Research On Nonmetallic Materials Defect Detection Method Based On Planar Capacitance Sensor

As a nondestructive testing technology evolved from electrical capacitive tomography,planar capacitive imaging technology has a wide application prospect in nondestructive testing of nonmetallic materials due to its features of strong adaptability,high sensitivity,non-intrusive and single-direction detection.The image reconstruction process based on the capacitance value and the sensitive field in the planar capacitance imaging technology is "ill-posed",which will lead to ill-health image reconstruction such as unclear representation and inaccurate positioning.In this paper,aiming at the quality problem of reconstructed visualized images in planar capacitive imaging technology,a research on defect detection methods of nonmetallic materials based on planar capacitive sensors is carried out.Firstly,aiming at the problem of visual image quality in planar capacitance detection technology,based on the analysis of the development status,detection mechanism and imaging principle of planar capacitance imaging technology,the planar 3×4 array capacitance detection method based on fusion excitation is studied.The advantages and disadvantages of visualized images under three excitation modes of single electrode excitation,double electrode excitation and cyclic alternating double electrode excitation are discussed,and the simple weighted fusion method is used to fuse the three excitation modes to achieve the purpose of improving the visual image quality.The effectiveness of the method is verified by experiments.Then,in order to improve the problem of poor visual image quality and blurred edges of planar capacitance sensor,combined with the sensitivity field analysis of planar single-pair capacitance sensor,the scanning detection method based on planar single-pair capacitance sensor is studied.The scanning and imaging scheme of scanning detection was designed,the model of scanning sensitive field was established and its uniformity was analyzed.The simulation and measurement experiments show that the planar single-pair electrode capacitance sensor is feasible for scanning detection and imaging,and its visual image has the advantages of smaller root mean square error and more accurate information of defect edge.Finally,in order to obtain the position information of defects quantitatively,the spatial location of defects in nonmetallic materials was studied based on the scanning detection technology of planar single-pair electrode capacitance sensor.After discussing the relationship between the spatial coordinates of the defect and the distribution matrix of the dielectric constant and the variable capacitance,the spatial localization of the defect is analyzed from the planar coordinates and the depth coordinates of the defect.The feasibility and accuracy of the proposed method are proved by experiments.