scholarly journals Lamb Wave Local Wavenumber Approach for Characterizing Flat Bottom Defects in an Isotropic Thin Plate

2018 ◽  
Vol 8 (9) ◽  
pp. 1600 ◽  
Author(s):  
Guopeng Fan ◽  
Haiyan Zhang ◽  
Hui Zhang ◽  
Wenfa Zhu ◽  
Xiaodong Chai
Keyword(s):  
Thin Plate ◽  
Lamb Wave ◽  
Spatial Information ◽  
Laser Doppler Vibrometer ◽  
Target Area ◽  
Flat Bottom ◽  
Wavenumber Domain ◽  
Time Space ◽  
Local Wavenumber ◽  
Rectangular Groove

This paper aims to use the Lamb wave local wavenumber approach to characterize flat bottom defects (including circular flat bottom holes and a rectangular groove) in an isotropic thin plate. An air-coupled transducer (ACT) with a special incidence angle is used to actuate the fundamental anti-symmetric mode (A0). A laser Doppler vibrometer (LDV) is employed to measure the out-of-plane velocity over a target area. These signals are processed by the wavenumber domain filtering technique in order to remove any modes other than the A0 mode. The filtered signals are transformed back into the time-space domain. The space-frequency-wavenumber spectrum is then obtained by using three-dimensional fast Fourier transform (3D FFT) and a short space transform, which can retain the spatial information and reduce the magnitude of side lobes in the wavenumber domain. The average wavenumber is calculated, as a real signal usually contains a certain bandwidth instead of the singular frequency component. Both simulation results and experimental results demonstrate that the average wavenumber can be used not only to identify shape, location, and size of the damage, but also quantify the depth of the damage. In addition, the direction of an inclined rectangular groove is obtained by calculating the image moments under grayscale. This hybrid and non-contact system based on the local wavenumber approach can be provided with a high resolution.

Lamb Wave Propagation Study Using Frequency-Wavenumber Analysis

2012 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu
Keyword(s):  
Wave Propagation ◽  
Lamb Wave ◽  
Experimental Testing ◽  
Wave Spectrum ◽  
Laser Doppler Vibrometer ◽  
Wave Mode ◽  
Wavenumber Domain ◽  
Time Space ◽  
Lamb Wave Propagation ◽  
Wave Modes

Lamb waves are dispersive and multi-modal. Various wave modes make the interpretation of Lamb wave signal very difficult. It is desired that different modes can be separated for individual analysis. In the this paper, we present our studies on the multimodal Lamb wave propagation and wave mode extraction using frequency-wavenumber analysis. Wave spectrum in the frequency-wavenumber domain shows clear distinction among Lamb wave modes being present. This allows separating them or extracting a desired Lamb wave mode through a novel filtering strategy. Thus a single mode Lamb can be identified and extracted for certain types of damage detection in structural health monitoring (SHM). These concepts are illustrated through experimental testing. A scanning laser Doppler vibrometer is used to acquiring the time-space wavefield regarding the multimodal Lamb wave propagation. Then the recorded wavefield was analyzed in frequency-wavenumber domain and decomposed into different wave modes.

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.

Damage Imaging and Quantification Using Spectral Field

2015 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu
Keyword(s):  
Damage Detection ◽  
Dispersion Curve ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Field Representation ◽  
Thickness Change ◽  
Time Space ◽  
Damage Imaging ◽  
Local Wavenumber ◽  
Aluminum Plates

This paper presents damage imaging and quantification by using the spectral field of Lamb waves. The spectral field is acquired through a piezoelectric transducer (PZT)-scanning laser Doppler vibrometer (SLDV) sensing. A wideband chirp signal is used for PZT excitation in order to generate wideband Lamb waves. With the SLDV, the time-space wavefield is acquired, and transformed into the spectral field representation through Fourier transform. The spectral field, which contains wideband Lamb wave responses of the structure, is further analyzed for damage detection and quantification. Using the spatial wavenumber analysis, the local wavenumber at each location are obtained, and represented as a spatial wavenumber image which can be used for damage detection and evaluation. Moreover, the dispersion curve regression method is developed to quantify the thickness change of a defect. For verification, experiments are performed on aluminum plates with blind holes of different depths. The experimental results show that the blind holes can be detected by both the spatial wavenumber imaging and dispersion curve regression. In addition, the dispersion curve regression can further quantify the depths of the blind holes.

