Remote sensing of physical parameters by means of passive surface acoustic wave devices ("ID-TAG")

Surface Acoustic Wave RFID Tags

“…The main feature of SAW RFID tags (Reindl & Ruile, 1993;Schmidt et al, 1994;Plessky et al 1995;Reindl et al, 1998;Hartmann, 2002) is that they do not use any autonomous power supply such as batteries. Moreover, they do not include any such circuitry that would need to be powered.…”

“…Comparison of the phases of the interrogation signal and the tag response signal permits a direct and accurate measurement of the tag temperature (Schmidt et al, 1994;Reindl et al, 1998;RFSAW, 2004). SAW tags thus have an inherent capability of functioning as sensors.…”

A wireless SAW-based temperature sensor for harsh environment

“…The device is processed on a YZ-cut Lithiumniobate, LiNbO 3 , crystal substrate ( suited material for temperature measurements because of its large temperature coefficient of delay (TCD) of -94 ppm/°C and its high electro-acoustic coupling factor. Up to now this material proved to be the only available SAW substrate valid for the operation both at radio frequencies near 2.4 GHz and at high temperatures [4]. The YZ propagation direction has also been chosen because of its low SAW diffraction effect and the in plane orientation of the pyroelectric vector.…”

“…This is due to the fact that SAW devices can operate even with very low signal levels at their input. SAW devices are also known to operate stable up to several hundreds of degrees, even up to 1000 °C for a short time [3,4]. For all these reasons, SAW devices are well suited for wireless temperature measurements in harsh environments: at high temperatures (HT), inaccessible and hazardous locations, in closed containers, at high voltage, in vacuum, on moving objects or rotating machine parts [1,4].…”

Ceramic patch antenna for high temperature applications

“…In case of a one-port SAW device only one IDT is connected electrically and all others are reflective. If such an IDT is connected to an antenna, the element can be employed as a passive wirelessly interrogable system [7,8]. Figure 1 points out the structure of such an ID SAW device.…”