Selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers

In this paper, we describe a modal expansion approach for the analysis of the selective generation of ultrasonic Lamb waves by electromagnetic acoustic transducers （EMATs）. With the modal expansion approach for waveguide excitation, an analytical expression of the Lamb wave＇s mode expansion coefficient is deduced, which is related to the driving frequency and the geometrical parameters of the EMAT＇s meander coil, and lays a theoretical foundation for exactly analyzing the selective generation of Larnb waves with EMATs. The influences of the driving frequency on the mode expansion coefficient of ultrasonic Lamb waves are analyzed when the EMAT＇s geometrical parameters are given. The numerical simulations and experimental examinations show that the ultrasonic Lamb wave modes can be effectively regulated （strengthened or restrained） by choosing an appropriate driving frequency of EMAT, with the geometrical parameters given. This result provides a theoretical and experimental basis for selectively generating a single and pure Lamb wave mode with EMATs.

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of I Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S2 and asymmetric modes A1 and A0 are analysed and compared. The results show that mode Ao is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0 mm in width, the presented mode Ao could be used potentially.

基于Barker码脉冲压缩技术的钢板多阵元Lamb波电磁超声换能器设计与优化

为了解决传统Barker码脉冲压缩技术受脉冲功率放大器额定参数(占空比,最大脉冲宽度等)限制而导致的脉冲压缩效果下降、检测速度降低等问题,提出一种基于Barker码脉冲压缩技术的多阵元Lamb波电磁超声换能器(EMAT)。建立了基于tone-burst信号激励-Barker码脉冲压缩技术的多阵元Lamb波EMAT检测过程的有限元模型,分析了永磁体的配置形式、阵元序列长度、激励信号周期数、曲折线圈匝数等因素对脉冲压缩后的主旁瓣比和主瓣宽度的影响,并进行了实验验证。结果表明:曲折线圈匝数为4和Barker码序列长度为13位的多阵元EMAT在配置3对外置永磁体后,其信噪比(SNR)可提高9.8 dB。综合考虑检测回波的空间分辨率和SNR,多阵元Lamb波EMAT最佳参数为:曲折线圈匝数为10、激励信号周期数为11、Barker序列为13位,并配置3对外置永磁体。

Non-contact air-coupled transducers Lamb wave signal multipath effect and blind separation for different modes using PZT as receiver

Due to the complexity and faintness of the detection wave patterns obtained by aircoupled transducers,if it is possible to effectively separate the various modes and obtain nondispersive signals for more accurate detection and positioning,it will help to improve the accuracy and reliability of air-coupled ultrasonic Lamb wave detection,providing better technical support for the application and development of related fields.Because of the increased complexity of aircoupled signals,there is no definite theoretical formula to describe the mode changes of aircoupled signals,so the method based on blind separation has unique value.To address these challenges,the paper proposes a single-channel blind source separation(SCBSS)method.The effectiveness of this method is evaluated through simulations and experiments,demonstrating favorable separation results and efficient computational speed.This work first conducts an in-depth analysis of the signal characteristics of air-coupled ultrasonic non-destructive testing,and simulates the ultrasonic excitation conditions of air-coupled sensors through finite element software.The study of modal changes and multipath effects caused by the variation of the incidence angle of the ACT signal is carried out,and the situation of the Lamb wave signal excited by ACT at the receiving end is analyzed.By combining ACT with PZT signals,the ultrasonic signals of air-coupled Lamb waves are compared and studied,and their modal purification is carried out.

Generation of narrowband Lamb waves based on the Michelson interference technique

An optical method of generating narrowband Lamb waves is presented. It is carried out with a laser line array in a thermoelastic regime implemented by the Michelson interference technique, where the formed array element spacing can be flexibly and conveniently changed to achieve selective mode excitation. In order to simulate the displacement response generated by this array, its intensity distribution function is presented to build a theoretical analysis model and to derive the integral representation of the displacement response. The experimental device and measuring system are built to generate and detect the Lamb waves on a steel plate. Numerical calculation results of narrowband Lamb wave displacement signals based on the theoretical model show good agreement with experimental results.

