电涡流传感器线圈阻抗计算方法

针对电涡流传感器的线圈阻抗值计算问题,提出理论计算法和有限元法两种方法.以厚度为δ的被测体(含磁性和非磁性导体)上方正对一圆柱型线圈为求解模型,根据传感器工作原理和电磁场理论导出线圈阻抗积分表达式,并将其转化为更易求解的级数表达形式,由MathematicTM计算线圈阻抗值.然后根据有限元建模理论建立传感器的有限元模型,通过仿真得到传感器磁力线分布和线圈阻抗值.最后比较两种方法得到的阻抗值,结果表明两种方法计算结果相符,其有效性和正确性得到相互验证.     

电涡流传感器的温度稳定性研究

本文研究了高频下电涡流传感器线圈在宽广的温度区间内阻抗温度特性，提出采用多股辨线消除或减小温度变化对线圈阻抗影响的方法。研究了多股辨线电涡流传感器线圈的阻抗在大温度区间的随温度变化的规律。理论分析和计算证明多股辨线线圈能有效抑制线圈阻抗温漂。     

含铁氧体磁芯的电涡流传感器线圈阻抗理论模型和数值计算

针对铁氧体磁芯对电涡流传感器线圈阻抗的影响问题,建立了含铁氧体磁芯的线圈阻抗理论模型,推导了单匝线圈阻抗的级数和矩阵形式,并通过积分获得圆柱线圈的阻抗表达式。因表达式参数多且计算复杂,用有限元法对含Ni-Zn铁氧体磁芯的线圈阻抗进行数值计算,并分析了铁氧体磁芯及其几何参数对传感器性能的影响。研究表明：通过理论模型和有限元法都可获得线圈阻抗值,但后者求解更加简便;铁氧体磁芯可将磁场限定在一定范围之内,提高了传感器的灵敏度;磁芯参数对传感器性能的影响因被测体材料而异。本文的研究可为传感器探头结构优化和性能改善提供理论依据。     

基于表面阻抗边界的变压器杂散损耗计算方法

表面阻抗法是基于电磁波理论并将导体表面阻抗作为一种边界条件进行有限元求解的方法,它具有求解规模小、计算效率高等优势。首先借助工程电磁场数值计算软件Magnet,使用有限元法和表面阻抗法对该模型进行仿真,然后基于TEAM Problem 21基准族中的P21-B模型搭建了变压器杂散损耗测试系统,用于测量在不同频率电流激励条件下的变压器杂散损耗。针对现有测量方法的不足,引入温度系数对测量结果进行修正,并采用改进线圈损耗法以得到更准确的杂散损耗测量结果。通过与实验值对比,验证了有限元法与表面阻抗法计算结果的准确性。从计算规模和时间角度分析,表面阻抗法远远小于有限元法,大大节省了计算资源。     

一种任意正交折线线圈阻抗的解析建模新方法

提出了一种位于导体上方正交折线线圈的阻抗解析建模方法。首先,在前人研究的基础上,定义了外形位置因子,得出了单矩形线圈的入射场感应电压及散射场电压简化计算方法;其次,将多个矩形线圈自感电压及两两之间的互感电压叠加,建立了串联等效电感模型;再次,根据任意正交折线线圈的几何原理,将该线圈拆解为有限个相同截面的矩形线圈并进行重构,得出入射场阻抗及散射场阻抗的广义二重积分表达式。最后,利用Mathematica对回折线圈实例进行了计算与实验比较,并根据影响阻抗的各个变量绘制阻抗平面图。拆解重构方法可用于不同形状、不同激励频率、不同提离高度的正交折线线圈平行置于任意电导率导体上方的阻抗解析计算。     

复杂机械零部件可靠性设计量的分布参数

本文介绍了结构形状复杂的机械零部件可靠性设计量分布参数的确定方法，包括实测数据统计法、Ｔａｙｌｏｒ级数展开法和数值计算法。文中以悬臂梁为例比较了Ｔａｙｌｏｒ级数展开法和数值计算法计算结果的差异，给出了数值计算法中工程上宜采用的△ｘｉ的合理取值。     

多级管状线圈加载装置的线圈优化及电参数影响

高能率粉末压制时加载速度不够大,会导致无法获得更高致密度粉末制品。通过电磁炮原理结合高能率粉末压制技术提出一种多级管状线圈冲击加载装置,利用演变法获得了不同线圈截面形状。采用有限元软件建立加载装置的仿真模型,分析计算了线圈截面形状和线圈级数以及电参数对铁芯电磁力的影响规律。结果表明:当线圈的截面形状为正方形时,产生的磁感应强度值,磁场梯度,铁芯的加载速度最大。相同高度下,线圈级数为三级能够产生较大的电磁力。增大电压或电流和减小线圈的阻值,可以获得更大的电磁力和加载速度,当产生电磁饱和时,进一步增大电压或电流和减小线圈的阻值是无意义的。为加载装置的设计优化提供了参考。     

