An Ultra-High-Frequency Wirelessly-Powered Smart Bandage for Wound Monitoring and Sensing Using Frequency Modulation

In this paper, a battery-less and wireless smart bandage is proposed, where the RF and sensor circuit are wirelessly powered, and the sensor data is modulated and wirelessly collected. The sensor is designed with minimalistic electronics to interface to tri-electrode electrochemical sensors. The RF electronics, power telemetry and data-communication antennas are realized via conductive thread embroidery on fabric substrate. The wireless power transmitter operates at frequencies between 350 MHz to 573 MHz, while the return communication signal path is designed to be around 915 MHz. The bandage electronics feature a rectifier for RF-to-DC conversion of received RF power, used for driving a voltage-controlled oscillator (VCO) and electrochemical sensor. It is demonstrated that restored wound, emulated by a resistive load, yields a modulated frequency of 845 MHz, which is tunable based on value of resistive load and wirelessly collected by a remote receiver at 3 ft. away from the bandage. This modulated frequency corresponds to a tuning voltage of 0.1 V for the VCO. The VCO consumes a total DC power of less than 6 mW. This is the first time a battery-less wirelessly powered smart bandage is demonstrated and this result can be served as a foundation for remote sensing of chronic wounds in the near future.