A differential double-coil inductive transducer for measuring electrical conductivity

A differential system of two double-coil inductive transducers for the contactless measurement of the electrical conductivity of conducting materials has been presented. The differential system can be employed in applications that require smaller measurement uncertainty than that provided by the single-transducer system. A mathematical model of the differential system is based on the model of a single double-coil inductive transducer; in this case, a so-called processing function is defined as a ratio of voltages at the measurement coil terminals with and without the test sample. The relative differential voltage of the differential system is derived as a difference of processing functions of two single transducers and depends on a relative difference between conductivities of the test and reference samples. The conductivity of the test sample is obtained either using precalculated graphs or by numerically processing the equation of the differential voltage. In order to verify the obtained theoretical results, experimental investigations have been carried out using a computer-controlled measurement system with the differential system of the transducers. The conductivity measurements have been carried out using samples made of aluminum rods. During the measurements, the temperature of the reference sample was equal to room temperature (20 degrees C), whereas the temperature of the test sample was changed in the range of 0-20 degrees C to obtain the conductivity variation. The obtained experimental results confirmed the accuracy of the theoretical model of the differential transducer.     

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。     

GMR array uniform eddy current probe for defect detection in conductive specimens

The usage of eddy current probes (ECP) with a single magnetic field sensor represents a common solution for defect detection in conductive specimens but it is a time consuming procedure that requires huge amount of scanning steps when large surface specimens are to be inspected. In order to speed-up the nondestructive testing procedure, eddy current probes including a single excitation coil and an array of sensing coils present a good solution. The solution investigated in this paper replaces the sensing coils for giant magneto-resistors (GMRs), due to their high sensitivity and frequency broadband response. Thus, the ECP excitation coil can be driven at lower frequencies than the traditional ones allowing defects to be detected in thicker structures.In this work an optimized uniform eddy current probe architecture including two planar excitation coils, a rectangular magnetic field biasing coil and a GMR magnetometer sensor array is presented. An ac current is applied to the planar spiral rectangular coil of the probe, while a set of GMR magnetometer sensors detects the induced magnetic field in the specimens under test. The rectangular coil provides the DC uniform magnetic field, assuring appropriate biasing of the GMR magnetometers of the probe, setting-up the functioning point on the linear region and at the same branch of the GMR static characteristics. The differences on the images obtained for the same specimen for each GMR are reduced if all sensors are biased on the same working point. Elements of the automated measurement system used to inspect the plate under test using the proposed eddy current probe, including a validation procedure based on a 2D template matching algorithm and the corresponding experimental results are included in the paper.     

户用射流热量表流量测量特性的研究

文章对基于恒磁励磁电磁检测方法的户用新型射流热量表流量传感器的结构原理、主要技术特征、流量测量特性,以及传感与信号处理技术等内容作了较为详细地描述、分析与研究;对涉及射流流量传感器关键核心技术的小流量测量特性,在理论和实验基础上提出了改进的见解与方法;经射流热量表及射流水表产品的批量生产验证,证明了改进小流量特性的见解与方法的有效性。     

A PORTABLE TUNGSTEN COIL ATOMIC EMISSION SPECTROMETER WITH TWO COILS

Tungsten coils have been employed recently in instruments that may be used for field applications. Intense emission signals and μg/L limits of detection (LOD) have been observed for alkali metals, alkaline earth metals, and some lanthanides (such as Yb and Eu). However, for many transition elements, relatively high LODs are observed due to the insufficient excitation energy provided by the coil at high temperature. In this study, two tungsten coils are employed in an attempt to increase the emission signal and lower the LOD. A lower coil is heated to vaporize the sample, and then a second upper coil is heated at high temperature to excite the sample atoms. The emission signal is viewed above the upper coil. Six test elements (Co, Fe, Ag, Cu, Cr, and Yb) are used to compare the performance with one and two coils. Double tungsten coil atomic emission is reported for the first time for all six elements. Addition of the second coil improved the LOD by a factor of 70 for Cu and Ag; a factor of 40 for Co; a factor of 12 for Fe; and a factor of 2 for Cr and Yb. All six elements can be determined in one simple spectrum with the two-coil system. Cobalt, Fe, Cr, and Cu were determined in a certified polluted water reference sample to evaluate the accuracy of the system. Recoveries were in the range of 93–102% for all elements.     

