A new wireless power transfer circuit with a single-stage regulating rectifier is designed and validated with satisfactory efficiency for flexible sensor patches. Since the battery is bulky and cannot be fabricated on a flexible substrate, the power source of the electronic patch is realized by wireless power transfer. Magnetic resonance transmission power at 13.56 MHz in the ISM band is adopted to make possible wireless power transfer. Furthermore, for high conversion efficiency, a new single-stage regulating rectifier is designed and implemented at the receiver side of the sensor patch. An active switching full-wave bridge rectifier is designed to reduce conduction loss and increase the voltage-conversion rate. A delay lock loop feedback controller overcomes the switching delays at high frequencies that significantly undermine power conversion efficiency. The voltage rectification and regulation are achieved simultaneously in a single-stage rectifier through 1X/0X mode control. The PFM control is adopted to select the switching frequency of the system in order to maximize the transient response during heavy load and to minimize the switching power losses during light load. The circuit is fabricated via the TSMC 0.35 µm process. The output efficiency of the circuitry was improved by 5-10% in light load as compared with the circuit without PFM control, while the peak efficiency reaches favorable 86%.