低频脉冲磁场中磁屏蔽体磁饱和效应的试验研究

针对磁屏蔽体在低频脉冲磁场环境中可能存在的磁饱和问题,利用试验方法开展了磁饱和效应研究,证实了常规工程屏蔽体可在低频脉冲磁场环境中达到磁饱和状态,并通过观测屏蔽效能的变化获得了磁饱和规律,同时分析了磁饱和效应对屏蔽效能的影响及其与屏蔽体的材料磁导率、壳体厚度、外形尺寸等参数的关系.研究表明：磁屏蔽体屏蔽效能在磁饱和效应影响下,呈现出明显的动态变化特点,具有与屏蔽壳体磁导率类似的变化趋势;壳体厚度2 mm以内、长宽高为2 m×2 m×2 m左右的屏蔽体在上升时间为300μs、持续时间为1.2 ms的磁场环境中,达到磁饱和状态的磁化场强度约为10 mT,其磁饱和难易程度与磁导率及外形尺寸负相关,与壳体厚度正相关.试验研究结果与理论分析结论一致,可为磁屏蔽体的科学合理设计提供参考,具有较高的工程应用价值.     

磁光晶体GdYBiIG的磁致退偏效应

建立了磁光晶体磁致偏振特性测试系统。该系统采用中心波长为1538nm的WGY型半导体激光器，在0～1500mT的大范围可调磁场下，对光隔离器用磁光晶体GdYBiIG样品的退偏效应进行了测试。测试结果表明，达到磁饱和或接近磁饱和时，GdYBiIG晶体的偏振性能最优；达到磁饱和后，随着磁场的增强，出现了磁致退偏效应。分析了磁致退偏效应的产生机理，给出磁致圆二向色性及磁致线双折射是产生退偏的原因。实验测试与理论分析表明，根据磁光晶体GdYBiIG这种退偏效应的规律性，在利用该类晶体制作磁光器件时，外加磁场强度稍大于它的磁饱和强度即可。     

半磁半导体Cd_(1-x)Mn_xTe的磁光开关效应

在半磁半导体Cd_(1-x)Mn_xTe中实现了不需改变施加磁场方向的新型磁光开关效应,该效应是由Cd_(1-x)Mn_xTe的巨大法拉弟效应和磁光反馈系统的饱和特性产生的。讨论了该效应用于光控、温控磁光开关及混合型磁光光学双稳态的可能性。     

软磁非晶丝巨磁阻抗效应传感器研究进展与应用

基于软磁非晶丝巨磁阻抗效应(GMI)的传感器是近年来磁传感器领域的研究热点之一.非晶丝具有良好的软磁特性:如低电阻率、高磁导率、高饱和磁感应强度、低矫顽力、低损耗以及特殊的磁畴结构等,利用其GMI效应制成磁传感器,其突出优点是微型化、高灵敏度、快速响应、高温度稳定性和低功耗.本文讨论了软磁非晶丝巨磁阻抗效应的机理,叙述了非晶丝GMI传感器的研究进展,着重对敏感材料性能及制备、GMI器件结构形式、传感电路等作了介绍,并指出了GMI目前存在的问题及将来的发展趋势.最后对GMI的应用作了展望.     

开关磁阻电机非线性电磁特性的磁链模型

开关磁阻电机调速系统具有直流和交流调速系统的优点,在航空航天、机械电子、家电等领域获得了广泛的应用。由于开关磁阻电机的磁路饱和、涡流、磁滞效应等产生的非线性,使其精确的数学模型非常复杂,且难以解析计算。本文采用理论推导和曲线拟合的方法,根据开关磁阻电机定子的相电感表达函数,计算得到其电磁特性和拟合曲线,并与实测的磁链数据对比研究,从而推导出开关磁阻电机运动电势和增量电感的解析表达式,为其在线控制系统的设计和研究提供了指导。     

基于巨磁阻抗效应的金属磁记忆探头研制

金属磁记忆检测是无损检测技术中一种新的检测技术,该技术的关键在于拾取铁磁构件应力集中区的微弱"纯天然"磁信号.利用非晶态合金的巨磁阻抗效应制出一种新的磁记忆探头,该探头灵敏度高,性能稳定.简单地介绍了非晶态合金的巨磁阻抗效应,较为详细地给出该探头的工作原理、结构、电路设计和实验结果.实验结果表明,这种新型金属磁记忆探头对微弱磁信号的检出效果明显,达到了磁记忆检测的要求.     