基于Lamb波的钢桥面板U肋-顶板节点疲劳损伤检测数值仿真分析

为解决Lamb波用于检测板类焊接结构疲劳损伤时受到多模态特性限制的问题,对Lamb波在无损和带损伤钢桥面板中的传播过程进行数值仿真分析。利用MATLAB软件计算Lamb波频散方程,得到对称模态和反对称模态下的群速度和相速度的频散曲线,并采用Hanning窗函数对Lamb波信号进行处理;以U肋-顶板节点疲劳损伤为例,基于Abaqus软件模拟Lamb波在无损和带损伤钢桥面板的传播过程,得到相应的幅值曲线,并通过小波分析确定钢桥面板的时频信号分布状态。结果表明:使用同一频率Lamb波检测时,有损信号的幅值增大;采用不同频率Lamb波检测带损伤钢桥面板,Lamb波的激励频率越高,信号幅值越大。200 kHz Lamb波相比150 kHz Lamb波的时频分布差异明显,且能量分布愈加集中,更利于实现损伤的精确定位,推荐采用200 kHz Lamb波检测钢桥面板的疲劳损伤。

Acoustic evaluation of cementing quality using obliquely incident ultrasonic signals

Ultrasonic cement bond logging is a widely used method for evaluating cementing quality. Conventional ultrasonic cement bond logging uses vertical incidence and cannot accurately evaluate lightweight cement bonding. Oblique incidence is a new technology for evaluating cement quality with improved accuracy for lightweight cements. In this study, we simulated models of acoustic impedance of cement and cementing quality using ultrasonic oblique incidence, and we obtained the relation between cementing quality, acoustic impedance of cement, and the acoustic attenuation coeffi cient of the A0-mode and S0-mode Lamb waves. Then, we simulated models of different cement thickness and we obtained the relation between cement thickness and the time difference of the arrival between the A0 and A0′ modes.

Analysis method and experimental study of ice accumulation detection signal based on Lamb waves

A quantitative identification method for in-flight icing has the capability to significantly enhance the safety of aircraft operations.Ultrasonic guided waves have the unique advantage of detecting icing in a relatively large area,but quantitative identification of ice layers is a challenge.In this paper,a quantitative identification method of ice accumulation based on ultrasonic guided waves is proposed.Firstly,a simulation model for the wave dynamics of piezoelectric coupling in three dimensions is established to analyze the propagation characteristics of Lamb waves in a structure consisting of an aluminum plate and an ice layer.The wavelet transform method is utilized to extract the Time of Flight(ToF)or Time of Delay(ToD)of S_(0)/B_(1) mode waves,which serves as a characteristic parameter to precisely determine and assess the level of ice accumulation.Then,an experimental system is developed to evaluate the feasibility of Lamb waves-based icing real-time detection in the presence of spray conditions.Finally,a combination of the Hampel median filter and the moving average filter is developed to analyze ToF/ToD signals.Numerical simulation results reveal a positive correlation between geometric dimensions(length,width,thickness)of the ice layer and ToF/ToD of B1 mode waves,indicating their potential as indicators for quantifying ice accumulation.Experimental results of real-time icing detection indicate that ToF/ToD will reach greater peak values with the growth of the arbitrary-shaped ice layer until saturation to effectively predict the simulation results.This study lays a foundation for the practical application of quantitative icing detection via ultrasonic guided waves.

冰层中Lamb波传播特性的数值模拟和实验研究

作为最常用的超声导波之一,Lamb波具有能量集中、传播范围广、沿程衰减小等特点,可以拓展应用于结冰探测领域。为探明Lamb波在冰层中的传播规律,基于Lamb波探冰实验平台构建物理模型,以COMSOL Multiphysics软件为计算工具,数值模拟了不同厚度、不同长度冰层中的Lamb波传播情况。在此基础上,搭建了Lamb波探冰实验平台,开展了无冰铝板和覆冰铝板Lamb波传播实验。结合数值模拟和实验结果,明确了温度、冰层几何特性、液态水对Lamb波传播特性的影响规律。结果表明:温度越低,Lamb波传播群速度越快;在一定冰层厚度范围内,接收端压电片电压幅值衰减量随冰层厚度增大而增大;随着冰层长度增加,接收端Lamb波B1模态时间延迟量线性增大;液态水仅对Lamb波A0模态产生影响,对S0模态影响不大。实验和数值模拟结果具有较好的一致性,为Lamb波结冰探测技术提供了理论参考。

Quality evaluation of laser welds based on air-coupled ultrasound

With the wide application of laser welding technology in automobiles and rail transportation, the non-destructive testing technology for laser welding seams is also getting better. Aiming at the laser welding seam of two-layer metal sheet below 3 mm, the possibility of laser welding seam detection by air-coupling ultrasonic detection technology is discussed. By numerical analysis and experimental analysis,Lamb wave is excited on aluminum plate in air. Through the propagation simulation of Lamb wave in laser weld specimen, the influence of laser weld width and weld quality on reflectivity and transmittance is analyzed. The propagation law of Lamb wave in laser weld specimen is clarified. The results show that the quality of laser weld can be evaluated by the mode of Lamb wave A0.

