平行激励下脉冲涡流热成像响应规律的研究

为探索脉冲涡流热成像技术中涡流与裂纹平行时的响应规律并分析致热机理,运用有限元仿真软件分析了具有贯穿裂纹缺陷的铁磁、非铁磁材料平行激励时的温度分布;运用MATLAB软件提取仿真及实验数据定量分析磁通密度、电流密度、温度等参数并探究了导致铁磁、非铁磁材料温度分布差异的原因;提出铁磁材料除尖端效应外,裂纹内表面趋肤效应导致裂纹边缘温度升高,非铁磁材料裂纹内表面趋肤效应和裂纹边缘涡流密度增大共同作用导致裂纹边缘温度升高.运用高周波电感应加热器进行了实验验证.实验结果与仿真分析存在较好的一致性.研究成果揭示了非铁磁材料平行激励下的温度响应规律,为工程应用中可能的各方向裂纹定性分析和定量表征奠定基础.     

脉冲涡流热成像裂纹检测机理仿真分析

脉冲涡流热成像技术由于在导电材料缺陷检测中的优势而成为无损检测的热点。本文运用电磁感应原理及热传导理论,建立感应加热数学模型,利用有限元法分析电磁激励热成像检测缺陷的机理。利用COMSOL有限元软件建模分析了导磁材料和非导磁材料中两种基本裂纹slot和notch附近涡流场和温度场的分布情况,通过分析裂纹附近涡流密度大小和温度场的变化曲线,指出检测导磁和非导磁材料裂纹的最佳观测时间以及温度响应,为下一步的裂纹定量检测提供理论指导。     

基于涡流热成像的铁磁材料近表面微裂纹检测

采用涡流热成像技术,对铁磁材料近表面微裂纹进行了检测研究。提出了平行激励热传导方式检测近表面微裂纹的检测方法;数值计算模拟了涡流激励下裂纹处的生热过程,分析了裂纹处的温度分布及其对检测结果的影响;采用平行激励方式对含近表面微裂纹的铁磁材料进行了检测实验,通过提取试件表面温度分布数据,获取其变化速率曲线,实现了对裂纹的检测和识别。结果表明:涡流热成像平行激励方式能够准确地检测到铁磁材料近表面的微裂纹缺陷;选择适当的涡流激励时间有助于提高裂纹处与非裂纹处温度对比,增强检测效果。该方法的研究为近表面微裂纹的检测和定量识别奠定了基础。     

浅谈电气工程中电涡流引起的危害和防范措施

在电气工程中,电涡流是一种电缆周围单芯电缆通过而产生的交变磁场相互作用下而产生的感应电流,由于其本身具有较强的破坏能力,这就需要我们对其采取一定防范措施,本文就电气工程中电涡流引起的危害与防范措施进行相关研究,希望能够我国电气工程的安全发展带来一定启发。     

填充电各向异性媒质的矩形波导的研究

导出了在直角坐标系中电各向异性媒质中的波动方程，并在单轴晶体填充的矩形波导中进行了求解，研究了场的特性，找出了一些规律性的结论。     

基于涡流锁相热成像的刹车片内部气泡检测

刹车片是汽车必不可少的制动部件,其内部气泡严重影响行车安全。传统敲击听声检测方法主观性强,检测效率低,难以满足准确高效的检测需求。基于涡流锁相热成像具有非接触、大面积检测的特点,将其应用于少金属摩擦材料汽车刹车片的内部气泡检测。采用有限元仿真探索了刹车片结构和内部气泡对相位的影响,并以背钢处相位为参考,分离出气泡存在。对刹车片试样进行检测,并采用水切割观察剖面的方法验证结果。实验表明涡流锁相热成像检测方法能有效检测少金属摩擦材料汽车刹车片的内部气泡。     

螺旋滤波器及其在电视差转机中的应用

1.简介在米波段,集中参数LC回路Q值不高,很难做到100以上。其原因是高频电流引起趋肤效应和线圈相邻各匝导线磁场的相互影响引起电流分布不均匀,使线圈的有效电阻增加很多;其次线圈的磁场在附近金属物内感应产生涡流损失;还有辐射损耗。这几项合起来所呈现的线圈有效电阻远比线圈的直     

