外加磁场对激光焊接熔深的影响

研究了外加磁场对激光焊接熔深的影响,结果表明,外加磁场对熔深存在一个最佳值,外加磁场达到该最佳值时,激光焊接熔深大大增加,当外加磁场过强或过弱时,熔深都有显著下降。     

外加纵向磁场对激光-MIG复合焊接接头形貌及微观组织的影响

研究了外加纵向磁场对SUS316L奥氏体不锈钢激光-稀有气体保护复合焊接接头成形特点、微观组织及显微硬度分布的影响。实验结果表明,在外加纵向磁场的作用下,接头的余高减小,熔宽增大,成形系数增大,截面宽而深。外加磁场改变了接头的热循环,使热影响区析出长条形δ-铁素体,抑制了晶粒的生长。外加磁场使熔池旋转,接头晶粒得到细化,结晶均匀性得到提高,显微硬度分布变得稳定。这种影响随着磁感应强度的增加而增强,随着接头深度的增大而减弱。     

基于磁流体的一维光子晶体磁场传感器的研究

基于磁流体的折射率对外加变化磁场的敏感特性,提出将磁流体作为缺陷层引入到一维光子晶体中实现磁场传感。由于缺陷的存在,使得光子晶体的透射谱中产生缺陷峰。该传感器可通过测量磁场变化时光子晶体缺陷模波长的移动对相应的磁场进行测量。利用传输矩阵法对不同结构参数下,缺陷模波长随在外加磁场的变化进行了模拟计算,为实际磁场传感器的设计提供了理论参考。     

外加太赫兹场与磁场作用下的高电子迁移率晶体管电流特性

外加太赫兹(THz)场垂直入射高电子迁移率晶体管(HEMT),使得HEMT中产生的载流子激发沟道内的等离子振荡,振荡频率处于太赫兹范围.论文研究了外加磁场对该器件电流特性的影响.结果表明,随着外加磁场强度的增加,HEMT的响应率峰值发生蓝移.因此通过改变磁场能够对HEMT的振荡响应实现有效调谐.     

外加太赫兹场与磁场作用下的高电子迁移率晶体管电流特性

外加太赫兹(THz)场垂直入射高电子迁移率晶体管(HEMT),使得HEMT中产生的载流子激发沟道内的等离子振荡,振荡频率处于太赫兹范围.论文研究了外加磁场对该器件电流特性的影响.结果表明,随着外加磁场强度的增加,HEMT的响应率峰值发生蓝移.因此通过改变磁场能够对HEMT的振荡响应实现有效调谐.     

静磁场下超导圆极化微带天线辐射性能研究

在液氦温度下，研究了工作频率为６．２６ＧＨｚ的Ｙ系超导圆极化微带天线的传输系数Ｓ２１及圆极化轴比随外加工磁场的变化，实验结果表明：在４．２Ｋ温度，外加磁场Ｂ≤１Ｔ时，其Ｓ２１及圆极化轴比基本不随外加磁场的变化而改变。     

外加磁场对微空心阴极放电的影响

采用C语言编程实现三维系综蒙特卡罗模型,外加磁场对微空心阴极放电的影响。研究结果显示,当气体压强和外加电压保持不变时,在微空心阴极放电系统中加入外部磁场后,对阴极方向上的电子密度分布变化不大,轴向和侧向上的电子漂移范围减小,电子能量向低能方向移动,但是外加磁场对高气压微空心阴极放电的影响整体上不如对低气压放电的影响明显。该研究结果对微空心阴极放电等离子体的机理研究具有一定的指导意义。     

双模气体激光器的磁起偏特性

本文从理论上研究了在外加横向均匀磁场作用下双模气体激光器输出光的偏振特性。用导出的双纵模偏振参数运动方程,计算了双模He-Ne激光器632.8nm谱线的偏振参数。当外加磁场大于某值时,可获得高偏振度的线偏振光输出。理论与实验结果相符合。     