Notice of Removal: Zero TCF resonator based on S0 Lamb wave mode in AlN thin plate films

2017 ◽  
Author(s):  
Mohammed Moutaouekkil ◽  
Abdelkrim Talbi ◽  
Omar Elmazria ◽  
El Houssaine El Boudouti ◽  
Philippe Pernod ◽  
...  
Keyword(s):  
Thin Plate ◽  
Lamb Wave ◽  
Wave Mode

Fast acquisition aperture correction in prestack depth migration using beamlet decomposition

Geophysics ◽  
2009 ◽  
Vol 74 (4) ◽  
pp. S67-S74 ◽  
Author(s):  
Jun Cao ◽  
Ru-Shan Wu
Keyword(s):  
Wave Equation ◽  
Correction Factor ◽  
Computing Time ◽  
Computation Time ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Wavenumber Domain ◽  
Amplitude Correction ◽  
Local Wavenumber ◽  
Local Angle

Wave-equation-based acquisition aperture correction in the local angle domain can improve image amplitude significantly in prestack depth migration. However, its original implementation is inefficient because the wavefield decomposition uses the local slant stack (LSS), which is demanding computationally. We propose a faster method to obtain the image and amplitude correction factor in the local angle domain using beamlet decomposition in the local wavenumber domain. For a given frequency, the image matrix in the local wavenumber domain for all shots can be calculated efficiently. We then transform the shot-summed image matrix from the local wavenumber domain to the local angle domain (LAD). The LAD amplitude correction factor can be obtained with a similar strategy. Having a calculated image and correction factor, one can apply similar acquisition aperture corrections to the original LSS-based method. For the new implementation, we compare the accuracy and efficiency of two beamlet decompositions: Gabor-Daubechies frame (GDF) and local exponential frame (LEF). With both decompositions, our method produces results similar to the original LSS-based method. However, our method can be more than twice as fast as LSS and cost only twice the computation time of traditional one-way wave-equation-based migrations. The results from GDF decomposition are superior to those from LEF decomposition in terms of artifacts, although GDF requires a little more computing time.

Theoretical Framework and Research Methods of Poyang Lake Smart Water Resource Monitoring Based on WSN and 3S Technologies

2014 ◽  
Vol 519-520 ◽  
pp. 1229-1234
Author(s):  
Jian Hua Wu ◽  
Jun Gong ◽  
Yue Zhi Hu ◽  
Yang Yang Wan
Keyword(s):  
Water Resource ◽  
Lake Water ◽  
Network Architecture ◽  
Spatial Information ◽  
Poyang Lake ◽  
Sensor Data ◽  
Detection Methods ◽  
Resource Monitoring ◽  
Smart Water ◽  
Time Space

Expounded research background and significance of Poyang Lake smart water resource monitoring, proposed a new theory research framework of Poyang Lake smart water resource monitoring based on WSN and 3S spatial information technologies, explored the related basic theories and methods which applied to the research of water resource smart monitoring, summarized the key issues in the researches of building wireless sensor network architecture and multi-sensor fusion physics platform for Poyang Lake water resource monitoring, methods of multi-sensor information extraction, access, processing and storage, the Poyang Lake water monitoring information spatializiation methods, multi-sensor data anomaly detection methods, and gave the research ideas and problem-solving strategies. Eventually, through the establishment of a practical and reliable Poyang Lake smart water resource monitoring system, improve flexibility, real-time, space visibility of water resource monitoring.

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.

Noncontact/Remote Material Characterization Using Ultrasonic Guided Wave Methods

2020 ◽  
Author(s):  
Zhaoyun Ma ◽  
Lingyu Yu
Keyword(s):  
Guided Waves ◽  
Broad Band ◽  
Laser Doppler Vibrometer ◽  
Pulsed Laser ◽  
Guided Wave ◽  
Target Plate ◽  
Ultrasonic Guided Wave ◽  
Time Space ◽  
Aluminum Plates ◽  
Wave Methods

Abstract Noncontact and remote NDE systems and methods are highly desired in a broad range of engineering applications such as material property characterization. This paper aims to develop such a noncontact/remote NDE system based on laser ultrasonic guided waves and establish its fundamental capability for material thickness evaluation. The noncontact system employs pulsed laser (PL) for guided wave actuation and scanning laser Doppler vibrometer (SLDV) for guided wave wavefield sensing. A cylindrical planoconvex lens is adopted to focus the pulsed laser beam to a line source in order to excite broad band signals in the target plate. Aluminum plates with different thicknesses are evaluated through SLDV line scans and 2D time-space wavefields are acquired. Frequency-wavenumber (f-k) spectra are obtained through 2D Fourier transform, and the A0 dispersion curve for each plate is extracted. Through Comparing the extracted A0 curve with the theoretical A0 dispersion curves, the thicknesses of the tested plates are identified. Reflective tape effect on the plates are also studied: the reflective tape attached for SLDV enhancement affects the guided waves in the target plate significantly when the plate is relatively thin.

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