Wireless remote passive temperature sensor for monitoring food

摘要

A passive wireless temperature sensor with a loop antenna is placed in a remote environment for exposure to its changing temperature conditions. The sensor includes a coil of wire wrapped around a cylinder to form an air-core inductor. The cylinder contains a small amount of eutectic material similar to a conventional thermometer which has the property of being magnetic. A capacitor is connected to the coil of wire to form a resonant LC “tank” circuit. As temperature increases, the eutectic material expands through the cylinder at the core of the inductor causing an increase in inductance and corresponding decrease in the resonant frequency of the LC “tank” circuit. The temperature of the remote sensor is proportional to resonant frequency and can be determined by generating an oscillating signal and measuring resonant frequency of the remote sensor.