Suppression of excess noise in Transition-Edge Sensors using magnetic field and geometry

We report recent progress at NIST on Mo/Cu Transition-Edge Sensors (TESs). While the signal-band noise of our sensors agrees with theory, we observe excess high-frequency noise. We describe this noise and demonstrate that it can be strongly suppressed by a magnetic field perpendicular to the plane of the sensor. Both the excess noise and =(T/R)(dR/dT) depend strongly on field so our results show that accurate comparisons between devices are only possible when the field is well known or constant. We also present results showing the noise performance of TES designs incorporating parallel and perpendicular normal metal bars, an array of normal metal islands, and in wedge-shaped devices. We demonstrate significant reduction of high-frequency noise with the perpendicular bar devices at the cost of reduced . Both the bars and the magnetic field are useful noise reduction techniques for bolometers.     

On the electromagnetic field of one- and two-dimensional gratings of large cylinders--Part II: Permeable cylinders in uniform field

The field pattern due to gratings of large ferromagnetic or conducting circular cylinders in a uniform external magnetic or electric field is calculated. The method used involves the relation between the size of the cylinder and the spacing of line charges forming dipoles codirectional with the external field. Solutions are provided for square as well as rectangular unit cells, including the one-dimensional (array) case. In the same context, a uniform field obliquely oriented towards the grating is considered, as is the flux pattern for the different configurations.     

Models for I and T pattern permalloy bars based upon bitter pattern observation of domain wall movements

The magnetostatic fields of the I and T pattern Permalloy overlay bars are analyzed by proposing a model based on the Bitter pattern observation of the domain wall structure in Permalloy bars. The magnetic charges that appear on the 90° domain walls are assumed to be the sources of the magnetic fields of the bars. The model has a two-dimensional reaction to an applied rotating in-plane field due to its two-dimensional domain wall movement and the consequent two-dimensional change of magnetic domain pattern inside the bar. The magnetization of the bar is equal to Msthe saturation magnetization of the bar at every section of the bar except on the domain walls. The magnetization curve and the magnetic field well Bz(bubble drive field) under the overlay bars are calculated and compared to that of the previous models. A qualitative explanation of the rotation of the bubble around the bars is given by the three-dimensional plots of the field well obtained for different orientations of the in-plane field.     

Some New Views on the Principles of Magnetron Sputtering

In this paper, some common phenomena in magnetron sputtering are freshly analyzed and discussed on the basis of the motion of electrons in non-uniform orthogonal electric and magnetic fields. There exist magnetic confinements in three spatial dimensions on moving charged particles (including electrons) in this kind of non-uniform field. They are the longitudinal cycloidal motion, the horizontal simple harmonic-like motion (with varying amplitudes), and the vertical repelling action. The horizontal magnetic confinement in a mirror-like magnetic field keeps glow discharge lane completely parallel to the corridor of magnetic force lines, therefore only an effectively closed magnet array structure can form a relatively uniform and closed discharge lane. The main reasons for electrons' releasing from magnetic confinement are the vertical magnetic repelling force as well as a more and more weak confinement action in outer range etc. The dominant reasons for a comparatively low increase of substrate's temperature are that the density of bombarding electrons near the substrate is relatively low and their spatial distribution is relatively uniform (compared with that near the target surface). The erosion lane with an inverted Gauss's distribution shape on a magnetron sputtered target is due to that,with sputtering, the distribution width of the critical density of electrons shrinks continuously but the sputtering effect in the centerline of the corridor is always the most powerful.     

均匀活塞阵辐射声场研究

主要研究了均匀活塞阵的近-远场的辐射声场。首先利用点源声波干涉原理建立均匀点源活塞阵的辐射声场理论,进而推导均匀活塞阵的近-远场的辐射声场函数表达式,并采用Matlab软件仿真了近-远场的辐射声场,分析了近-远场的声场变化规律、声轴方向声压的变化规律和旁瓣级的变化规律。通过与实测的80 kHz均匀活塞阵换能器近-远场的辐射声场对比,表明了实测结果与仿真结果基本一致,验证了理论与测量方法的可行性,能够为实际测量工作提供指导。     

DeltaE effect for polycrystalline ferromagnetic rods.

We performed experimental and computational studies of the acoustic transfer power coefficient for carbon steel cylindric bars placed in axial magnetic field. By experiment, the transmission coefficients of velocity were measured for ferromagnetic bars during the first magnetization curve below saturation. Using the magnetic and magnetostriction material measurements we obtained the profile of the magnetostriction along the distance for a ferromagnetic cylindrical rod placed in a magnetic field parallel with its axis. The data were compared with numerical results obtained by computer simulation, under the assumption of spatial dependent acoustic impedance and phase velocity, leading to the conclusion that the Young modulus is affected by the magnetoelastic interaction according to a linear decrease.     