交流磁光调制大角度检测技术研究

基于交流磁-光调制及频谱分析原理,实现了对交流磁-光调制大角度检测。首先从频谱结构图的角度分析了大角度的检测过程,得出利用本文方法检测的交流调制角度不受角度周期性影响的结论;其次采用相对频谱幅度的方法实现对特定范围内的大角度进行检测,同时分析了检测灵敏度和相对误差。采用了差除和的信号处理技术消除了光源发光功率不稳定以及光强吸收等误差因素。本文技术将在相关领域具备较好的应用潜力。     

磁电子学研究概述

简要介绍了磁电子学的基本概念、研究对象和几种重要效应 ,以及基于这些效应的几种新型器件的工作原理 ,提出了磁电子学研究中的几个前瞻性课题 ,对磁电子学的未来发展方向作了评述和展望     

超磁致伸缩执行器磁滞模型的参数辨识

准确辨识磁滞模型参数是保证超磁致伸缩执行器位移控制精度的关键,而单一算法难以实现对超磁致非线性模型参数的精确辨识。该文提出了一种新型混合优化策略,即改进的遗传退火算法,并将其应用于对超磁致伸缩执行器位移磁滞模型参数的辨识。该算法兼顾了遗传算法和模拟退火算法的优点,同时还引入了机器学习原理,将模拟退火算法作为遗传算法中的种群变异算子,并将模拟退火算法中的抽样过程与遗传算法相结合。此算法不仅充分发挥了遗传算法并行搜索能力强的特点,且增强和改进了遗传算法的进化能力,同时提高了系统的收敛性和收敛速度,避免最优解的丢失。通过仿真和试验研究表明,该算法相对于遗传算法有更高的精度,可有效精确辨识超磁致伸缩执行器磁滞模型的参数。     

正激式开关电源变压器磁饱和机理分析与实验

本文阐述了变压器磁饱和的物理意义及其对开关电源的影响,说明了三种判断磁性材料饱和的方法,即理论计算、有限元仿真分析和电路实验验证。以正激式开关电源为例,阐明其工作原理,分析其变压器磁饱和的三种原因。详细阐述了变压器磁通饱和机理,计算不同磁材不同尺寸的罐形磁芯的安全工作区间,并在一个正激式开关电源样机上进行实验,给出了输出功率和开关频率对正激式开关电源变压器最大磁通密度的影响,验证了磁通饱和机理的正确性和计算的合理性。     

A Computer Model of Magnetic Saturation and Hysteresis for Use on SPICE2

Magnetic saturation and hysteresis are simulated on SPICE2 using a model containing two nonlinear controlled sources. The model is applied to inductors and transformers made from a variety of core materials, and procedures are given for determining the model parameters directly from magnetic core catalog data. Four examples of circuit applications are given: a saturating instrumentation transformer, a saturating snubber inductor, a ferroresonant regulator transformer, and a Royer saturation oscillator.     

利用磁力显微镜研究倾斜溅射对TbFe薄膜磁性能的影响

磁力显微镜(MFM)作为研究表面磁结构的有力工具已广泛应用于磁性薄膜的研究TbFe磁致伸缩薄膜在实际应用中要求易磁化轴平行于膜面，以获得较低的面内饱和场Hs。传统的成膜技术难以实现这一目标，采用倾斜溅射方法制备ThFe薄膜可有效降低面内饱和场Hs。通过测量样品的磁滞回线可以发现，易磁化轴随着溅射角度的增加逐渐偏离样品的法线方向，而取向于平行膜面。本研究工作利用MFM研究了不同溅射角度得到的TbFe薄膜的磁畴结构。发现薄膜的磁畴结构随着溅射角度的增加逐渐由垂直畴转化为水平畴，与磁滞回线测量得到的易磁化轴方向发生偏转的结果相吻合。     

