电磁超声传感器机理的理论研究

电磁超声传感器作用于铁磁性材料中,由洛仑兹力和磁致伸缩力产生超声波,建立了两种力分别作用下超声波幅值与铁磁性材料磁感应强度的函数关系,分析了洛仑兹力、磁致伸缩力及洛仑兹力和磁致伸缩力共同作用三种情况下,超声波幅值与磁感应强度的变化趋势。     

基于磁滞回线原理的铁磁性材料应力测试方法

提出了一种检测铁磁性材料应力的新方法。铁磁性材料的磁致伸缩特性与材料本身的微观结构有关,材料的微观结构会随着自身应力状态的改变发生一定的改变。由此,根据铁磁性材料的磁滞现象,对试件施加应力,通过基于磁致伸缩的电磁超声检测(EMAT)平台,得到不同应力下磁滞回线对应的超声信号幅值-静态激励电流关系曲线。提取曲线中的特征参数,绘制出特征参数-应力值关系曲线。试验结果表明,此方法可定性检测出材料的应力状态。     

电流传感器用FeCoV薄膜的性能

采用磁控溅射方法制备FeCoV薄膜作为电流传感器中的磁敏材料.采用应变片法测量了FeCoV合金的磁致伸缩曲线,其饱和磁致伸缩系数约97×10-6;扫描电镜观察发现FeCoV薄膜致密度良好,颗粒均匀连续,断面形貌图可以看出薄膜呈柱状结构生长.FeCoV薄膜样品呈(110)取向生长,呈现明显的单轴各向异性.实验发现,FeCoV合金的磁致伸缩曲线与电流传感器的电流响应曲线趋势一致,具有线性区域,这些特性都为获得高灵敏度的磁传感器创造了条件.采用80 MHz的声表面波反射延迟线制备了电流传感器探头,FeCoV薄膜电流传感器的检测灵敏度可以达到6.7 kHz/A.     

兆赫兹磁致伸缩超声导波管道检测系统的研制

研制的扭转模态磁致伸缩管道检测系统采用排线式磁致伸缩传感器时,可在管道中激励出低频T（0,1）模态超声导波,并有效检测出管道中截面缺失率为3％的通孔缺陷。为拓展检测系统的工作频率范围,设计出一款柔性印刷感应线圈,对其进行的实验验证结果表明,柔性线圈式磁致伸缩传感器可在管道中激励出兆赫兹T（0,1）模态超声导波,传感器的中心频率达1．30MHz,有望进一步提高磁致伸缩传感器的缺陷检测灵敏度。柔性印刷线圈无需使用适配器,可直接卷曲贴覆在管道表面,易于拆装。由此,研制的磁致伸缩管道检测系统的频率范围可覆盖几十千赫兹到兆赫兹,适合应用于实际工程检测。     

磁致伸缩传感器技术探测钢管隔热层下腐蚀缺陷的研究

介绍西南研究院在磁致伸缩传感器技术用于钢管隔热层下腐蚀缺陷探测研究工作的进展，包括实验设施，实验结果和讨论，总结和建议。     

基于磁致伸缩传感器的辊压机压下位移监测及误差补偿

考虑到辊压机工作时设备温度变化范围大、外界干扰强烈等特点,研究了基于磁致伸缩传感器的辊压机压下位移监测及误差补偿方法。通过理论分析和实验手段,对磁致伸缩位移传感器的精度影响因素进行研究。分析了磁致伸缩位移传感器的工作原理,结合传感器实际使用经验,确定外界环境干扰主要是使用环境温度的变化以及电磁干扰的影响,并通过理论分析磁致伸缩位移传感器受温度和电磁干扰的机理。使用最小二乘支持向量机补偿模型,针对温度变化和电磁干扰产生的误差进行补偿。实验研究结果表明,磁致伸缩位移传感器测量精度受使用环境温度和电磁干扰影响较大,使用本文研究的补偿模型后,可以减小温度和电磁干扰对传感器精度的影响。     

