Key Technologies For Performance Enhancement In SAW Resonator Wireless Passive Sensor

Compared with traditional temperature sensor,passive and wireless surface acoustic wave(SAW)resonator sensors have characteristics such as long life,low cost and wide temperature measurement range.Besides its advantage that works without external power supply SAW sensor can also be used in harsh environment such as high temperature and strong magnetic.All these advantages make SAW sensors popular in engineering field such as aeronautics and astronautics and automation.However,there are some problems that need to be solved.The query and demodulation system of available readers can't be changed after production.The measurement distance and accuracy needs to be improved.Also the measurement data is easily interfered by electromagnetic waves from the environment.To address these problems,some key technologies for performance enhancement in SAW resonator wireless passive sensor are studied,including three main parts: enhancement of query and demodulation algorithm based on general reader,the influence of external circuit on SAW resonator transient response characters and error correction method for SAW measurement temperature data based on adaptive Kalman filter.The results can also be applied to enhance the performance of SAW sensors in other measurement field.The query and demodulation method of available readers is fixed which means they can't be changed according to demand after production.Software defined radio technology and USRP B200 are used to design general reader development platform.With this platform we can generate customized conventional interrogation programs such as dual-frequency synchronous query in short time.With this general reader it's verified that the digital IQ demodulation algorithm can quickly determine the frequency offset of the resonant frequency of SAW sensor which lays the foundation for optimizing the query strategy and improving the query speed.This general reader development platform can meet the pre-development process validation requirements and offers high flexibility.In order to further improve the wireless,passive SAW resonant temperature sensor measurement distance and accuracy,the equivalent model of SAW sensor,antenna and matching circuit is established and the parameters of sensor equivalent circuit are extracted.Based on the theoretical analysis,the influence of antenna on the length,amplitude and frequency of sensor echo signal is simulated and the principle of SAW sensor antenna impedance design is given.The influence of the series and the parallel matching circuit on energy and frequency of echo signal is obtained.Parallel matching circuit is selected as the solution to improve the energy of echo signal.And the optimal matching inductance values of single-resonator and dual-resonator SAW sensor are calculated respectively.Finally,the effectiveness of the parallel matching circuit is verified by experiments.In the practical application of passive wireless SAW temperature measurement system,the signal received by reader is often interfered by electromagnetic waves from the environment.These interferences will make the reader get wrong measurement data.One new adaptive algorithm is presented,which is fault-tolerant to outliers and achieved in the framework of Kalman filter.Polynomial prediction is used to describe the time-variant system model.The variance of measurement data is estimated using the wavelet transform.By introducing the difference between the measured value and the corrected value as a statistic,the algorithm can distinguish the data that affected by interferences and improve the precision of the system.