Research On Signal Detection Of The Passive Wireless SAW Resonator Sensor

As a novel sensor, the surface acoustic wave (SAW) sensor can be used to measure different sorts of physical, chemical and biologic quantities. Compared with traditional sensors, the SAW sensors can be used for wireless passive sensing with no need for a separate power supply, which makes it possible to measure parameters of fast moving or rotating objects. In addition, wireless passive sensing in extreme environment likes strong electromagnetic interference and low temperature becomes obtainable.The major researches in this thesis include: applying the digital signal processing technology and theory of signal detection & estimation to estimate carrier frequency of the sensing signal that reflects the measurand; implementing the algorithm in LabVIEW, a virtual instrument development platform.Chapter 1 reviews the development of SAW technologies and SAW sensors; introduces classification and operating principal of SAW sensors; shows the research significance of passive wireless SAW sensors and introduces the main research contents of this thesis as well.Chapter 2 introduces the surface acoustic wave propagation property in piezoelectric substrate and the wireless sensing principal of passive SAW resonator; explains the construction, operation principal and flow process chart of the wireless interrogating system. (Chinese patent, ZL0222116022)Chapter 3 analyses the response signal of one-port passive SAW resonator, which is stimulated by wireless request signal; adopts the method of maximum likelihood estimate to measure the carrier frequency of the transient response signal.Chapter 4 designs and determines the parameters of the algorithm adopted in the instrument system. Analyzes and compares the different effects to frequency estimation when using digital filters with different group delay; determines the data length, a parameter of frequency estimation; introduces the method of available judgment of sensing signal and determines the judgment threshold as well. Chapter 5 introduces the flow process chart of the instrument system; evaluates the performance of frequency estimation in the system; measures the resonance frequency of one-port SAW resonator at different temperature.Conclusions are summarized in chapter 6 and the expectation on the further development of this subject is presented too. The experimental results show that it isfeasible to measure resonant frequency of passive wireless resonator and the corresponding measurand by using digital signal processing technology and theory of signal detection & estimation. At present, the detection distance of the instrument system is longer than 4 meters for 1 watt output mean power and the system runs stably, which indicates that the instrument system is possible to be put into practice in the future.