Design and development of a smart wireless system for passive temperature sensors

The design and development of a smart wireless system for remote reading of a passive surface acoustic wave (SAW) sensor is presented in this paper. The SAW sensor is a lithium niobate wafer with an inter-digital transducer (IDT) with reflectors, which is inductively coupled to a microstrip meander antenna (ICMA). The reading system is a special FM radar, which transmits and receives FM electromagnetic signals. The transmitted FM signal is picked up by the ICMA which subsequently, converts into a SAW in the LiNbO3 wafer through the IDTs. These SAWs are reflected back to the IDTs by the reflectors, converted back to an electromagnetic wave and returned to the FM radar by the ICMA. The acoustic velocity varies as a function of the propagation characteristics of the SAW in the substrate and results in varying time delay of the echoes, which is detected by the system. The resolution and accuracy of such a system are investigated theoretically and experimentally. The operating principle is evaluated for a remote temperature measurement system. The salient feature of this system is that no power source is required at the sensor and thus is applicable for remote temperature sensing of propellant in barrel-launched adaptive munitions (BLAM), tank rounds and other munitions and missiles. This is also suitable for other remote reading SAW sensors such as indentity tags, wireless pressure sensors, wireless gas sensors, strain sensors, hospital sterilizer sensors, etc.