SAW Temperature Sensor and Remote Reading System

Abstract

A system for remotely reading a SAW temperature sensor has been adapted from an existing, commercially available personnelherchandise detector system. The SAW sensor is a Lithium Niobate wafer with an inter-digital transducer (IDT) which is directly connected to a small transducer which is directly connected to a small microwave antenna and two reflectors. The reading system is a special Fhl radar. The FM electromagnetic signal is transmitted by the system and picked up by the small antenna that is connected to the IDT and is subsequently, converted into a surface acoustic wave in the Lfib03 wafer, reflected by the reflectors, converted back to an electromagnetic wave and returned to the FM radar. The acoustic velocity varies as a function of the ambient temperature and results in varying time delay of the echoes, which is detected by the system. The resolution and accuracy of such a system arr investigated theoretically and experimentally. The operating principle is also suitable for other remote reading SAW sensors.