HgCdTe和HgZnTe在横向磁场中的定向凝固

用定向凝固法在横向磁场中垂直生长Hg_(0.8)Cd_(0.2)Te晶体。通过测量这些晶锭轴向和径向组分的变化,研究了磁场对该熔体中流体流动性质的影响。磁场的影响在整个外加场强范围内(即2～5kG)都是明显的。当外加上磁场时,CdTe克分子分数的轴向组分分布(用精密的密度测量结果确定)急剧下降,用红外透射和X射线能量色散光谱术测绘的径向组分分布表明:当外加上磁场时,固-液界面经历了三个阶段的演变,即:当磁场初加时,它从径向对称的一种凹形界面变成一个偏心的凹形,然后变成一种倾斜的平面,最后变成一个偏心的凹形界面。一根Hg_(0.84)Zn_(0.16)Te晶锭的轴向组分分布表明了类似的磁场效应。     

磁场对周期性极化铌酸锂晶体中产生的窄带太赫兹波的控制研究

本文 利用飞秒激光作用于光折变周期性极化铌酸锂(PPLN)晶体和掺 镁(Mg)的PPLN(PP-Mg:LN)晶体通过光整流效应产生窄带太赫兹(THz) 辐射,通过外加磁场的 办法对THz脉冲串的振幅和寿命进行有效控制。随着外加磁场的增强,在光折变PPLN晶体中 产生的THz 波的振幅和寿命都随之减小;当外加磁场足够强时,光折变PPLN晶体中产生的THz波将完 全被抑制。外 加磁场之所以能够对THz波的振幅和寿命进行有效控制,主要是由于洛伦兹力的作用使光折 变晶体内部产生了空间电荷场。     

Weak magnetic field pattern detection by CMOS magnetic latch

A CMOS magnetic latch for digital magnetic field detection is reported. It is based on a single split-drain magnetic field-effect transistor with a positive feedback imported by a pair of lateral floating gates. The magnetic latch achieves its maximum magnetic sensitivity when latch-up takes place. A linear equation is used to model the positive feedback and the latch-up process. By imposing a reset-evaluation mechanism, the magnetic latch is evaluated for digital magnetic pattern detection. Experimental results show that the minimum detectable magnetic flux density for the magnetic latch could be down to less than 0.1 mT with low bit error rate.     

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.     

接近表面磁力显微镜成像方法的研究

在当今信息社会时代,需要存储的信息总量正在急剧增加。与光存储技术和半导体存储技术相比而言,磁记录技术占领着几乎90％的存储市场。磁力显微镜( magnetic force microscope,MFM)的发展与磁记录工业密切相关。然而,从1987年至今,MFM的分辨率仍然停留在50~10 nm的水平,传统思路已经很难再实现突破。本论文基于MFM探针的窄带－频率调制机理,发展接近表面磁力显微镜方法,实现对纳米结构中磁畴状态的超高分辨率成像。该工作的关键在于合理利用MFM探针的窄带－频率调制机理,优化设计动态信号处理模块,精确控制探针－样品间距(5 nm 以下),独立分离磁力像和表面像(磁力像为交流信号,原子力像为直流信号),由此测量和解释纳米尺度磁畴结构。该方面的工作对于纳米磁畴结构的设计、核心磁性器件的研究起到非常关键的作用,为下一代磁记录技术的发展提供了新型的有力工具。     

低温烧结平面六方铁氧体的非线性磁性研究

介绍了低温烧结Y型平面六方铁氧体的非线性磁性能。采用固相反应法制备样品,使用HP4284A,配合HP42841A直流源,测试外加磁场对软磁铁氧体高频磁导率的调制特性。研究表明,随外磁场强度增加,材料的磁导率呈非线性下降。定义了磁性可调率,用以表征外磁场调制下磁导率的改变量,此参数与材料本身的磁性能和显微结构密切相关。随Zn含量升高,材料的磁导率和可调率同时上升,可调率最高可达50%以上。     

一种高频脉冲磁场测量装置的制作与应用

本文结合具体的高频脉冲磁场测量要求,设计制作了一种基于法拉第电磁感应原理的磁场测量装置,较为详细 地描述了设计思路和制作过程,并对一空芯脉冲变压器中频率为20k-30kHz,幅值约为0.01-0.02T 的磁场信号进行了测量, 给出了测量得到的变压器内部磁场时空分布的实验结果,测量结果与软件模拟结果基本一致,能够较为准确的反映待测 磁场的时空分布。     

