Optical probe for input-impedance measurement of in vivo power-receiving microstructure

An optical method is proposed to measure the input impedance of a microstructure in vivo operating at microwave frequencies. It makes use of the non-linearity of an AC-DC conversion circuit and encodes the received power level to the pulse rate of an LED which can be accurately measured by a photodiode outside the tissue medium. An accurate measurement of the characteristics of the power-receiving structures in a wireless powering system greatly enhance the power transfer efficiency.