表面聲波式射頻識別標籤在無線感測之應用

Abstract

Devices based on surface acoustic wave (SAW) are applied to wireless communications, such as passive SAW based radio frequency identification tags (SAW RFID tags). They can be operated in some harsh environments. Due to the wireless capability, they are also suitable for remote monitoring and sensing. For SAW based RFID tags, the operating frequency and number of possible codes are both critical. In this study, the interdigital transducers (IDT) are operated in their higher harmonic modes to achieve to 915MHz. Moreover, a new idea of decimal coding scheme will be introduced to increase the number of possible codes. First, the Abbott’s coupling-of-modes model is used to simulated and analyze the frequency responses of SAW based RFID tags. Furthermore, inverse fast Fourier transform is applied to transform the responses into time domain. The information of tags is obtained and decoded. Using the simulation results, the three-finger IDT and double-electrode IDT are analyzed along with their harmonic responses, and the new idea of decimal coding scheme is also introduced. Finally, the SAW RFID tags with central frequency of 915MHz are fabricated on the 128°Y-X LiNbO3 using Nano/Micro-Electro Mechanical Systems (N/MEMS) techniques. The experimental result and simulation results are compared, and the new idea of decimal coding proof to be achieved. In conclusion, the study utilized the COM theory to analyze SAW based RFID tags. The tag with improvement decimal coding scheme can include more data bits, and has smaller die area (i.e. lower cost)