Design and Implementation of Dual-Mode Inductors for Dual-Band Wireless Power Transfer Systems

We propose a dual-band wireless power transfer (WPT) system employing a dual-mode inductor. The dual-mode inductor is possible through enforcing a self-resonance condition by loading an inductor in series by a tank circuit. In return, two distinct resonances are achieved, simultaneously, utilizing a single compensation capacitor as the inductance of the dual-mode inductor appears with a smaller value after its self-resonance. Also, by maintaining the same mutual coupling, the coupling coefficient becomes larger at the higher resonance, which allows for the employment of the same source/load admittance inversion network to achieve maximum power transfer at both of the operating frequency bands, concurrently. We verify the operation by fabricating a dual-band WPT system, which shows measured efficiencies of 70% and 69% at 90.3 MHz and 138.8 MHz, correspondingly. The size of the WPT system is <inline-formula> <tex-math notation="LaTeX">$\boldsymbol {50} \boldsymbol {\times } \boldsymbol {50}$ </tex-math></inline-formula> mm<inline-formula> <tex-math notation="LaTeX">$^{\boldsymbol {2}}$ </tex-math></inline-formula> and has a transfer distance of 40 mm.