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The amplitude of an ultrasonic signal generated by electromagnetic acoustic transducers (EMATs) is typically low when compared to those generated by contacting transducers, which restricts the application of EMATs in the fields of nondestructive testing and nondestructive evaluation. The transmission process of a surface wave EMAT is studied, based on a previously established 3-D model, with the aim of enhancing the amplitude of ultrasonic waves generated by the EMAT. The effect of changing various EMAT parameters on the surface wave is investigated, by utilizing the orthogonal test method. Results indicate that after optimization, the signal amplitude of the EMAT has increased by 25.2%. 相似文献
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The main disadvantage of electromagnetic acoustic transducers (EMATs) is their inefficiency in generating ultrasound. A new design of Rayleigh-wave EMAT is proposed with improved ultrasonic generation efficiency on non-ferromagnetic materials. The new EMAT's magnet is narrower than the meander-line coil used in the transducer and the coil itself has an uneven distribution of conductors. The principle of the new design is informed by finite element simulations, which show that the EMAT generates Rayleigh waves more efficiently by taking advantage of both horizontal and vertical magnetic fields of the magnet simultaneously. Experimental measurements verify that the maximum amplitude of the ultrasonic signal generated by the new design of EMAT working under a pulse-echo configuration has been enhanced by 90%, when compared to conventional designs. 相似文献
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通过试验确定了不同材质钢管的磁致伸缩曲线,得到了不同材质钢管缺陷检测的电磁超声传感器(EMAT)直流电磁铁的励磁电流与超声波幅值的关系,确定了最佳励磁电流,并得出其变化规律与磁致伸缩曲线变化趋势一致的结论。为电磁超声传感器设计和开发提供了依据。 相似文献
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Beam steering has been achieved using shear horizontal waves generated using a periodic permanent magnet (PPM) electromagnetic transducer (EMAT). Unlike phased arrays, where steering is achieved by carefully controlling the firing of individual elements, the spatial periodicity of the PPM EMAT is ultilised to steer the beam whilst exciting all elements simultaneously. Due to the periodic nature of the array, the interference of individual waves from each of the elements creates a highly frequency dependent angle of propagation, allowing the directivity to be changed by simply varying the frequency of the input signal. Simultaneous excitation precludes the need for complicated and expensive phased array hardware. A frequency domain model is developed so that the beam characteristics, such as steering angle and beam width, can be calculated, allowing for investigation into the beam steering qualities of the PPM transducer. Broadband pulsed generation is also demonstrated, showing how a wave is generated over a large range of angles, meaning a large area can be covered with a single pulse. Interesting properties of this wave, such as a variation of frequency as a function of angle, and how this can be useful, are also discussed. 相似文献
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Hirotsugu Ogi Takayuki Hamaguchi Masahiko Hirao 《Journal of Alloys and Compounds》2000,310(1-2):436-439
Using electromagnetic acoustic resonance (EMAR), we studied the evolution of the surface-shear-wave attenuation and phase velocity during rotating bending fatigue of a 0.45% C steel. In the EMAR method, we used a magnetostrictively-coupled electromagnetic acoustic transducer (EMAT) for the contactless measurements of the axial shear wave that is a surface-shear wave, propagating in a cylinder-specimen circumference direction with the axial polarization. The attenuation coefficient always showed sharp peaks around 90% of the fatigue life, independent of the fatigue-stress amplitude. In addition to the ultrasonic measurements, we made crack-growth observations using replicas and measured recovery of attenuation and velocity after stopping the cyclic loading just before and after the peak. From these results, we concluded that the evolution of the ultrasonic properties is caused by a drastic change in dislocation mobility being accompanied by the crack growth. 相似文献
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电磁超声技术利用洛伦兹力或磁致伸缩原理在金属或磁性材料中激发出超声波,它是一种超声无损检测新技术。相对于其他无损检测技术而言,电磁超声具有所有的超声检测的优势。声波的激发发生在材料的表面而不是在传感器内部。所以它与传统的基于压电换能器的超声检测相比,具有无需耦合剂、可非接触、可适用于超低温或超高温环境、有利于工业自动化以及可方便有效地实现横波检测及导波检测等优势。Innerspec Technologies公司致力于电磁超声技术的研发和应用,在近十几年中开发了150多台工业在线电磁超声检测系统,广泛应用于钢铁、汽车制造、石油天然气管道和压力容器等领域。作为一种超声波技术,电磁超声可以应用于各种厚度测量、缺陷检测以及材料表征。举例讨论了电磁超声在焊缝检测中的应用。第一个应用是利用导波对激光拼焊板的检测。第二个应用是电阻焊钢管的在线检测。利用沿着周向传播的超声导波对焊缝进行检测,克服了由于焊缝位置偏转对传统超声焊缝检测设备带来的困难。第三个应用是水平横波以及多通道电磁超声相控阵技术实现奥氏体不锈钢焊缝的检测。 相似文献
