scholarly journals Modes Control of Lamb Wave in Plates Using Meander-Line Electromagnetic Acoustic Transducers

2020 ◽  
Vol 10 (10) ◽  
pp. 3491 ◽  
Author(s):  
Yinghong Zhang ◽  
Zhenghua Qian ◽  
Bin Wang
Keyword(s):  
Magnetic Field ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Single Mode ◽  
Plate Surface ◽  
Electromagnetic Acoustic Transducer ◽  
Bias Magnetic Field ◽  
Low Frequencies ◽  
Aluminum Plates ◽  
Meander Line

The multimode and dispersion characteristics of Lamb waves make them difficult to apply to nondestructive evaluation. This paper presents a paired configuration of a meander-line coil electromagnetic acoustic transducer (EMAT) to generate a single-mode symmetric and antisymmetric Lamb wave in aluminum plates. In the paired structure, the bias magnetic field of the EMAT that generates symmetric mode Lamb waves is perpendicular to the plate surface, while the bias magnetic field of the EMAT that generates antisymmetric Lamb waves is parallel to the plate surface. The symmetric and antisymmetric exciting forces generated by these two EMATs are consistent with the dispersion equations of single symmetric and antisymmetric Lamb wave modes, respectively. The numerical simulations and experiments verified that the presented paired configurations of meander-line coil EMATs can effectively control the generation of single-mode Lamb waves at low frequencies.

Thin-Plate Imaging Inspection Using Scattered Waves Cross-Correlation Algorithm and Non-Contact Air-Coupled Transducer

2020 ◽  
Vol 4 (2) ◽  
Author(s):  
Wenfeng Xiao ◽  
Lingyu Yu
Keyword(s):  
Lamb Wave ◽  
Cross Correlation ◽  
Lamb Waves ◽  
Imaging Technique ◽  
Laser Doppler Vibrometer ◽  
Correlation Method ◽  
Single Mode ◽  
Wave System ◽  
Wave Imaging ◽  
Incident Waves

Abstract This paper presents a non-contact air-coupled Lamb wave imaging technique using a two-dimensional (2D) cross-correlation method that not only detects the damage but also precisely quantifies for orientations and sizes. The air-coupled transducers (ACT) is used together with a scanning laser Doppler vibrometer (SLDV) for sensing, making a fully non-contact Lamb wave system used for this study. We first show that single-mode Lamb wave actuation can be achieved by the ACT-based on Snell's law. Detailed study and characterization of the directional ACT Lamb waves are conducted. For damage detection, a 2D cross-correlation imaging technique that uses the damage introduced scattered waves of all directions is proposed for correlating with the incident waves. The frequency-wavenumber filtering technique is used to implement the acquisition of the scatted waves and incident waves, respectively. In the end application to notches with various orientations and various sizes in terms of depth and length is given. The results show the proposed technique can precisely imaging the damages and can quantitatively evaluate the damage size in terms of length and depth.

Structural Health Monitoring of Thin Aluminum Plate Using Acoustic Sensors

2012 ◽  
Vol 622-623 ◽  
pp. 1389-1395
Author(s):  
R. Nishanth ◽  
K. Lingadurai ◽  
V. Malolan ◽  
Gowrishankar Wuriti ◽  
M.R.M. Babu
Keyword(s):  
Lamb Wave ◽  
Damage Identification ◽  
Lamb Waves ◽  
Time Domain Analysis ◽  
Ultrasonic Waves ◽  
Aluminum Plate ◽  
Identification System ◽  
Time Frequency ◽  
Thin Aluminum ◽  
Aluminum Plates

SHM is defined as “an emerging technology that can be defined as continuous, autonomous, real time, in-service monitoring of the physical condition of a structure by means of embedded or attached sensors with minimum manual intervention” .SHM provides the ability of a system to detect adverse changes within a system’s structure to enhance reliability and reduce maintenance costs. There are different Non-Destructive techniques like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves which are nowadays investigated for the development of an efficient and user-friendly damage identification system. This paper deals with the latter which is based on Lamb wave propagation. It has been developed especially for distinguishing different kinds of damages. The Lamb wave-based active SHM method uses piezoelectric (PZT) sensors to transmit and receive Lamb waves in a thin Aluminum plate. The Lamb wave modes (AO &SO) travel into the structure and are reflected by the structural boundaries, discontinuities, and damage. By studying their propagation and reflection, the presence of defect in the structure is determined. Laboratory level experiments have been carried out on thin Aluminum plates with angular, horizontal and vertical defect. The obtained waveform is filtered to avoid unwanted noise & disturbances using Savitzky-Golay filtering. The filtered waveforms are compared to differentiate the defects. Short Time Fourier Transform has been carried out on the acquired waveform. This study provides significant insight into the problem of identifying localized damages in the structure using PZT and dispersion of signal after they interact with different types of damage. Those small defects like the horizontal one that may be nearly missed in time domain analysis can also be clearly identified in the STFT analysis. Moreover the occurrence of So mode is also clearly seen. Thus, Lamb waves generated by PZT sensors and time-frequency analysis techniques could be used effectively for damage detection in aluminum plate. This study has given a complete idea of the working and the basic requirements of SHM system.

scholarly journals A Novel Complementary Method for the Point-Scan Nondestructive Tests Based on Lamb Waves

