Research Of The OFC And Its’ Derivative Coding For SAW Tag

In recent years,as the “nerve endings” of the networking technology,surface acoustic wave RF tag has attracted the interests of many researchers with its unique advantages.Various organizations like NASA,European Space Agency and CETC have invested lots of resources for the research of SAW RFID.The most common used RFID is in base of IC.But because of the shortcoming of its architecture of the data storage and the character of Si,the using field of IC-based RFID is limited.SAW RFID with a wide temperature limitation and a physical structure to store the information make it possible to use the RFID in some special field such as outer space,high temperature or high pressure environment,complicated electromagnetic surroundings.So SAW RFID cover the shortcoming of IC-based RFID and make the RFID system environment more perfect.In this paper,the basic theory and parameter of piezoelectric material are calculated.The basic structure and the theory to analysis the piezoelectric devices are introduced with the steps of δ model,COM model,P matrix model and the parasitic effects.Three correlated coding ways on the basis of OFC theory are introduced.The basic theory,transfer functions,space of adjacent frequencies and some other functions are derived for those coding ways.According to the analysis in time domain and frequency domain,the character of those coding ways can be directly showed in picture.By the combination of basic theory and the structure of OFC model,the parameters of P matrix can be calculated.The parameters in P matrix show the character of SAW device,including reflection coefficient,wear coefficient,pressure change coefficient,distributions of center frequencies and so on.By the analysis of those parameters,the performance of the OFC system can be ensured.A strategy to determine the value of frequency space factor for POFC system is prevented in addition.After that,an example of POFC system with the frequency spacing value of 1.5 is modeled to analyze.Also in this paper,an attempt is done to take the finite element analysis for a reduced OFC SAW RFID tag.The center frequency of IDTs can be got by the ananlysis of a 3D periodic model.The center frequencies of reflectors can also be extracted by the reflected signal in time domain from a one-reflector model.At last,the FEA for the OFC system can be done.By the reflected signal in both time domain and frequency domain,the frequency characters can be directly showed.