Research On Wireless Passive Surface Acoustic Wave Device And Sensing System

The surface acoustic wave(SAW)device is based on the piezoelectric effect of the material to realize the transformation between the electrical signal and the surface acoustic wave signal through the structure of the interdigital transducer(IDT).Surface acoustic wave signal transmits in the piezoelectric substrate surface,and its transmission characteristics influenced by the surrounding environment,therefore SAW devices are widely used as a physical quantity,such as temperature,humidity,stress and strain sensors.If a chemical sensitive film is placed on the transmission path of the surface acoustic wave,the SAW device can also be used as a chemical sensor or biosensor.The surface acoustic wave sensor has the characteristics of wireless passive that can adapt to a variety of complex and harsh environments,and has a unique application prospect in extreme scenarios such as high temperature,high speed and high pressure.In addition,the surface acoustic wave sensor can also realize the function of radio frequency identification(RFID),in which the sensor and label recognition functions are integrated to realize multi-point real-time perception.Wireless passive surface acoustic wave sensor and system have become a research hotspot in recent years and it has extensive practical value.In this thesis,the principle,structure characteristics and preparation technology of SAW sensor are described.The theory design and finite element analysis(FEA)of the SAW sensor of resonant and delayed linear structure are carried out,and then we fabricate the SAW device and test the performance.The results show that the Quality factor of the resonant SAW device is 1760,and the delayed linear SAW device can realize the 8-bit coding function,which conforms to the design expectation.On this basis,the reader of SAW sensor system was analyzed and studied.We proposed a system scheme based on FPGA and power detection technology,designed PCB circuit,and tested the performance of each functional module.The main work and achievements of the thesis include:1.On the 128° Y tangential lithium niobate piezoelectric substrate,we design,simulate and fabricate the resonant SAW device.We carried out the finite element analysis using the Comsol Multiphysics software to analyze the displacement field distribution of the particles in the resonance case,and the resonant frequency obtained is consistent with the theoretical analysis.The resonant SAW device was tested by a vector network analyzer.The resonant frequency is 428 MHz and the Quality factor is 1760,which is consistent with the theoretical analysis and the finite element simulation.The relationship between the resonant frequency and the temperature of the device was measured.The measured results show that the resonant frequency and temperature of the device are linearly negative with good temperature sensing properties.2.On the lithium niobate piezoelectric substrate,a delayed linear SAW device with 8-bit radio frequency label coding was designed and simulated.The radio frequency label coding was realized by the distribution of the reflector in a fixed position,where an existing reflector represents code 1 and no reflector represents code 0.By using finite element method,the time domain signal of the device was simulated and the corresponding coding situation can be clearly identified.The network analyzer was used to test the time-domain echo characteristics of the SAW device,and the results showed that the delay line SAW device of this structure can realize the 8-bit coding through reflect grating,which was comply with the design expectations and can be used to make radio frequency identification.3.Designed a based on FPGA and power detection technology of surface acoustic wave sensor reader system,the reader system includes RFtransmitting module,RF receive module,as well as signal control and processing module.The signal control and processing module is based on FPGA implementation,and the parameters of RF transmitter module and RF receiver module are controlled,and the received signals are analyzed and processed.After testing,the RF transmission circuit able to transmit 433 MHz frequency signal stability,conform to the wireless radio frequency passive surface acoustic wave sensor system demand information signal,the signal frequency and timing can be adjusted by the FPGA real-time.The signal received by the receiving circuit is transmitted through the variable gain amplifier then reach the power detection module.The power detection module can realize the conversion of the power signal to the voltage signal.