Structure and soft magnetic properties of Fe-Co-Ni-based multicomponent thin films

Soft magnetic thin films with suitable uniaxial anisotropy and high saturation magnetization are required for high frequency applications, since the ferromagnetic resonance frequency (f_FMR) is proportional to the multiplication of the saturation magnetization and anisotropy magnetic field. In this study, multicomponents of Fe-Co-Ni-based soft magnetic thin films were deposited on the Si substrate by radio frequency (RF) magnetron sputtering with various Ar/N₂ ratios at room temperature. The composition, crystal structure, surface morphology, and magnetic domain were analyzed. Without nitrogen doping, the domain of the magnetic thin film was arranged randomly. The effect of N₂ content in the thin film on the magnetic properties was evaluated and further discussed. Magnetic properties, including saturation magnetization (M_s) and coercivity (H_c), were determined. The saturation magnetization of the undoped magnetic thin film was around 1.3 T. However, when the nitrogen was added, the magnitude of the anisotropy field could reach 30 Oe, while the saturation magnetization was around 1 T. It is expected that the derived magnetic thin film is a promising candidate for potential usage in high frequency inductors.     

Fe膜及磁场沉积对TbDy-Fe膜磁伸性能的影响

为了提高TbDv-Fe膜的低场磁敏性,采用离子束溅射沉积(IBSD)法制备TbDy-Fe超磁致伸缩薄膜,分别研究了纯Fe膜与TbDy-Fe单层膜、TbDy-Fe/Fe耦合多层膜的复合及磁场下溅射沉积对TbDy-Fe膜磁致伸缩性能的影响;用振动样品磁强计(VSM)测试薄膜磁滞回线,用电容位移测量仪测试薄膜悬臂梁自由端偏转量,并计算出磁致伸缩系数λ.结果表明,由IBSD法制备的纯Fe膜、TbDy-Fe单层膜、TbDy-Fe/Fe复合膜的易磁化轴均平行于膜面,TbDy-Fe/Fe复合膜在低场下的磁化强度与磁导率均高于TbDy-Fe单层膜(在100 kA/m时,TbDy-Fe/Fe复合膜的磁化强度比TbDy-Fe单层膜高173%).纯Fe膜分别与TbDy-Fe单层膜、TbDy-Fe/Fe耦合多层膜进行复合均可提高薄膜磁致伸缩性能;磁场下溅射沉积所得180 nm纯Fe膜 640 nmTbDy-Fe/Fe耦合多层膜,由于在其膜面内短轴方向产生感生磁各向异性,从而使磁致伸缩性能得到进一步的提高,在150 kA/m的磁场下它的λ值可达到650×10-6.     

Identification of rod dynamics under influence of Active Magnetic Bearing

The purpose of this paper is to apply the wavelet transform algorithm to identify the magnetic damping and magnetic stiffness coefficients of the drive rod with which a set of 4-pole Active Magnetic Bearing (AMB) is equipped. By taking advantage of time–frequency analysis feature, the ridge curve of rod free response after wavelet transformation can be extracted to find the natural frequency of the rod/AMB system. In other words, due to the influence of magnetized field by the AMB, the stiffness of the rod dynamics is not linear any more and can be estimated from the curve of the amplitude versus frequency by wavelet transformation. On the other hand, the nonlinear damping coefficients can be estimated from the derivative of amplitude versus amplitude by wavelet transformation of rod free vibration. It is found that the nonlinear magnetic damping coefficients are up to 2nd-order in polynomial and the stiffness coefficient is mainly of 3rd-order respectively. In addition, the identified 2nd-order damping coefficient is negative and hence implies that under specific rod displacement and speed, the dynamic of the rod/AMB system in axial direction is unstable.     

