Electromagnetic responses on microstructures of duplex stainless steels based on 3D cellular and electromagnetic sensor finite element models

Microstructures determine mechanical properties of steels,but in actual steel product process it is difficult to accurately control the microstructure to meet the requirements.General microstructure characterization methods are time consuming and results are not rep-resentative for overall quality level as only a fraction of steel sample was selected to be examined.In this paper,a macro and micro coupled 3D model was developed for nondestructively characterization of steel microstructures.For electromagnetic signals analysis,the relative permeability value computed by the micro cellular model can be used in the macro electromagnetic sensor model.The effects of different microstructure components on the relative permeability of duplex stainless steel(grain size,phase fraction,and phase distribu-tion)were discussed.The output inductance of an electromagnetic sensor was determined by relative permeability values and can be val-idated experimentally.The findings indicate that the inductance value of an electromagnetic sensor at low frequency can distinguish dif-ferent microstructures.This method can be applied to real-time on-line characterize steel microstructures in process of steel rolling.

A Nano-Micro Engineering Nanofiber for Electromagnetic Absorber,Green Shielding and Sensor

It is extremely unattainable for a material to simultaneously obtain efficient electromagnetic(EM)absorption and green shielding performance,which has not been reported due to the competition between conduction loss and reflection.Herein,by tailoring the internal structure through nano-micro engineering,a NiCo2O4 nanofiber with integrated EM absorbing and green shielding as well as strain sensing functions is obtained.With the improvement of charge transport capability of the nanofiber,the performance can be converted from EM absorption to shielding,or even coexist.Particularly,as the conductivity rising,the reflection loss declines from −52.72 to −10.5 dB,while the EM interference shielding effectiveness increases to 13.4 dB,suggesting the coexistence of the two EM functions.Furthermore,based on the high EM absorption,a strain sensor is designed through the resonance coupling of the patterned NiCo2O4 structure.These strategies for tuning EM performance and constructing devices can be extended to other EM functional materials to promote the development of electromagnetic driven devices.

Possibility of the Application of the Ultra-long Electromagnetic Wave Remote Sensor to Marine Geological Exploration

The ultra-long electromagnetic wave remote sensing technique developed by Peking University is one of new future techniques, which can detect the submarine geological information from the depth of 20 to 10000 m below the surface by receiving natural ultra-long electromagnetic waves (n Hz to n 100 Hz). The new remote sensor is composed of three parts: a main instrument with a portable computer, an antenna with an amplifier and an external power.

Direction finding of coexisted independent and coherent signals using electromagnetic vector sensor

The existing direction of arrival （DOA） estimation algorithms based on the electromagnetic vector sensors array barely deal with the coexisting of independent and coherent signals. A two-dimensional direction finding method using an L-shape electromagnetic vector sensors array is proposed. According to this method, the DOAs of the independent signals and the coherent signals are estimated separately, so that the array aperture can be exploited sufficiently. Firstly, the DOAs of the independent signals are estimated by the estimation of signal parameters via rotational invariance techniques, and the influence of the co- herent signals can be eliminated by utilizing the property of the coherent signals. Then the data covariance matrix containing the information of the coherent signals only is obtained by exploiting the Toeplitz property of the independent signals, and an improved polarimetric angular smoothing technique is proposed to de-correlate the coherent signals. This new method is more practical in actual signal environment than common DOA estimation algorithms and can expand the array aperture. Simulation results are presented to show the estimating performance of the proposed method.

Joint 2D-DOA and polarization estimation for sparse nonuniform rectangular array composed of spatially spread electromagnetic vector sensor

In this paper,a sparse nonuniform rectangular array based on spatially spread electromagnetic vector sensor(SNRASSEMVS)is introduced,and a method for estimating 2D-direction of arrival(DOA)and polarization is devised.Firstly,according to the special structure of the sparse nonuniform rectangular array(SNRA),a set of accurate but ambiguous direction-cosine estimates can be obtained.Then the steering vector of spatially spread electromagnetic vector sensor(SSEMVS)can be extracted from the array manifold to obtain the coarse but unambiguous direction-cosine estimates.Finally,the disambiguation approach can be used to get the final accurate estimates of 2DDOA and polarization.Compared with some existing methods,the SNRA configuration extends the spatial aperture and refines the parameters estimation accuracy without adding any redundant antennas,as well as reduces the mutual coupling effect.Moreover,the proposed algorithm resolves multiple sources without the priori knowledge of signal information,suffers no ambiguity in the estimation of the Poynting vector,and pairs the x-axis direction cosine with the y-axis direction cosine automatically.Simulation results are given to verify the effectiveness and superiority of the proposed algorithm.

