2.4GHz WLAN RF energy harvester for passive indoor sensor nodes

This paper presents the design and measurement results of an RF Energy Harvester aimed to power sensor nodes like temperature, humidity, chemical, or radiation in an indoor industrial or residential environment. The harvester operates at 2.42 GHz WiFi-WLAN frequency band. It consists of multiple microstrip patch antennas, power combiner, voltage quadruple Greinacher rectifier circuit, and a super capacitor to store the harvested energy. All elements are designed using low-loss Rogers RO3206 substrate. The impedance matching of the power combiner with a rectifier is a non-trivial issue due to change in diode impedance with the input power. The peak efficiency is measured to be 57.8% at 6 to 8dBm input power. In the presence of realistic -10dBm continuous signal, the system can charge a 33mF super capacitor to 1.6V in 20 minutes. This collected energy is enough to power 10mW sensor node for a period of more than 4 seconds to perform wake up, sense and transmit functions, and put a sensor back to sleep mode.