A method to control the power distribution among receivers by the load values in a single-input, multiple-output (SIMO) wireless power transfer (WPT) system is investigated. We first derive the value of loads to maximize total efficiency. Next, a simple, but effective analytical formula of the load condition for the desired power distribution ratio is presented. The derived load solutions are simply given by system figure of merits and desired power ratios. The formula is validated with many numerical examples via electromagnetic simulations. We demonstrate that with the choice of loads from this simple formula, the power can be conveniently and accurately distributed among receivers for most practical requirements in SIMO WPT systems.

This paper presents a method for solving receiver misalignment (axial or angular) problems in wireless power transfer systems using a multiple-input single-output system. The optimum magnitudes and phases of the transmitter voltages and receiver load for maximum efficiency are derived in convenient analytical forms when negligible mutual couplings between transmitters. These solutions are validated by genetic algorithm optimization and electromagnetic-simulation results for a design ex-ample of two transmitters and one rotating receiver.

Microwave-based wireless power transfer in the near field (up to about 10 m) is now drawing much interest since the transfer range when using current magnetic induction or magnetic resonance methods is limited in current industry. The Friis efficiency formula is valid only in the far field, so this paper proposes a new efficiency formula for use in the near field as well as in the far field. The proposed formula is derived under the assumption that the fields generated from transmitting-antenna elements are coherently (or constructively) added at a receiving antenna. The proposed formula is validated by EM-simulations and measurements using a 1 × 8 phased array antenna. The proposed efficiency formula is shown to be accurate in the near field and converge to the Friis formula in the far field.

In this paper, we proposed a method to control input powers and receiver loads for maximum efficiency in multiple-input multipleoutput(MIMO) wireless power transfer(WPT) systems. The input voltage ratio between transmitters and receiver loads for maximum transfer efficiency is derived in terms of figure of merits. The theoretically derived input voltages for the transmitters and optimum loads for the receivers were found to be similar to those obtained by a genetic algorithm. We demonstrate the effectiveness of the theory using a few design examples. Using the results obtained from this study, effective and simplified designs of MIMO WPT systems will be possible.