Inductive power transfer for autonomous sensors in presence of metallic structures

Abstract

This work proposes powering autonomous sensors via inductive links in presence of metallic structures. The intended application is occupancy and belt detection in removable vehicle seats. The final aim is to maximize the powering distance and minimize the influence of the metallic structures, which was achieved by using resonant networks and magnetic core materials for the coils. First, a theoretical analysis was carried out in order to identify critical parameters. Then, simulations were performed at a frequency of 130 kHz with three different coil types, two with ferrite-core coils and one with an air-core coil. Numerical results show that ferrite-core coils, in especial that with an ETD-core coil, are less affected by the presence of metallic structures. Finally, both the maximum achieved distance and the effect of a nearby metallic plate were assessed experimentally. Without the metallic plate, the air-core coils provided the maximum powering distance, thanks to its much larger winding diameter. However, with the metallic plate present the transferred power with the air-core coils to the load was insufficient for the intended application. On the other hand, the ferrite-core coils barely noticed the presence of the metallic plate, achieving the ETD-core coils the highest powering distance, around 3 cm.