In-situ Temperature Measurement Using In-Contact Thin-Film Sensors and Radio Frequency Identification (RFID)

Abstract

Radio Frequency Identification (RFID) has proved to be a better alternative for barcode technologies in logistics and consignment tracking. Unlike the optical technologies (say., barcode, QR code, etc), RFID does not depend on the line of sight for communication. Instead, it uses Radio Frequency (RF) electromagnetic waves for data transfer. RFID works on the principle of impedance matching between Interrogator and passive RFID tag. This principle could be utilized to measure the impedance of passive temperature sensors based on a passive RFID tag for measuring temperature. The impedance of a receiver antenna can be easily measured wirelessly from the transmitter power requirements in the near-field (λ/2π) of the transmitter antenna. In the passive temperature sensor, impedance changes as a function of the surface temperature. When this sensor is connected in series with a receiver antenna (predesigned impedance) of an RFID tag, sensor impedance could be read wirelessly from the RFID reader (interrogator). Also, the impedance measurement of the sensor depends on the distance of separation between the transmitter and the receiver. This distance is measured by adding an auxiliary Ultra High Frequency (UHF) RFID tag alongside the sensor RFID tag, which helps in measuring the distance using Received Signal Strength Indicator (RSSI) or reflected power. The sensor tag would be using either LF (125kHz) or HF (13.56MHz) passive tag, not to interfere with the auxiliary UHF tag. Since only the antenna impedance is altered by the sensor, existing anti-collision algorithms can be utilized to read multiple tags using a single reader.