复合材料板的空耦超声Lamb波原位应力测量方法

为了实现大部件复合材料板的原位应力测量,提出了基于Lamb波的复合材料板空气耦合超声应力测量方法。目前,由于空耦超声换能器声阻抗的严重不匹配导致能量损失严重、空耦超声信号较为微弱,在声学特征准确提取上难度较大。与此同时,空耦超声Lamb波应力测量方法在复合材料中的应用仍处于理论与实验的探索阶段。通过实验方法探究碳纤维复合材料的Lamb波声弹性效应规律。根据复合材料板相速度与最佳入射角频散特性分析确定了空耦超声换能器的中心频率与相对纯净A0模态Lamb波的激励方式,使空耦超声Lamb波具有较好的信噪比,保证声时提取的准确度。为了验证所提出方法的有效性,分别沿着0°、15°、30°、45°、60°、75°以及90°纤维方向获得7个不同的拉伸试样进行应力测量。实验结果表明,在0~100 MPa范围内测量误差小于±8.1 MPa,测量重复性为7.5 MPa。该方法在测量精度和测量重复性等方面具有显著优势,可为大部件复合材料板的原位应力测量提供一种先进可行的技术。

Non-Contact Stress Measurement during Tensile Testing Using an Emat for SH₀-Plate Wave and Lamb Wave

The stress on a test specimen during tensile testing is generally measured by a strain gauge. This method has some problems in that it would influence the measurement conditions of the tensile test and can evaluate only the position at which the strain gauge is attached. The acoustoelastic method is proposed as a method replacing the strain gauge method. However, an ultrasonic sensor with a piezoelectric oscillator requires a coupling medium to inject an ultrasonic wave into a solid material. This condition, due to the error factor of the stress measurement, makes it difficult for the ultrasonic sensor to move on the specimen. We then tried to develop a non-contact stress measurement system during tensile testing using an electromagnetic acoustic transducer (EMAT) with an SH0-plate wave and S0-Lamb wave. The EMAT can measure the propagation time in which the ultrasonic wave travels between a receiver and a transmitter without a coupling medium during the tensile testing and can move easily. The interval between the transmitter and the receiver is 10mm and can be moved along the parallel direction or the vertical direction of the tensile load. The transit time was measured by a cross-correlation method and converted into the stress on the test specimen using the acoustoelastic method. We confirmed that the stress measurement using an SH0-plate wave was superior to that with an S0-Lamb wave.

基于超声Lamb波的固井质量评价新技术与应用

为了解决传统的CBL/VDL声波测井、扇区水泥胶结测井以及超声脉冲回波测井均不能准确评价轻质水泥固井质量的难题,提高低密度轻质水泥固井质量评价的准确性,基于超声“脉冲-回波”检测原理,研制超声Lamb波固井质量评价测井仪,建立弯曲型Lamb波衰减率、垂直回波共振效率与套管外介质声阻抗之间的关系模型,构建固液气三相介质评价图版,结合轻质水泥刻度井测试,建立了基于超声Lamb波的固井质量评价新方法。该方法可有效评价低密度轻质水泥固井质量和检测确定水泥返高位置,解决了轻质水泥固井质量评价难题。应用表明,该技术为低密度轻质水泥固井质量检测与评价提供了新思路,同时超声Lamb波固井质量评价测井仪还可以实现套管居中度和套损检测评价,可为固井质量评价和井筒完整性检测提供依据,应用前景广阔。

超声Lamb波混频激励效率与模式选择

研究了超声Lamb波混频的激励效率与模式选择。在非零能量流和相匹配条件的基础上,结合Lamb波在结构中的状态分布,提出了以激励效率参量作为超声Lamb波混频模式选择的依据。根据混频条件筛选混频模式对,计算相应的激励效率参量,并通过超声Lamb波混频的仿真模拟与实验测量进行验证。通过对比仿真与实验中得到的非线性参量与激励效率参量的关系,证明了激励效率参量作为模式选择依据的有效性。研究表明,激励效率参量可以有效地表征超声Lamb波混频的激发效率,从而筛选非线性效应明显的模式对,更好地实现损伤的检测与表征。

