Design of a cellular energy-harvesting radio

Wireless sensor networks often suffer from battery power drain below threshold values. If the battery is not replaced, the sensor node expires. To remedy the situation, we propose a system design that allows for instance an nRF401 radio to wake up and transmit data above its threshold battery level of 2.7 V. The proposed cellular energy-harvesting circuit (rectenna) basically consists of a receiving antenna, rectifier circuit and a gold capacitor accumulator. Operating at 24.7 percent efficiency, the rectenna managed to accumulate 500 mV above 2.7 V of the nRF401 battery voltage in 10.4 days. The nRF401 radio woke up after the 10.4 days with 3.2 V battery voltage and was able to flash 312 packets at 1250 bps in 10 seconds before the battery drained to 2.7 V threshold. Each packet is 5 byte long. The transmission range is between 80 m and 110 m, given effective transmit antenna length of 6 m and 9.5 m respectively. Effective receive antenna height of 1.8 m, and constant received power of -25.7 dBm (2.79 uW), typical of incident cellular signal power was assumed. In this system design, the nRF401 radio is supervised by a PIC16F877A microcontroller.