Nondestructive Testing Based On The Coplanar Array Capacitive Image Sensing

The main protection system of aircraft surface is mainly composite material, usually the composite material is attached to the surface layer of the aircraft through the bonding agent, the defect or damage of the bonding layer can lead to the increase of the crack propagation and the decrease of the bond strength of the composite, even stripping the whole, seriously affects the flight safety of the aircraft, so it is very important to detect the bonding quality.The development of electrical capacitance tomography(ECT) is earlier, but it is mainly used in the detection of two-phase flow in pipeline, the planar array capacitance sensor not only has the advantages of traditional ECT, but also can be close to the measured object from a single plane. In recent years, the application of planar array capacitance imaging technology in nondestructive testing is a new technology in the world.In this paper, focus on defects of the aerospace composite bonding layer, the composite materials for testing are anisotropy, porosity, low thermal conductivity, low conductivity,high sound absorbing of the comprehensive characteristics and large area, single side for detect, a nondestructive testing method based on planar array capacitance imaging technology is proposed.Firstly, based on the analysis of the traditional electrical capacitance tomography technology, the principle of planar array electrode detection is studied, and based on capacitance sensing mechanism, through theoretical analysis and finite element modeling and simulation, a new type of planar array electrode sensor is designed and fabricated, and study the effect of electrode structure parameters on the test, and realized the optimized design of the array electrode.Secondly, use the finite element analysis technique studied the sensitive filed distribution of planar sensor, through the analysis of the "soft field" characteristics of electromagnetic field, built a three dimensional electromagnetic field model for the planar array electrode system, obtained the relationship between the dielectric distribution of the detected object field and the change of the capacitance of the electrode. Hierarchicalprocessing of sensitivity field, and used the linear back projection algorithm studied the image reconstruction problem of dielectric distribution.Finally, built a planar electrode array detection platform, and use the sensitivity matrix of different layers for the detect image. The experimental results reflect the information of the shape and the plane position of the object being measured. Further study the penetration depth of the planar array sensor, and according to the composite layer within the defect / damage effect on the dielectric properties of materials for defects or damage detection by simulation and experiment. Studied the composite layer with typical defects and electrode array sensor capacitance change amount. According to the imaging results, it is possible to identify the location and size of typical defects and the detection results are consistent with the theoretical analysis, which verifies the feasibility and effectiveness of the proposed method.