Uniformity condition for a rectangular field coil with a split winding

A generalized Helmholtz condition for field uniformity is derived from the closed form solution of the magnetic field in a multilayer rectangular coil pair as a function of coil dimensions and pair separation. The relation among the dimensions satisfying this condition is found and plotted in parametric form for single layer coils and for a multilayer coil with a specific winding thickness. For square coils of cross section small compared to their mean radius, the gap separation approaches half the coil radius, analogous to the classical condition for circular coils. Comparison between theoretical and measured values for tolerances within +/-5% of the field at the system center agree within a 6% maximum deviation. For the experimental coil, the area enclosed by the +/-5% contour was 58% of the area of the full coil.     

非接触电感式角位移传感器的设计与校准

本文设计了一种非接触电感式角位移传感器,该传感器由定子和转子组成,其中转子由扇形铜箔获得,定子包含一组激励线圈,一组接收线圈以及后续处理电路。当给激励线圈通入交变电流时,相邻两个接收线圈产生的感应电动势大小相等,方向相反,此时感应电压为0,当转子在接收线圈上方转动时,转子中产生的涡流会导致相邻两个接收线圈感应电压产生不同的变化,经过理论与仿真分析,验证了随着转子的转动,接收线圈中感应电压的幅值呈现正余弦变化。本文编写算法对正余弦信号进行识别与校准,以定位精度为0.000 3°的高精度时栅转台为基准对样机进行测试,结果表明校准完成后,在0°～360°范围内该传感器误差为0.1°,满足实际生产需求,验证了该方案的可行性。     

Dynamic performance of high speed solenoid valve with parallel coils

The methods of improving the dynamic performance of high speed on/off solenoid valve include increasing the magnetic force of armature and the slew rate of coil current, decreasing the mass and stroke of moving parts. The increase of magnetic force usually leads to the decrease of current slew rate, which could increase the delay time of the dynamic response of solenoid valve. Using a high voltage to drive coil can solve this contradiction, but a high driving voltage can also lead to more cost and a decrease of safety and reliability. In this paper, a new scheme of parallel coils is investigated, in which the single coil of solenoid is replaced by parallel coils with same ampere turns. Based on the mathematic model of high speed solenoid valve, the theoretical formula for the delay time of solenoid valve is deduced. Both the theoretical analysis and the dynamic simulation show that the effect of dividing a single coil into N parallel sub-coils is close to that of driving the single coil with N times of the original driving voltage as far as the delay time of solenoid valve is concerned. A specific test bench is designed to measure the dynamic performance of high speed on/off solenoid valve. The experimental results also prove that both the delay time and switching time of the solenoid valves can be decreased greatly by adopting the parallel coil scheme. This research presents a simple and practical method to improve the dynamic performance of high speed on/off solenoid valve.     

基于平面线圈的高分辨力时栅角位移传感器

针对现有时栅角位移传感器采用漆包线绕制工艺加工线圈,导致线圈布线不均且容易随时间发生变化进而影响测量精度的问题,提出一种基于PCB技术的新型时栅角位移传感器。该传感器通过在PCB基板的不同层上布置特定形状的激励线圈和感应线圈,形成两个完全相同并沿圆周空间正交的传感单元;当在两传感单元的激励线圈中分别通入时间正交的两相激励电流后,通过导磁定子基体和具有特定齿、槽结构的导磁转子对传感单元内的磁场实施精确约束,使两传感单元的感应线圈串联输出初相角随转子转角变化的正弦感应信号;最后通过高频时钟脉冲插补初相角实现精密角位移测量。利用有限元分析软件对传感器进行了建模和仿真。根据仿真模型制作了传感器实物,开展了验证实验,并对实验中角位移测量误差的频次和来源进行了详细分析。经过标定和补偿,最终获得了整周范围内误差在-2.82″~2.02″的时栅角位移传感器。理论推导、仿真分析和实验验证均表明,该传感器不仅能实现精密角位移测量,还能在激励线圈和感应线圈空间极距和信号质量不变的情况下,将位移测量的分辨力从信号源头提高1倍,且结构简单稳定、极易实现,特别适用于环境恶劣的工业现场。     

