An efficient wireless power transmission system by employing 3 × 3 stacked coil antenna arrays

New achievement of employing near-field coil array either on energy transmitter (Tx) or receiver (Rx) sides is introduced for the application of mid-range wireless power transmission (WPT). According to the theory of strongly coupled magnetic resonance (SCMR), the coil elements properly stacked without contact for constituting a vertically arranged array, could be optimized to enhance the reduced coupling coefficients between the transceiver antennas of the WPT systems over the extended mid-range distance. In this paper, the conjunction of 3 Txs and 3 Rxs coil elements (so-called the 3 × 3 coil arrays) have been tried out to realize more efficient WPT systems which can provide even higher system power transfer efficiencies than the single-to-single WPT system excluding the coil array (so-called the 1 × 1 WPT system). Within each single compact planar antenna element, the structures of a loop coil placed outside and a spiral coil put inside are composed together and spaced tightly. It is shown that the total power transfer efficiency of around 84% over a mid-range distance of 0.5 m can be achieved for the 3 × 3 WPT system proposed. Furthermore, as for evaluating the robustness of the 3 × 3 WPT system to varying the power transfer distance, the variation curve of the defined total power transfer efficiency with the changing size of the transfer separation distance from 1.0 cm to 100.0 cm is given.