A High Power Density and Nearly Constant Voltage WPT System Based on Bendable PCB

Most existing wireless power transfer (WPT) systems are built using rigid materials [normal printed circuit board (PCB) with rigid magnetic coupler] that offer limited adaptability for applications such as biomimetic implants or wearable devices. In this research, a WPT system based on a flexible printed circuit board (FPCB) is presented throughout the entire system. The proposed system using FPCB can achieve a nearly constant voltage (CV) output under soft-switching operation with bending in both circuitry and the wireless charging coils (or magnetic couplers). The system exhibits CV in a triangular region while considering both coupling and load variations. This triangular region has been verified with experimental results verifying the correctness of the theoretical analysis. Since the proposed system does not require any controller, driver, or protection circuit. Hence, only a limited number of components are employed for the benefit of the power density. A 10 W prototype system using FPCB that has 0.2 mm thickness in coils and the main circuit (excluding the switches, capacitors, and resistors) has been built. The system has been tested under large bending conditions for both the circuitry and the coils. The whole system exhibits a power density of 309 W/in³.