Research Of Surface Acoustic Wave Based Rfid Tag And System

Surface Acoustic Wave (SAW) tag is passive and can perform better in harsh environments than other passive RFID tag; so much attention has been paid to it.Theoretical analysis about SAW Tag system and reader is discussed. The emphasis of this paper was put on the improvement of identification probability, multi-tags identification and enhancement of accuracy in detection. A complete SAW tag system which includes SAW tag and reader is designed and manufactured. At first, theories on radiation field, antenna model, and antenna noise are introduced in this thesis.Secondly, different code methods of SAW tag are discussed and their merit and demerit are given. The influence of multi-reflection of SAW tag reflector is analyzed. The suggestion on selection of SAW tag material is proposed.Thirdly, the system structure of reader is discussed based on signal detection theory and free space propagation technique. The different composition and principle of time-domain sampling and frequency-domain sampling method are described and compared, as a conclusion, time-domain sampling method is chosen in reader designing here.Detection method of time-domain sampling is investigated, which comprises amplitude detection system, phase detection system and phase evaluation system. Amplitude detection can achieve higher detection probability when SNR is high, on contrary, frequency detection can achieve better detection probability when SNR is low. According with this fact, a fusion detection method depended on the working distance is proposed to improve the identification probability for single tag in this thesis.Fourthly, since SAW tags do not contain any intelligence, the question of multiple reads in the capture window comes up. The currently anti-collision methods are introduced. A new Walsh Matched-Threshold Filtering based anti-collision is proposed.Fifthly, the peak and position of reflected pulse are two main parameters of tag decoding. A weighted data fusion algorithm based on the matching pursuit (MP)-wavelet packet (WP) atomic decomposition method, which estimates the tag feature parameters of surface acoustic wave (SAW) is presented.Sixth, a total SAW tag system is designed successfully, which includes SAW tag and reader. The reader includes RF transceiver, analog-to-digital convertor with high speed, data processing etc. It can detect SAW tag signal by amplitude and phase. The improved radio channel can achieve more than 60dB isolation.Finally, test and experiment are made, the result indicates that the working distance reached over 4.5 meter by this own-made reader, it is proved also that the proposed theories and methods are correct and feasible.The creations performed in this thesis are:1. Fusion detection method depended on working distance is proposed to improve the identification probability for single tag;2. A new anti-collision method, the Walsh Matched-Threshold Filtering, used for multi-tags identification;3. To estimate the tag's information presented by amplitude and position using weighted data fusion algorithm based on the matching pursuit(MP)-wavelet packet(WP) atomic decomposition method;4. Designing and manufacturing a complete tag reader system successfully.