Finite element analysis of harmonic frequency for 2.4GHz SAW tags

Surface acoustic wave (SAW) radio frequency identification (RFID) tags were invented more than 30 years ago, but only nowadays the conditions are united for mass-application. A 2.4GHz SAW tag that is significantly smaller than earlier reported tags can be routinely produced with optical lithography. The operation principle of SAW tag is shown in Fig.1 [1]. When a SAW tag enters the monitoring range of the reader, an interrogating microwave signal from reader antenna is received by the tag antenna and then converted into a surface acoustic wave by the inter-digital transducer (IDT). The excited SAW propagates with a relatively low velocity compared to the speed of electromagnetic wave. Several reflectors locate at the SAW propagating path on the tag surface, and each reflector gives rise a partial reflection of the interrogating pulse. After a certain delay, which is proportional to the distance between the reflectors and the IDT, the reflected SAW is reconverted into an electrical signal by the IDT and is retransmitted by the tag's antenna as a microwave signal to the reader.