A Wireless Sensing Platform Utilizing Ambient RF Energy Ambient RF Sources In practical wireless sensor usage, the RF Harvesting Sensor Node Ubiquity WiFi Routers 30mW - 100mW Power need for a battery limits the application space and increases initial and recurring costs. Ambient RF (Radio Frequency) energy harvesting offers a unique solution to this practical problem and facilitates the implementation of a battery- and supercapacitor-free wireless sensing node with 24-hour operation. Cellular BTS Harvesting Cellular Base Stations (BTS) 2.5W – 10’s of kW FM Radio Broadcast ~6 kW – 100 kW Available power around a 1 MW DTV transmitter in Seattle, WA Running a sensor node on energy harvested from a cellular base station. (2 dBi TX gain, 6 dBi RX gain at 539 MHz) The dotted circle indicates 10.4km, the maximum tested range TV Broadcast ~45 kW – 1 MW (Digital TV) Exploring Harvesting Topologies Type 1 Harvester Efficiency-optimized for higher power levels (shorter range) Type 2 Harvester Sensitivity-optimized for longest operating range Modular architecture allows easy experimentation and extensibility TV Harvesting Goal: Improve operating sensitivity The minimum input power required for operation depends on many factors, with one major factor being the magnitude of the quiescent current draw of the storage capacitor and power management circuit during the charging state. In improving sensitivity, it’s critical to minimize the leakage current of these devices. Startup time TV-powered sensor node transmits data once per second over a 5 hour interval Seconds 1 10k 20k Activity rate 1 0.1 0.01 10k 20k Efficiency with duty cycling 60 (2 dBi TX gain, 6 dBi RX gain at 539 MHz) Aaron N. Parks, Alanson P. Sample, Yi Zhao, Joshua R. Smith % average power requirements. The majority of the time is spent in a low power mode, waiting for a specified charge to accumulate on a storage capacitor. When enough charge has been collected, the system switches to an active state and performs one Sense → Process → Transmit operation. The cycling period is therefore determined by the amount of power available. Startup time, activity rate, and efficiency measurements for varying free space distance from a 1 MW TV transmitter. Type 1 Type 2 10 Hz The system is duty-cycled to reduce the 100 40 20 10k 20k Equivalent free space distance from 1MW TX (m)