线性测微电感的精化

为提高测微电感传感器的测量精度,提出了基于赫姆霍兹线圈理论设计螺线管线圈的方法,改善了螺线管线圈内轴向上磁场的分布均匀性。首先,分析了螺线管线圈模型,建立了螺线管线圈参数与轴向磁场强度分布相互关系的广义函数模型。然后,通过线圈与磁芯的尺寸确定了系统轴向磁场强度分布函数模型,结合磁芯移动区间范围设置磁场均匀度最小误差目标函数,通过对目标函数寻优得到各螺线管线圈的各项参数。最后,搭建了测微电感传感器的测试系统,测试了传感器性能。实验结果表明:与传统线圈相比,改进型螺线管线圈在100μm测量范围内的线性度由0.46%提高到0.30%。实验显示通过对不同规格的螺线管线圈进行组合,可使得螺线管内轴向上磁场强度分布均匀,从而提高了测量精度。     

多参数协同调制的高分辨力直线时栅位移传感器

为了解决高精度的直线时栅位移传感器依赖空间超精密刻线和刻线不均匀等问题,提出一种采用多参数协同调制的新型直线时栅位移传感器。该传感器通过在PCB基板上布置阵列的激励线圈和特定形状的感应线圈,通过调制感应的面积和线圈的参数,感应出电行波信号,经过整形后用高频时钟脉冲插补得到位移量。通过仿真分析设计与样机实验,得出实验结果表明,在不改变空间极距的情况下,使得分辨力在信号源头上提高1倍且有±68μm的测量精度。     

探头引线热损失对TPS法测量导热系数的影响

瞬态平面热源(Transient plane source,TPS)法是一种近年来发展起来的用于测量材料导热系数的方法.在测量过程中,加热功率受到探头引线传热的影响,进而会影响导热系数的测量准确度.针对这个问题,本文研究了测量过程中探头引线热损失对加热功率的影响,推导了热损失的数学计算公式,并提出了相应的修正模型.利用hot disk热常数分析仪对不同材料进行了一系列测量实验.实验结果表明引线热损失对测量的影响随着测量材料以及测试探头尺寸的不同而发生变化.当材料的导热系数大于0.2 W/(m·K)时,探头引线热损失的影响小于0.16％,可以忽略不计;但对于低导热系数材料的测量,对引线热损失进行补偿可以有效地提高导热系数的测量准确度.     

电感式磨粒传感器中铁磁质磨粒特性仿真研究

针对机械装置的在线监测传感器,模拟了铁磁质磨粒通过传感器过程中传感器线圈的磁场和感应线圈的感应电压瞬态变化特性.考虑了线圈与铁磨粒的材料、线圈匝数和激励线圈的输入电压等因素,应用Jmag Designer I0.4软件建立了传感器的二维有限元模型.仿真结果揭示了磨粒运动过程中线圈磁场与感应线圈中感应电压的变化规律,获得了感应电压与球形磨粒的直径大小的立方成正比,与磨粒运行速度成正比.研究结果对于电感式磨粒传感器的开发具有重要的指导价值.     

磁流变液传动装置时间响应特性

针对磁流变液传动装置扭矩调控过程中时间响应长问题,分析了励磁线圈、涡流和磁滞对磁路时间响应特性的影响机理,设计并搭建了磁流变液传动装置实验平台,开展了输出扭矩响应时间实验。理论分析和实验结果表明:改变励磁线圈参数和抽头数量可有效缩短电流响应时间;优化磁路尺寸和减小材料电导率可减小涡流影响;磁滞对响应时间影响显著,撤销线圈电流响应时间比施加电流时增加了一倍。     

Optimization of multilayer cylindrical coils in a wireless localization system to track a capsule-shaped micro-device

A wireless electromagnetic localization method has been presented to track capsule-shaped micro-devices in the gastrointestinal tract. And a prototype for the novel localization system has been developed. In the localization method, cylindrical coils placed on the patient’s abdomen generate alternating electromagnetic fields one by one. The system of equations from the localization model has been established and then transformed into a nonlinear optimization problem. The localization method presents excellent anti-interference ability and high stability. In order to solve the magnetic inverse problem in the localization model, an analytical expression between the magnetic flux density and the position & orientation should be derived by superposition of the fields generated by the coil turns, which causes systematic errors. As a result, the geometry of the cylindrical coils is optimized to reduce the errors. A full factorial experiment with two factors has been carried out. The experiment shows that the optimal L/Dout ratio and Din/Dout ratio are 0.4 and 0.8, respectively. In this case, the mean error and the standard deviation are reduced to 0.89% and 0.77%, respectively, where the distance along the axis of the cylindrical coil from the coil’s center to a measured point is 30 mm. Furthermore, the experimental results also show that the imitation error decreases significantly with increased distance from the coil. The accuracy of the localization model can be further improved using the optimized coil.     

