Injection-locked Oscillator Coupled to Two External Resonators for Wireless Power Transfer

We present a near-field wireless power transfer system based on an injection-locked oscillator coupled to two external resonators, one used as a relay element. We demonstrate that injection locking mitigates the instability problems observed in free-running conditions and provides a more regular behavior versus the coupling conditions. The system is investigated with a semi-analytical formulation based on a nonlinear oscillator model extracted from harmonic balance (HB) in the presence of the input source. This model is combined with the input admittance of the coupled network, accounting for the two external resonators. We analyze the output power of the locked solution and its dependencies on the coupling factors and load resistance. A versatile design methodology is derived, which is validated with full HB simulations and measurements.