Aiming at the undersea WPT (Wireless Power Transfer) system, improvement of power transfer efficiency through saltwater is studied. We have examined the unloaded Q (Q,,) 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.

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Dielectric or magnetic materials introduced in a wireless power transfer (WPT) system affect the properties of WPT. This paper quantitatively studies the coupling between the transmitting and receiving elements for a WPT system including either dielectric or magnetic materials. The transmitting and receiving elements are open spirals and solenoid coils which are usually used in WPT systems. The analysis method is the perturbation method which can calculate the total coupling coefficient k, the electric coupling component k e and the magnetic coupling component k m simultaneously. This paper gives quantitatively analyzed data on k m and k e to indicate how much k m and k e are affected by a dielectric or magnetic material introduced in a WPT system.

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