An Online Nondestructive Testing System Based On Electromagnetic Wave Transmission Features

The material properties of metallic and nonmetallic components may change after long time service. In the worst cases, the failure of the components could lead to accidents. It is important to acquire the condition of a component without compromising its utility. Compared with regular nondestructive testing(NDT) methods, electromagnetic wave transmission features based approaches are noncontact, fast, well adapted, easy to setup and befitting for online detection. In this thesis, an online nondestructive testing system is demonstrated based on electromagnetic wave transmission features.Firstly, the bridge between the physical electromagnetic wave mode-mixing model and mathematical mode decomposition model is demonstrated. The transmission models of rectangular waveguide is discussed. A feature enhancement algorithm based on variational mode decomposition is proposed for microwave waveguide. Coated steel defect detection experiment is conducted to evaluate the efficacy of the proposed method.Secondly, the effection of model electromagnetic parameters and defects properties on transmission features is studied through simulation at very high frequency(VHF). Models are created to simulate the reflection and penetration coefficients under component condition variation. The simulations are conducted to cover regular nondestructive testing situations.Thirdly, the hardware structure are demonstrated based on simulation results. Essential components are configured to satisfy NDT requirements, including signal generator, amplifier, coil sensor, signal processing circuit and signal acquisition card. Moreover, a detection control software is developed based on LabVIEW. The software consist of graphics display unit, parameters input unit, statistics unit, acquisition control unit, data functions unit and analysis functions unit. Its interface is friendly and its function can be easily extended. The proposed detection system can handle general detection situations.Finally, three experiments are conducted to verify the efficiency of proposed system. The preparation of test sample and experimental scheme are demonstrated. The experiment results of oil debris detection, metal surface defects detection, metal tensile deformation detection as well as their simulation results coincidently suggest that the proposed system fulfills the detection requirements of the applications.This thesis demonstrates a practicable approach on portable online nondestructive testing system. The proposed detection system will gain broad prospects.