Wirelessly powered receiver system and sensors are described. In an embodiment, the power receiver system, includes an inductive coil that receives wireless power from an external transmitter, a capacitor bank that optimizes power transfer to an energy harvesting device, and a power-receiving frontend RF-DC rectifier with a periodically enabled closed feedback loop that adapts settings of the capacitor bank in real-time to adapt to changes on the inductive coil to maximize power transfer efficiency.