Wireless Passive Remote Sensing with Saw Resonators and a New Solution for Identification Problems in Multiple Sensor Systems

There is an permanently increasing interest of the marked in solutions for wireless remote sensing applications during the recent years. Such important physical quantities as pressure, temperature, strain, torque etc. are to be detected on rotating or inaccessible parts of machines, power plants or other conceivable structures without power supply. Furthermore sensor applications for aggressive environmental conditions like high temperatures etc. are possible. Surface acoustic wave (SAW) devices - especially SAW resonators (SAWRs) - are a kind of sensitive elements in such sensor systems which fulfill these requirements in an excellent way. SAWR sensors have been proved to be excellent high Q sensing elements which are using the advantages of their sensing elements: high sensitivity, accuracy, long-term stability, the possibility of storing electromagnetic energy and the function without batteries. When a SAWR is interrogated by a RF sine burst the stored energy will cause an attenuated oscillation after switching off the exciting signal. This SAWR response can be used for sensor applications. Based on the differential measurement method the suppression of unwanted dependencies of the radio channel and the increase of the sensor sensitivity is possible by using double SAWRs. In the paper improved SAWR sensor designs for pressure and temperature and their measured results will be presented in the paper. SAW devices are characterized by particularly good coding and correlation capabilities which is used in matched filter application.