A SAW Passive Wireless Sensor System for Monitoring Temperature of an Electric Cord Connector at Long Distance

This paper proposes a surface acoustic wave (SAW) passive wireless sensor system for monitoring the temperature of the electric cord connectors. The low-loss sensor consists of a temperature-sensing high-Q SAW resonator, a small antenna and a matching circuit. The resonant frequency of the SAW sensor is varied with the temperature. While the interrogational signal is a sinusoidal burst, the response is a damped resonant signal. In order to detect the weak response signal, an ultra-high-sensitivity receiver with a low-noise amplifier, a programmable gain amplifier (PGA), a high-precision correlation detector, and an active 8th-order bandpass filter is designed. A method for decreasing coherent noise is used in transceiver system. To track precisely the resonant frequency of the sensor, a high-resolution hardware direct digital synthesis (DDS) signal source with a wide changeable frequency range (1MHz) is implemented. A small-size prototype instrument is built. The maximum detecting distance of the sensor system is over 20 meter at a transmitting power of 24 dbm, and a temperature measurement resolution of 0.1 degree can be obtained.