13.56 MHz magnetic backplate-integrated PAWC wireless power transfer: an innovative switchless control and no-load protection approach

This study first proposes a planar alternating winding coil (PAWC) integrating a magnetic backplate, adopting a dual-sided alternating winding architecture on dielectric substrates. The proposed PAWC system features three fundamental characteristics: load-independent constant-current output, broad-range high-efficiency power transfer, and inherent no-load protection. During no-load operation, the transmitter exhibits high-impedance characteristics, effectively entering a zero-current shutdown state that completely prevents the overcurrent risks typical of series-series (S-S) compensated systems. When the receiver approaches the charging position, the system autonomously shifts to a zero-reactance operating mode at the same working frequency, achieving efficient power transfer without supplemental compensation networks. This design enables state switching purely through relative coil positioning, eliminating the need for additional sensing or switching components. Experimental validation confirms 92.8% coil-to-coil transfer efficiency at 5 mm separation, with efficiency exceeding 90% across 50−300 Ω load variations. These advancements offer particular value for safety-critical applications, including smart home ecosystems and medical implants, where the system's self-regulating switching capability and robust efficiency significantly enhance operational reliability.