ΔE effect for polycrystalline ferromagnetic rods

We performed experimental and computational studies of the acoustic transfer power coefficient for carbon steel cylindric bars placed in axial magnetic field. By experiment, the transmission coefficients of velocity were measured for ferromagnetic bars during the first magnetization curve below saturation. Using the magnetic and magnetostriction material measurements we obtained the profile of the magnetostriction along the distance for a ferromagnetic cylindrical rod placed in a magnetic field parallel with its axis. The data were compared with numerical results obtained by computer simulation, under the assumption of spatial dependent acoustic impedance and phase velocity, leading to the conclusion that the Young modulus is affected by the magnetoelastic interaction according to a linear decrease.     

Positive Ion Mobility in Normal Liquid 3He Under High Magnetic Fields

Positive ion mobility in normal liquid ³ He has been measured as a function of external magnetic fields up to 15 T at various pressures and temperatures down to 3 mK. At 20 mK, a monotonic decrease of the mobility with increasing the magnetic field has been observed at the pressures above 10 bars. At 3.2 mK, the field dependence for pressures above 20 bars is found to exhibit a pressure dependent broad peak, followed by a big decrease. Possible origins for these anomalous behaviors are discussed.     

阵列永磁体产生旋转磁场的机理及实验

 诊疗微机器人外磁主动驱动是一种重要的可行的驱动方式,而如何产生合适的外部磁场是一个比较复杂的问题．相对于目前常用的通过电磁线圈组合产生驱动磁场方式,提出一种新的简单可行的永磁体组合产生旋转磁场方法,即圆周阵列永磁体并将其调整到对应的初始方位角后,同步转动在阵列中心区域产生旋转磁场,作为微机器人的主动驱动场．对于阵列中心区域的磁感应强度分布,作了理论分析和数值计算,并搭建了实验台．实验表明,采用边长为50 mm、高为18 mm的钕铁硼永磁体阵列,阵列数为6,阵列直径为275 mm时,可以在±50 mm×±50 mm×±20 mm阵列中心区域产生一个大小为0.012 T的均匀磁场,该磁场与永磁体同步旋转但是方向相反．这种新的磁场产生方法可以用于微机器人特别是诊疗微机器人的驱动,具有广阔的应用前景．     

Cylindrical-domain propagation by Permalloy bar stray fields

The field gradients of magnetic stray fields which affect the propagation of cylindrical domains in a T-bar pattern are investigated. The magnetization of the Permalloy bars which gives rise to the propagating field gradient is found to be influenced by the stray field of the cylindrical domain itself. Considering this interaction, the propagating field gradients are calculated first for single bars and then for a geometric arrangement as it occurs in a T-bar pattern. Those forces leading to a forward propagation and those leading to a trapping of the domain are studied. Useful relations for the distance between the adjacent bars are deduced. The calculated propagating field gradient is found to have considerable local variations. This causes corresponding velocity variations of the domain. The marked velocity minima which occur along the domain path represent a strong restriction to high data rates in domain memory devices. Average propagation fields for the different propagation steps are shown as a function of the bar width.     

Linear array arrangement using composite right-/left-handed transmission lines for magnetic resonance imaging

Array coils for magnetic resonance imaging have been used to improve field uniformity, improve signal-to-noise ratios, and increase imaging speed. Alternative radio frequency (RF) coils that use metamaterials, such as loop or microstrip coils, have recently been proposed and are expected to provide better performance than the traditional RF array coils. Transmission lines (TLs) based on metamaterials are known as composite right- and left-handed (CRLH) TLs, which are artificially created by adding inductances and capacitances to a common TL. CRLH TLs have a zero-order resonance mode, wherein wave propagation is independent of the TL's electrical length. Decoupling between array elements is important for obtaining the benefits of parallel imaging. In this study, we analyze the decoupling properties between two CRLH TLs. In addition, we design a linear array of four CRLH TLs to obtain a uniform magnetic (|B₁|)-field in the axial- and longitudinal-direction at 7T for the corresponding frequency of 300 MHz.     

Response of visual mechanisms to stimulus onsets and offsets

Transient and sustained visual mechanisms were studied with single, flickering bars of various widths. Wide bars were largely detected on the basis of temporal luminance transients whereas thin bars were detected on the basis of the sustained contrast. A rapidly flickering uniform field selectively masked wide flickering bars, which suggests that different mechanisms detect wide versus thin flickering bars. For coarse spatial patterns, stimulus onsets were slightly more visible than stimulus offsets, and the response to onsets and offsets approximately summated.     

