| Tags based on surface acoustic wave (SAW) techniques have the characteristics of wireless sensing, completely passive operation and high robustness against environmental impacts which make them superior to other techniques when used in a radio frequency identification (RFID) system. This paper has done some research on the SAW RFID system composed by tag and transceiver, especially argued on lowering the system cost, increasing the coding capacity and the identification rate in the low signal noise ratio (SNR), and preliminarily studied the problem of multi-tags anti-collision at the end of the paper.SAW RFID system usually adopts time domain sampling as the decoding method. Its transceiver works under the pulse-radar mechanism which can be described as impulsing analog signal of the single narrow pulse and measuring the impulse response of the tag. The main disadvantages of this method are described as follows: (1) to avoid the symbol interference of the two returning impulse among the unit impulse signal, it is advised to select a high-bandwidth signal of the inquiry, but it is often limited by the industrial scientific medical (ISM) bandwidth regulation. (2) sampling the transceiver's access to time-domain signal on the high speed, it call for the good performance of the A/D conversion and transmission and reception (T/R) switch. Therefore, this paper has adopted frequency domain sampling as the decoding method, directly receiving the frequency domain function of the tag system. The traditional measurement method of frequency domain sampling is to use the inverse Fourier transform to change the measured frequency-domain signal into time-domain signal which is for the follow-up deal. But with the decrease of the bandwidth, the time-domain resolution will reduce. So, frequency-stepped continuous wave (FSCW) can be used as the transmitting signal, and the high-resolution arithmetic to pick out the frequency information of the mixer signal from the echo and the launch signal to decode.This paper has presented theory and technology on the SAW ID-tag, including: the structure and character of each component, the general framework of the SAW tag, the indicators of the performance measurement on the substrate cut and the common used coding scheme. As for the factual application of this paper, the single-phased unidirectional interdigital transducer (SPUDT) inline structure is adopted as the framework of the SAW ID-tag, the LiNbO3 crystal is chosen as the substrate material, the basic rule of the selection of the optimum cut is promoted, and the computational program of calculating the indicators of the performance measurement on the substrate cut is established. According to the computational results, the optimum cut is finally determined at the (0?, 37.86?, 0?). This paper has also made out the coding scheme with self-check function to meet the needs of high capacity encoding.This paper has adopted the method of finite element method/bourndary element mothod (FEM/BEM) based on the generalized Green function and source regeneration mothod to compute out the influence of electrode framework, electrode number, electrode thickness and metallization ratio change on the reflection, transmission and scattering of the reflector, on which the guide line of the reflector design is promoted, that is, to compensate the loss brought by transmission and bulk wave scattering, it is reasonable to adopte suitable electrode framework and change the electrode thickness or the metallization ratio.This paper has analyzed and designed the transceiver in detail. Based on the working principle, this paper has set up the model of transmission and reception, promoted the information theory to pick out the number of the reflectors, introduced several frequency estimation methods and comparing their computational complexity. This paper has designed each functional module of the transceiver. Considering the difficulty of T/R separation under CW structure, this paper has designed a T/R separation scheme based on the directional coupler and the Schiffman style 180o hybrids,the isolation can be not less than 60dB. The receiving part of the transceiver has also adopted zero-intermidiate frequency (zero-IF) receiver in order to reduce the cost further more.A SAW RFID system based on the frequency domain sampling is made out and progressed in the experiment. The experiment has made the SNR as the important factor judging the system performance, and compared the performance of information theoretic criteria in calculating the number of reflectors and the accuracy and resolution in frequency calculation of every algorithm. At last, the MMDL criterion and the PRO-ESPRIT arithmetic of the least computation and best performance under low SNR are adopted.Through the primary research on the multi-tags anti-collision problem of SAW-RFID system, the resolution based on the smart antenna is promoted. Its process can be described as: the use of the direction of arrival (DOA) to figure the space position of every tag and genetic algorithm (GA) to pick up DOA has created the corresponding array weight vectors; then, the main beam is formed according to the array weight vectors, separately pointing to every direction of tags under identification; at last, every tag is renewed and recoded. The simulation operation has verified its initial feasibility.
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