多层导电结构电涡流检测探头阻抗解析模型及数值计算

基于准静磁场条件下的Maxwell方程组,建立半无限大任意多层导电结构上方圆柱形线圈模型,推导线圈阻抗变化量的解析表达式。该表达式是含有Bessel函数积分的积分区域从零到无穷大的非常复杂的二重广义积分,并且被积函数在零点处有奇点。为选择合适的数值计算方法,证明线圈阻抗增量解析表达式的被积函数在零点处极限的存在性和极限值以及被积函数从零到无穷积分区域上的收敛性。在线圈阻抗增量的数值计算中分块化计算被积函数以提高计算效率,并采用自适应辛普森算法计算Bessel函数积分以提高计算精度。针对厚度检测问题进行仿真与试验验证。计算结果与试验结果吻合良好,表明研究结果是有效的,不仅有助于电涡流检测探头阻抗仿真器的建立,也可用于试验系统的参数优化。     

基于电涡流的金属种类识别技术的理论与实验研究

通电线圈与其附近的金属导体之间将产生电涡流效应，由于不同种金属有着不同的电导率和磁导率，从而使得相应的探测线圈等效阻抗的变化量互不相同。本文用电容三点式振荡电路将线圈等效阻抗的变化转换成电压信号，通过离线训练的方法获得神经网络辨识模型，以此来进行金属种类的识别。本文设计了一套基于微机检测系统为核心的电涡流金属种类识别的实验装置，选用实验室易获得的吸铁、黄铜和铝合金3种金属为对象展开实验研究，结果表明利用电涡流技术以及神经网络辨识的方法能有效的识别金属种类，为智能金属探测器的推广应用奠定了理论基础。     

频响函数计算的级数展开法

运用级数展开原理,导出了频响函数计算的级数展开法。该方法在非完备模态集下仍能给出高精度的频响函数,从而可在工程中广泛应用。算例表明,该算法是有效的。     

Coil impedance calculation of an eddy current sensor by the finite element method

An eddy current sensor utilizes the variation of coil impedance to perform the measurement of physical parameters, and the coil impedance is an important parameter for investigating the properties of an eddy current sensor. Therefore, the study of approaches to calculation of coil impedance is very important. In this paper, an integral expression for coil impedance with a magnetic substance is given directly. For the convenience of calculation of the coil impedance, this integral expression is further expanded in series form and the coil impedance is computed using Mathematica. Then, two different finite element models of the eddy current measurement system are built on the basis of the finite element modeling theory. The infinite boundary of model 1 is truncated. On the contrary, the infinite boundary of model 2 is simulated completely by an infinite element. The coil impedance and the magnetic distribution are obtained by the finite element method, respectively. The comparison shows that the result obtained by the finite element method is in good agreement with that of the theoretical calculation approach, which indicates the correctness and reasonability of modeling of the eddy current measurement system and calculation of the coil impedance by the finite element method. The text was submitted by the authors in English.     

Analytical approach to pulsed eddy current nondestructive evaluation of multilayered conductive structures

This paper proposes an analytical approach that can describe the Pulsed Eddy Current Testing (PECT) of stratified conductive structures by a single air-coil used for detecting and sizing of metal loss due to interlayer corrosion. Specifically for a single air-cored coil above a multilayered conductive structure, the coil impendance response of the cylindrical eddy-current probe is calculated based on the truncated region eigenfunction expansion (TREE) method using the generalized matrix coefficients in series form. Analytical modeling of pulsed eddy current is developed using the Fourier series for multilayered conductive structures. A simulation study is carried out for demonstrating the capability of the proposed approach for sizing the metal loss in a two-layer specimen. Furthermore, the experiment is set up to confirm the simulating results of the analytical model for multilayered steels. Good agreement between the theoretical results and measured signals is observed.     

管道平衡电磁内检测技术串联谐振激励电路研究

针对平衡电磁技术对管道内表面周向、轴向裂纹缺陷检测的灵敏度问题,提出采用串联谐振激励电路增大激励电流,提升检测灵敏度的方法.利用电磁场理论分析了平衡电磁技术激励电流对检测信号的影响,以有限元仿真的方式计算了不同激励电流下检测信号的曲线与幅值,研究了串联谐振电路减小激励线圈阻抗,增加激励电流的机理,设计了基于串联谐振的激...     

The stressed state of shell structures under local loads

A method for Fourier series expansion is developed to describe strongly localized mechanical loads that can affect thin-walled shell structures in the form of bodies of revolution. The results of calculations for shells loaded by local loads of various types are reported. The results of calculation of the stressed state using the Fourier series are compared with those obtained by the finite element method.     

多层厚度电涡流检测反演算法及实验研究

介绍了有限截面线圈置于多层结构上方的阻抗变化数学模型,研究了根据检测电压变化值反演厚度的3种算法模型:最小二乘数值优化逼近、反向传播神经网络及径向基函数网络模型,结合1个两层厚度检测的例子进行了比较分析,指出BP神经网络模型在多层厚度反演中具有良好的稳健性。     

Improved circuit for impedance measurement at very high frequency and its application in testing dielectric properties of insulating materials

This paper describes improvements on an impedance measuring circuit for the measurement of very small conductance at very high frequency and one of its applications, viz., the accurate measurement of dielectric constant and loss angle of very low loss materials. In this circuit, a feedback loop for the stabilization of the output level of the high-frequency oscillator unit also provides compensation for the changes of the series resistance of resonance coil and the transfer characteristic of the detector that occur with their temperature drifts. This circuit has the sensitivity and stability to detect a 0.002 mumho change in a 16-pF specimen at 100, 150, or 200 MHz. It is capable of measuring a loss angle of several murad with the electrode system developed for the varying gap immersion method. The warming-up time is also shortened to about 10 min even for measurements requiring the highest sensitivity.