A Research Of Temperature And Strain Characteristic Of SAW Sensor Based On LGS Substrate

Surface acoustic wave device is suitable for sense in harsh environment such as high temperature,high pressure,high-speed movement or rotation and harm or toxic for its characteristic like small volume,high quality factor,fast response and passive and wireless capability.With the growing demands of structure health monitor in aerospace and manufacture,SAW sensors that can work passively and wirelessly have wide application prospects.Thus,the research on SAW sensors that monitor temperature and strain in harsh environment has very important significance.In this paper,a piezoelectric substrate Langasite?LGS?,which has excellent hightemperature and strain characteristic,was adopted to fabricate SAW sensors for monitoring temperature and strain.The sensors designed in this paper had resonator structure;the IDT deposited on the LGS substrates contained 100 pairs of electrodes with finger width of 2?m,the metallization ratio is 0.5 and the aperture length is 100?.The distance between IDT and reflector bank is 6?m.The simulation of the sensor was conducted with software COMSOL Multiphysics.In this work,microelectronics technology was used to fabricate SAW resonators on LGS substrates with Euler angle of?0°,138.5°,27°?.With the optimization of the technological parameters,we have successfully fabricated SAW sensors with high quality.In this paper,we studied the temperature characteristics of the LGS sensor.The range of the temperature is 20? 400?.LGS sensors have maintained excellent SAW characteristics under different temperature,the resonate frequency of LGS sensors decreased with the increase of the temperature.The first and second of temperature coefficient of frequency are 4.229×10^-4 and-2.034×10^-5 respectively.In order to verify the temperature repeatability of LGS sensors,we have conducted temperature circulation test,the result showed that the repeatability of LGS SAW sensor was excellent under such test and the maximum error was 2.39%,which met the test requirement.In this paper,we also studied the strain characteristics of LGS sensors using cantilever experiment setup under temperature range from 20?²50?.The result shows that the resonate frequency of LGS sensor decreased linearly with the increase of strain,the strain sensitivity was-162.94 Hz/??,and the strain frequency coefficient was-0.488ppm/??.The result of strain test under different temperature shows that with the increase of temperature,the strain sensitivity of the sensor decreased;when temperature reached 250?,the strain sensitivity of the sensor was-120.7 5Hz/??,and the strain frequency coefficient was-0.363 ppm/??.In this paper,we have also studied the relationship between the direction of SAW propagation and strain direction.By bounding the sensors with different angle,we altered the angle between the direction of SAW propagation and strain direction,and studied the strain response to the strain in such setups,the angle we studied in this paper are 0°,30°,60°,90°.The result shows that when the angle changed,the strain response of the sensor also changed,and the resonate frequency of the sensor increase with the increase of strain,the strain sensitivity of the sensor were 179.17 Hz/??,325.09 Hz/??,162.48 Hz/?? respectively and the strain frequency coefficient were 0.536 ppm/??,0.973 ppm/??,0.486 ppm/?? respectively.We have also tested the strain response of these sensors under different temperature,and the result shows that the strain sensitivity also decreased with the increase of temperature.Finally,in this paper,we studied the strain error of LGS sensors.First,we calculated the relative error of the sensors,the error ranged from 0.22%¹.68% under test temperature,which manifested that the LGS strain sensor has excellent linearity.Next,we studied the hysteresis error of the sensors by conducting strain circulation experiment.The result shows that under room temperature the hysteresis error of all devices were under 3%,and with the increase of temperature,the hysteresis error increased,and were under 10%.