| In recent years,coplanar capacitance testing technology,as an emerging non-destructive testing technology,has received extensive attention and research due to its low cost,non-destructive,and one-sided detection characteristics.It can be applied to the detection of defects in the bonding layer of hyped thermal protective materials.Aiming at the problems of low imaging resolution of coplanar capacitance detection technology,difficulty in detecting the number,shape,and size of defects,and inability to realize depth localization,this paper carried out optimization research on coplanar capacitance sensors for scanning detection.Firstly,aiming at the problems that the current scanning detection imaging of the coplanar capacitive sensor is not accurate in the shape and size of the defect and the detection results are seriously affected by the scanning method,the influence law of the sensor electrode structure parameters on the sensor sensitivity distribution and the scanning detection results is explored,and the adjacent edges of the electrodes are found to play an important role in the scanning detection imaging.It is verified by measurement experiments that when the electrode area is equal,the length of the adjacent edge of the electrode determines the distribution of the high sensitivity area of the sensor,and the detection depth and detection accuracy increase with the shortening of the adjacent edge of the electrode.Secondly,a method is proposed to improve the detection accuracy of the coplanar capacitive sensor by changing the adjacent side length of the electrode.By establishing a sensor model,the relationship between the length of adjacent edges of a single pair of electrodes and the sensitivity distribution of the sensor was found,as was the influence of adjacent edges on the sensitivity distribution.By optimizing the sensitivity distribution of a single pair of coplanar capacitive sensors,the detection depth and imaging accuracy of the sensors were improved.The feasibility and effectiveness of the method were verified by measurement experiments.Simulation and experiment results show that this method of optimizing sensitivity distribution fundamentally improves the scanning resolution of a single pair of coplanar capacitive sensors,makes the scanning detection no longer constrained by the scanning mode,greatly reduces the stretching deformation problem,and improves the image correlation coefficient and detection accuracy of the reconstructed image.Finally,aiming at the problem that the scanning detection technology of coplanar capacitive sensors cannot accurately characterize the depth information of defects,an analysis method for depth localization of defects is studied.In this method,the asymmetric diagonal triangle electrode coplanar capacitive sensor is excited by cyclic excitation,so that the sensor has a variety of detection depths at the same time.At each scanning point,the cyclic excitation is carried out,and the defect information at different depths is finally obtained to realize the localization and analysis of the defect depth. |