The Electromagnetic Compatibility Design of the Wireless Sensor Network Node

This paper is concerned with the sensor nodes’ hardware design of the wireless sensor network.We focus on the electromagnetic compatibility design of the printed circuit board.In this paper,we will give a schematic diagram first,and then,according to the layout,wiring rules and the knowledge of electromagnetic compatibility, we will present the design of the printed circuit board which has a good characteristic of electromagnetic compatibility.

A Combined Numerical-Experimental Study on the Noise Power Spectrum Produced by an Electromagnetic Sensor for Slurry Flow

The signals generated by electromagnetic flow sensors used for slurry fluids are often affected by noise interference produced by interaction with the slurry itself.In this study,the power spectrum characteristics of the signal are studied,and an attempt is made to determine the relationship between the characteristics of the related noise and the velocity and concentration of the slurry fluid.Dedicated experiments are conducted and the related power spectrum curve is obtained processing the signal measured by the sensor with Matlab.Numerical simulations are also carried out in the frame of an Eulerian approach in order get additional insights into the considered problem through comparison with the experimental results.The following conclusions are drawn:(1)The intensity of noise is directly proportional to the number of solid particles colliding with the electrode of the electromagnetic flow sensor per unit time,and to the square of the average velocity of the flow layer near the pipe wall.(2)With an increase in the slurry noise intensity,the power spectrum curve shifts upward in the logarithmic coordinate system(and vice versa).

Porous and Ultra-Flexible Crosslinked MXene/Polyimide Composites for Multifunctional Electromagnetic Interference Shielding

Lightweight,ultra-flexible,and robust crosslinked transition metal carbide(Ti3C2 MXene)coated polyimide(PI)(C-MXene@PI)porous composites are manufactured via a scalable dip-coating followed by chemical crosslinking approach.In addition to the hydrophobicity,anti-oxidation and extreme-temperature stability,efficient utilization of the intrinsic conductivity of MXene,the interfacial polarization between MXene and PI,and the micrometer-sized pores of the composite foams are achieved.Consequently,the composites show a satisfactory X-band electromagnetic interference(EMI)shielding effectiveness of 22.5 to 62.5 dB at a density of 28.7 to 48.7 mg cm−3,leading to an excellent surface-specific SE of 21,317 dB cm^(2)g^(−1).Moreover,the composite foams exhibit excellent electrothermal performance as flexible heaters in terms of a prominent,rapid reproducible,and stable electrothermal effect at low voltages and superior heat performance and more uniform heat distribution compared with the commercial heaters composed of alloy plates.Furthermore,the composite foams are well attached on a human body to check their electromechanical sensing performance,demonstrating the sensitive and reliable detection of human motions as wearable sensors.The excellent EMI shielding performance and multifunctionalities,along with the facile and easy-to-scalable manufacturing techniques,imply promising perspectives of the porous C-MXene@PI composites in next-generation flexible electronics,aerospace,and smart devices.

ELECTROMAGNETIC TOMOGRAPHY (EMT): THEORETICAL ANALYSIS OF THE FORWARD PROBLEM

Inductance-bared electromagnetic tomography (EMT) is a novel industrial process tomographic technique. Exact expressions of the magnetic field distribution in a two-dimensional object space were derived by analytically solving the forward problem for a particular two-component pow. The physical mechanisms within the sensor and the detectability limits of the EMT technique were quantitatively analyzed. Direct mathematical expressions for the field sensitivity and the sensitivity maps were established. To a certain extent, mathematical and theoretical bares are given for quantitative design of the sensor, detectability analysis of the EMT technique and image reconstruction of two-component processes based on the linear back-projection algorithm.

Stretchable electromagnetic interference shielding and antenna for wireless strain sensing by anisotropic micron-steel-wire based conductive elastomers

We prepare stretchable elastic electromagnetic interference(EMI) shielding and stretchable antenna for wireless strain sensing using an elastic composite comprising commercial steel wool as a conducting element. The prepared elastic conductor shows anisotropic electrical properties in response to the external force. In the stretchable range, the electrical resistance abnormally decreases with the increase of tensile deformation. The EMI shielding effectiveness of the elastic conductor can reach above-30 d B under 80% tensile strain. The resonance frequency of the dipole antenna prepared by the elastic conductor is linearly correlated with the tensile strain, which can be used as a wireless strain sensor. The transmission efficiency is stable at about-15 d B when stretched to 50% strain, with attenuation less than 5%. The current research provides an effective solution for stretchable EMI shielding and wireless strain sensing integrated with signal transmission by an antenna.

