Single Lamb Wave Mode Research Articles

Research on Delamination Damage Quantification Detection of CFRP Bending Plate Based on Lamb Wave Mode Control.

The carbon-fiber-reinforced polymer (CFRP) bending structure is widely used in aviation. The emergence and spread of delamination damage will decrease the safety of in-service bending structures. Lamb waves can effectively identify delamination damage as a high-damage-sensitivity detection tool. For this present study, the signal difference coefficient (SDC) was introduced to quantify delamination damage and evaluate the sensitivity of A0-mode and S0-mode Lamb waves to delamination damage. The simulation results show that compared with the S0-mode Lamb wave, the A0-mode Lamb wave exhibits higher delamination damage sensitivity. The delamination damage can be quantified based on the strong correlation between the SDC and the delamination damage size. The control effect of the linear array PZT phase time-delay method on the Lamb wave mode was investigated by simulation. The phase time-delay method realizes the generation of a single-mode Lamb wave, which can separately excite the A0-mode and S0-mode Lamb wave to identify delamination damage of different sizes. The A0-mode Lamb wave was excited by the developed one-dimensional miniaturized linear comb transducer (LCT), which was used to conduct the detection experiment on the CFRP bending plate with delamination damage sizes of Φ6.0 mm, Φ10.0 mm, and Φ15.0 mm. The experimental results verify the correctness of the simulation. According to the Hermite interpolation results of the finite-element simulation data, the relationship between the delamination damage size and the SDC was fitted by the Gaussian function and Rational function, which can accurately quantify the delamination damage. The absolute error of the delamination damage quantification with Gaussian and Rational fitting expression does not exceed 0.8 mm and 0.7 mm, and the percentage error is not more than 8% and 7%. The detection and signal processing methods employed in the present research are easy to operate and implement, and accurate delamination damage quantification results have been obtained.

Delamination imaging in composites using cross-correlation method by non-contact air-coupled Lamb waves

This paper presents a cross-correlation damage detection technique using damage scattered waves of all directions cross-correlate with the incident waves for delamination imaging in carbon fiber reinforced polymer (CFRP) composite plate. The presented imaging can not only detect the delamination but also precisely quantify the damage with locations and sizes. First, a CFRP composite sample with interlaminar delamination by inserting the Teflon layer is designed and manufactured in house using the hot-press machine. And a three-dimensional model of composite sample is simulated using the finite element method. Next, the cross-correlation imaging algorithm is introduced in detail, and the cross-correlation imaging proof-of-concept study is conducted with the simulated Lamb waves in the composite sample. Finally, a fully non-contact air-coupled transducer and scanning laser Doppler vibrometer system with a single-mode Lamb wave method is established to actuate and sense the interrogating Lamb waves in the structure. The imaging method is experimentally implemented for the one delamination and two delaminations imaging and quantification.

Non-invasive analysis of macro-crack on the characteristics of ultrasonic guided wave

The effects of macro-crack in plates on the characteristic of ultrasonic guided wave were studied. Using the Finite Element Model and numerical calculation method, the finite element mesh models of various macro-crack in aluminum plate were established. The single S0 or A0 mode Lamb wave was excited in plate by the wave structure loading method. The propagation time and amplitude of wave packet in the received signal were analyzed to study the phenomenon of mode transformation and the relationship between macro-crack size and signal amplitude. The simulation results show that there is mode conversion when the single mode Lamb wave interacts with an asymmetric macro-crack, and no mode conversion with a symmetric macro-crack. The energy of reflected wave increases with the increase of the depth and width of macro-crack, and the energy of transmitted wave decreases correspondingly. The size and inclined angle of macro-crack can be quantitatively estimated by the fitting function from the energies of reflected and transmitted waves. The variation of crack depth, width and angle is approximately linear with the amplitudes of reflected and transmitted wave packets. A fitting function is constructed by using the amplitude ratio of reflected wave packet or transmitted wave packet to total wave packet, which can be used to estimate the macro-crack depth, width and angle. This conclusion is helpful to the detection of macro-crack in the actual production and service of plate structures.

Phased Array System for Damage Detection in Plate-Like Structures Based on Single Lamb Wave Mode Extraction

Phased Array System for Damage Detection in Plate-Like Structures Based on Single Lamb Wave Mode Extraction

Single-mode Lamb wave excitation at high-frequency-thickness products using a conventional linear array transducer

