Wireless SAW based high-temperature measurement systems

The paper exemplifies the development of a surface acoustic wave (SAW) temperature measurement system, showing the advantages of wireless data transmission and passive sensor operation. It includes results of research on lithium niobate, langasite and gallium-orthophosphate, three piezoelectrica used as substrate crystals for the SAW devices. Critical parameters, limits and prospects of the materials as well as technological issues concerning the metallization and the lifetime of reflective SAW delay lines are discussed. The packaging and assembly of high temperature (HT) stable transponders is explained. A slot antenna, a patch antenna and a dipole antenna, thus providing maximum flexibility for the sensor geometry, are investigated. A phase matching algorithm, enhancing the measurement resolution by two orders of magnitude compared to a conventional peak detection algorithm, is described. A fully integrated SAW temperature sensor system is presented, basing on a frequency modulated radar operating in the 2.45 GHz ISM band and designed for a world wide legal usage