Magneto-optic microscope for visually detecting subsurface defects

A visual test method for detecting microdefects under fine surfaces is described. A new MO microscope that has a laser source, a CCD camera, and an exciting coil is developed for this work. A pulse generator supplies an intermittent square pulse to the exciting coil, which can intensify eddy currents yet reduce the working temperature of the exciting coil and sample. The magnetic field variation produced by the imbedded defect causes a rotation of the polarization plane of the reflected beam. Therefore the reflected beam carries an image of the defect, which is received by a CCD camera. The optical arrangement guarantees that no light is reflected back to the laser. The system was tested with a calibrator, which has an artificial subsurface defect; such a test attains a visual detected image. To our knowledge this is the first time an image of a subsurface defect has been distinctly detected with a MO sensor system.     

Numerical analysis of high-frequency induction heating includingtemperature dependence of material characteristics

We have carried out a numerical analysis of the magnetic field on high-frequency induction heating. This analysis includes the dependence of various magnetic properties on temperature. The required characteristics are obtained experimentally. We compare the experimental results with the theoretical values obtained by approximations. Until now, the current density inside the exciting coil on this kind of problem has been assumed to be uniform, which is different from actual phenomena. We propose a new method which takes the inhomogeneous distribution of exciting current into account. In this analysis, the eddy current of the exciting coil is also taken into account     

Finite element analysis of leakage magnetic flux from an induction heating system

The finite element method is applied to calculate the leakage magnetic field from an induction heating system consisting of an exciting coil and a conducting circular plate. The basic technique of the method is to draw a mathematical sphere to enclose the system. The total energy functional is assumed to be given by the interior and exterior functionals. The former is represented by using the usual axisymmetric triangular elements. On the other hand, the latter is given in a simple form by expanding exterior fields in terms of the solutions of a differential equation governing exterior empty spaces. The interior and exterior potentials are then matched on the spherical interface. After the validity of the method is verified by comparing results with analytic solutions for a single coil, the leakage magnetic flux from an induction heating system is computed at large distances.     

A novel planar mesh-type microelectromagnetic sensor. Part II. Estimation of system properties

The use of planar-type sensors for the estimation of system properties has gained considerable importance in recent times because of its noncontact and nondestructive nature. The impedance of a coil in proximity of any conducting/nonconducting, magnetic/nonmagnetic surface is a complex function of many parameters, such as conductivity, permeability, and permittivity of near-surface materials, liftoff and coil pitch of the coil, etc. The transfer impedance (i.e., the ratio between the sensing voltage and the exciting current) of the planar-type microelectromagnetic sensors consisting of exciting and sensing coils is used for the estimation of the near-surface system properties. Two methods have been discussed for the postprocessing of output parameters from the measured impedance data. Based on the estimation of near-surface properties, it is possible to detect the existence of defects, to predict the degradation of material, fatigue, etc.     

Applying a metric space to design a primary transducer ofelectromagnetic flow meter for open channels

This paper deals with a problem of selecting an appropriate liquid level as a parameter in designing the exciting coil of the electromagnetic (EM) flow meter. The influence of variable liquid level on the transfer function of the EM flow meter is explained. The method of selecting the optimal liquid level utilizing the metric spaces is described. Some examples of metrics and the results of numerical calculations are presented. With this method, the transfer function of the EM flow meter can be significantly improved     

Systematic Analysis of the Improvements in Magnetic Resonance Microscopy with Ferroelectric Composite Ceramics

The spatial resolution and signal‐to‐noise ratio (SNR) attainable in magnetic resonance microscopy (MRM) are limited by intrinsic probe losses and probe–sample interactions. In this work, the possibility to exceed the SNR of a standard solenoid coil by more than a factor‐of‐two is demonstrated theoretically and experimentally. This improvement is achieved by exciting the first transverse electric mode of a low‐loss ceramic resonator instead of using the quasi‐static field of the metal‐wire solenoid coil. Based on theoretical considerations, a new probe for microscopy at 17 T is developed as a dielectric ring resonator made of ferroelectric/dielectric low‐loss composite ceramics precisely tunable via temperature control. Besides the twofold increase in SNR, compared with the solenoid probe, the proposed ceramic probe does not cause static‐field inhomogeneity and related image distortion.     

