Research On Eddy Current Phase Spectrum Analysis Method Under Pulse Excitation

As one new eddy current nondestructive testing(NDT)technology,pulsed eddy current(PEC)nondestructive testing(NDT)could be used to optimize the coil optimization of electromagnetic sensor and realize the advantages of multi-parameter detection.The signal parameter estimation and Fourier operation and the phase spectrum analysis of pulse excitation were studied in this paper.Based on the equivalent circuit model of the eddy current sensor,the COMSOL finite element simulation method was used to study and optimized the parameters of the electromagnetic sensor,analyzed the influence of the variation of the coil thickness,inner and outer diameter,and equivalent radius on the detection resolution,The thickness of the probe coil,the difference between the inner and outer diameter was conducive to improve the detection resolution,at the same time be elected to use the equivalent radius to lift the height of 0.8~1.4 times,the probe coil detection resolution was best.Based on the theory of electromagnetic field,the parametric modeling and calculation method of pulsed eddy current testing system were studied.The magnetic field distribution and impedance characteristics of inductive eddy current of coil sensor were studied by COMSOL finite element simulation.The influences of different tested materials and different lifting Height of the pulse eddy current test results was analyzed.different materials in the same detection distance,the coil resistance and inductance was a linear relationship;different detection distance,the coil resistance and inductance curve was parallel,A method of characterizing the material to be tested using phase analysis of impedance was derived.Based on the phase spectrum analysis method,the multi-frequency signal analysis of pulse eddy current testing was studied.The phase spectrum of the pulse eddy current detection was transformed by FFT.The application of "phase zero crossing point" in studying the classification of material defects was proposed.Finally,When the height of the tested material is within a certain range,the phase zero crossing point fPZ remains unchanged;the surface defect of the tested material is larger than the zero-crossing point fPZ without defect;the defect within the tested material is smaller than the zero-crossing point fPZ without defect.