Study On Surface Acoustic Wave Pressure Sensors And Their Wireless Passive Measuring System

With the rapid development of industrial internet of things and military wireless sensor network technology in the background of the information age,it has important academic significance and application value in enriching wireless passive sensing means and methods and promoting the application of acoustic surface wave(SAW)sensors in industrial and military fields,that we try to study the pressure sensors based on the surface acoustic wave technology and explore the wireless passive sensor measurement technology and its system construction.The theoretical analysis,project design and experimental research about the SAW pressure sensors and their wireless passive measurement systems were carried out,and its application in industrial and military fields was discussed.Firstly,the historical background of SAW sensor technology was described,and the research status of SAW pressure sensors and wireless passive measurement system was analyzed,on this basis the basic research ideas and contents were put forward.Scondly,the performance and application characteristics of the two kinds of SAW sensors,namely the delay lines type(SAWDL)and the resonator type(SAWR),were analyzed and compared after accounting for the basic composition and working principle of the SAW devices.The propagation equation of SAW in non-piezoelectric medium and piezoelectric medium was each deduced in detail,and the SAW velocity in free condition was solved.By using the effective elastic coefficients which introduces external pressure and the general Green's function,the velocity variation of surface acoustic wave can be solved.The numerical calculation of SAW velocity in piezoelectric medium under surface pressure was done,which verified that there is good linear relationship between the pressure increment and SAW velocity increment.Then,the main factors affecting the performance of the SAW resonator sensors were analyzed,thus we knew how to design the SAW pressure sensor with high sensitivity.From the intrinsic sensitivity of the SAW device,the SAW pressure sensor with surface sensitive structure,which is non-packed and can be directly affected by the external pressure,was studied.And the test showed it has high sensitivity(725Hz/kPa or 889Hz/g),while its repeatability error and consistency error are not good.The simply-supported-beam SAW pressure sensor with a double-paralell-four-spring guiding mechanism,was designed on the basis of comprehensive consideration of all key factors affecting the performance of the SAW resonator sensors.In the design,the external pressure guided by the guiding mechanism was exerted on the centre area of the simply-supported beam,and the sense signal was achieved by the wire from the anchor position of the beam.The simulation results by the ANSYS software showed that the ratio between the deviation displacement(horizontal direction)and the effective displacement(vertical direction)of the guiding mechanism is only 0.21426‰ in the course of pressure transporting.Test was designed and taken,which showed the simply-supported-beam SAW pressure sensor with guiding mechanism has a high sensitivity(520Hz/kPa or 425Hz/g),and both its repeatability error(1.71%FS)and the consistency error(1.41%FS)are very small.Furthermore,the working principle of the wireless passive SAW measuring system was described,and the working link and each key component of the system were analyzed in detail.We set up the wireless passive pressure sensing and measuring system with virtual instrument(VI),on the basis of the design of each key component,including the stimulus signal source,the switch,the measuring/sensing antenna,the AGCA circuit and the EMC circuit.Especially a frequency estimation method based on the Welch method and the improved Rife method was put forward,which can both decrease the measuring error and improve the measurement resolution.Experiment was designed and made based on the professional VI experimental setup,and the result showed the system has a effective measurement distance of 5 meters.In the effective distance there is only a little error of 0.8% between the performance curve achieved by the system and by cable measurement using a network analyzer.And the system runs well where the electromagnetic environment comprehensive field strength is 1.6V/m in the bandwidth of 100Hz~10GHz.Finally,the demand of wireless passive sensors used in the special application surroundings was analyzed,and the future of its application in industrial and military fields was described.The SAW pressure sensor was utilized in the two military projects,namely the pressure and temperature monitoring system in the assemble course of some sort equipment and multi-sensor net node.In allusion to the system implementation of the two projects,the feasible design ideas were provided and discussed.