两种脉冲涡流轴对称有限元模型的比较

脉冲涡流检测技术是近年来发展迅速的一种新型涡流检测技术。由于其激励信号频谱宽广,不同频率分量的涡流能够渗透到不同深度,使其检测信号包含更丰富的深度方向的缺陷信息,在航空维修等工业领域有着重要的意义。对脉冲涡流检测的仿真可以指导脉冲涡流检测技术的研究。本文利用二维轴对称模型,介绍r脉冲涡流有限元仿真的两种方法一傅里叶变换法和时间步进法,并详细比较了这两种方法的优缺点。     

考虑趋肤效应和涡流效应的柱形导体内部磁场和内部电感的有限元分析

有限元方法的特点是通过数值计算来解决较为复杂的电磁场问题,它是随着计算机技术的发展而被广泛用来解决复杂的场的问题的一个非常有效的工具.本文作者在考虑趋肤效应和涡流效应的前提下,用有限元方法分析计算了柱形导体的内部磁场和内部电感,这一分析结果对集成电路、电力传输线及电气接头等的设地都有着十分重要的意义.     

基于阻抗分析法的电桥式涡流检测系统研究

涡流检测技术采用频谱丰富的正弦信号作为激励源,响应中包含多个频率成分,增强了涡流检测的抗干扰能力.将涡流检测技术、数据采集技术与虚拟仪器技术有机结合起来,开发了适用于在线检测的涡流检测系统.系统由脉冲涡流检测硬件电路、PXI总线系统以及相关软件组成.硬件电路可产生性能良好,频率、幅值稳定的激励信号,频率范围为0～5 M...     

各向异性材料涂覆金属二面角反射器的RCS分析

该文基于均匀平面波入射下无限大金属衬底各向异性材料表面等效电磁流的一般表达,利用物理光学法结合多次反射,研究了各向异性材料涂覆金属二面角反射器的后向电磁散射特性,分析了不同材料参数及不同二面角对后向RCS的影响,得到了一些有益的结论。     

Filefish‐Inspired Surface Design for Anisotropic Underwater Oleophobicity

Surfaces with anisotropic wettability, widely found in nature, have inspired the development of one‐dimensional water control on surfaces relying on the well‐arranged surface features. Controlling the wetting behavior of organic liquids, especially the motion of oil fluid on surfaces, is of great importance for a broad range of applications including oil transportation, oil‐repellent coatings, and water/oil separation. However, anisotropic oil‐wetting surfaces remain unexplored. Here, the unique skin of a filefish Navodon septentrionalis shows anisotropic oleophobicity under water. On the rough skin of N. septentrionalis, oil droplets tend to roll off in a head‐to‐tail direction, but pin in the opposite direction. This pronounced wetting anisotropy results from the oriented hook‐like spines arrayed on the fish skin. It inspires further exploration of the artificial anisotropic underwater oleophobic surfaces: By mimicking the oriented hook‐like microstructure on a polydimethylsiloxane layer via soft lithography and subsequent oxygen‐plasma treatment to make the PDMS hydrophilic, artificial fish skin is fabricated which has similar anisotropic underwater oleophobicity. Drawn from the processing of artificial fish skin, a simple principle is proposed to achieve anisotropic underwater oleophobicity by adjusting the hydrophilicity of surface composition and the anisotropic microtextures. This principle can guide the simple mass manufacturing of various inexpensive high surface‐energy materials, and the principle is demonstrated on commercial cloth corduroy. This study will profit broad applications involving low‐energy, low‐expense oil transportation, underwater oil collection, and oil‐repellant coatings on ship hulls and oil pipelines.     

