Wireless sensor system using surface acoustic wave devices

A new RFID tag system has been designed by utilizing a reflective surface acoustic wave (SAW) delay line. A shear horizontal mode SAW (SH-SAW) has the unique characteristic of complete reflection at an edge normal to the direction of propagation. This characteristic makes it possible to construct a reflective delay line. The reflective delay line can be used to construct passive sensors that measure from a remote location. In this paper, a reflective SAW delay line is utilized to fabricate a passive sensor and radio frequency identification (RFID) tags. Experimental results showed that the reflective delay lines are very suitable in making SAW RFID tags. Moreover, some applications of the SH-SAW RFID tags are demonstrated for measurement of the acoustic properties of liquids and strain of solid.