Lamb wave excitation at high-frequency-thickness products offers a potential solution for high-resolution guided wave testing. The method is attractive for crack imaging and corrosion mapping, especially in hidden locations where direct access is limited. However, multiple modes may propagate, complicating signal interpretation, which is undesirable. In this work, a systematic approach is presented, in an effort to determine the influence of the key parameters related to single higher order Lamb wave mode excitation using a conventional linear array transducer. Specifically, a linear time delay law is used to enhance the targeted mode, while the array's length, pitch and apodisation profile remain to be optimally selected. First, an analytical solution is derived based on modal analysis. This provides a natural decomposition of the amplitude of a guided wave mode into the product of the response of a single element and the excitation spectrum. Then, a key observation is made, associating the excitation spectrum to the directivity function for bulk wave phased array steering. This allows the application of well-established phased array analysis tools to guided wave phased array excitation. In light of this fact, minimisation of the spectrum’s bandwidth, elimination of the grating lobes and derivation of an apodisation profile are performed, to enhance the purity of the targeted mode. Finally, experiments conducted on an aluminium plate verify the above theoretical results. The Full Matrix is acquired, and all signals are reconstructed synthetically.

Damage imaging method for composites laminates based on sparse reconstruction of single-mode Lamb wave

To address the problems of anisotropy and mode mixing in damage imaging on anisotropic composites laminates using ultrasonic Lamb wave, a sparse reconstruction imaging method based on S0 single-mode is proposed in this paper. In this approach, the sparsely arranged piezoelectric ceramic drivers sensor group on the surface of the measured composite laminate is employed to excite and receive Lamb wave. The received signal shows sparse under a pre-built damage dictionary with damage scattering signal waveform, and the damages can be localized and imaged using a sparse reconstruction method. Considering the velocity difference between S0 and A0 mode of the received Lamb wave signal, the S0 mode is extracted by intercepting the signal before the peak of the first wave packet to eliminate the influence of Lamb wave mode mixing. In order to minimize the influence of anisotropy of composites laminates on Lamb wave propagation, the Lamb wave propagation direction is divided evenly into several sectors, and Lamb wave propagation direction within a certain sector is considered as propagation in a quasi-isotropic material. The sparse reconstruction is solved by using the basis pursuit de-noising algorithm, which can find the optimal solution with a small number of iterations in noise interference. The experiments on composite fiber laminate specimens show that the proposed method can accurately locate simulated single delamination damage and has less artifact interference compared to the delay-and-sum method.

A Lamb waves-based wireless power transmission system for powering IoT sensor nodes

Sensor nodes (SNs) are widely deployed for condition monitoring within closed thin-walled structures. Conventional wired power supply using cables will affect the structural integrity, and wireless power supply based on inductive coupling will be shielded by metal structures, therefore, neither is desirable. Motivated by these issues, this article presents a Lamb waves wireless power transmission (WPT) technology based on piezoelectric wafer active sensors (PWASs). A PWAS with a diameter of 7 mm was used to excite A0 single-mode Lamb waves on a 1.6 mm aluminum plate at a frequency of 150 kHz for power transmission. Two optimization strategies for the Lamb waves-based WPT system were proposed and designed, including electrical impedance matching and beamforming with a linear PWAS array. The optimization effects of these two methods were analyzed experimentally. By combining these two approaches, the maximum received power is 1.537 mW, which is 384.25 times higher than that without the optimization method. The corresponding transmission efficiency is 0.217%, which is 43.4 times higher than that without the optimization method. A power management circuit was built with a maximum output power of 1.41 mW and a corresponding conversion efficiency of 77.5%. Finally, an internet-of-things (IoT) SN is designed, and a test proves that the proposed WPT system can power IoT SNs.

A Novel Single-Mode Lamb Wave Generation Method for Crack Localization of Beam Structures

Structure health monitoring of beam structures is important in civil and mechanical engineering. Lamb waves have the advantages of long propagation distance and low power loss, which are widely used in the field of nondestructive testing. However, Lamb waves generated via conventional methods usually contain multiple modes, and in many cases, the multi-mode Lamb waves cause difficulties in damage detection and localization. This research proposes a novel single-A<SUB>0</SUB> mode Lamb wave generation technique; the actuator is attached on the side surface of a beam structure, and the sensor is attached on the top or bottom surface, which is perpendicular to the side surface, such that the single-A<SUB>0</SUB> mode of the Lamb wave can be generated. Due to the mode conversion effect of the Lamb wave when it passes through a crack, the existence of the crack can be determined by evaluating the existence of the S<SUB>0</SUB> mode. In addition, the crack can be localized accurately using the proposed algorithm. Numerical and experimental investigations are performed to verify the performance of the proposed method. Comparisons with other single-mode Lamb wave generation methods are also performed to validate the advantages of the proposed method.

A0 Mode Excitation and Defect Detection in Aluminum Beam Structure

As a method to realize the defect detection in beam structure, this paper constructs an EMAT-laser detection system to detect the notch defect in an aluminum beam. EMAT is designed as a transmitter to generate single Lamb wave mode. A high precision laser detector is used as a receiver to obtain the received signals. The defect is localized and quantified with the help of space-frequency-wavenumber analysis. The evaluated depth of the defect is 2.006 mm, while the actual size is 2 mm. It shows good agreement between the evaluated result and actual size, the error is only 0.3%. This method also can be used in the evaluation of defect in other materials.

