Showing papers on "Lamb waves published in 2013"
TL;DR: In this article, the authors describe a method to effectively image structural features and defects using local estimates of the wavenumber of propagating guided Lamb waves at a fine grid of spatial sampling points.
Abstract: This paper describes a method to effectively image structural features and defects using local estimates of the wavenumber of propagating guided Lamb waves at a fine grid of spatial sampling points. The guided waves are rapidly excited at each grid point using a scanning Q-switched laser system and sensed by a single fixed ultrasonic transducer. Through reciprocity, this produces a full-wave-field time history of a virtual wave being excited from the transducer. Using frequency–wavenumber processing, localized wavelength estimates are obtained by isolating each wave mode, narrowband filtering to one or more high-energy frequency bands, and identifying the center-wavelength of a sliding wavenumber band-pass filter that maximizes the energy at each grid point. The approach was capable of producing detailed images of hidden wall-thinning in an aluminum plate and a steel pipe section and local impact delamination in a complicated composite component.
161 citations
TL;DR: In this paper, a two-dimensional planar array of small lead discs on an aluminum plate with silicone rubber is shown numerically to focus low-frequency flexural guided waves.
Abstract: Bonding a two-dimensional planar array of small lead discs on an aluminum plate with silicone rubber is shown numerically to focus low-frequency flexural guided waves. The “effective mass density profile” of this type of elastic metamaterials (EMMs), perpendicular to wave propagation direction, is carefully tailored and designed, which allows rays of flexural A0 mode Lamb waves to bend in succession and then focus through a 7 × 9 planar array. Numerical simulations show that Lamb waves can be focused beyond EMMs region with amplified displacement and yet largely retained narrow banded waveform, which may have potential application in structural health monitoring.
143 citations
TL;DR: In this article, the authors make an overview of the progress made during the last decade with regard to a novel class of piezoelectric microwave devices employing acoustic Lamb waves in micromachined thin film membranes.
Abstract: This work makes an overview of the progress made during the last decade with regard to a novel class of piezoelectric microwave devices employing acoustic Lamb waves in micromachined thin film membranes. This class of devices is referred to as either thin film Lamb wave resonators or piezoelectric contour-mode resonators both employing thin film aluminum nitride membranes. These devices are of interest for applications in both frequency control and sensing. High quality factor Lamb wave resonators exhibiting low noise, low loss and thermally stable performance are demonstrated and their application in high resolution gravimetric and pressure sensors further discussed. A specific emphasis is put on the ability of these devices to operate in contact with liquids. Future research directions are further outlined.
140 citations
TL;DR: The Hybrid Algorithm for Robust Breast Ultrasound Tomography (HARBUT) as discussed by the authors was developed to give high-resolution, accurate and robust reconstructions of ultrasonic velocity through the breast; in this paper, we extend the method to generate thickness maps for guided wave tomography.
136 citations
TL;DR: This paper presents a methodology referred to as sparse wavenumber analysis based on sparse recovery methods, which accurately recovers the Lamb wave's frequency-wavenumber representation with a limited number of surface mounted transducers.
Abstract: Guided waves in plates, known as Lamb waves, are characterized by complex, multimodal, and frequency dispersive wave propagation, which distort signals and make their analysis difficult. Estimating these multimodal and dispersive characteristics from experimental data becomes a difficult, underdetermined inverse problem. To accurately and robustly recover these multimodal and dispersive properties, this paper presents a methodology referred to as sparse wavenumber analysis based on sparse recovery methods. By utilizing a general model for Lamb waves, waves propagating in a plate structure, and robust l1 optimization strategies, sparse wavenumber analysis accurately recovers the Lamb wave's frequency-wavenumber representation with a limited number of surface mounted transducers. This is demonstrated with both simulated and experimental data in the presence of multipath reflections. With accurate frequency-wavenumber representations, sparse wavenumber synthesis is then used to accurately remove multipath interference in each measurement and predict the responses between arbitrary points on a plate.
123 citations
TL;DR: A method of making flexible SAW devices using ZnO nanocrystals deposited on a cheap and bendable plastic film is reported, demonstrating the great potential for applications in electronics and MEMS.
