ABSTRACT
The operation of SAW devices is based on piezoelectricity, a coupling between a material’s electrical and mechanical properties [4]. In certain dielectric crystals, the application of mechanical stress produces an electric polarization and, conversely, such a crystal undergoes a mechanical distortion when an electric field is applied., The working principle of SAW RFID tags is as shown in Figure 1. High frequency electromagnetic waves are fired from a reader, after it is accepted by the antenna of SAW tags, passed through interdigital transducer, stimulating SAW on piezoelectric substrate. Then the generated SAW pulse propagates along the surface of the substrate, which is usually made of a material with strong piezoelectricity, such as lithium niobate (LiNbO3). The SAW pulse is partially reflected and partially transmitted by each of the code reflectors, placed at precisely determined positions on the chip. These reflectors usually consist of one or a few narrow aluminum strips. The reflected SAW pulse returning to the interdigital transducer carries a code based on the positions of the reflectors.
