A Lamb wave denoising method based on fractional differentiation

Abstract

The invention provides a fractional differentiation-based lamb wave denoising method, and aims at overcoming the defects of the prior art, and improving the signal to noise ratio of the denoised signal. The method comprises the following steps: carrying out fractional differentiation on an amplitude spectrum containing a noise lamb wave signal; proposing a triple relationship between the maximal value, the zero crossing point and the differentiation order of the fractional differentiation of the amplitude spectrum; building a calculated mode of amplitude spectrum characteristic parameters to rebuild the amplitude spectrum of an original signal, and combining with a phase spectrum to rebuild the denoised lamb wave signal.

Description

Technical field: [0001] The invention relates to the technical field of ultrasonic Lamb wave signal processing in nondestructive testing, in particular to a Lamb wave denoising method based on fractional differentiation. Background technique: [0002] In the ultrasonic Lamb wave detection, because the Lamb wave excitation and inspection methods are flexible, and can effectively interact with the plate defects, and carry a large amount of information, it can be used as an effective means of plate defect detection, especially in large areas. It is more widely used in the non-destructive testing of plate structures. Ultrasonic Lamb wave signal is a typical non-stationary signal. In actual detection, because the signal is subject to different degrees of noise interference, the received signal components become very complex, which brings errors to the later processing and directly affects the reliability of detection. Therefore, it is necessary to denoise the non-stationary ultr...

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Problems solved by technology

Li Gang et al. used the EMD method to denoise the ultrasonic Lamb wave signal. Although the EMD method does not need to be based on a specific function, it can adaptively extract data according to the signal characteristics, but the denoising effect is not thorough, and a lot of noise is retained. The characteristics of the signal cannot reflect the original signal well, and the denoising effect is not very ideal (LiG, ShiLH, WangXW. EMD denosing method and its application in Lambwave detection, Acta Metrologica Sinica, 2006, 27: 149-152)

Due to the advantages of wavelet transform in denoising, it has been widely used in the field of non-destructive testing. Siqueir et al. used discrete wavelet transform to process ultrasonic Lamb wave measured signals, and decomposed the signals smaller than a given threshold value through the hard threshold method. The coefficient is set to 0. However, although this method removes the noise, the denoising effect is not ideal, and the signal still contains a lot of noise, so the reconstructed signal cannot accurately reflect the characteristics of the signal (SiqueiraMHS, GattsCEN, SilvaRRetal.Theuseofultrasonicguidedwavesandwaveletsanalysisinpipeinspection, Ultrasonics, 2003, 41:785-798)

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