Design And Implementation Of Surface Acoustic Wave Delay Line Sensing System

With the urgent demand for high-precision,integrated and high-frequency core sensing components for Wireless Communications,Artificial Intelligence and Internet-of-things,Surface Acoustic Wave(SAW)sensors become a research spotlight in sensor research field because of the high sensitivity,ease of integrate and wireless.Through the research of SAW sensing system with strong stability and high integration,SAW sensor is expected to be widely used in the fields of intelligent technology and smart construction.At present,SAW delay line sensing system is mainly composed of two parts:SAW sensor and matching circuit system,both of them are indispensable.This paper studies SAW delay line sensor system.The content is divided into two parts:one is the design,fabr:ication and testing of SAW delay line sensor macroscopic system,another is the design of FPGA-based SAW delay line sensor semi-integrated system.About the SAW delay line sensor macroscopic system,around 300MHz SAW delay line sensor,macroscopic system was designed through the reasonable analysis of SAW sensor sensing mechanism,system stability and anti-interference ability.The macroscopic system consists of two parts:the lower computer and the upper computer.1)In the lower computer hardware,the front-end sensing circuit is composed of a two-channel SAW sensor oscillating circuit.The stable output of high-frequency sinusoidal signal was realized by adopting a two-stage closed-loop amplification structure to design the high-frequency oscillating circuit with introducing a third-stage amplifier into the loop output end.The mixing circuit was designed based on AD831 chip,the hardware consumption can be effectively reduced by down-converting dual-channel high-frequency signal to obtain low-frequency signal.Introducing low-frequency signal conditioning module can effectively improves the reliability of frequency detection.According to the application requirements,common functions such as sound and light alarm,upper computer communication were realized by designing the multi-function expansion module.The power management module with multi-voltage output capability was designed to meet the needs of power supply,which ensures the stability of the system.The lower computer software mainly realizes the driving of sound and light alarm module,the information processing of display module and the matching of the serial communication protocol of the upper computer.2)In terms of upper computer,based on the Lab VIEW development platform,the upper computer application program was designed to realize multi－node sensor information monitoring,user login management,serial port communication,and historical data viewing.Anti-false warning algorithm was added to the multi-node sensing information monitoring design,and misjudgment was effectively reduced.Finally,SAW delay line sensor macroscopic system was successfully fabricated through the design,welding and debugging of the lower hardware PCB,and related performance test and analysis were carried out.About FPGA-based SAW delay line sensor semi-integrated system:According to system demand and functional requirements,the system design was determined.Design and simulation of the algorithm,hardware circuit and timing control of this system were performed.1)In the aspect of algorithm,design of feedback frequency sweeping DDS based on FPGA provides reliable excitation signal for SAW sensor,and solved the problems of traditional DDS fixed-point/frequency sweeping inflexibility and low logic resource utilization.The feedback positioning algorithm,closed-loop feedback pipeline algorithm and ROM compression algorithm were simulated to verify the feasibility of the logic design.2)In the aspect of hardware circuit design and timing control,AD9767 chip was selected to realize digital-analog conversion;CG2185X2 chip was used as the core component to design an RF switching circuit,and the timing control of the RF switching circuit is designed to verify the logic function.In addition,the MAX2614 chip was selected to design a low-noise amplifier circuit and achieve high gain of the RF signal under the condition of low noise.The semi-integrated system provides the lab with the technology to quickly test SAW devices,which lays the foundation for building an integrated wireless sensing platform.In this paper,the macroscopic system of SAW delay line sensor was designed and fabricated.The performance test and analysis show that the system is stable and the circuit design is reasonable.Based on this,a design scheme of semi-integrated sensing system based on FPGA was proposed.Functional simulation verification of algorithms,hardware circuits and timing control were done.This work is not only an extension of the macroscopic system design,but a necessary link to achieve the integration of the sensing system.This study has great significance for the miniaturization,integration and practical application of the SAW delay line sensing system.