Engineered and miniaturized 13.56 MHz omni-directional WPT system for medical applications

This paper proposes the design of an engineered Wireless Power Transfer circuit for a 13.56 MHz miniaturized Inductive Resonant Wireless Power Transfer (IR-WPT) link for medical applications. The IR-WPT system is composed of a miniaturized receiver realized through three orthogonal coils winded up around a 3D-printed spherical structure. In order to create a compact system and maximize the EM coupling all the rectification circuitry needs to be placed inside the geometrical sphere. Thus, the PCB dimensions and arrangement are limited by the small volume available inside the plastic structure, less then 1 cm3, and by the 3D shape of the system, which forces the PCB layout to exploit an orthogonal arrangement with separated blocks. The circuitry component packages are chosen in order to minimize the encumbrance and ease the connection with each orthogonal coil. The equivalent circuit model is optimized with respect to the Power Transfer Efficiency (PTE) at a 5 cm Tx-Rx distance. To investigate the effect of the human body on the system performance, simulations are carried out exploiting an equivalent model of the human body tissues inside which the receiver is placed, at the same reference distance. The system performance is comparable for both cases: a 15 % average PTE and dc-output voltage exceeding 1.5 V are calculated for a 10 V input source.