Battery-free wireless sensors for industrial applications based on UHF RFID technology

This work provides an overview of the current state-of-the-art of the RFID technology in the Wireless Sensor Network (WSN) field. The different RFID alternatives are described with their pros and cons. The benefits and limitations of battery-free wireless sensors based on RFID technology are presented. Subsequently, the paper describes the design of an UHF RFID integrated circuit (IC) designed to harvest and store the power from an incoming RF signal in order to supply low power analog or digital sensors. The IC has been implemented using a low cost 0.35 μm CMOS process and it incorporates a serial peripheral interface (SPI) in order to communicate with the sensor. Battery-free wireless operation for industrial monitoring using the designed IC has been demonstrated by implementing two wireless sensors that monitor both temperature, using a thermistor, and pressure, using a commercial digital sensor. The wireless temperature sensor shows an error below ±1°C from -25°C to 105°C, whereas the pressure sensor error is below ±2 mbar from 325 to 1000 mbar. A battery free communication range of 1.5 meters is demonstrated for both sensors using a 2-W effective radiated output power reader.