Fiber in-line magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid

In this paper, magnetic fluid (MF), a new type of optical functional nanomaterial with interesting optical characteristics under the external magnetic field, is adopted to form a novel fiber-optic magnetic field sensor. The proposed sensor is based on Mach-Zehnder interferometer (MZI) and has a multimode-singlemode-multimode (MSM) fiber structure. The MSM structure was fabricated by splicing a section of uncoated single mode fiber (SMF) between two short sections of multimode fibers (MMFs) using a fiber fusion splicer. The magnetic field sensing probe was made by inserting the fiber-optic structure in an MF-filled capillary tube. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0.6 mT to 21.4 mT produces a shift in the peak position of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.6%. The achieved sensitivity of the proposed magnetic field sensor is 0.123 nm/mT,which is improved by several folds compared with those of most of the other reported MF-based magnetic field sensors. Furthermore, we build the corresponding circuit-based measurement system, and the experimental results show that the voltage change indirectly reflects the change of the external magnetic field strength. Therefore, this provides the potential to fiber-based magnetic field sensing applications.     

Estimating equivalent dipole polarizabilities for the inductive response of isolated conductive bodies

Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time-varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polarizability matrix. The polarizability matrix and its associated equivalent dipole location are estimated from magnetic field measurements made with at least three linearly independent polarizations of external magnetic fields at the body. Uncertainties in the polarizability matrix elements and its equivalent dipole location are obtained from analysis of a linearized inversion for polarizability and dipole location. Polarizability matrix uncertainties are independent of the scale of the polarizability matrix. Dipole location uncertainties scale inversely with the scale of the polarizability matrix. Uncertainties in principal polarizabilities and directions are obtained from the sensitivities of eigenvectors and eigenvalues to perturbations of a symmetric matrix. In application to synthetic data from a magnetic conducting sphere and to synthetic data from an axially symmetric elliptic conducting body, the estimated polarizability matrices, equivalent dipole locations, and principal polarizabilities and directions are consistent with their estimated uncertainties.     

A planar conducting microstructure to guide and confine magnetic beads to a sensing zone

A novel planar conducting microstructure is proposed to transport and confine magnetic micro/nano beads to a sensing zone. Manipulation and concentration of magnetic beads are achieved by employing square-shaped conducting micro-loops, with a few hundred nano-meters in thickness, arranged in a unique fashion. These microstructures are designed to produce high magnetic field gradients which are directly proportional to the force applied to manipulate the magnetic beads. Furthermore, the size of the microstructures allows greater maneuverability and control of magnetic beads than what could be achieved by permanent magnets. The aim of the microstructures is to guide magnetic beads from a large area and confine them to a smaller area where for example quantification would take place. Experiments were performed with different concentrations of 2 μm diameter magnetic beads. Experimental results showed that magnetic beads could be successfully guided and confined to the sensing zone.     

Diffraction of millimeter-wavelength electromagnetic waves by nanostructure material specimens based on 3D lattices of carbon nanotubes with magnetic nanoparticles and of magnetic nanowires in a waveguide

A mathematical model of the electromagnetic wave diffraction by specimens of anisotropic nanocomposite materials (3D lattices of oriented carbon nanotubes (CNTs) with magnetic nanoparticles and magnetic nanowires) in waveguides is developed. It is made with the help of a computational algorithm based on a multilevel recomposition and the method of autonomous blocks with the Floquet channels. The transmission coefficients of the H₁₀ wave with the frequency of 26 GHz that propagates through plates of magnetic nanocomposites in a waveguide are electrodynamically calculated as dependences of an external constant magnetic field (a magnetic bias field) and the number of magnetic nanoparticles filling the CNT.     

Formation of a periodic magnetic field by a sequence of rings with different magnetic and electric properties

The electrodynamic analysis of the topography of magnetic fields generated in a spatially periodic structure is performed. The structure is a solenoid containing periodically spaced rings made from materials with different electric and magnetic properties. The system of equations relating the amplitudes of spatial harmonics of the magnetic field is derived and numerically analyzed. Dependences of the amplitudes of longitudinal and transverse components of the modulated magnetic field on the ring dimensions, the current frequency, and the magnetic and electric properties of the ring materials are investigated. The field amplitudes obtained during the complete electrodynamic analysis are compared with the amplitudes of a periodic magnetic field obtained in the impedance approximation.