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Time-frequency overlapping multi-mode lamb wave signal separation method

A signal separation and multi-mode technology, applied in the direction of character and pattern recognition, complex mathematical operations, instruments, etc., can solve the problems of nonlinear amplitude change, complex Lamb wave detection, difficult to apply multi-mode separation, etc., to reduce the Difficulty, effect of achieving separation

Pending Publication Date: 2019-01-04
NANJING UNIV OF INFORMATION SCI & TECH
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Problems solved by technology

However, the multi-mode aliasing signal will cause nonlinear changes in amplitude due to the dispersion characteristics, making it difficult for the characteristic parameter extraction value of time-frequency analysis to accurately reflect the real single-mode signal energy distribution, making it difficult to apply to excessive aliasing in both time and frequency in the multimodal separation of
[0005] Due to the multi-mode and dispersion characteristics of the Lamb wave, in the actual detection, under the same excitation frequency, there are often mixed signals of multiple modes, and the signals of each mode have different dispersion trends, so that in the case of time-frequency aliasing The detection of lower Lamb waves becomes very complicated

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  • Time-frequency overlapping multi-mode lamb wave signal separation method
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Embodiment Construction

[0036] The time-frequency overlapping multi-mode Lamb wave signal separation method of the present invention comprises the following steps:

[0037] (1) Dispersion compensation of multi-mode Lamb wave signal

[0038] Suppose g(t) is a multi-mode mixed signal, and its spectrum is G(ω), first use the first extraction mode corresponding to the dispersion compensation function H -1 (ω) Compensate the multi-mode signal to obtain the compensated spectrum GS(ω):

[0039] GS(ω)=G(ω)H -1 (ω)

[0040] Dispersion compensation function H -1 (ω) can be expressed as:

[0041]

[0042] where x is the dispersion distance, cp(ω) is the phase velocity of the corresponding mode

[0043] cp(ω) is calculated as follows:

[0044] S mode:

[0045]

[0046] A mode:

[0047]

[0048] in, c L is the longitudinal wave velocity of the plate, c S is the shear wave velocity of the plate, b is 1 / 2 plate thickness, k=ω / cp(ω).

[0049] Finally, inverse Fourier transform is performed to o...

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Abstract

The invention discloses a time-frequency overlapping multi-mode Lamb wave signal separation method, comprising the following steps: (1) frequency dispersion compensation of the multi-mode Lamb wave signal; (2) windowing the compensation signal; (3) Fourier transform of windowed signal; (4) calculating fractional derivative of amplitude spectrum; (5) calculating the fractional differential maximumof amplitude spectrum of Gaussian model and the polynomial coefficients of corresponding frequency and differential order; (6) calculating amplitude spectrum parameters; (7) calculating amplitude spectrum based on Gaussian model; (8) calculating and extracting non-dispersive Lamb wave signal by inverse Fourier transform; (9) recovery of Lamb wave signal by dispersion function; (10) the mixed signal after removing the extracted signal repeating the above steps to realize the separation of each pattern. Compared with the prior art, the invention can reduce the difficulty of the mixed signal through the frequency dispersion compensation, can effectively extract the characteristic parameters of each mode, and realize the reconstruction of the amplitude spectrum of each mode to realize the separation of the multi-mode mixed 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 time-frequency overlapping multi-mode Lamb wave signal separation method based on dispersion compensation and fractional differentiation. Background technique [0002] With the rapid development of material science and industrial technology, the application of non-destructive testing technology has become more common. Compared with conventional non-destructive testing methods, ultrasonic lamb wave has the advantages of fast, efficient, accurate, low cost, and harmless, and is widely used. It is widely used in industrial testing and plays an important role in non-destructive testing. [0003] The main characteristics of Lamb waves are dispersion and multi-mode characteristics, that is, the phase velocity will change with the change of frequency, and the same excitation frequency may generate multiple modes of Lamb waves, a...

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Application Information

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IPC IPC(8): G06K9/00G06F17/14G06F17/13G06F17/12
CPCG06F17/12G06F17/13G06F17/14G06F2218/08
Inventor 陈晓倪龙梅永高扬
Owner NANJING UNIV OF INFORMATION SCI & TECH
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