3D modeling of electromagnets fed by alternating voltage sources

A method allowing 3D simulation of AC voltage driven electromagnets is described. Since the harmonic current in the exciting coil depends on the air gap width, the electromotive force in the windings has to be taken into account. A computation method based on the finite element method was developed in order to obtain the static attractive force characteristics of AC electromagnets used for circuit breakers. This method is based on nodal finite elements and loop equations of the electric circuit. Both magnetic field and electric circuit equations are solved simultaneously in the frequency domain. Computation results are compared with measurements on a 32-A contractor/circuit breaker     

励磁线圈电压对刀具42CrMo钢表面离子镀TiAlSiN涂层性能的影响

采用电弧离子镀技术在刀具42CrMo钢表面沉积制备TiAlSiN涂层,实验测试分析励磁电压对其的组织结构及其摩擦性能的影响。研究结果表明不同电压制备的TiAlSiN涂层表面形成了大量孔洞。随着电压升高后,涂层的粗糙度和厚度明显增加。所有层都形成了紧密结合状态,未产生明显缝隙结构,涂层都形成了具有柱状结构。当电压上升后,产生了更多的空隙,导致涂层致密度发生减小。逐渐提高电压后,获得了具备更高显微硬度的涂层,达到了比合金钢基体更高的硬度。随着电压升高,涂层的摩擦系数和磨损率先降低再升高,到达30 V电压时达到了最小的磨损率。涂层主要发生了磨粒磨损的情况。30 V电压时形成了更加平整的涂层表面,涂层的组织结构也变得更加致密,显著提高了耐磨性。     

Metal Detector for Tracing Submarine Telecommunication Cables

The characteristics and the optimum design of a metal detector are studied theoretically and experimentally. This metal detector is expected to be mounted on an unmanned submersible and to be used for the location finding and tracing of the submarine telecommunication cables. The detector consists of one exciting coil and two receiving coils which are fixed perpendicularly to the excitation coil. The receiving coils detect the magnetic field induced by the eddy current flowing in the outer conductor of the submarine cable. Although the detection range is narrow, about 40 cm, this detector has some advantages that the other cable-locating sensors do not have. The detecting characteristics are calculated numerically under several assumptions and compared with experimental results.     

Finite element solution of 3D magnetostatic field problems involving distributed current using a single scalar potential--The modification and application of the fictitious magnetic monopole model

In this paper the authors present a new model for magnetostatic field problems - the modified fictitious magnetic monopole model, in which a new kind of scalar potential is used which is suitable for the whole region, including the distributed current region. In the FMMM the exciting action of the distributed current density has been replaced by that of a distributed fictitious magnetic monopole density, and the problem of loss of precision (subtraction of two large but similar quantities in the computer) has been solved by putting a magnetic shell into the coil and/or current-carrying conductor loop. According to the new model, the formulation of a magnetostatic problem has almost the same form as that of an electrostatic problem, thus the calculation of magnetostatic problems can be simplified significantly. The new model can also be regarded as a modification for the two-scalar potential model or for the T-Q method in magnetostatic cases. Calculation and test results of some examples of 3D magnetostatic problems are given to verify this new method.     

磁流变液减振器的磁路设计方法研究

针对传统的磁流变减振器磁场利用率不高的问题,提出了一种基于多级径向流动模式的磁流变减振器。以磁流变液作为控制介质,研究其流变学特性与磁化特性;选择相应的软磁材料,利用多项式描述其磁化特性,并辨识相应的参数。根据动态磁路设计理论,建立磁路分析模型,确定工作间隙内磁感应强度与励磁线圈激励电流的理论关系。为了验证理论推导的正确性,利用有限元分析软件对阻尼调节器内的磁路进行仿真,并按照轨道车辆抗蛇行减振器的技术要求,设计制作了基于多级径向流动模式的磁流变减振器,利用型号为A1322ELHLT-T3的霍尔传感器对其工作间隙的磁感应强度进行检测,与理论结果进行对比分析。     

Scanning SQUID Microscope NDT System Based on Eddy Current Testing

A scanning SQUID microscope based on HTS dc SQUID has been developed. The SQUID is mounted inside the insulation vacuum of a cryostat, which is separated from room temperature samples by a 65 μm thick sapphire window. Operating with a double-D exciting coil, it could be assembled to a scanning SQUID microscope Nondestructive Testing (NDT) system based on eddy current testing. The current is excited by an appropriate sinusoidal alternating (double-D coil) current in the conducting material, and then it induces a corresponding magnetic field. The vertical component of the field is then detected by the scanning SQUID system. The distortion of the field could be detected at the regions of discontinuities, such as flaws. Thereby, the defects inside the materials will be detected with neither contact nor destruction.     

高压电缆铝护套焊缝缺陷ACFM检测方法及检测系统的研究

针对在氩弧焊型高压电缆铝护套焊接过程中易出现表面漏焊、埋藏未焊透和焊穿等缺陷的问题,提出了焊缝缺陷的交流电磁场检测（alternating current field measurement, ACFM）方法。首先,利用COMSOL多物理场仿真软件建立高压电缆铝护套焊缝缺陷ACFM模型,研究U形磁芯上的励磁线圈在不同类型铝护套焊缝缺陷区域产生的感应电流的密度分布特点和和磁场信号特征;其次,设计了可获取缺陷长度和深度信息的正交式接收线圈,制作了带有缺陷的电缆铝护套焊缝试件及ACFM实验平台;最后,进行了不同类型铝护套焊缝缺陷的检测及结果分析。实验结果表明,ACFM方法能够有效用于3 mm厚的高压电缆铝护套焊缝表面漏焊和焊穿缺陷的检测,并且能够有效识别埋深为2 mm,长、宽、深分别为10,0.3,1 mm的埋藏未焊透缺陷。研究结果为高压电缆铝护套焊缝缺陷的识别和焊缝质量的评价提供了重要参考。     

