Wireless sensor marking and temperature measurement with SAW-identification tags

A wireless sensor marking system based on surface acoustic wave (SAW) identification tags is presented. The proposed solution is compatible with existing measurement systems and can be applied directly in the sensor or by means of a unique sensor identification cable (SIC). The SAW tag operates completely passive, and withstands temperatures up to 400 °C as well as shocks up to 35 000 m/s2. It contains a unique serial identification number, which is encoded on the high-temperature stable SAW device by means of metallic reflector gratings. The interrogation unit uses the sensor cable for transmission but is not directly connected to it, thus the identification system can be even used with high impedance measurement equipment, e.g. charge amplifiers. Interrogation is done in frequency-domain based on well-known radar principles and is realized in a low-cost add-on circuit to the existing sensor evaluation circuitry. Furthermore, by simply enhancing the evaluation software, a temperature measurement of the SAW tag itself, and thus often of the sensor or the sensor environment can be done without additional hardware requirements.