Research On Super Resolution Measurement Method Of Wireless Passive Surface Acoustic Wave Sensors

The resonant wireless passive surface acoustic wave(SAW)sensor can realize the measurement of long-range wireless passive parameters by extracting the frequency of the resonant echo signal.And the sensor can be used for Various complex environments,such as high temperature,low temperature,high voltage,high acceleration,strong corrosive and strong electromagnetic fields.The existence of these advantages has made SAW wireless measurement technology be valued.With the development of SAW wireless measurement technology,there are many problems that are difficult to solve,mainly including:(1)The echo signal energy of passive SAW sensor is low and the effective signal duration of echo signal short.So in various complex environment,the echo signal is interfered easily.And the SAW sensor is not intelligent.it could not distinguish the error echo signal.Therefore,the reliability of the measurement results is poor.(2)In the case where the measurement distance is less than 5 m,there is no special algorithm to estimate the frequency of the resonant surface acoustic wave echo signal.Traditional algorithms are often used,such as the Fourier transform(FT)method and the singular value decomposition method(SVD)and so on.However,the resolution of the FT method is limited by the effective signal duration of the echo signal,so the resolution is low.Although the resolution of the SVD method is higher,the frequency estimation has large fluctuations occurred when measurement non-stationary SAW echo signal.it will change with the measurement distance.(3)When the measurement distance is greater than 5 m,the energy of the echo signal has been seriously attenuated.Although the reader can still receive the echo signal,the effective signal duration of the echo signal is already very short.There are currently no effective algorithms that enable high-precision measurements with extremely short effective times.Through the research of signal processing algorithms,the resolution,accuracy and reliability of wireless passive surface acoustic wave sensor measurement system is improved.The main contents of the research include:(1)According to the characteristics of the surface acoustic wave echo signal(mixed signal composed of a sinusoidal signal with equal amplitude oscillation and a sinusoidal signal with exponential decay),the signal model is established.Through analyzing the time-frequency character of the echo signal,A "screening method for echo signals of surface acoustic wave resonators" is proposed.The method can effectively distinguish the interfered echo signal,the masked echo signal and the shadow echo signal from the normal echo signal.The echo signal quality can be evaluated effectively in real time.(2)If the measurement distance is within 5m,that is,the effective signal duration(equal amplitude oscillation sinusoidal signal)accounts for more than 10% of the whole echo signal,this paper proposes a high accuracy and high stability frequency estimation algorithm,"Digital frequency significant place tracking method".The frequency estimation obtained by this method not cause large fluctuations with change of the measurement distance,and the method can determine the number of significant digits of digital frequency according to the difference of signal-to-noise ratio.The larger the SNR,the more significant numbers are determined.(3)If the measurement distance is between 5m and 18 m and the effective time ratio is very small(10% to 2%),a "super-resolution frequency measurement method" is proposed.This method uses convex optimization to recover the details of the spectrum.Even if the number of effective observable sample points is only about 10,the frequency estimation of the echo signal can be completed with high precision.