Proposal of a Wireless Power Transfer Technique for Low-Power Multireceiver Applications

In this paper, we proposed and verified the feasibility of a unique wireless power transfer structure called a rail transformer to drive multiple low-power devices such as electronic shelf label (ESL) devices. The rail transformer is composed of a rectangular, circular-shaped transmitting yoke and two transmitting coils to provide wireless power. Multiple receiving yokes coupled with receiving coils are installed across the elongated edge of the transmitting yoke. It can be driven by low-frequency ac power at 50/60 Hz. In our prototype, the transmitting yoke is 900 mm long and 15 mm wide. We obtained the minimal induced wireless power, and the voltage was similar to 61 mW and 3.5 V, which is sufficient to drive a typical ESL device. By designing a nonuniform gap thickness between the transmitting and the receiving yokes at the specific locations, we improved the uniformity of the induced power for multiple ESL devices.ArticleIEEE TRANSACTIONS ON MAGNETICS. 51(11):8402904 (2015)journal articl

LLC resonance power transformers using magnetoplated wire

The use of magneto-plated wire (MPW) allows for reduction of winding loss component from the proximity effect. compared with a copper wire (COW). A MPW is a COW with a circumference that is plated with a magnetic thin film. In this paper, we clarify the basic characteristics and the efficiency characteristics of a transformer using a MPW and a COW. We found that the resistances of a primary coil made of COW and MPW at a frequency f = 500 kHz are 1.56 Omega and 1.12 Omega, respectively, and decreased 28%. The short circuit inductances of the COW and the MPW at a frequency f = 500 kHz are 26 mu H and 29.6 mu H, respectively, and increased 13.8%. The efficiencies of an LLC resonant converter using the COW and the MPW at a frequency f = 500 kHz are 90.2% and 92.2%, respectively, and increased 2%.ArticleINTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS. 47(3):719-727 (2015)journal articl

Examination of Wireless Power Transfer Combined With the Utilization of Distance Detection

Wireless power transfer using magnetic resonant coupling is expected to be widely used in the charging of an electric vehicle and in the use of home electric appliances. Wireless power transfer requires a high efficiency and power transfer over a long distance. However, the efficiency is reduced by the increase of the transmission distance and the change of the impedance of the receiving load. Therefore, a distance sensor using magnetic resonant coupling is proposed. In this paper, we propose a method of power transfer and distance detection using one couple of coils in real time. We also propose to use different frequencies in the power transfer and the distance detection, which are superposed and separated. Using the proposed approach, we demonstrated that the power transfer and the distance detection can be performed without relying on the change of the transmission distance.ArticleIEEE TRANSACTIONS ON MAGNETICS. 50(11):4005304 (2014)journal articl

Magnetic spring characteristic of an oscillatory actuator with silicone rubber torsion springs for optical scanner applications

A compact electro-magnetic oscillatory actuator was proposed based on a pair of torsion springs for optical scanners operating at low oscillating frequencies, such as 50 Hz for a portable barcode scanner. Each torsion spring in the actuator is made of silicone rubber and is dually supported at both ends. A yoke is coupled with the driven coil to enhance the driving torque of the actuator. In this study, we analyzed the effect of the yoke on the resonant frequency of the actuator, as well as the torsion moment. We also experimentally determined the relationship between the resonant frequency and the magnetic gap of the yoke. Compared with the mechanical resonant frequency in the experiments, which was designed to be 50 Hz, the frequency was modified to 57.4 Hz, 54.7 Hz and 52.9 Hz when the gap between the yoke and the permanent magnet was 1.5 mm, 1.7 mm and 1.9 mm, respectively. The proposed actuator, which combines a yoke with flexible torsion springs, is potentially useful as a compact optical scanner, taking advantages of both low power consumption and high reliability.ArticleInt. J. Appl. Electromagn. Mech. 46(3):463-470(2014)journal articl

A Novel High-Speed Electromagnetic Oscillatory Actuator With a Dual Mover for Optical Scanner Applications

In this paper, we propose a high-speed moving magnet-type oscillatory actuator in which a dual-mover structure is designed to reduce magnetic damping force. Both movers have independent resonant frequency, and the actuator is driven at the larger resonant frequency. The smaller mover serves as the optical scanning element and maintains large oscillation amplitude. The larger mover, with moving magnets, serves as the magnetic driving element and maintains relatively smaller amplitude because of the magnetic damping.ArticleIEEE TRANSACTIONS ON MAGNETICS. 50(11):8203504 (2014)journal articl

Examination of Wireless Power Transfer Combined With the Utilization of Distance Detection

Wireless power transfer using magnetic resonant coupling is expected to be widely used in the charging of an electric vehicle and in the use of home electric appliances. Wireless power transfer requires a high efficiency and power transfer over a long distance. However, the efficiency is reduced by the increase of the transmission distance and the change of the impedance of the receiving load. Therefore, a distance sensor using magnetic resonant coupling is proposed. In this paper, we propose a method of power transfer and distance detection using one couple of coils in real time. We also propose to use different frequencies in the power transfer and the distance detection, which are superposed and separated. Using the proposed approach, we demonstrated that the power transfer and the distance detection can be performed without relying on the change of the transmission distance.ArticleIEEE TRANSACTIONS ON MAGNETICS. 50(11):4005304 (2014)journal articl

Proposal of a Wireless Power Transfer Technique for Low-Power Multireceiver Applications

In this paper, we proposed and verified the feasibility of a unique wireless power transfer structure called a rail transformer to drive multiple low-power devices such as electronic shelf label (ESL) devices. The rail transformer is composed of a rectangular, circular-shaped transmitting yoke and two transmitting coils to provide wireless power. Multiple receiving yokes coupled with receiving coils are installed across the elongated edge of the transmitting yoke. It can be driven by low-frequency ac power at 50/60 Hz. In our prototype, the transmitting yoke is 900 mm long and 15 mm wide. We obtained the minimal induced wireless power, and the voltage was similar to 61 mW and 3.5 V, which is sufficient to drive a typical ESL device. By designing a nonuniform gap thickness between the transmitting and the receiving yokes at the specific locations, we improved the uniformity of the induced power for multiple ESL devices.ArticleIEEE TRANSACTIONS ON MAGNETICS. 51(11):8402904 (2015)journal articl

Reducing Rotor Temperature Rise in Concentrated Winding Motor by Using Magnetic Powder Mixed Resin Ring

The demand for high-speed servomotors is increasing, and minimal losses in both high-speed and high-torque regions are required. Copper loss reduction in permanent magnet motors can be achieved by configuring concentrated winding, but there are more spatial harmonics compared with distributed winding. At high-speed rotation, the eddy current loss of the rotor increases, and efficiency tends to decrease. Therefore, we propose a motor in which a composite ring made from resin material mixed with magnetic powder is mounted on the stator to suppress spatial harmonics. This paper describes three characteristic motor types, namely, open-slot motors, composite-ring motors, and closed-slot motors. Spatial harmonics are reduced significantly in composite-ring motors, and rotor eddy current loss is reduced by more than 50% compared with open-slot motors. Thermal analysis suggests that the saturation temperature rise value is reduced by more than 30 K. The use of a composite ring is effective in reducing magnet eddy current loss during high-speed rotation. Conversely, the torque characteristics in the closed-slot motor are greatly reduced as well as the efficiency. Magnetic circuits and simulations show that on electrical steel sheets with high relative permeability, the ring significantly reduces the torque flux passing through the stator, thus reducing the torque constant. To achieve reduced eddy current loss during high-speed rotation while ensuring torque characteristics with the composite ring, it is necessary to set the relative permeability and thickness of the composite ring according to motor specifications