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Rahim Gorgin ◽  
Zhanjun Wu ◽  
Yuebin Zheng
Keyword(s):  
Lamb Wave ◽  
Test Piece ◽  
Damage Identification ◽  
Lamb Waves ◽  
Complementary Method ◽  
Nondestructive Tests ◽  
Damage Probability ◽  
Scan Test ◽  
Aluminum Plates ◽  
Probability Index

This study presents a novel area-scan damage identification method based on Lamb waves which can be used as a complementary method for point-scan nondestructive techniques. The proposed technique is able to identify the most probable locations of damages prior to point-scan test which lead to decreasing the time and cost of inspection. The test-piece surface was partitioned with some smaller areas and the damage probability presence of each area was evaluated.A0mode of Lamb wave was generated and collected using a mobile handmade transducer set at each area. Subsequently, a damage presence probability index (DPPI) based on the energy of captured responses was defined for each area. The area with the highest DPPI value highlights the most probable locations of damages in test-piece. Point-scan nondestructive methods can then be used once these areas are found to identify the damage in detail. The approach was validated by predicting the most probable locations of representative damages including through-thickness hole and crack in aluminum plates. The obtained experimental results demonstrated the high potential of developed method in defining the most probable locations of damages in structures.

Lamb wave imaging with actuator network for damage quantificationin aluminum plate structures

2020 ◽  
pp. 1045389X2095253
Author(s):  
Zhaoyun Ma ◽  
Lingyu Yu
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Inspection System ◽  
Synthetic Image ◽  
Target Area ◽  
Time Space ◽  
Wave Imaging ◽  
Triangular Profile ◽  
Aluminum Plates

Lamb waves have been widely used for damage detection on plate-like structures. However, there are still considerable interests on quantifying damage with complex profile. In this article, quantification of complex damage in plate-like structures using a network of actuators and time-space Lamb wavefield is investigated. The actuator network inspection system is implemented with multiple PZT transducers for Lamb wave actuation in round robin pattern and scanning laser Doppler vibrometer for wavefield sensing. The PZT network is arranged in a way that the target area is fully enclosed and Lamb waves come to the damage from all directions. Waves induced by the damage are subsequently obtained through frequency-wavenumber filtering, using the experimentally acquired dispersion curves presented in the paper. The filtered waves from all wave actuators are then used to generate a synthetic image of the damage being inspected. Two cases of complex damage are evaluated on aluminum plates, mass loss with triangular profile and mass addition with a three-letter cluster profile. Our results show that the damages are not only detected but also their profiles are clearly outlined in the images. We believe the subject methods provide improved evaluation of damage profile for Lamb wavefield based damage quantification.

scholarly journals Mode Separation for Multimodal Ultrasonic Lamb Waves Using Dispersion Compensation and Independent Component Analysis of Forth-Order Cumulant

2019 ◽  
Vol 9 (3) ◽  
pp. 555 ◽  
Author(s):  
Xiao Chen ◽  
Dandan Ma
Keyword(s):  
Independent Component Analysis ◽  
Fourth Order ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Dispersion Compensation ◽  
Single Mode ◽  
Component Analysis ◽  
Independent Component ◽  
Mode Separation ◽  
Fourth Order Cumulant

Ultrasonic Lamb wave testing has been successfully applied in nondestructive testing. However, because of Lamb wave multimodal and dispersion characteristics, the received signals are often multimodal and overlapping, which makes them very complicated. This paper proposes a mode separation method by combining dispersion compensation with the independent component analysis of fourth-order cumulant. Taking two-mode overlapped signals as an example, the single-mode dispersion compensation is performed according to the measured distance difference between the two sets of signals. The two sets of signals are returned to the same distance. The fourth-order cumulant independent component analysis method is further used to process the Lamb wave signals of different superposition situations at the same distance. The corresponding mode signal contained in the two sets of signals is separated through the joint diagonalization of the whitened fourth-order cumulant matrix. The different modes are compensated and separated successively, achieving the multimodal signal separation. Experimental results in steel plates show that the presented method can accurately achieve mode separation for the multimodal overlapping Lamb waves. This is helpful for the signal processing of multimodal Lamb waves.

scholarly journals Damage identification in welded structures using symmetric excitation of Lamb waves

2018 ◽  
Vol 10 (9) ◽  
pp. 168781401879481 ◽  
Author(s):  
Jian He ◽  
Liang Yang ◽  
Xiaodan Sun ◽  
Muping Hu
Keyword(s):  
Lamb Wave ◽  
Damage Identification ◽  
Lamb Waves ◽  
Steel Structures ◽  
Single Mode ◽  
Industrial Applications ◽  
Crack Identification ◽  
Monitoring Methods ◽  
Welded Steel ◽  
Symmetric Methods

Damage monitoring systems based on Lamb wave health monitoring technology have attracted considerable attention for scientific research and industrial applications. In this article, two types of single-mode Lamb waves are obtained using symmetric and anti-symmetric methods, respectively, to determine a crack identification signal. A numerical simulation of a welded steel plate model was conducted using the ABAQUS/EXPLICIT module, which is a dynamic solver. The propagation process and the corresponding effect of the Lamb waves over the complete and damaged models are simulated. According to the propagation characteristics and with the assistance of the ellipse localization method with MATLAB, the location of crack damage is simulated by the amplitude addition method and the crack damage location is determined. The results show that the simulation results are in good agreement with the actual crack damage. Furthermore, the received signals are compared and analyzed from an energy perspective. Two types of single-mode Lamb wave monitoring methods are also compared. In addition, it is demonstrated that a symmetric excitation can simplify the received waves and recognize crack damage in plates in welded steel structures from an experimental perspective of this work.

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