RF Wireless Power Transfer Using Integrated Inductor

Wireless power transfer (WPT) is an ideal power delivery solution for many light-load applications, such as for the Internet of Things. A regulated solution for WPT may utilize a power distribution unit (PDU). Previous works have designed planar inductors for integration with switched-inductor buck regulators, but these inductors will not be as efficient for light-load applications. This paper reevaluates the inductor loss for light-load applications by taking into account the frequency spectrum of the inductor current. Using this revised analysis, a planar inductor with screen printed NiZn ferrite epoxy composite magnetic core is designed for an RF near-field coupling system with 1-10-mW load power. In measurement with a 6-MHz buck converter, the PDU with designed inductor demonstrated up to 3% improved efficiency compared to surface-mount technology inductor in the pulse-frequency modulation mode and pulsewidth modulation mode. The designed embedded inductor was subsequently demonstrated in an integrated, compact RF near-field coupling system with peak 43% system efficiency.