应变电阻片法测定Fe_(bac)Cu_1Nb_3Si_(15.5)B_7/硅橡胶复合薄膜的磁致伸缩性能

研究了不同Fe_(bac)Cu_1Nb_3Si_(15.5)B_7非晶粉体与硅橡胶质量比的复合薄膜的磁致伸缩性能,确定了粉体和硅橡胶的比例与复合薄膜的磁致伸缩效应的内在联系,并根据广义变分原理确定了这种复合薄膜的弹性模量、泊松比和内应力值的范围。结果表明:Fe_(bac)Cu_1Nb_3Si_(15.5)B_7非晶粉体与硅橡胶的质量比为3∶1时,复合薄膜的磁致伸缩系数存在极大值。该复合薄膜具有很好的柔性磁弹性能,是制备柔性力敏传感器的优良材料。     

基于磁致伸缩技术的超声导波波速及最大检测长度试验

针对基于磁致伸缩超声导波技术的导波波速及检测长度进行了试验研究。试验中采用干耦合方式,分别对两种不同材质(不锈钢、合金钢)管道试样进行了超声导波检测。试验结果表明,分别单向激励64和128 kHz的T(0,1)模态超声导波在两种不同材质的管道管端位置,波速及检测长度有着明显的差异。     

磁致伸缩导波在钢管中传播的研究

介绍了导波在无限长钢管中传播的频散现象和多模式特点，研制了用于磁致伸缩导波检测的实验系统。通过正确的电磁屏蔽措施和合适的信号处理方法，改善了系统的信噪比，在钢管上进行了低阶纵向模态波传播实验，观察和分析了频散现象。用实验结果验证了理论计算。     

磁致伸缩导波模式控制传感器技术

超声导波在构件中传播具有多种模式的特征,给导波无损检测信号分析及其应用带来一定难度,通过导波传感器的合理设置实现导波模式的可控具有重要的实用意义。系统综述了国外基于磁致伸缩效应的导波传感器模式控制技术,详细介绍了纵向导波、扭转导波、弯曲导波三种模态传感器的设置。通过比较可得,磁致伸缩传感器中偏置磁场和交变磁场方向和大小设置决定了所激励出的导波模式。     

A hybrid nondestructive testing method of pulsed eddy current testing and electromagnetic acoustic transducer techniques for simultaneous surface and volumetric defects inspection

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.     

一种优化激发电磁超声Lamb波的方法

超声Lamb波的频散特性和多模式特性导致回波信号复杂难于分辨。为了解决该问题,结合电磁超声换能器(EMAT)的主要设计参数和Lamb波的特征方程,推导电磁超声Lamb波的激发方程和激发曲线。通过选取电磁超声Lamb波在激发曲线上的工作点以削弱多模式和频散现象,进而提出了一种优化激发电磁超声Lamb波的方法。采用该方法分析了零模式Lamb波在工程应用中的有效性,并进行了试验验证。     

确定电磁超声换能器钢管检测最佳磁化强度的试验研究

由于电磁超声换能器检测钢管缺陷时,其磁场强度影响超声波幅值,进而影响检测灵敏度。为此设计了确定最佳磁化强度的试验方案,通过试验得到超声波幅值随电磁场激励电流的变化曲线。确定了最佳磁化强度时的激励电流。     

电磁超声和涡流组合检测方法

两栖装甲车工作环境恶劣,车体尤其是底部容易破损。提出了一种电磁超声和涡流组合检测的快速方法,利用电磁超声的激励信号在被测金属表面感应的涡流,实现表面和近表面缺陷的涡流检测,无须额外增加专门的涡流线圈及其激励电路。设计了组合检测系统和探头,对带有表面缺陷和内部缺陷的装甲钢试块进行了检测试验。结果表明,该方法可以实现装甲钢试块内部缺陷和表面裂纹的检测,比单一的电磁超声检测或涡流检测能获取更全面的有用信号。     