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In this paper, a hybrid nondestructive testing (NDT) method combining with the pulsed eddy current testing (PECT) method and the electromagnetic acoustic transducer (EMAT) method has been proposed and validated through numerical simulations and experiments. First, a numerical code is developed for the simulation of hybrid EMAT/PECT signals based on the developed EMAT and PECT code. Second, based on the numerical simulation, the influences of the eddy current induced by the excitation coil and the eddy current due to the velocity effect of the ultrasonic wave are compared and analyzed. In addition, the features of the EMAT and the PECT signals are analyzed respectively. Third, several signal separation and extraction methods are proposed on the basis of the spectral analysis and filtering strategies for extracting EMAT and PECT signals from the mixed signals of the hybrid EMAT/PECT method and their validity are evaluated through experiments. Finally, hybrid EMAT/PECT experiments are conducted and three types of defects (surface defects, bottom thinning defects, composite defects) in an aluminum plate and a SUS304 plate are successfully detected at the same time using the proposed hybrid NDT method and the signal feature parameters. Based on the numerical and experimental results, the proposed hybrid PECT/EMAT NDT method is demonstrated both high detectability and high efficiency for detecting surface and volumetric defects at the same time. 相似文献
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This article describes a three-dimensional Gaussian beam model for calculating transducer-generated ultrasonic wave fields in inhomogeneous anisotropic media. The model is based on a formulation presented recently for homogeneous anisotropic materials. The inhomogeneity is modeled by dividing the material into several homogeneous layers, the approach accounting for the propagation through the various layers and the reflection/refraction processes at the interfaces. It thus calculates ultrasonic field patterns, including proper amplitude information and allows a quick evaluation of the sound fields. Application of the model in view of ultrasonic nondestructive testing of layered composite material and of austenitic steel components is addressed. In the latter case, examples are given for various weldment structures, wherein ultrasonic inspection using commercial angle beam transducers is of interest. 相似文献
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电磁超声检测技术由于无需媒介以及与被测物体非接触,不但可提高检测效率,而且可将超声检测技术的应用扩展到高温、高速和在线检测。根据电磁超声传感器的工作原理,建立了基于有限元的电磁超声无损检测数值分析方法,开发了相应的计算程序,验证了其有效性。应用开发的电磁超声数值模拟程序,研究了不同激励方式对电磁超声波的影响,得到了相应超声波在均匀各向同性金属介质中的传播过程。该计算方法和程序为实际电磁超声检测中缺陷的定量和探头优化提供了手段。 相似文献
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This paper presents an efficient method for the detection of delamination using a combined technology of ultrasonic guided wave and electromagnetic acoustic transducer (EMAT). The material for inspection studied in this paper is a three-layered brass/copper/brass metal composite for coin stocks. We first observed a cyclic behavior of wave sensitivity to delamination width in the experiment. This observation is then confirmed with finite element simulation. We found out that the cyclic behavior is related to the phase velocity of the converted wave modes in the two subsystems after delamination. To compensate for the cyclic behavior, two wave modes are used in an industrial inspection system to ensure effective detection of delamination in the composite sample. The inspection speed achieved with this EMAT inspection system is 1.8 m2/s. 相似文献
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电磁超声是超声波无损检测的一个分支。该技术利用电磁场的相互作用,在被测材料表面产生超声波。因此,电磁超声无损检测过程无需使用耦合剂,并且支持非接触检测。不停工情况下的在役管道以及其他压力容器的剩余壁厚测量是当今无损检测领域的一个研究热点。在常温管道测量方面,使用传统的压电超声可以比较精确地测量管道的剩余壁厚。但是,在高温管道测量方面,目前高温耦合剂还是存在易于挥发、效果不稳定的缺点,而且价格昂贵,不利于实际应用。文章介绍了电磁超声测厚的基本原理、电磁超声厚度测量的仪器设备、探头及其使用范围。结合高温管道测厚的实际应用案例,对电磁超声测厚应用进行了阐述、分析和总结。最后得出,电磁超声由于无需接触、不需要耦合剂等特点,对材料的高温测厚具有独特的优势。 相似文献
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In this work a method is presented for detecting and locating stress corrosion cracking (SCC) in stainless steel pipe samples. The method combines laser generation and either laser or electromagnetic acoustic transducer (EMAT) detection, scanning the generation point across the sample surface. Using laser-generated ultrasonic waves that interact with the cracks, and performing time–frequency analysis techniques to examine changes in the generated wavemodes, surface plots that clearly resolve the spatial extent and geometric alignment of the cracks are created and presented here. The method is demonstrated using components removed from service after exhibiting SCC. 相似文献
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目的 对纵扭复合超声端面铣削加工表面微结构进行预测,以优化加工参数。方法 对纵扭复合超声端面铣削进行运动学分析,并在其基础上建立三维运动轨迹方程。对刀尖轨迹仿真,且研究该运动方式下的加工特性。通过对切削刃和工件离散化建立纵扭复合超声端面铣削表面微结构理论模型,并利用MATLAB进行三维表面仿真。对TC4钛合金进行超声振动切削试验。结果 理论仿真和切削试验结果均表明超声纵扭端面铣削时,随振幅的增加,由振动引起的表面微观结构特征愈加明显。扭纵幅值比增大时,加工表面微观结构凹坑效应弱化,At/Al=0.55时,加工表面呈条形片状微观结构。振动频率和主轴转速会影响表面微观结构单元的疏密程度。结论 加工表面微结构的生成与振动频率、振幅、扭纵复制比、切削速度等加工参数相关,铣削实验得到的加工表面变化趋势与表面理论模型吻合,该表面模型能够优化超声加工参数。 相似文献