Nonlinear response to picosecond pulse excitations inmagneto-dielectric media

Nonlinear responses of magneto-dielectric thin layers to picosecond excitation have been calculated utilizing direct time-domain integration. Relaxations, hysteresis, and magnetic saturation phenomena, associated with the response are discussed in depth. The purpose of the calculation is to provide an analytical method by which physical properties of materials can be identified under picosecond-pulse excitation as well as to explore special cases of excitations in which picosecond pulses are efficiently absorbed. The calculations indicate that by examining the reflected waveform of the incident rectangular picosecond pulse, the amount of magnetic hysteresis and saturation of the material may be estimated. It is shown that magnetic hysteresis will affect the shape of the trailing edge of the reflected signal, whereas the magnetic saturation effect can be identified from the slope of the reflected pulse step. Examples of designs for effective picosecond-pulse screening structures are given     

High Frequency Resonance Features of Giant Magnetoresistance Multilayers

High frequency resonance technique was applied to study of magnetic multilayer Co/Cu films possess the giant magnetoresistance. The results of the ferromagnetic resonance study in 60GHz-80GHz and 1OGHz bands revealed low temperature changes of g-factor after annealing and a very small value of high frequency saturation magnetization. An abrupt change of the specimen impedance was registered in low field low field range for 10GHz. The static magnetic characteristics as hysteresis and magnetoresistance loops were obtained at room temperature for the planar orientation of external magnetic field.     

Frequency-Saturation Effects in Transferred Electron Oscillators

Frequency-saturation effects have been observed in the mechanical tuning characteristics of transferred electron (Gunn) oscillators operating in conventional waveguide cavities at frequencies from 12 to 40 GHz. Their existence leads to a restriction in oscillator tuning range and enhances frequency switching and hysteresis effects in the oscillators. Investigation of oscillator behavior in coaxial cavities as well as in waveguide cavities of varying height has shown that frequency saturation is caused by a coaxial resonance along the mounting post, which in the limit of fully reduced-height waveguide becomes the resonance of the diode with the encapsulation itself, or by a frequency limitation imposed by the diode thickness and operating voltage. The transverse coaxial resonance will occur in any waveguide size at a frequency near to if not within the band of interest. Simulation of the encapsulated diode by a localized reduction in mounting-post diameter shows that the frequency of transverse resonance can be increased by moving the encapsulation to a central position in the waveguide cross section. It is suggested that this technique and that of using cavities with a local reduction of height will make an important contribution to improving the performance characteristics of waveguide-mounted oscillators.     

High-Frequency Magnetoresonance and Magnetoimpedance in Co/Cu Multilayers with Variable Interlayer Thickness

The paper is devoted to the investigation of high frequency magnetic features of multilayered metallic structures (Co/Cu) demonstrating the Giant Magnetic Resistance effect (GMR-effect) and Giant Magnetic Impedance effect (GMI-effect). Dynamic features have been investigated in dependence on the distance between magnetic Co-layers and analyzed in comparison with static magnetic features. Ferromagnetic resonance response as well as non-resonance magnetoimpedance at small applied static magnetic field have been studied. Experiments were carried out at room temperatures in frequency band 20-37GHz for the ferromagnetic resonance technique and in frequency band 30-140GHz for study the low field non-resonance magnetoimpedance effects.     

CW and pulsed mode transfer impedance measurements in coaxialcables

Transfer impedance measurements have been performed both in frequency and time domains. CW measurements were performed using a matched triaxial system, a quintaxial system, and stripline injection. For nuclear electromagnetic pulse (NEMP) purposes, measurements up to a maximum frequency of 200 MHz are sufficient. For this frequency range the matched triaxial system was found to be the most convenient. Amplitude and phase measurements in different cables are discussed. Direct and indirect injection was employed in the time domain measurements. A delayed coupling is demonstrated when the diffusion term is dominant in the transfer impedance. In a magnetically shielded cable, hysteresis and saturation effects have been observed. At 5 kA the transfer impedance of the magnetically shielded cable increased by an order of magnitude due to saturation