Optimal Design of Electromagnetic Acoustic Transducer

This paper considers the design of EMAT （Electro-Magnetic Acoustic Transducer） based on numerical simulation. The EMAT consists of an exiting coil and two permanent magnets, which transmits the ultrasonic wave by the Lorentz force between the eddy current and the static magnetic field by the magnets. From the experimental result on self-prepared EMATs, the intensity and the directivity of the transmitted wave depend on the widths of the coil and the magnets. By means of EEM analysis the authors attempt to determine the optimal values of the above widths such that both the intensity and the directivity achieve the maximum or allowable performance.

基于电磁感应自驱动传感器的呼吸率监测系统研究

呼吸率是呼吸功能的一个重要参数,实时监测呼吸率对发现和预防呼吸疾病有着重要意义。设计了一种基于电磁感应自驱动呼吸气流传感器的呼吸率监测系统,该系统将传感器置于口腔/鼻下通过监测呼吸气流的变化来监测人体的呼吸率。实验测得传感器在呼吸缓慢、呼吸正常、呼吸急促时周期分别为3.8,2.3,1.6 s,小于人呼吸周期时间(3~6 s),系统采用蓝牙通信技术传输数据,方便测试者移动。该系统实现了对人体呼吸率稳定、实时、准确的采集,为后续呼吸疾病的预防和诊断提供了一定的研究价值。

基于容性耦合的钢轨压力传感器电磁干扰分析

目前随着弱电装置在铁路通信、传感测量等方面的普及,电磁干扰问题越来越引起人们的重视,但是关于电磁干扰机理的耦合分析等方面的工作开展较少。本文针对一则典型的钢轨压力传感器电磁干扰问题,从干扰源排查入手,建立了电源线与信号线的容性耦合物理模型,提取线缆间分布电容参数,定量分析了耦合电场大小;同时找出干扰源,确定为电源线容性耦合导致的串扰电压干扰,给出了相应抑制干扰的措施,该分析与实测相符合。研究结果表明,接地装置对电源线地线的电磁干扰影响很大,从而进一步影响了信号线的信号电压。当接地电阻的埋入深度从0.1 m增加到0.6 m时,电源线的干扰电压得到了抑制;信号线的连接端头是容易耦合到外界电磁干扰的薄弱环节,是改善屏蔽效能的关键点。本文所提出的关于容性耦合的机理分析、计算方法、以及传感器信号的电磁干扰抑制措施,能够为今后电气设备的电磁干扰分析抑制提供普遍的借鉴意义。

电磁脉冲电场测量技术研究综述

宽频带大动态范围的脉冲电场测量是电磁脉冲效应、防护以及电磁兼容等相关领域的一项共性基础技术,在过去50年以来受到研究人员的广泛关注,并发展出不同手段的测量技术。无源微分(D-dot)测量传感器带宽相对较高,但尺寸较大、集成度低;有源光纤测量系统最大测量带宽约为1 GHz,尺寸相对较小、集成度高、实用性强。集成光学传感器作为一种带宽宽、体积小的无源传感器,各国均有研究。本文主要回顾上述几种脉冲电场测量技术近期研究进展,并结合发展现状分析脉冲电场测量技术存在的挑战和未来可能的研究方向,为相关领域研究人员提供参考。

基于环形阵列的油管损伤三维成像检测方法研究

传统的瞬变电磁套管损伤检测技术是通过采集数据来反映套管损伤情况的二次场信息,反演套管二维壁厚曲线,为套管损伤提供解释依据。为了使套管损伤解释得更加高效、直观、精准,满足井口油管三维成像的需求,建立一种基于环形阵列式的井口油管三维成像检测系统,利用探测仪器中环形阵列分布的TMR传感器,对井口油管各个方位的信息进行采集,使得采集到的数据能够描述不同深度、不同角度的损伤情况。结合套管半径、涡流扩散时间以及径向探测角度之间的关系,通过对井口三维数据的处理,实现套管内外壁三维成像,进而实现井口油管的非对称损伤解释。通过与传统的电磁探伤曲线的对比,验证了所提井口油管三维成像检测方法的有效性,为现场套管损伤解释工作提供重要依据。

考虑电磁干扰的差动式电容力矩传感器动态校准方法

在差动式电容力矩传感器校准过程中,受设备电磁干扰的影响,造成校准结果存在较大偏差。为解决这一问题,在考虑电磁干扰的前提下,提出差动式电容力矩传感器动态校准方法。在差动式电容力矩传感器存在电磁干扰的情况下,采用小波变换方法抑制传感器中的电磁干扰。通过差动式电容力矩传感器的组成结构构建参数化数学模型,获取动态激励和结构响应两者之间的频域传递关系,利用最小二乘法分析传递函数的频域几何关系式,对传感器展开动态解耦和动态补偿。通过冲击剪断装置形成的力矩信号对传感器动态标定,利用检测电路测量阶跃信号对标定结果校准,完成差动式电容力矩传感器动态校准。实验测试结果表明,所提方法可以获取满意的动态校准结果。

