric bus in the 85 kHz band, the candidate frequency for a wireless charging system for light-duty vehicles that is currently undergoing standardization. For field operation of this WPT system using the 85 kHz band in Japan, permission for use as industrial facilities emitting radio waves is required under the Radio Act. A two-channel WPT system with currents of opposite phase in the two transmit pads of the channels is introduced to reduce radiated emissions to within the Radio Act limits of electromagnetic radiation disturbance by cancelling the emission from each channel. Then, the diagonal placement of the transmit pads for the two channels is proposed to avoid the interference between the two channels where the interference couplings become null. Finally, the measured emission of the 44 kW WPT system in a 10 m anechoic chamber is shown.

Optimization of thickness and shape of core block in resonator for 7 kW-class wireless power transfer system for PHEV/EV charging

Transmitting and receiving resonators for 7 kW-class wireless power transfer/transmission (WPT) systems operating at 85 kHz have been developed for contactless Electric Vehicle (EV)/Plugin Hybrid EV (PHEV) charging. The light weight and small volume of the on-board receiving resonator to be mounted on the vehicle are required attributes. A thickness and a shape of the core in the resonance coil are optimized considering a coil weight, a core loss and a coupling coefficient between the resonators. The coupling coefficient and a coil loss included the core loss of the on-board prototype resonator with the core weight of 4.3 kg and a size of 600 mm by 400 mm are measured for 7 kW-class WPT system. Coil-to-coil power efficiency at the rated transfer power can be estimated with high accuracy by evaluating the core loss. The coil-to-coil efficiency of 93.8% at 160-mm air gap is achieved for the prototype resonator to be mounted on the vehicle.