Wireless power transmission based on resonant electrical coupling

Abstract

A novel technique for wirelessly transferring power over nonnegligible distances is shown in this poster. This technique is based on resonance and electrical coupling. Preliminary experimental results have shown that this technique can be used for wireless power transfer (WPT) purposes. So far an efficiency of approximately 40% was obtained at a distance of 5 meters using a prototype measuring 16 by 16 cm by 3.7 cm at most. In this case the ratio between distance and maximum dimension of the prototypes is therefore approximately 30. The efficiency of the power transfer remains stable even if the relative orientation between the transmitter and the receiver is significantly altered. Some years ago, in 2007, a team of researchers at the Massachusetts Institute of Technology (MIT) made a substantial contribution to the state of the art of WPT. They proposed a system composed of 4 copper coils (largest diameter of 60 cm, wire cross sectional radius of 3 mm). Using this system they were able to wirelessly light up a 60 W incandescent light bulb across a 2 m gap with an efficiency of 40% (see Fig. 1). The attention given to this demonstration by both the scientific community and the media was remarkable. It was shown that a very interesting trade-off between power transfer capability, efficiency, maximum range, size of the devices involved, complexity and cost was possible. Previous WPT proposals were, in general, either very large and expensive or severely limited in terms of maximum range (see Fig. 2). In this technique the efficiency of the power transfer relies on the strong magnetic coupling formed between coils with very high Qs (quality factors) at resonance. The first coil, a single turn loop, is connected to a power source. The second coil, a multi turn, is placed near the loop on the same axis. A capacitor is added to the loop in order to make it resonant precisely at the self-resonant frequency of the multiturn coil. The receiver is defined identically, except that the loop is connected to the load. The loops are magnetically coupled to the nearby multi turn coils because of the close physical proximity. The multiturn coils are magnetically coupled to each other because the very high Qs counteract the effect of distance. Such high Qs are only achievable at resonance. Resonant magnetic coupling (RMC) is now a well established WPT technique, however, the possibility of a dual technology resonant electrical coupling (REC) was never considered. The principal objective of this research is to investigate the feasibility of REC as a novel method for transferring power wirelessly across non-negligible distances with high efficiency. Several encouraging results were already achieved: 1) A circuit model which exhibits a very specific behavior (see Figs. 3 and 4) previously observed only in RMC was found; 2) An efficiency of approximately 40% across a gap of 5 m was obtained in the laboratory using prototypes with dimensions of 16 by 16 cm by 3.7 cm at most (see Figs. 5, 6, 7 and 8). Conclusions The REC concept was presented for the first time in the 2014 edition of the IEEE Wireless Power Transfer Conference that took place in Jeju, South Korea, from May 8 to May 9, 2014. It was considered the best paper in the conference. Regarding intelectual property, a patent for this technology was filed in March 14, 2014. References Fernandes R. D.; Matos J. N.; Carvalho N. B., “Behavior of resonant electrical coupling in terms of range and relative orientation”, 2014 IEEE Wireless Power Transfer Conference (WPTC), 8-9 May 2014. Fig 3 / Circuit model proposed for resonant electrical coupling. Fig 4 / Theoretical behavior of the proposed circuit model. Fig 8 / Experimental S21 behavior observed with the proposed prototype. Fig 6 / Experimental setup (proposed prototypes, polystyrene supports and a vectorial network