Research On The Sensing Mechanism And Key Technology Of Three-dimensional MEMS Acoustic Emission Sensor

Acoustic emission(AE) technology,as a dynamic nondestructive testing method,mainly realizes the dynamic monitoring of the defects generated by the material and the prediction of the damage location.At present,most of the sensors used for AE monitoring are piezoelectric materials or resonant or wide-band sensors,which have the advantages of fast response,high sensitivity,and ease of use.However,traditional sensors will detect stress waves in all directions at the same time,and are not specific The ability of directional stress waves cannot distinguish AE signals in different directions.To solve the above problems,a new three-dimensional micro-electromechanical system acoustic emission sensor was designed to realize the three-dimensional dynamic displacement detection of engineering structure cracks.The main research contents are as follows:(1)Establish three equivalent models of three-dimensional acoustic emission sensors and conduct theoretical analysis.In the parallel plate capacitance model,the capacitance,collapse voltage,damping and sensitivity of the z-direction sensing unit are analyzed;the output voltage of the z-direction sensing unit is calculated using an equivalent circuit model;Through the thin-film vibration model,the parameters such as displacement and resonance frequency at the resonance point of the sensor unit in the z-direction are studied.(2)Design of three-dimensional acoustic emission sensor.According to the required response frequency and processing technology,the parameters of the thickness of the three sensing units,the size of the spring and the gap between the plates are preliminarily determined.The three-dimensional acoustic emission sensor model is established using SolidWorks software,mainly including the sensor unit model responding in three directions of x,y and z;In order to detect the acoustic emission signals in three orthogonal directions and reduce the area of the sensing unit,the CAD software is used to design the array layout of the three-dimensional acoustic emission sensor;Optimize the design of the sensor preparation process.(3)Use ANSYS Workbench software to simulate and analyze the three-dimensional sensing model.Based on the theoretical analysis and structural design results of the three-dimensional acoustic emission sensor,a modal and harmonious response analysis is performed on the z-direction response sensor unit.The maximum deflection displacement and resonance frequency of the sensor unit are within the design requirements;The modal and harmonious response analysis of the sensor units responding in the x and y directions respectively,the simulated values obtained are in good agreement with the theoretical values,which verifies the rationality of the structural design,and at the same time,the response in the x and y directions The sensor unit can effectively isolate the required mechanical response in the x and y directions from the unwanted mechanical response in the z direction.(4)Realize the host computer software programming of the three-dimensional acoustic emission sensor signal acquisition system through LabVIEW software.Using LabVIEW as the platform,combined with the characteristics of the three-dimensional acoustic emission sensor,a multi-channel synchronous acquisition signal acquisition system is established,including the design and programming of analog signal generation,signal acquisition,waveform analysis,data storage and signal playback.The designed signal acquisition system is tested and the simulated signal is used as input.The test results show that the designed signal acquisition system can meet the signal acquisition and analysis functions of the three-dimensional acoustic emission sensor.