The Reflected Impedance of a Circular Coil in the Proximity of a Semi-Infinite Medium

Most analyses on a circular coil when used in the eddy current method for nondestructive testing are empirical. Theories based on simple models are often inadequate to account for some experimental observations when the spacing between the coil and the material became small. In the present paper this problem is formulated as a boundary value problem. Wave equations of the magnetic vector potential are solved. The change in the coil impedance, when placed above a semi-infinite medium, is obtained by means of the induced voltage method, which is shown to depend only on the ? component of the magnetic vector potential. This change in impedance is found to be dependent on a number of factors: the shape and size of the coil; the spacing between the coil and the metal; the thickness, conductivity, and composition of the material, etc. Numerical computations are discussed for a few selected materials in connection with experimental results obtained elsewhere. The comparison made lent support to the present analysis. Extension of this method to the case of a stratified media is included.     

干盘管系统设计中风机盘管冷量修正法的研究

从干盘管系统设计的角度出发，分析现有形式的风机盘管样本参数并不能满足设计人员按照实际工况准确选取设备的要求，并结合我国目前大多数风机盘管生产商的实际情况，提出基于干球温度效率的风机盘管冷量修正法。该方法既满足了设计人员获取不同工况下运行的风机盘管冷量数据的要求，也大大减轻生产商为提供其设备多工况下性能参数的实验负担。最后通过实验，验证该冷量修正法的可靠性和有效性。     

Noncoaxial Inductance Calculations Without the Vector Potential for Axisymmetric Coils and Planar Coils

This paper presents an exact method for calculating the mutual inductance between a general axisymmetric coil and a second planar coil consisting of either a disk coil or a planar loop of essentially arbitrary shape. The approach is based directly on the magnetic field rather than the vector potential . The paper gives detailed results for two circular loops, a circular loop and an elliptic loop, and a circular loop and an annular disk coil. The method can be extended to cover the cases where all these loops and coils are extruded in the axial direction to give the corresponding solenoids. The method is also applicable to calculations for nuclear radiation detectors.     

设备对船体结构的激励力及其应用研究

针对以不平衡力为主的设备台架试验激励力向实船的转换方法进行研究,推导给出了设备对船体结构的激励力公式,并提出了设备与船体耦合振动分析的简化方法。将设备-隔振器-安装基础视为多自由度振动系统,基于振动理论,建立了设备与安装基础耦合振动的分析模型,得到了设备向安装基础传递的激励力计算公式;在此基础上,给出了设备向船体结构传递激励力的计算公式,提出了设备与船体结构耦合振动分析的简化方法,并验证了方法的正确性。研究表明：设备对船体结构的激励力不仅与设备激励力密切相关,还与设备质量、隔振器刚度及阻尼、船体结构刚度等密切相关;所提的设备与船体结构耦合振动简化方法具有较高精度,可满足工程要求。     

Calculation of the magnetic field of a coil

An approximate method is given for calculating the magnetic field of a coil of circular cross section with continuous coil windings.     

Magnetic Field and Displacement Sensor Based on Giant Magneto-Impedance Effect

A two-core transducer assembly using a Fe_73.5Nb₃Cu₁Si_13.5B₉ ribbon to detect a change of magnetic field is proposed and tested for displacement (linear and angular) and current sensor. Two identical inductors, with the ribbon as core, are part of a two-series resonance network, and are in a high impedance state when excited by a small AC field of 1 MHz in the absence of a DC biasing field (H_dc). When the magnetic state of one inductor is altered by the biasing field, produced by a bar magnet or current carrying coil, an AC signal proportional to H_dc is generated by the transducer. The results for the sensitivity and linearity with displacement (linear and angular) of a magnet and with field from the current carrying coil are presented for two particular configurations of the transducer. High sensitivities of voltage response as much as 12 µV/µm and 3 mV/degree have been obtained for the transducer as a linear and angular displacement sensor, respectively, in the transverse configuration of exciting AC and biasing DC fields.     

Quench detection method without a central voltage tap by calculating active power

In this paper, we present an electric quench detection method without a central voltage tap which may cause the short-circuit of the lead-wires from the voltage taps in the quench detection of a large AC superconducting coil. In this method, an inductive voltage detection coil is used instead of the central voltage tap. The inductive voltage detection coil is electrically insulated from a superconducting coil and therefore the lead-wires do not break down. Through the quench detection tests for a Bi-2223/Ag HTS coil, we show the feasibility of the proposed method for detecting the quench of the large AC superconducting coil.