Modeling of passive wireless sensors for RFID tag applications

The design and modeling of a passive radio frequency wireless identification system based on surface acoustic wave (SAW) devices is presented in this paper. This radio frequency identification (RFID) system is developed based on the response of the reflected phase from a SAW device which consists of two or more arrays of SAW IDTs and reflectors with different IDT-reflector spacing. Pulse modulated signals are transmitted from a remote reader system and their echoes are returned with different time delays due to the different IDT-reflector distances. Corresponding IF signals are generated in a mixer and their phase differences can be used as an ID tag. Using coupled-mode theory of SAW, the phase characteristic was examined. The effect of relative distance between the two reflector arrays is demonstrated. Since this passive sensor is coupled with a small planar antenna, it is well suited for applications that require passive and conformal sensors for identification and tracking.

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