Abstract: Flexible electronics are a very promising technology for various applications. Several types of flexible devices have been developed, but there has been limited research on flexible electromechanical systems (MEMS). Surface acoustic wave (SAW) devices are not only an essential electronic device, but also are the building blocks for sensors and MEMS. Here we report a method of making flexible SAW devices using ZnO nanocrystals deposited on a cheap and bendable plastic film. The flexible SAW devices exhibit two wave modes - the Rayleigh and Lamb waves with resonant frequencies of 198.1 MHz and 447.0 MHz respectively, and signal amplitudes of 18 dB. The flexible devices have a high temperature coefficient of frequency, and are thus useful as sensitive temperature sensors. Moreover, strong acoustic streaming with a velocity of 3.4 cm/s and particle concentration using the SAW have been achieved, demonstrating the great potential for applications in electronics and MEMS.
110 citations
TL;DR: In this article, a hybrid lead zirconate titanate (PZT)-laser vibrometer system and frequency-wave number analysis is used to acquire high-resolution time-space Lamb wavefield excited by a PZT actuator.
Abstract: Lamb waves are dispersive and multi-modal, which makes the interpretation of Lamb wave signals very difficult in either the time or frequency domain. In the this article, we present our studies on Lamb wave propagation characterization and crack detection using a hybrid lead zirconate titanate (PZT)-laser vibrometer system and frequency–wave number analysis. A scanning laser Doppler vibrometer is used to acquiring high-resolution time–space Lamb wavefield excited by a PZT actuator. The recorded wavefield is then transformed to frequency–wave number domain by two-dimensional Fourier transform. Wave spectrum in the frequency–wave number domain shows clear distinction among Lamb wave modes being present. These concepts are illustrated through several experimental tests. However, the space information is lost during this transformation. A short-space two-dimensional Fourier transform is then adopted to obtain the frequency–wave number spectra at various spatial locations, resulting in the space–frequency–wave...
86 citations
TL;DR: In this paper, a multi-feature integration method based on a second-order multivariate regression analysis is proposed for the prediction of fatigue crack lengths using sensor measurements, and the model parameters are obtained using training datasets from five specimens.
Abstract: This paper presents an experimental study of damage detection and quantification in riveted lap joints. Embedded lead zirconate titanate piezoelectric (PZT) ceramic wafer-type sensors are employed to perform in situ non-destructive evaluation (NDE) during fatigue cyclical loading. PZT wafers are used to monitor the wave reflection from the boundaries of the fatigue crack at the edge of bolt joints. The group velocity of the guided wave is calculated to select a proper time window in which the received signal contains the damage information. It is found that the fatigue crack lengths are correlated with three main features of the signal, i.e., correlation coefficient, amplitude change, and phase change. It was also observed that a single feature cannot be used to quantify the damage among different specimens since a considerable variability was observed in the response from different specimens. A multi-feature integration method based on a second-order multivariate regression analysis is proposed for the prediction of fatigue crack lengths using sensor measurements. The model parameters are obtained using training datasets from five specimens. The effectiveness of the proposed methodology is demonstrated using several lap joint specimens from different manufactures and under different loading conditions. (Some figures may appear in colour only in the online journal)
79 citations
TL;DR: An omni-directional SH magnetostrictive patch transducer that consists of an annular magnetostriction patch, a toroidal coil and a permanent magnet is proposed.
75 citations
TL;DR: In this article, the authors proposed a method based on the concept of cointegration that is partially built on the analysis of the non-stationary behaviour of time series to remove the undesired temperature effect from Lamb wave data.
Abstract: Lamb waves are often used in smart structures with integrated, low-profile piezoceramic transducers for damage detection. However, it is well known that the method is prone to contamination from a variety of interference sources including environmental and operational conditions. The paper demonstrates how to remove the undesired temperature effect from Lamb wave data. The method is based on the concept of cointegration that is partially built on the analysis of the non-stationary behaviour of time series. Instead of directly using Lamb wave responses for damage detection, two approaches are proposed: (i) analysis of cointegrating residuals obtained from the cointegration process of Lamb wave responses, (ii) analysis of stationary characteristics of Lamb wave responses before and after cointegration. The method is tested on undamaged and damaged aluminium plates exposed to temperature variations. The experimental results show that the method can: isolate damage-sensitive features from temperature variations, detect the existence of damage and classify its severity.
TL;DR: The thermal sensitivity gives insight to how temperature affects Lamb wave speeds in different frequency ranges and will help those developing structural health monitoring algorithms.
TL;DR: Guided ultrasonic waves are increasingly used in all those structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivit... as mentioned in this paper.
Abstract: Guided ultrasonic waves are increasingly used in all those structural health monitoring applications that benefit from built-in transduction, moderately large inspection ranges, and high sensitivit...
