Yusuke Inada, Toru Kawajiri, Ukyo Takeda, and Hiroki Ishikuro, “Arbitrary Magnetic Field Control Technique by Multi-Coil Transmitter Voltage Phase Shifting for Omni-Directional Free-Positioning Magnetic Resonance Wireless Power Delivery,” 48th European Microwave Conference (EuMC), pp.186-189, Sept. 2018.