The increasing sophisticated power and communication demands have motivated a variety of research on simultaneous wireless information and power transfer system, aiming to provide higher power transfer efficiency and improved communication rate. This letter demonstrates that resonant wireless power transfer system with relays can be a candidate to reach these aims. Based on coupled resonator filter theory, mathematical equations for transmission efficiency and bandwidth are derived for arbitrary number of relays. Improved efficiency and bandwidth are verified by equations, simulation and experiments. Experimental results show that under the distance of two times the diameter of the resonator, system efficiency increases from 5.43% (no relay) to 29.47% (one relay) and 38.02% (two relays), with the fractional bandwidth broadened from 1.33% (no relay) to 3.31% (one relay) and 4.47% (two relays) at operation frequency of 42.55 MHz, providing available channel for simultaneous power and data transfer. The procedure for the design of relays is also listed in detail.
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