光热辐射方法测量各向异性材料的热导张量

报道了一种用光热辐射（PTR）技术测量各向异性材料热导张量的简单方法。本文从各向异性介质的热传导理论出发，推导出该材料的幅频和相频关系；在实验上用PTR方法测出幅频和相频曲线，拟合出热导率，并得到各向异性材料的热导张量。     

A comparison of anisotropic PML to Berenger's PML and itsapplication to the finite-element method for EM scattering

The use of an anisotropic material for the boundary truncation of the finite-element method is considered. The anisotropic material properties can be chosen such that a plane-wave incident from free space into the anisotropic halfspace has no reflection. Because there is no reflection, the material is referred to as a perfectly matched layer (PML). The relationship between the anisotropic PML and the original PML proposed by Berenger (see J. Comp. Phys., vol.114, p.185-200, October 1994) is considered. The anisotropic PML is applied to the finite-element solution of electromagnetic (EM) scattering from three-dimensional (3-D) objects. Numerical results are presented to demonstrate the accuracy of the PML     

Permeability measurement on composites made of oriented metallicwires from 0.1 to 18 GHz

In this paper, we study the microwave properties of strongly anisotropic materials made of orientated conducting wires. We have developed a broad band method to determine their permeability μ∥ parallel to the direction of the wires. We investigate the magnetic properties of strongly anisotropic composites made of different types of paramagnetic and ferromagnetic wires. A simple model is proposed to account for the skin effect, and agrees with our observations. This leads to a unique broad band method for measuring the permeability of thin conducting wires     

UARAC的电磁特性分析

为了解决单轴各向异性吸波涂层(UARAC)的分析和设计中所遇到的反射系数计算问题,从电磁场理论出发,导出了电磁波以任意角入射时UARAC的反射系数公式。同时,给出了计算曲线的例子,通过实例计算分析了UARAC的斜入射特性和电磁波的入射角、极化状态等对UARAC的隐身效果的影响。得到负单轴各向异性吸波涂层(MUARAC)的吸波性能优于正单轴各向异性吸波涂层(PUARAC)的吸波性能及MUARAC的吸波性能主要取决于单轴各向异性吸波材料的横向参数等结论。为UARAC的计算机辅助分析和设计提供了基础。     

Coupling efficiency of butt-joined isotropic and anisotropicsingle-mode slab waveguides

Studied is the effect of axial displacement and angular misalignment on the power-coupling efficiency of a butt-joint between an isotropic and an anisotropic single-mode slab waveguide. The power-coupling coefficient is formulated by means of the boundary conditions at the interface of the butt-joint and the orthogonality relations between the modes in the outgoing waveguide. It is found from the numerical results that proper amounts of angular misalignment and axial displacement remarkably suppress transmission losses when the material coordinate system of the anisotropic waveguide is not aligned with its waveguide coordinate system in the plane defined by the propagation axis and the normal of the waveguide surface     

Wave propagation in pyrolytic-graphite slow-wave circuits

The possibility of using an anisotropic resistive material to simulate sheath-type microwave slow-wave structures is investigated experimentally. The specific anisotropic material considered in the present study is pyrolytic graphite which has an anisotropic electrical conductivity. A sheath model of the Karp line is simulated by replacing wires and slots by a sheet of pyrolytic graphite. The mode of propagation in this waveguide structure is measured and compared with the theory. The Karp-line mode with a relatively high attenuation is found to be present in this structure.     

2维各向异性正方介质柱的带隙研究

因各向同性介质组成的正方晶格方形介质柱不能产生绝对带隙,而三角晶格正方介质柱可以产生很小的带隙,为了得到更大带隙,引入各向异性介质来代替各向同性介质,由于各向异性介质在不同方向上的介电常数不同,可以产生较大的绝对带隙,利用平面波展开法分别计算了正方晶格各向异性介质柱产生的绝对带隙宽度为0.03095ωe(ωe为中心频率),三角晶格各向异性正方介质柱产生的完全禁带宽度为0.03831ωe,是各向同性介质所产生带宽的3.6倍。这一结果对光子晶体带隙的研究是很有帮助的。     

带有填充各向异性介质凹槽的金属目标电磁散射的FDTD法分析

本文利用各向异性时域有限差分法(FDTD)分析填充各向异性介质凹槽的金属目标的电磁散射.就一种特定的典型金属目标模型,详细计算分析了开槽位置、宽度和深度以及填充材料对其电磁散射特性的影响,计算结果显示在目标的特定部位开适当宽度和深度的槽并填充负单轴各向异性介质能显著降低目标的后向雷达散射截面(RCS).