2D aperture synthesis for Lamb wave imaging using co-arrays

2014 ◽  
Author(s):  
Lukasz Ambrozinski ◽  
Tadeusz Stepinski ◽  
Tadeusz Uhl
Keyword(s):  
Lamb Wave ◽  
Aperture Synthesis ◽  
Wave Imaging

Damage localization with fiber Bragg grating Lamb wave sensing through adaptive phased array imaging

2018 ◽  
Vol 18 (1) ◽  
pp. 334-344 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu ◽  
Xiaoyi Sun ◽  
Bin Lin
Keyword(s):  
Fiber Bragg Grating ◽  
Electromagnetic Interference ◽  
Lamb Wave ◽  
Phased Array ◽  
Minimum Variance ◽  
Bragg Grating ◽  
Damage Localization ◽  
Weighting Factors ◽  
Wave Imaging ◽  
Grating Array

Fiber Bragg gratings are known being immune to electromagnetic interference and emerging as Lamb wave sensors for structural health monitoring of plate-like structures. However, their application for damage localization in large areas has been limited by their direction-dependent sensor factor. This article addresses such a challenge and presents a robust damage localization method for fiber Bragg grating Lamb wave sensing through the implementation of adaptive phased array algorithms. A compact linear fiber Bragg grating phased array is configured by uniformly distributing the fiber Bragg grating sensors along a straight line and axially in parallel to each other. The Lamb wave imaging is then performed by phased array algorithms without weighting factors (conventional delay-and-sum) and with adaptive weighting factors (minimum variance). The properties of both imaging algorithms, as well as the effects of fiber Bragg grating’s direction-dependent sensor factor, are characterized, analyzed, and compared in details. The results show that this compact fiber Bragg grating array can precisely locate damage in plates, while the comparisons show that the minimum variance method has a better imaging resolution than that of the delay-and-sum method and is barely affected by fiber Bragg grating’s direction-dependent sensor factor. Laboratory tests are also performed with a four–fiber Bragg grating array to detect simulated defects at different directions. Both delay-and-sum and minimum variance methods can successfully locate defects at different positions, and their results are consistent with analytical predictions.

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.

Designing of sparse 2D arrays for Lamb wave imaging using coarray concept

2015 ◽  
Author(s):  
Łukasz Ambroziński ◽  
Tadeusz Stepinski ◽  
Tadeusz Uhl
Keyword(s):  
Lamb Wave ◽  
Wave Imaging ◽  
2D Arrays

scholarly journals Time-Domain Topological Energy Imaging Method of Concrete Cavity Defect by Lamb Wave

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Wen-Fa Zhu ◽  
Wei Shao ◽  
Le-Le Peng ◽  
Guo-Peng Fan ◽  
Xing-Jie Chen ◽  
...  
Keyword(s):  
Time Domain ◽  
Lamb Wave ◽  
Wave Dispersion ◽  
Imaging Method ◽  
Sound Fields ◽  
Wave Imaging ◽  
Reference Medium ◽  
Synthetic Aperture Focusing ◽  
Synthetic Aperture Focusing Technique ◽  
Defect Imaging

This paper presents an ultrasonic Lamb wave imaging method based on time-domain topological energy to address artifacts in the results of traditional ultrasound imaging methods. This method is based on topological theory and the calculation of the direct and adjoint sound fields in a defect-free reference medium. It focuses the direct and adjoint sound fields at the cavity defect using time reversal and their time-domain topological energy as the pixel values of the image to reduce the artifacts. The physical mechanism of time-domain topological energy (TDTE) imaging is revealed by finite element simulation and experiment. The feasibility of this method for multilayer concrete cavity defect imaging is verified. Compared with the traditional synthetic aperture focusing technique (SAFT) imaging method, the numerical simulation and experimental results show that the method can overcome the influence of ultrasonic Lamb wave dispersion and locate cavity defects with high accuracy and few artifacts. These features indicate the potential of the method in imaging damage concrete structures.

On the Use of Ultrasound-Based Technology for Cargo Inspection

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Yuri Álvarez-López ◽  
José A. Martínez-Lorenzo
Keyword(s):  
Real Time ◽  
Lamb Wave ◽  
Low Cost ◽  
Guided Wave ◽  
Image Resolution ◽  
Scanning System ◽  
Reflected Waves ◽  
Imaging Results ◽  
Cargo Inspection ◽  
Wave Imaging

A new guided wave imaging application for fast, low-cost ultrasound-based cargo scanning system is proposed. The ultimate goal is the detection of high-atomic-number, shielding containers used to diminish the radiological signature of nuclear threats. This ultrasonic technology has the potential to complement currently deployed X-ray-based radiographic systems, thus enhancing the probability of detecting nuclear threats. An array of ultrasonic transceivers can be attached to the metallic structure of the cargo to create a guided Lamb wave. Guided medium thickness and composition variation creates reflections whose placement can be revealed by means of an imaging algorithm. The knowledge of the reflection position provides information about the shielding metallic container location inside the cargo. Moreover, due to the low coupling between metallic and nonmetallic surfaces, only the footprint of metallic containers shows up in the imaging results, thus avoiding false positives from plastic or wooden assets. As imaging capabilities are degraded if working with dispersive Lamb wave modes, the operating frequency is tuned to provide a tradeoff between low dispersion and real-time image resolution. Reflected waves in the guided domain bounds may limit the performance of imaging methods for guided media. This contribution proposes a solution based on real-time Fourier domain analysis, where plane wave components can be filtered out, thus removing nondesired contributions from bounds. Several realistic examples, scaled due to limited calculation capabilities of the available computational resources, are presented in this work, showing the feasibility of the proposed method.

scholarly journals Enhancement of Lamb Wave Imaging Resolution by Step Pulse Excitation and Prewarping

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Shangchen Fu ◽  
Lihua Shi ◽  
Yinghui Zhou ◽  
Zhikai Fu
Keyword(s):  
Lamb Wave ◽  
Pulse Excitation ◽  
Accurate Estimation ◽  
Plate Structures ◽  
Localization Accuracy ◽  
Narrowband Signal ◽  
Wave Imaging ◽  
First Arrival ◽  
Imaging Resolution ◽  
Peak Value

For the purpose of improving the damage localization accuracy, a prewarping technology is combined with step pulse excitation and this method is used in Lamb wave imaging of plate structures with adjacent damages. Based on the step pulse excitation, various narrowband or burst response can be derived by signal processing technology and this method provides flexibility for further prewarping approach. A narrowband signal warped with a preselected distance is then designed, and the dispersion in the response of this prewarping signal will be greatly reduced. However, in order to calculate the distance for prewarping, the first arrival needs to be estimated from the burst response. From the step-pulse response, narrowband responses at different central frequencies can be obtained, and by averaging peak-value time of their first arrivals, a more accurate estimation can be calculated. By using the prewarping method to the damage scattering signals before imaging, the imaging resolution of the delay-and-sum method can be highly enhanced. The experiment carried out in an aluminum plate with adjacent damages proves the efficiency of this method.

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