Measuring efficiency of AC power transfer

Hi all,

I am investigating the efficiency of wireless power transfer using a resonating, coupled LC system. I have a parallel LC circuit attached to a function generator (outputting a simple 50% duty cycle sine wave) and another identical LC circuit to receive the transmitted power.

Is there a way I can quantitatively determine the efficiency of this power transfer? I have tried measuring voltage and current on both sides, however due to phase shift I cannot measure total useful power effectively. Is there some way I can measure phase shift and then use Power_rms = V_rms * I_rms * sin(phase shift), or should I take a different approach?

Thanks for your help.

– Henry