Research And Application Of Electromagnetic Ultrasonic Signal Filtering Method Based On Fitting Threshold SVD

Electromagnetic ultrasonic testing is one of the nondestructive testing methods.Its principle is to excite ultrasonic waves inside the metal through electromagnetic induction.The advantage of this method is non-contact,but the disadvantage is that the signal is weak.The SVD(singular value decomposition)method of image processing uses sparseness to judge images.In this paper,electromagnetic ultrasonic excitation surface waves are generated by non-ferromagnetic materials to detect the surface,and the obtained signals are processed through data partitions,and the fitted threshold SVD is used.The advantages and disadvantages of different filtering methods are obtained by comparison.First,the electromagnetic ultrasound Rayleigh wave and Lamb wave models were established through COMSOL multiphysics simulation software.Comparing the displacement time difference and wave velocity,the validity of the Rayleigh wave excitation model is proved.By verifying the symmetry and wave speed of the A0 and S0 waveforms in the Lamb wave model,the effectiveness of the Lamb wave excitation model is proved.Secondly,the relationship between the number of non-zero singular values and frequency in the signal is analyzed through theoretical calculations.The singular value of the electromagnetic ultrasonic signal is found through the simulation signal.And there is a mutation in the singular value.A fitting threshold selection method is proposed.The data is aggregated through sample entropy,and the singular value fitting interval is selected by the modal interval method.The fitting threshold SVD filtering method is completed and compared with different thresholds.It's proved that the fitting threshold selection method is suit for the Rayleigh wave.Finally,an electromagnetic ultrasound Rayleigh wave excitation experiment is designed based on the above simulation model,and the obtained experimental signal is filtered by the method of fitting threshold selection,and the lift-off slope is used as a feature quantity to compare the advantages and disadvantages of different filtering methods.Studies have shown that the fitting threshold SVD filtering method has better accuracy and stability in the processing of electromagnetic ultrasound Rayleigh waves.