超声Lamb波监测铝合金结构疲劳裂纹扩展实验研究

对应用超声Lamb波在线监测金属结构裂纹在疲劳载荷作用下的扩展进行了实验研究。制备了含中心裂纹的铝合金平板结构试件,并在试件表面布设了压电晶片传感网络。疲劳实验中,在观测裂纹扩展的同时,采用压电晶片分别进行Lamb波信号的激励和接收,监测驱动器与传感器间的疲劳裂纹扩展行为。通过时域信号处理提取了Lamb波信号峰值点的幅值(AMP)与传播时间(ToF)特征,由柯西隶属度函数定义了改进的信号健康度指标及相应的损伤指标,并评估了健康度指标和损伤指标随裂纹扩展的变化趋势。最后,结合损伤概率成像方法,融合Lamb波激励-接收路径的所有损伤指标,近似表征了裂纹长度的变化,验证了该方法的可行性和有效性。

钛合金薄板Lamb波相控阵超声检测工艺研究

Lamb波适于板型结构的缺陷检测。为探究适合钛合金薄板缺陷超声检测工艺,以某海洋工程结构件用板材为研究对象,通过相控阵技术激发不同角度的lamb波声束,研究表明以40°声束入射时,能够得到最佳化检测结果,其声波传播规律符合常规超声检测规律,且缺陷识别距离长;对条形缺陷检测,以5°步进对探头进行移动旋转,当旋转角度大于15°时缺陷不可识别,同时基于相控阵技术激发多模态混合lamb波检测能力优于常规超声。实验证明,采用40°入射的lamb波混合模态相控阵检测工艺,去除前置单模态lamb波提取工作,可有效应用于实际工程应用中的薄板小缺陷检测。

基于有限元方法的薄板超声Lamb波频散曲线计算

采用基于有限元方法对薄板超声Lamb波频散曲线进行计算是一种有效的方法。首先,对自由边界条件下Raleigh-Lamb频率特征方程进行数值求解,求得铝板中超声Lamb波的理论频散曲线。然后,利用有限元数值模拟方法,研究不同频厚积时超声Lamb波在薄板结构中的传播过程,并分别计算10组不同频厚积对应的群速度和相速度大小,绘制了频厚积在2 MHz·mm以下范围的频散曲线。结果表明,该频散曲线与通过频率特征方程求解的超声Lamb波理论频散曲线相吻合。

基于Lamb波的CRTSⅡ型板式无砟轨道层间损伤检测方法

CA砂浆层间损伤直接影响CRTSⅡ型板式无砟轨道的服役性能。通过建立刚性边界条件下Lamb波在CRTSⅡ型板式无砟轨道中传播的理论模型,研究了无砟轨道Lamb波的频散特性,确立对缺陷敏感的Lamb波模态以及在空气耦合方式下该模态的激励参数。通过实验室等比例模型试验对所提CA砂浆层间损伤空气耦合Lamb波检测方法进行验证。结果表明:当空气耦合超声探头中心激励频率为28 kHz、入射角3.5°时,可在CRTSⅡ型无砟轨道板中激励产生Lamb波A3模态,利用该模态可以进行无砟轨道层间损伤检测;随着CA砂浆层间脱空损伤尺寸增加,能量泄漏减少,接收的Lamb波A3模态能量增加,幅值增大,呈现线性变化规律;采用非接触式空气耦合Lamb波可实现CRTSⅡ型板式无砟轨道层间损伤的快速定量检测。

宽波束超声波流量计Lamb波发射技术研究

宽波束超声波流量计的研究是超声波流量计发展的趋势,但目前专门针对管道流量测量的宽波束理论研究较少.为此,在建立管道声路模型的基础上,推导了适用于管道流量测量的Lamb波的色散方程,给出了在管道中通过调整超声波发射频率激发Lamb波的方法,并分析了在该条件下管道中的声场分布,从而建立了一套管道Lamb波理论.在此理论基础上,设计了验证管道Lamb波理论的实验方案,实验数据与理论推导基本吻合,因此从实验角度验证了管道Lamb波理论的合理性.

高分辨率超声Lamb波频散曲线测量与板厚估计

超声Lamb波在工业无损检测与评价中具有广阔的应用前景。但受制于超声导波多模式频散与混叠的影响,如何实现高分辨率超声导波的模式分离与频散曲线提取,进而定量分析材料的健康状况一直是研究的热点与难点。本文旨在将现代信号处理中广泛采用的谱估计技术应用于超声Lamb波阵列信号分析,并通过提取频散曲线定量测量板厚度。以经典参数谱估计法中的Yule-Walker法与Burg法为例,实验测量和分析了3mm,4mm和5mm厚铝板中的宽带多模式Lamb波信号,准确地提取了铝板中的宽带Lamb波频散曲线,并比较了两种经典谱估计方法与二维傅氏变换法的性能,最终实现了铝板厚度估计。