TL;DR: In this article, the semi-analytical finite element (SAFE) method is applied as it is suitable for both isotropic homogeneous plates and anisotropic composite laminated plates.
Abstract: Lamb wave propagation in plates is multi-modal, dispersive and highly dependent on the material properties. In homogeneous isotropic plates, Lamb modes can be grouped into symmetric and anti-symmetric modes, and they are decoupled from the shear modes. Due to the material isotropy, Lamb wave propagation behavior is independent from the propagation direction. This property can be used to find analytical solutions for the field of displacements in the frequency domain. However, in composite plates having anisotropic material properties, Lamb wave propagation behavior depends on the propagation direction. For this reason, the complexity of Lamb wave propagation modes increases, and no direct analytical solutions are available. Thus, numerical methods need to be used. In this paper, the semi-analytical finite element (SAFE) method is applied as it is suitable for both isotropic homogeneous plates and anisotropic composite laminated plates. Dispersion curves for these complex materials are calculated using SAFE. The effect of obstacles on the reflection and transmission of Lamb waves is considered. SAFE is also used for 2D point force response analysis. By applying the 2D point response analysis for perfectly bonded strip actuators, mode tuning behavior is calculated for general composite plates. A method to consider plate edge reflections in the 2D force response analysis is also presented.
TL;DR: In this paper, a multi-element matrix ultrasonic probe is driven using the well-known phased array principle, for launching and detecting pure Lamb modes in/from specific directions along the plate, which are arbitrary for isotropic materials and limited to specific directions for anisotropic materials.
Abstract: This article presents a technique for the generation and detection of Lamb waves guided along large plate-like structures made from various types of materials (metal, polymer, fibre-reinforced composite, etc.). A multi-element matrix ultrasonic probe is driven using the well-known phased array principle, for launching and detecting pure Lamb modes in/from specific directions along the plate, which are arbitrary for isotropic materials and limited to specific directions for anisotropic materials, e.g. principal directions or directions for which both phase and group velocities are collinear. The probe is gel-coupled to the tested specimen and allows quick inspection of large area from its fixed position, even of zones with limited access. The technique, which takes into account the frequency dispersive effects, is different than SHM-like (Structural Health Monitoring) inspection, since all transmitting or receiving elements are grouped together in a localized area defined by the active surface of the probe, and not permanently attached to the tested structure. The use of a multi-element probe, for long range Lamb waves-based inspection, is also distinctive from that usually performed, which consists of very local inspection of a material by steering the ultrasonic beam below and nearby the probe. A prototype is presented, as well as measurements of its performances in terms of modal selectivity and directivity. Finally the detection and localisation of a through-thickness hole in a large aluminium plate, of a delamination-like defect in a carbon epoxy composite plate and of an impact damage on a stiffened composite curved plate are shown.
TL;DR: In this paper, an ultrasonic based Lamb wave propagation method for identifying and measuring the damage location in a material for SHM is presented, which determines the experimental and analytical effects of various parameters on the sensitivity of damage detection and a methodology is proposed for estimating and measured the location of damage in the test specimens.
TL;DR: In this paper, an image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed, where a linear array consisting of 16 piezoelectric elements is attached to a 1-mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively.
Abstract: Several Lamb wave modes can be coupled to a particular structure, depending on its geometry and transducer used to generate the guided waves. Each Lamb mode interacts in a particular form with different types of defects, like notches, delamination, surface defects, resulting in different information which can be used to improve damage detection and characterization. An image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed. A linear array consisting of 16 piezoelectric elements is attached to a 1 mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively. For each mode two images are obtained from amplitude and phase information: one image using the Total Focusing Method (TFM) and one phase image obtained from the Sign Coherence Factor (SCF). Each TFM image is multiplied by the SCF image of the respective mode to improve contrast and reduce side and grating lobes effects. The high dispersive characteristic of the A0 mode is compensated for adequate defect detection. The information in the SCF images is used to select one of the TFM mode images, at each pixel, to obtain the compounded image. As a result, dead zone is reduced, resolution and contrast are improved, enhancing damage detection when compared to the use of only one mode.
TL;DR: It is demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.
Abstract: Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb wave dispersion ultrasound vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50-400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ1, and viscosity, μ2 as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.
TL;DR: In this article, the applicability of a Bayesian system identification theory for localizing damage in plate-like structures, while considering the uncertainties from modeling and measurement, is investigated.
