Influence of exposure guidelines on the design of on-body inductive power transfer

Designers of on-body health sensing devices with inductive power transfer (IPT) face a number of trade-offs. Safe exposure limits should be maintained, and protective housing and padding are generally needed; however, these impose compromises on the power-transfer-system design. This paper analyses these trade-offs and proposes a design route to achieving high power transfer in the presence of field restrictions and separations for padding or housing materials. An IPT system using a Class D coil-driver and switched-mode power-conditioning is designed to provide regulated d.c. and energy storage. Compliance with ICNIRP 1998 guidelines is demonstrated, at a power level that is sufficient to power typical on-body medical sensing devices.