Inductive power transmission for autonomous sensors: Voltage regulation effects on efficiency

This work proposes the use of inductive links in order to wirelessly power autonomous sensors. In order to increase the powering distance and the power efficiency, resonant tanks were considered. To drive the transmitting resonant network, a commercial class D amplifier was used. Working frequency was restricted to 150 kHz. Commercial magnetic-core coils were selected as they provide high coil values and quality factors in a small-size factor, which is a requirement for the intended application. At the receiving network, a rectifier and a voltage regulator were used to provide a DC voltage supply to the autonomous sensor. Three kinds of voltage regulators were compared from the point of view of the power efficiency. Both a theoretical analysis and experimental results are presented. Computed graphs show that operating points for the shunt regulator always lead to a higher power efficiency. Experimental tests were carried out using a mechanical setup to fix the coil-to-coil distances. Results show that shunt regulators provide the best power efficiency over the other alternatives, which are linear series and switching buck regulators.