面向超高场核磁共振应用的微型接收线圈制作与实验研究

为实现纳升级微量样品检测,结合商业常规核磁共振3.2毫米探头,本文研究了两种类型的自谐振微型接收线圈。当无线传输能量时,探头螺旋管形成射频脉冲激励能量。而微型接收线圈对该能量进行接收后以样品为作用目标,并采集信号回传,把感应获取的磁共振信号传输到探头螺线管。与现有磁共振探头不同,本文提出Pigtail型和Stripline型微接收线圈结构。实测结果显示,线圈谐振频率达128MHz和935.7MHz,应用于3T超导核磁共振设备初步完成了蔗糖波谱的测试分析实验,表明微型接收线圈对提高谱线分辨率有重要作用。     

Design and characterization of immersion ultrasonic transducers for pulsed regime applications

Ultrasonic transducer design is focused to maximize performance in specific applications, usually leading to complex design and expensive construction and assembly. With the aim to overcome this drawback, a general-purpose immersion ultrasonic transducer for pulsed regime applications has been developed. The design of each element of the transducer is described in this paper, wherein materials and geometries for each part have been recommended. A simple theoretical model has been proposed in order to predict the form of the received electric signal in the target transducer. The model is based on the assumption that the piezoelectric element acts as an underdamped oscillator, forced by the acoustic field coming from the propagation medium. Excellent agreement between the experimental measurements and the analytical model is achieved. Electrical impedance measurements reveal negligible differences between the resonance frequency of the active element and that of the assembled transducer. The designed devices have been characterized in water using two identical transducers placed face to face with changeable orientation. The experimental results show a highly linear response and the generation of a collimated acoustic field. The effects of the thickness of the matching layer on the transmission coefficient have been also studied, resulting in a smooth decrease in the received amplitude, which may significantly lower large-scale production costs.     

Frequency dependence of magnetic permeability of hollow cylindrical ferromagnetic pieces

The frequency dependence of the magnetic permeability of hollow cylindrical samples has been studied. Experiments were conducted in an inhomogeneous ac magnetic field generated by a narrow cylindrical coil. The pickup coil axis was aligned with the driving coil and the sample, and the distance between the coils varied during the experiment. The experimental data were compared to calculations of the real and imaginary components of the complex magnetic permeability of samples. Experimentally determined hodographs are given, alongside frequency dependences of the magnetic permeability components obtained at different diameters, wall thicknesses, separations between the coils, and sample lengths.     

交流电机谐波电动势节距因数出现负值的分析和处理

针对运用现有交流电机谐波电动势节距因数公式计算电动势有效值出现负值问题,采用了电路时域分析、相量分析以及物理学中场强矢量分析相结合的方法,对整距和短距线圈谐波电动势的构成依次进行了研究,对短距线圈谐波电动势构成中的节距因数采用划分区间分段讨论的方法着重进行了探讨,提出了一个基于v次谐波节距半值γv/2(电角度形式)区间的分段函数新节距因数公式,并以通常的线圈节距值y1=5τ/6(槽数形式)选取1~19次奇次谐波分别对新旧公式进行了数据验证。研究结果表明,与现有公式当v=3,9,13,17,19时出现负值不同,新的公式在计算谐波电动势节距因数时全程未出现负值,说明克服了现有公式的缺陷,未来可替代现有公式使用。     

轴类镀层结构材料力学性能声学表征方法研究

针对轴类镀层结构材料力学性能无损表征方法开展理论和实验研究,对于表面工程的质量检测与评价具有重要意义。利用自主开发的超声显微测量系统与PVDF线聚焦探头,对不同厚度的轴类镀层材料进行散焦测量。针对轴类试件表面波传播路径与散焦距离的非线性关系,分析了线聚焦探头几何尺寸与散焦距离和试件轴径间的匹配关系,优化检测参数,并在V(f,z)分析法的基础上,采用相位相关分析法获得轴类镀层材料的实验频散曲线。结合镀层材料声波传播特性,采用基于模拟退火的粒子群优化算法(PS-B-SA)将理论频散曲线与实验频散曲线相拟合,反演轴类镀层结构材料的声学参数,进而表征镀层材料的弹性常数。多个不同厚度轴类镀层结构材料弹性常数及镀层厚度的反演结果与实际值相吻合,表明该测量方法可靠、结果准确。该研究成果为轴类镀层结构力学性能无损检测提供了技术手段,也为工程材料表面工程加工性能的评价提供了新方法。