利用磁场差值的水下磁传感器阵列校准技术

为了实现磁噪声环境中水下磁传感器阵列位置和姿态的高精度校准,提出一种利用动态磁源和阵列磁场差值的磁传感器阵列校准方法。构建校准设备、水下磁传感器阵列和磁噪声环境的数学模型,对一字型、十字型和四面体型的水下磁传感器阵列进行定位定姿校准的数值仿真验证实验,分别利用阵列磁场差值和直接使用磁场值的方法对水下磁传感器阵列的位置和姿态进行求解。实验结果表明:对于水下20 m深度处的磁传感器阵列,利用磁场差值的方法可实现位置和姿态的高精度校准,在校准精度和稳定性方面都要优于直接使用磁场值的方法;对于不同类型的磁传感器阵列,十字型阵列的定位误差均值为0.13 m,角度误差均值为0.51°;一字型阵列的定位误差均值为0.13 m,角度误差均值为0.82°;四面体型阵列的定位误差均值为0.16 m,角度误差均值为0.89°。新方法和技术不易受地磁场环境噪声干扰的影响,具有较高的应用潜力。

面向新型电力传感器的能量收集技术

电力传感器作为能源互联网的关键基础设施,其持续稳定的电力供应是保证能源互联网高效运行的前提。然而,传统供电方式存在诸多局限。全面梳理了面向新型电力传感器的能量收集技术,包括振动能量收集、温差能量收集、光伏能量收集和电磁能量收集等,这些技术利用环境中的分布式能源,通过不同的转换机理为传感器提供电力,有望解决供电难题。阐述了各种能量收集技术的应用现状,分析了目前所面临的关键技术挑战,如能量转换效率低、工作条件要求苛刻、器件可靠性和集成度有待提高等;探讨了未来能量收集技术的创新方向,包括开发新型高性能材料、优化器件结构设计、使用复合式收集技术等,以期实现更高的能量利用效率,满足新型电力传感器的实际需求,推动智能电网等相关领域的技术创新。

基于磁平衡的钢丝绳探伤数字传感器研究

针对钢丝绳在长期运行过程中会出现断丝、截面磨损、锈蚀等损伤而形成安全隐患的问题,指出应进行钢丝绳健康状态定期安全检测和评估。针对常用的强磁检测法的不完善之处,提出基于空间磁场平衡机制检测的新型钢丝绳损伤判别方法。首先研究采用PRO/E进行三维实体建模,进行了磁路设计;其次采用有限元分析,比较X轴、Y轴磁化方向的优劣,依据磁力线密度、中间直线磁场变化强度得出Y轴磁化方向优于X轴磁化方向;最后通过运用三维磁场数值分析软件,设计计算出合适的传感器聚磁环结构和感知单元。实验研究结果表明,基于空间磁场平衡机制的新型钢丝绳探伤传感器的检测效果较传统强磁探伤传感器的检测效果有明显改善。

EMVS互质面阵张量波束成形

相比于标量传感器均匀阵列,电磁矢量传感器(electromagnetic vector sensor,EMVS)稀疏阵列能够在降低系统软硬件成本的同时感知更大范围、更高维度的空间信号信息,并通过精尖波束扫描实现信源测向性能的综合提升。然而,传统基于矩阵信号建模的波束成形算法难以利用EMVS接收信号的多维结构化信息,且存在由阵元稀疏排布所引入的虚峰干扰问题。为了应对上述挑战,提出了面向EMVS互质面阵的张量波束成形算法,有效利用了空域互质采样的波束分布特性和张量信号处理的优势实现指向性张量波束扫描测向。具体而言,将EMVS互质面阵中稀疏均匀子面阵的接收信号表示为一对涵盖多维度空间电磁信息的高维张量,并从张量信号空域滤波的准则出发,设计面向稀疏均匀子面阵的张量化最小方差无畸变响应优化问题。为了克服由上述优化问题中张量内积项所造成的传统求解方法失效难题,提出通过张量权重的canonical polyadic分解,将原始张量化最小方差无畸变响应优化问题转换为对应波达方向信息维度与极化状态信息维度的子问题,并基于各子问题的局部最优解设计交替迭代求解方法,以获得张量权重的全局最优解。进而,基于张量空间的质数分解唯一性分析,理论证明一对满足互质阵元排布的稀疏均匀子面阵所对应的虚峰具有互不重叠特性,并提出张量波束功率的互质合成处理方法,以此构造具备精尖主瓣且虚峰抵消的张量波束功率图,从而实现多信源空间方位的精准估计。仿真结果验证了所提EMVS互质面阵张量波束成形算法的有效性。