A Wireless Power Transfer System for Spinal Cord Stimulation Based on Generalized Parity–Time Symmetry Condition

In recent years, the parity–time (PT) symmetry principle has been introduced into wireless power transfer (WPT) systems, which can improve the stability of WPT within a certain range. In this article, we analyze the generalized PT-symmetry conditions of four basic WPT topologies based on circuit theory (CT) and coupled mode theory (CMT). The results show that the series–parallel (SP) topology meets the PT-symmetry condition based on the CMT, although it does not meet the condition obtained by the CT. The symmetry between the energy of the two-resonance system is established in the SP topology. According to this unique characteristic, a constant-voltage WPT system for spinal cord stimulation is designed, which is independent of the transfer distance and load in a wide range.