Leaky Lamb Wave Radiation from a Waveguide Plate with Finite Width

In this paper, leaky Lamb wave radiation from a waveguide plate with finite width is investigated to gain a basic understanding of the radiation characteristics of the plate-type waveguide sensor. Although the leaky Lamb wave behavior has already been theoretically revealed, most studies have only dealt with two dimensional radiations of a single leaky Lamb wave mode in an infinitely wide plate, and the effect of the width modes (that are additionally formed by the lateral sides of the plate) on leaky Lamb wave radiation has not been fully addressed. This work aimed to explain the propagation behavior and characteristics of the Lamb waves induced by the existence of the width modes and to reveal their effects on leaky Lamb wave radiation for the performance improvement of the waveguide sensor. To investigate the effect of the width modes in a waveguide plate with finite width, propagation characteristics of the Lamb waves were analyzed by the semi-analytical finite element (SAFE) method. Then, the Lamb wave radiation was computationally modeled on the basis of the analyzed propagation characteristics and was also experimentally measured for comparison. From the modeled and measured results of the leaky radiation beam, it was found that the width modes could affect leaky Lamb wave radiation with the mode superposition and radiation characteristics were significantly changed depending on the wave phase of the superposed modes on the radiation surface.

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

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.

Selective generation of ultrasonic guided waves for damage detection in rectangular bars

Ultrasonic guided waves are used in non-destructive testing and structural health monitoring solutions for long-range inspection, in applications ranging from Civil Engineering to Aerospace. In order to ease the inspection process, it is generally preferable to generate a carefully selected single mode. Although single mode Lamb wave generation is not difficult to achieve in infinite plate-like structures, with carefully polarized or sized piezoceramic elements, for example, such selective generation is much more difficult in a rectangular bar. In this article, we consider the propagation along a thin plate of finite rectangular cross section, which corresponds to a rectangular bar. The finite lateral width leads to a greater density of modes compared to an infinite plate. The authors have previously addressed this matter and developed a methodology for the selective generation of modes in the harmonic regime. This article extends this methodology to selective mode generation for finite time excitation, such as bursts. Results are presented for single mode generation of A0,0 and A0,1 in an aluminum bar instrumented with eight piezoelectric transducers. The waveguide modal basis is calculated with the two-dimensional semi-analytical finite element method, and measurements are conducted using a three-dimensional laser-Doppler vibrometer. To illustrate the potential of the method for structural health monitoring purposes, the detection of a defect simulated by a pair of magnets placed at various positions over the bar width is demonstrated.

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

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.

A Microcrack Location Method Based on Nonlinear S0 Mode Lamb Wave and Probability Scan Positioning Imaging Matrix

Early damage, such as microcrack, occupies most of the fatigue life of materials, and timely detection of early damage and positioning has great engineering and economic value. In this paper, a matrix scanning and positioning imaging method based on a probabilistic algorithm is proposed. Cooperating with the single-mode (S0) lamb wave, the microcrack in the thin plate material can be efficiently positioned. Taking the S0 mode lamb wave as the fundamental wave can effectively reduce the influence of the dispersion effect on the signal analysis. Meanwhile, in order to reduce the noise interference, the signal is reconstructed by empirical mode decomposition (EMD) to achieve the filtering effect. Then, the ABAQUS finite element simulation software is used to compare the positioning results under different locations of microcrack and different arrangements of probe. Finally, the feasibility of the localization algorithm is verified by the RAM-5000 SNAP nonlinear ultrasound system. The experimental results are consistent with the simulation theory, and the microcrack is effectively positioned. This facilitates our timely remedial action or further assessment of the remaining value of the material.

Impact Localization of Thin Plate Structures Using Pzt-Array Based Passive Wave Method

Impact of foreign objects is one of the main reasons for the damage of thin plate structures, resulting in property losses or unexpected accidents. Therefore, a rapid and effective impact localization of thin plate structures is of great value. In this paper, a localization method is proposed based on the passive wave method, aiming at locating the impact quickly and accurately. First, a square PZT array composed of 4 PZT sensors was designed, and a hyperbolic localization algorithm was derived according to time-different of arrival (TDoA) for different sensors in the array. Then, Matlab calculation software was used to perform DB wavelet decomposition on impact signals, the time delay was calculated by Lamb wave of A0 mode in D5 detail signals, and the velocity of A0 mode wave was determined by the dispersion curve for 1 mm thick aluminum plate. Finally, the impact point was located to experimentally verify the effectiveness of the proposed localization method. Experimental results show that the hyperbolic positioning algorithm based on TDoA can accurately identify impact locations, and wavelet decomposition can effectively identify single mode Lamb waves. The proposed method has the characteristics of fastness and accuracy, which is suitable for single object impact localization on thin plate structures.

