Research On Key Technology Of High Temperature Sensor With Integrated Temperature/strain Parameters

In the fields of aerospace,energy extraction,and others,real-time measurement of temperature,strain,and other parameters of key components is of great significance for health detection,safe operation,and early warning of entire equipment.Traditional silicon based sensors are difficult to monitor temperature,strain,and other parameters in harsh environments above 600℃.However,surface acoustic wave（SAW）sensors based on piezoelectric materials have the characteristics of high temperature resistance,small size,strong anti-interference ability,and high sensitivity.They also have important application prospects in fields such as aerospace and energy mining.In view of the testing requirements under harsh environments such as high temperature and high rotation,this dissertation studies the structural design of temperature/strain dual-parameter integrated SAW sensor,the deposition method of multi-layer composite film of integrated sensor,the temperature/strain decoupling algorithm,the design,preparation and related testing methods of high temperature wide-range strain sensor.The main research content of this dissertation is as follows:1.Structure of a resonant SAW temperature/strain dual-parameter sensor has been proposed.The COMSOL software was used to simulate the structure of temperature/strain sensing units and to optimize the design parameters for achieving frequency separation of temperature/strain sensing units.The SAW temperature/strain dual-parameter sensor was prepared by MEMS manufacturing crafts.The temperature and strain sensing performance of the two sensor units were tested in the temperature range of 25℃-250℃ and the strain range of 0-700μεby using a temperature/strain composite test platform.Sensitivities of the temperature sensor reached 7.62k Hz/℃ and the strain sensor reached 100 Hz/μεat room temperature.In addition,by extracting the slope and intercept of relation curve between strain and frequency at different temperatures,decoupling of temperature and strain was realized.2.Method of depositing composite thin films on the surface of sensors has been proposed to protect piezoelectric substrates and electrodes for improving high-temperature performance of the sensors.Multilayer composite films Al₂O₃/ZnO/Al₂O₃/ZnO were deposited on the surface of SAW sensor by pulsed laser deposition（PLD）to prevent the dehumidification,recrystallization and electrode agglomeration of the substrate.The high-temperature performance of the sensor was tested using a high-temperature testing platform,and results showed that maximum testing temperature of the sensor could reach1050℃,with a frequency temperature coefficient of-90.52 ppm/℃.In order to achieve strain measurement at high temperature and reduce the interference of temperature corresponding strain,it is necessary to ensure that the frequency temperature coefficient is small.Therefore,a silicon dioxide protective film based plasma enhanced chemical vapor deposition（PECVD）is not only used to protect the substrate and electrode,but also plays a vital role for temperature compensation.Furthermore,high temperature strain test was carried out,and the sensor was tested in the temperature range of 20℃-700℃ and the range of0-500με.The strain sensitivity reached 220Hz/με.3.To improve the strain measurement range of strain sensors,a SAW strain sensor based on LGS thin film was presented.The COMSOL software was used to simulate structure of the corresponding variable sensing unit for optimizing the structural parameters.The LGS thin films were prepared using chemical mechanical polishing technology,and the SAW strain sensors were prepared on the surface of LGS thin films using MEMS manufacturing crafts.The temperature and strain composite test platform was used to test performance of the strain sensor in the range of 20℃-800℃ and 0-1800με.Measurement results showed that sensitivity of the sensor reached 44.88Hz/με.After analyzing the test data,a temperature strain decoupling algorithm with decoupling error of±5.00%was proposed.Therefore,it turns out that the sensor can achieve accurate measurement of strain parameters at high temperatures.Overall,this dissertation studies the sensing mechanism,the design and manufacturing,the performance testing,and the temperature strain decoupling algorithm of SAW temperature/strain sensors.It achieves real-time monitoring of temperature/strain parameters at high temperatures and can be used for health detection,safe operation,and early warning of entire equipment in fields of aerospace and energy mining etc.