The majority of existing wireless power solutions are capable of 2-Dimensional surface charging of one or two devices, but are not well suited to deliver power efficiently to large numbers of devices placed throughout a large 3-Dimensional volume of space. In this work we propose an unexplored type of wireless power transfer system based on electromagnetic cavity resonance. Here we use the natural electromagnetic modes of hollow metallic structures to produce uniform magnetic fields which can simultaneously power multiple small receiver coils contained almost anywhere inside.An analytical model is derived that predicts the coupling coefficient and power transfer efficiency from the cavity resonator to a small coil. These predictions are verified against simulated results with a coefficient of determination of 0.9943. By using two resonant modes we demonstrate that a 3 inch diameter receiver can be powered in nearly any location in a 140 cubic foot test chamber, at greater than 50% efficiency. Additionally, we show that 10 receivers can be powered simultaneously and that this system is capable of recharging consumer electronics such as a cell phone.

We report on the magnetic field and coupling enhancement for increased wireless power transfer efficiency using intermediate materials. We examine the physical mechanisms for enhancement using a metamaterial (MM) and magnetic resonant field enhancement (MR-FE) and present an analytical and simulation analysis as well as an experimental study of these enhancement mechanisms. While both increase the mutual coupling, the loss of the contrasting enhancement mechanisms significantly impacts WPT efficiency enhancement. Our analysis shows that the MR-FE approach can have up to a 4 times higher efficiency over the MM approach due to the lower loss of its field enhancement mechanism.Index Terms-Wireless power transfer, metamaterials, magnetic resonance, wireless energy transfer.Wireless power transfer (WPT) using magnetoquasistatic fields has become an important means to transfer energy over short to medium distances. Recent work has shown that by using resonant systems [1], [2], the transfer efficiency can be optimized, making longer distances and higher efficiencies possible. These systems have shown efficiencies of greater than 80% when the source and receiver coils are several coil diameters apart.To further enhance WPT efficiency, previous works have proposed the addition of an intermediate material between the source and receiver of a WPT system [3]-[7]. This intermediate material is placed between the source and receive coil assemblies and is independent of the source/receiver realization, Fig. 1. In these previous works, two materials were suggested to enhance WPT efficiency. The first was a metamaterial (MM) that acts as a near field super-lens [3], [6] to focus or concentrate the magnetoquasistatic field generated by the source at the receiver coil. A potential mutual coupling improvement of up to 50 times has been reported [3], suggesting a significant improvement. The second method was the use of intermediate magnetic resonant field enhancers (MR-FE) that enhance the coupling between the source and load [4], [7]. Both methods show potential for increased coupling; however, no work has compared these methods quantitatively in a consistent manner, nor examined how the different physical enhancement mechanisms contributed to the resulting efficiency improvement. In this letter we investigate the physical mechanism of the enhanced coupling of each method and show that while each achieves enhanced coupling in different ways, both can increase WPT efficiency. Our analysis shows, however, that the inherent loss in the different physical mechanisms for field enhancement plays a decisive M.

This letter proposes using the electromagnetic resonant modes of a hollow metallic structure to provide wireless power to small receivers contained anywhere inside. The coupling between a large chamber (used as a cavity resonator) and a small wire loop (used as a receiver) is studied. An analytic expression for the coupling coefficient between the fields in the cavity and a loop receiver is derived. This model is validated against simulation and experimental results. Finally, wireless power transfer is demonstrated at an efficiency of over 60% for large volumes in the structure, even though the receiver is a small 7.6 cm square shaped loop and the distance to the source probe is greater than 1 m. This technique for wireless power transfer has thus far been unexplored, and the results here serve as a starting point for resonant cavity mode wireless power systems with many receivers having arbitrary locations and orientations.

In this work, we show experimentally that wireless power transfer (WPT) using strongly coupled magnetic resonance (SCMR) and traditional induction are equivalent. We demonstrate that for a given coil separation, and to within 4%, strongly coupled magnetic resonance and traditional induction produce the same theoretical efficiency of wireless power transfer versus distance. Moreover, we show that the difference between traditional induction and strongly coupled magnetic resonance is in the implementation of the impedance matching network where strongly coupled magnetic resonance uses the mini-loop impedance match. The mini-loop impedance mach provides a low-loss, high-ratio impedance transformation that makes it desirable for longer distance wireless power transfer, where large impedance transformations are needed to maximize power transfer.

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