Backscatter Efficiency Modeling of Inductive Links Applied to Wireless Power Transfer Systems

In this paper, we analyze the backscatter response of inductive link-based wireless power transfer systems. This analysis leads to a model that predicts the power levels received back on the primary side of the inductive link. The proposed model considers the inductive link characteristics as the magnetic coupling factor, the quality factors of the inductors, and the impedance matching at the secondary side, but also accounts for the equivalent on-resistance of the switch used to apply the response on the secondary side. The modeling of the backscattering response can be helpful to choose design variables of the system such as the duty cycle of the response and the size of the switching transistors. Moreover, the estimation of the reflected power can be used to specify the receiver sensitivity on the primary side. The model is validated with experimental results on two different inductive links: one using only FR4-printed inductors with a PIN diode acting as backscatter switch and the other using a CMOS fully integrated wireless power receiver. The measured backscattered power in both cases agrees with the predicted values.