Abstract: This paper presents an investigation of the applicability of a Bayesian system identification theory for localizing damage in plate-like structures, while considering the uncertainties from modeling and measurement Diagnostic Lamb waves are excited and received by a piezoelectric sensor network before and after damage to obtain scattered waves that contain characteristic information about the damage After the time-of-flight (ToF) of the scattered waves in each actuator–sensor path is measured by a continuous wavelet transform (CWT), a Bayesian approach is developed to identify the damage location and wave velocity By combining the prior information and the measured ToF data, Bayes’ theorem is used to update the probability distributions of the parameters about the damage location and wave velocity In particular, a Markov chain Monte Carlo (MCMC) method is employed for sampling the posterior distributions of the unknown parameters A numerical study for an aluminum plate and experimental studies for a stiffened aluminum panel and a composite laminate are conducted to validate the proposed Bayesian damage localization approach
TL;DR: In this paper, a crack detection and imaging approach using a Lamb wave-focusing array algorithm was developed and applied to both simulation and experimental data to generate intensity images of the structure under interrogation.
Abstract: Cracks are common defects in aluminum plate-like components that are in widespread use in aerospace, shipbuilding, and other industries. Ultrasonic detection using Lamb waves has proven to be an efficient method for crack detection and localization. However, quantitative information regarding crack size or orientation is of paramount importance for damage diagnosis and life prediction. In this article, employing a sparsely arranged piezoelectric sensor array, a quantitative crack detection and imaging approach using a Lamb wave–focusing array algorithm is developed and presented. Additionally, Lamb wave propagation on thin-wall plates and wave interaction with crack damage was studied using three-dimensional elastodynamic finite integration technique. The focusing array imaging algorithm was then developed and applied to both simulation and experimental data to generate intensity images of the structure under interrogation. Experimentally, wafer-type piezoelectric actuators/sensors are permanently install...
TL;DR: The paper explores a newly proposed, very efficient numerical simulation tool for Lamb wave propagation modelling in aluminum plates exposed to temperature changes using a local interaction approach implemented with a parallel computing architecture and graphics cards.
Abstract: Temperature has a significant effect on Lamb wave propagation. It is important to compensate for this effect when the method is considered for structural damage detection. The paper explores a newly proposed, very efficient numerical simulation tool for Lamb wave propagation modelling in aluminum plates exposed to temperature changes. A local interaction approach implemented with a parallel computing architecture and graphics cards is used for these numerical simulations. The numerical results are compared with the experimental data. The results demonstrate that the proposed approach could be used efficiently to produce a large database required for the development of various temperature compensation procedures in structural health monitoring applications. (Some figures may appear in colour only in the online journal)
TL;DR: In this article, a non-linear Lamb wave signal processing strategy aimed at extending the capability of activepassive networks of PZT transducers for defect detection is proposed, which allows to use chirp shaped pulses in actuation, instead of classically applied spiky pulses, requiring thus lower input voltages.
TL;DR: In this paper, the third order harmonic generation due to the cubic interaction of two collimated elastic waves in a homogeneous, isotropic, weakly nonlinear plate is investigated by using a fourth order expansion of strain energy density to formulate the nonlinear boundary problems.
Abstract: The third order harmonic generation (third harmonics as well as cubic sum and difference harmonics) due to the cubic interaction of two collimated elastic waves in a homogeneous, isotropic, weakly nonlinear plate is investigated by using a fourth order expansion of strain energy density to formulate the nonlinear boundary problems. Waves with both shear horizontal (SH) and Rayleigh Lamb (RL) nature are considered as primary or tertiary wave fields. The non-zero power flux condition is evaluated using characteristic parity matrices of the cubic nonlinear forcing terms and third order harmonic mode shapes. Results indicate that waves with either SH or RL nature receive power flux from a specific pattern of primary mode interaction. Further analytical evaluation of the synchronism condition enables identification of primary SH and RL modes that are able to generate cumulative third harmonics. The primary SH modes are shown to be holo-internal-resonant with third harmonic SH fields. This simply means that all points on the primary dispersion curves are internally resonant with third harmonics, which is not the case for second harmonics. Such flexibility will be advantageous for laboratory and field measurements.
TL;DR: In this paper, it is shown from numerical solutions of the acoustoelastic wave equation for an isotropic plate that it is possible to decouple the effects of a homogeneous biaxial stress into its two principal components.
