Pulsed Eddy Current Testing Based On Magnetic Sensor

Multilayer metal structure is widely used in aerospace industry. Owing to thecomplex internal structure of multilayer metal structure, detection of its hiddeninternal defects has been a difficulty for Non-destructive Testing. Pulsed eddy currenttesting, based on electromagnetic theory, is widely used in the detection of complexstructure with its wide spectrum, fast speed and high accuracy, and can obtain avariety of parameter information in one scan.This thesis designs a pulsed eddy current testing system to detect cracks andcorrosion defects in multilayer metal structure.Hardware system of the platform mainly includes computer, signal generator,signal conditioning module, sensor module, data acquisition module and test blockmodule. Software design is based on Labview and consists of data acquisition andsignal processing. Single channel and multichannel sensor array are designed.A self-adaptive signal processing algorithm, based on Kalman filter is designedto reduce noise. Experimental results show that the Kalman filter works very well inprocessing of non-stationary noise signals. A method is put forward to suppresslift-off effect based on lift-off database and experiments are carried out.The detection of crack defects in multilayer metal structure is conducted by usingsingle channel probe. Crack defects in different depth and size are detected andquantified in the experiment by analyzing peak value and peak time of signals. Andchanges of signal peak are observed, magnetic horizontal component is analyzed.Crack defects orientation are judged by the results of horizontal and vertical scan ofthe probe. Array probe is used for the detection of corrosion defect of multilayer metalstructure in this paper. Detection signals are obtained to form the characteristic matrixand converted into gray value data for C scan imaging.Some suggestions for future work are presented.