Wireless Passive SAW Sensor System And Its Typical Application

As the core foundation of Internet of Things(Io T),the importance of wireless sensing technology is self-evident,especially in healthcare and industrial high-temperature monitoring scenarios.In the field of healthcare,current medical devices are bulky,expensive and not suitable for home use,while wireless passive Surface Acoustic Wave(SAW)sensor systems are miniaturized,portable and low cost,which can be better applied to human wearable medical devices.In the field of high-temperature monitoring,the ranges of current sensor systems are usually small and the measurement accuracy is low.In addition,they are susceptible to complex industrial environments.In contrast,wireless passive SAW sensor systems can be leveraged in harsh environments with high sensitivity,and thus have great potential for application in industrial environments.This paper designs and implements a wireless passive SAW sensor system with the following main research contents.1.Explain the basic composition and working principle of the SAW sensor,propose a design method of resonant quartz SAW sensor,and prepare it by a semiconductor process.With the 3D finite element simulation function of COMSOL software,the effects of the delay line length of the forked finger electrode,the number of reflective grid pairs,and the number of forked finger pairs on the quality factor of the SAW sensor can be analyzed.Then the dimensional parameters of the SAW sensor with the resonant frequency in the national radio frequency band of 433 MHz can be obtained.With the semiconductor process,SAW devices are designed via the parameters configured in the simulation,and the SAW devices are tested to meet the simulation results.2.Design and fabricate three types of SAW sensor antennas for different scenarios with the frequency of 433MHz: microstrip antenna,spiral antenna and dipole antenna.Based on the working principle of microstrip antennas,design and fabricate microstrip antennas using antenna miniaturization technique with the help of HFSS electromagnetic simulation software.Study the effect of pitch and number of turns on the antenna of normal spiral antenna,verify the consistency of the antenna's simulation results and experimental results.Based on the principle of the dipole antenna,research the effect of antenna arm folding on antenna,design and fabricate planar folding dipole antenna on 300 um thick quartz wafer.3.Complete the hardware and software design of the system reader.From the workflow,I choose frequency domain sweeping as the transmitting mode,mixing and power detection as the receiving mode,and then design the reader's hardware,including transmitting link,receiving the link,RF selector switch and main control module.In this fashion,the development of the reader program with different working modes can be completed.Finally,the PC-based host computer is achieved with the help of Py Qt,which can interact with the reader through the software interface.4.Complete the application of the system in the field of human respiratory real-time monitoring and industrial high-temperature real-time monitoring.For obstructive sleep apnea syndrome,the respiratory testing scheme of SAW sensor with graphene oxide as the sensitive membrane is used to test the effect of different thicknesses of graphene oxide on the response time,respiration time and amplitude during respiration measurement.Then the system can be verified to characterize human respiration in real-time accurately.In addition,the SAW sensor and spiral antenna of this system are calibrated and applied to a real industrial high-temperature environment,and the results demonstrate that the system works within 2% of the error.