Abstract: Spatially distributed arrays of piezoelectric disks are being applied to monitor structural integrity using Lamb waves. Applied loads directly affect waves propagating between array elements because of dimensional changes and the acoustoelastic effect. Resulting changes in phase velocity depend upon the propagation direction as well as the Lamb wave mode and frequency. This paper shows from numerical solutions of the acoustoelastic wave equation for an isotropic plate that it is possible to decouple the effects of a homogeneous biaxial stress into its two principal components. As a consequence of both this decoupling and material isotropy, the acoustoelastic response of a specific mode and frequency is described by only two constants, which can be determined from a uniaxial loading experiment. Using this formulation, a method is developed and verified via simulations to estimate an arbitrary biaxial load from phase velocity changes measured along multiple directions of propagation. Results from uniaxial loading experiments on two different plates further demonstrate the efficacy of the method. It is also shown that opening fatigue cracks may significantly degrade results by interfering with Lamb wave direct arrivals, but that this degradation can be mitigated by using a reduced set of data from unaffected paths of propagation.
TL;DR: The reflection of obliquely incident symmetric and anti-symmetric Lamb wave modes at the edge of a plate is studied and energy reflection coefficients are calculated for the reflected wave modes as a function of frequency and angle of incidence.
TL;DR: In this article, a time-frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed, which returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal.
Abstract: A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments.
TL;DR: The generation of omnidirectional Lamb waves by a new magnetostrictive patch transducer (MPT) is presented and the mechanism of the Lamb wave generation and its frequency characteristics are investigated.
Abstract: This work presents the generation of omnidirectional Lamb waves by a new magnetostrictive patch transducer (MPT) and investigates its generation mechanism. Although MPTs have been widely used for wave transduction in plates and pipes, no investigation reports the generation of omnidirectional Lamb waves in a plate by an MPT. For the generation, we propose an axisymmetrically-configured MPT that installs multiple axisymmetric turns of coil outside of a permanent cylindrical magnet located above the center of a circular magnetostrictive patch. After confirming the omnidirectivity of the proposed MPT experimentally, the mechanism of the Lamb wave generation and its frequency characteristics are investigated. It is also shown that the Lamb wave is most efficiently generated in a test plate when its wavelength is equal to two-thirds of the magnetostrictive patch diameter. If this wavelength?patch diameter relation holds, the second radial extensional vibration mode of the patch of the proposed MPT is shown to be the mode responsible for generating the Lamb wave in a plate.
TL;DR: In this article, a three-dimensional numerical model was applied to generate irregular waves, and transformation of irregular waves was simulated in a numerical wave tank, and the model was then used to generate directional monochromatic and irregular waves in three dimensions.
TL;DR: In this paper, a linear phononic device that shows asymmetric Lamb wave transmission in low-frequency domains was proposed and studied using numerical simulation of the Lamb wave propagation in phononic crystal slabs with graded grating.
Abstract: Asymmetric Lamb wave propagation is important for control and manipulation of the Lamb wave signals in various devices. Through numerical simulation of the Lamb wave propagation in phononic crystal slabs with graded grating, we proposed and studied a linear phononic device that shows asymmetric Lamb wave transmission in low-frequency domains. This exotic phenomenon stems from the threshold frequency of the fundamental antisymmetric Lamb mode conversion to the fundamental symmetric Lamb mode is different at the different locations of the acoustic diode. Remarkably, a bi-directional asymmetric Lamb wave propagation is achieved by tuning the grade of the grating depths. The back propagating acoustic waves of the second band of hybridized Lamb modes plays the essential role in the phenomena for relatively high-frequency regions. This should be potentially significant in helping design chip-scale integrated phononic devices.
TL;DR: In this article, a finite element approach for modeling of acoustic emission sources and signal propagation in hybrid multi-layered plates is presented, validated by Laser vibrometer measurements and comparison to calculated dispersion curves.
Abstract: A finite element approach for modeling of acoustic emission sources and signal propagation in hybrid multi-layered plates is presented. Modeling results are validated by Laser vibrometer measurements and comparison to calculated dispersion curves. We investigate hybrid plates as typically found in composite pressure vessels, composed of fiber reinforced polymers with arbitrary stacking sequences and attached metal or polymer materials. Hybrid plate thickness, the ratio between anisotropic and isotropic materials and material properties are varied. Lamb-wave propagation in a geometry representative of a pressure vessel is modeled. It is demonstrated, that acoustic emission sources in multi-layered structures can cause Lamb-waves superimposed by guided waves within the individual layers.