Obliquely incident EMAT for high-order Lamb wave mode generation based on inclined static magnetic field

Lamb waves have the characteristics of long propagation distance, and they can be used to realize rapid and wide-scale nondestructive testing of plates. The detection sensitivity can be improved by using a high-order Lamb wave mode with a short wavelength. However, Lamb waves have multimode characteristics. The number of Lamb wave modes greatly increases at high frequencies, and it is difficult to obtain a pure single high-order Lamb wave mode with electromagnetic acoustic transducers (EMATs); this increases the difficulty of signal processing and analysis. In this study, an obliquely incident EMAT based on the inclined static magnetic field was designed to solve this problem. The mode selectivity of the proposed obliquely incident EMAT is superior to that of the traditional EMAT. A new parameter is proposed to improve the mode selectivity of EMATs: the polarization angle of the permanent magnet. The incident angle of incident ultrasonic waves is controlled by selecting the polarization angle of permanent magnet. A rectangular permanent magnet is obliquely polarized to provide a biased inclined static magnetic field. The obliquely incident Lorentz force is formed through the coupling between the eddy current and the inclined static magnetic field by an obliquely polarized permanent magnet. The obliquely incident Lorentz force is the source of the obliquely incident ultrasonic wave. Simulation and experimental results show that the developed obliquely incident EMAT can reduce the amplitude of the unwanted modes and enhance the mode selectivity. It was also verified that the developed obliquely incident EMAT had better frequency-response characteristics and sound-field directivity.

Damage Localization in Composite Laminates by Building in PZT Wafer Transducers: A Comparative Study with Surface‐Bonded PZT Strategy

Lamb waves provide sensitive and effective approach for nondestructive inspection of large‐scale composite structures. Traditionally in Lamb wave‐based damage detection systems, the piezoelectric (PZT) wafer transducers are attached on the surface of composite components. However, surface‐bonded PZT wafers are fragile, and they may lose serviceability when external load happens. In this paper, numerical and theoretical investigations are firstly carried out to analyze the Lamb wave features generated by PZT wafers that are located in the mid‐thickness of a thin‐walled plate. Subsequently, the authors integrate the PZT wafer arrays in woven glass fiber reinforced epoxy (WGF/epoxy) laminates with stacking sequence of [90°/0°]4. It is found that the approximate single S0 Lamb wave mode is generated by the built‐in PZT wafers. This makes the received signals very simple and easy to be interpreted. Utilizing the signals obtained by the built‐in and surface‐bonded PZT wafer transmitter‐receiver arrays, damage localization algorithms that considered the slowness profiles are compiled to help locating the defects. The compared results demonstrate that the built‐in PZT strategy has great potential for quantitative non‐destructive evaluation of composite structures.

Damage identification in welded structures using symmetric excitation of Lamb waves

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.

Damage Detection in a Plate Structure based on FBG sensing Technique under a Single-Mode Lamb Wave

Lamb wave is widely acknowledged as one of the most encouraging tools for damage identification in plate structures, and relevant research has been conducted intensively. However Lamb wave modes have different wave structure, frequency dispersion and attenuation characteristics, which are sensitivity to different types of damages and it is difficult to solve such engineering problems by conventional techniques. Although the single pattern detection method has been researched by piezoelectric wafers, there is little research about FBG sensing detection under single-mode ultrasonic Lamb wave technique currently. So this paper puts forward a single-mode Lamb wave technique for crack detection based on Fiber Bragg Grating sensor, which is used to receive the waves in the plate. First of all, measuring principle of single-mode ultrasonic Lamb technique and demodulation principle of the FBG sensor are introduced. And simulation analysis in the acoustic field is devoted, whose results lay the foundation for the damage detection in the plate. Then, the experimental system is built by a single-mode Lamb wave excitation, and the feasibility of fiber Bragg grating sensors in single-mode excitation method is verified by experiments.

A modified design of the omnidirectional EMAT for antisymmetric Lamb wave generation

This work presents a modified design of electromagnetic acoustic transducer (EMAT) that generates only antisymmetric (A0) omnidirectional Lamb wave. The new magnetic configuration includes a solid cylindrical magnet and a ring-shaped magnet surrounding the outside of the solid cylindrical magnet. The diameter of the solid cylindrical magnet is slightly small than the inner diameter of the ring-shaped magnet. The double-turn coil is used instead of a single spiral coil. Numerical simulation is applied to characterize the magnets and determine the coil parameters. Experimental results on a 3 mm-thick aluminum plate show that the modified EMAT we proposed can generate and receive pure single A0 mode Lamb wave with high signal to noise ratio and can effectively meet the imaging requirements.