Yuichi Sawahara

Study on a purely electric-field coupled resonator for WPT systems

We investigate a toroidal coil as a purely electric-field coupled resonator in the present paper, since we have studied a two-layered spiral coils as a purely magnetic-field coupled resonator before. We will explain the difference of structure and property of each resonator first, and then check the parametric characteristic of the toroidal coil resonator through measurement and analysis. Then, we compare it with the conventional electric field coupling system. In consequence, the benefits and features of the toroidal coil resonator could be clarified for use in WPT systems.

Choice of resonators for a WPT system in lossy materials

In order to cope with the necessity of transferring electric power through lossy dielectric materials such as house walls, human body or water, use of magnetically coupled resonator WPT system is recommended. A simple spiral resonator with series capacitance is the first candidate, followed by the second candidate, a little more sophisticated two layered spiral resonator with series capacitance. Since they confine electric energy in a narrow space effectively, the coupling becomes magnetic, which reduces dielectric loss appreciably.

Fabrication of a new high-performance WPT system by electric energy confinement

A WPT system based on coupled resonators makes use of the electric and magnetic couplings. Considering one can control the ratio of those couplings, it should be useful to reduce the electric coupling, since it is affected by the dielectric material that intrudes between the two resonators, resulting in the shift of operating frequency, deterioration of matching and increase of transfer loss. The present paper studies two methods to avoid them, that is, electric energy confinement by external lumped capacitor and by double layered coils. Both try to confine the electric energy of the resonators into a limited space and remove from the coupling space. Carrying out a comparative study, it concludes the latter is more desirable by the overall rating.

Applicaions of a novel disk repeater

New applications of a proposed disk repeater are described. Taking advantages of its low loss, simple structure and easy handling, it could be used for power tunneling, power catering and power mendicanting. The basic properties of the disk repeater is clarified first, being followed by parametric properties of three possible applications.

Wireless power transfer to moving ornamental robot fish in aquarium

We have constructed an underwater wireless power transfer system for the swimming robot fish using a coupled resonator WPT technique. The WPT systems are usually affected by dielectric material, the resonant frequency being shifted, and the power transfer loss being increased. By use of the primarily magnetic coupling, we have tried to realize a system that is hardly affected by the water. In addition, we have devised the resonator structure and the way of coil winding aiming at distribution everywhere in the aquarium. Then, a switching regulator for the power supply has contributed to improve the efficiency of the system.

Wireless power transfer guides

It is experimentally studied that the power transfer efficiency is improved by inserting a proper structure made of dielectrics, magnetic materials or metals between two spiral coils constituting a coupled-resonator WPT (Wireless power transfer) system. The structures can be hollow/solid circular cylinder, plate or rectangular parallelepiped. The power transfer is based on the coupling of evanescent fields, not propagating fields. The principle of power guide is temporarily considered to be the refraction of the electric and magnetic fields at the boundary of 2 different materials. But it is still not clear.

Construction of a secure wireless power transfer system for robot fish

We have designed a prototype wireless power feeding system to the ornamental robot fish, considering it also as a preliminary experiment for application to the capsule endoscope. We insert a solenoidal resonator instead of the button battery in a robot fish, and send power wirelessly from the resonators which are placed above and below the aquarium. In order to mitigate the high voltage induced in the power transmitting coil due to the low coupling coefficient to the receiving resonator, the effect of operation frequency is studied, resulting in the choice of lower frequency. So as to comply with the EMC problems, electric/magnetic field distributions are measured being compared with ICNIRP recommendation. In addition, we have the real goldfish swim at the same time as the robot fish in the demo experiment for qualitative safety evidence.

Study on high efficiency WPT underseas

Aiming at the undersea WPT (Wireless Power Transfer) system, improvement of power transfer efficiency through saltwater is studied. We have examined the unloaded Q (Qu) and coupling coefficient (k) of the spiral coil resonators for different diameters and different operating frequencies with the number of turns fixed. In addition, introducing a new structure of 4-layered spiral coil resonators, we found the improved transfer efficiency, especially by adopting dense winding of litz wire.

Power catering with a non-contact single wire

A new disk repeater can deliver power highly efficiently, being integrated into the resonator coupling type WPT system. Thus, we will demonstrate 2 useful examples in order to show the benefits of the disk repeater.