Experimental and numerical evaluation of electromagnetic acoustic transducer performance on steel materials

Electromagnetic Acoustic Transducers (EMATs) are an attractive alternative to standard piezoelectric probes in a number of applications thanks to their contactless nature. EMATs do not require any couplant liquid and are able to generate a wide range of wave-modes; however these positive features are partly counterbalanced by a relatively low signal-to-noise ratio and by the dependence of EMAT performance on the material properties of the test object. A wide variety of steel materials is employed in many industrial applications, so it is important to assess the material-dependent behaviour of EMATs when used in the inspection of different types of steel. Experimental data showing the performance of bulk shear wave EMATs on a wide range of steels is presented, showing the typical range of physical properties encountered in practice. A previously validated Finite Element model, including the main transduction mechanisms, the Lorentz force and magnetostriction, is used to evaluate the experimental data. The main conclusion is that the Lorentz force is the dominant transduction effect, regardless of the magnitude and direction of the bias magnetic field. Differently from magnetostriction, the Lorentz force is not significantly sensitive to the typical range of physical properties of steels, as a consequence the same EMAT sensor can be used on different grades of ferritic steel.     

电磁超声技术在焊缝检测中的应用

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。     

Evaluation of an EMAT–EC dual probe in sizing extent of wall thinning

An electromagnetic acoustic transducer (EMAT)–eddy current (EC) dual probe is developed to assess wall thinning. With a view to developing compatible EMAT and EC operating modes, probe’s capability to size width and depth of wall thinning is quantitatively evaluated. Experiments carried out on austenitic stainless steel plates with various groove sizes show that the EMAT mode of the dual probe functions best when thinning is shallow but wide, whereas the EC mode functions best when thinning is deep but narrow. Mode complementarity indicates that this dual probe offers greater reliability in wall thinning monitoring.     

Research on a novel force sensor based on giant magnetostrictive material and its model

A novel magnetostrictive force sensor which can measure static force and dynamic force using giant magnetostrictive material rod as the sensitive element was studied. A special structure was proposed which was a stainless steel ring around the Hall sensor to improve the force measuring sensitivity. In view of the hysteresis nonlinearity of the giant magnetostrictive material and actual working process of the sensor, a model was established based on the combination of Jiles-Atherton model and magnetomechanical effect method. The unknown magnetic and magnetostrictive parameters in the model were identified by a hybrid algorithm of genetic algorithm and simulated annealing algorithm. Moreover, the numerical solution method and simulation process of the model were expounded in detail. The results showed that the force measuring sensitivity is about 6.14 times higher than that of the sensor without this special structure. The model can reveal the magnetization process mechanism clearly and describe the relationship between force input and electromagnetic output effectively.     

Development of an on-line evaluation system of formability in cold-rolled steel sheets using electromagnetic acoustic transducers (EMATs)

An on-line evaluation system of in cold-rolled steel sheet with EMATs has been developed. First the principle of nondestructive measurement is described. Next the characteristics of a Lorentz and a magnetostrictive type EMAT are evaluated to permit an optimum sensor for on-line measurement. Based on the results, a system with a magnetostrictive type EMAT was fabricated. The capability for measuring was evaluated using many samples and products in a continuous annealing line. The system was confirmed to continuously measure in the production line with an accuracy of 1 σ = 0.07.     

电涡流测功器低速检测时最佳匹配问题的研究

针对矿用轻型胶轮车低速检测时底盘输出功率与电涡流测功器外特性曲线不匹配的问题进行研究,建立胶轮车行驶阻力功率和电涡流测功器吸收功率的数学模型,对电涡流测功器进行参数化分析并获得外特性曲线,利用COMSOL软件对不同转盘材料进行电磁模拟仿真。分析了气隙长度、定子极对数、励磁电流和转盘材料对电涡流测功器吸收功率和临界转速的影响。结果表明:改变电涡流测功器定子极对数和使用不同转盘材料对其外特性曲线有较显著的影响。