一种圆鞍形磁屏蔽线圈的设计与性能研究

以毕奥-萨伐尔定律为基础,推导了一种圆鞍形线圈在空间任意点处的磁场分布表达式,优化了一种线圈结构,证明了圆鞍形线圈可以产生一定区域的稳恒磁场,并定量地给出了线圈内部磁场的空间分布情况。所设计线圈产生的磁场中,1%均匀度的磁场均匀区占轴上区域的28%,0.1%均匀度的磁场均匀区占轴上区域的10%;在1 mA的电流下,单圈线圈最大磁场补偿值为15 nT,相对偏差量不超过0.14 nT,验证了所推导表达式的正确性,为多维磁场补偿系统设计与研究提供了理论依据和参考。     

Wiggler improvement based on single axis magnetic measurement, synthesized 3-D field simulation of trajectories and sorting of lateral focusing magnets

A method is presented for correcting magnetic field imperfections in an assembled wiggler of the Halbach configuration. The method is employed in a configuration in which lateral focusing is needed along the wiggler (at low beam energies and large length) and is provided by external magnet bars alongside the wiggler. Field deviations in both vertical and lateral dimensions due to wiggler imperfections are repaired by sorting and reassembly of the focusing magnets. A single Hall probe measurement along the wiggler axis and individual measurements of the focusing magnet bars provide sufficient data for sorting and optimal choice of the positions of the focusing magnets. Moreover, this data enables 3D simulation of the e-beam transport trajectories in the virtually synthesized field of the wiggler with the contemplated repair configuration of the focusing magnet bars before actually assembling them. It thus provides in advance a realistic prediction of the quality of the repair.     

磁性流体在均匀梯度磁场中的摩擦学性能测试研究

基于均匀梯度磁场能较准确反映出磁场影响磁性流体摩擦性能的认识,制造了一对产生均匀梯度磁场的线圈安置于改造后的UMT3摩擦试验机中。选用聚α-烯烃合成油基磁性流体为润滑油,测试不同均匀梯度磁场大小、不同载荷和不同往复频率下的磁性流体摩擦学性能。结果显示：载荷、往复运动频率一定时,磁性流体的摩擦系数随均匀梯度磁场的增大而减小;载荷、均匀梯度磁场一定时,磁性流体的摩擦系数随随往复运动频率的增大而减小;磁性流体在均匀梯度磁场中比无磁场中具有更高的承载能力和更长的耐磨寿命。     

磁浮列车工程中的Halbach永久磁体结构的优化

Halbach磁体结构是工程上理想结构的近似,故可予以优化设计。磁体结构优化的目标是用最少量的磁体产生最强的磁场。针对磁浮列车用直线型Halbach磁体,提出优化指标,得到磁体结构的优化结果(解析表达式),并用实验验证。该解析表达式对直线型Halbach磁体的工程应用具有意义,因为在减轻磁体重量同时提高磁场强度是磁浮列车来的关键技术。     

Positive Ion Mobility in Normal Liquid 3He under High Magnetic Fields

The positive ion mobility in normal liquids ³ He has been measured as a function of external magnetic field up to 15 T at temperatures down to 3 mK. At 3.2 mK, the field dependence is found to exhibit a pressure-dependent broad peak for pressures above 20 bars. On the other hand, at 20 mK, a monotonic decrease with increasing magnetic field has been observed in the same pressure region. Possible origins for these anomalous behaviors are discussed.     

Time-stepping finite-element analysis of eddy currents in the form-wound stator winding of a cage induction motor supplied from a sinusoidal voltage source

The eddy-current effects of multi-conductor form-wound stator winding because of the fundamental and high-frequency magnetic flux in a cage induction motor are studied. The time dependence of the field and circuit variables and the motion of the rotor are modelled by the backward Euler time-stepping method. The motor was supplied from a sinusoidal voltage source. The series and parallel connected stator bars are strongly coupled with the circuit and field equations. The Newton-Raphson method is applied to solve the system of non-linear equations. The eddy-current loss distribution of the stator bars and the quantitative results of eddy-current losses are studied. The radial distance of the stator bars from the air gap has a remarkable effect on the losses and the hot spots. Methods to minimise the losses and to avoid the local hot spots are studied.     

The development of jump discontinuities in radiative magnetogasdynamics

The theory of shock wave formation from weak discontinuities is applied to radiative magnetogasdynamics, and the analysis is performed in detail to study the development of jump discontinuities in the following situations: (i) a planar motion with uniform transverse magnetic field, and (ii) a cylindrical motion with a uniform axial or a varying azimuthal magnetic field. Attention is drawn to the connection between the set of transport equations for the jump discontinuities and the corresponding Bernoulli type equation. It is found that in all the cases, both the radiation and the magnetic field resist shock formation. However, in the absence of thermal radiation, although the magnetic field causes an increase in the shock formation distance, it cannot offset the tendency of a compression wave to grow into a shock wave as it happens in the presence of thermal radiation.     

Convective and Absolute Instability in the Incompressible Boundary Layer on a Rotating Disk in the Presence of a Uniform Magnetic Field

The stability of a conducting fluid flow over a rotating disk with a uniform magnetic field applied normal to the disk, is investigated. It is assumed that the magnetic field is unaffected by the motion of the fluid. The mean flow and linear stability equations are solved for a range of magnetic field-strength parameters and the absolute/convective nature of the stability is investigated. It is found that increasing the magnetic field parameter is in general stabilizing.