Wireless Power Transmission for Autonomous Sensors in Removable Vehicle Seats

This work proposes the use of magnetic coupling for powering autonomous sensors in space-constrained applications, such as occupancy and belt detection in removable vehicle seats. The power demand of the autonomous sensor is considered between tens and hundreds of milliwatts. A theoretical analysis first highlights the critical parameters in order to achieve a large powering range and high efficiency. Series-resonant tanks are considered for both the primary and secondary networks. Because the intended application is space-constrained, small coils have to be used. In order to increase their quality factor, commercial ferrite-core coils are used. A class D power amplifier is proposed for the primary network. Experimental results show that a power of tens of milliwatts can be transferred to a 100 Ω load placed at the secondary network up to a distance of 2cm, near seven times the radius of the coils (3mm). The addition of a rectifier and a voltage regulator at the secondary network in order to properly power an autonomous sensor (3V@30mA) limits the powering range to 1cm. Overall power efficiencies around 45% and 20% are achieved respectively at distances of 5mm and 1cm.