General Formulas for the Average Magnetic Field at a Receiving Circular-Loop Antenna Placed Arbitrarily to a Radiating Loop

For testing the sensitivity of receivers having loop antennas, radiating and receiving loops have been located either coplanar or coaxial to each other. Theoretical analyses of the magnetic fields have been carried out for such alignments of loops. It is often necessary in the actual tests to estimate the effects of deviations from these ideal arrangements of the loops. In this paper, the radiating and receiving circular loops are located arbitrarily in direction, and a formula is derived to obtain the average normal component of the magnetic-field strength incident on the receiving loop using the Eulerian angles. The theory is applied to the design of a generator in which a rotating field is used as the standard field. In this case, the calculated values of the magnetic field are in agreement with the measured ones to within ±0.1 dB.     

Magnetic Polaritons, Magnetostatic Waves and Effective-Medium Approximation for Antiferromagnetic Superlattice with Impurity in Parallel Magnetic Field

We derive the general effective-medium expression for the surface-guided magnetic polaritons and magnetostatic waves, which propagate in the antiferromagnetic superlattice with antiferromagnetic impurity film, and investigate the influence of the external magnetic field on the energy of localized magnetic polaritons. Similarly as in the free-standing antiferromagnetic film, the spectrum of magnetic polaritons in the presence of an external magnetic field is reciprocal in the sense that the frequency is independent of the direction of propagation. In the system under consideration one finds both the surface polaritons which are strongly localized in the antiferromagnetic film which acts as a waveguide, and waves which are weakly localized within film. The first waves are the pure surface modes or guided modes where excitations have a standing-wave-like character. This important feature of the localized magnetic polaritons enables us to use these antiferromagnetic systems in the technologies for devices (for example, in resonators) that work at wavelengths in the infrared region. Second waves have the very small value of the decay parameter and appear in the regions where the surface mode penetrates into the bulk band, i.e. the magnetic polaritons are weakly localized in the impurity film region. Now we obtain the mixed type mode having both bulk and surface characteristics. Also, the general way in which the dispersion curves vary with the volume fraction of the superlattice components and with impurity film is illustrated in this study.     

New Results for Superconductivity in κ-(BEDT-TTF)2Cu(NCS)2 When an Applied Magnetic Field is Aligned Parallel to the Conducting Planes

Using a Tunnel Diode Oscillator technique, we have measured the effect of a parallel magnetic field on the in-plane rf penetration depths in organic [α- (BEDT-TTF)₂NH₄Hg(SCN)₄ and κ-(BEDT-TTF)₂Cu(NCS)₂] and heavy fermion (CeCoIn₅) superconductors. We show that in this particular ge- ometry, the effects due to vortex activity are minimized. The penetration depth is then governed by the density of superconducting carriers. It is shown in many experiments including rf penetration depth measurement that α-(BEDT-TTF)₂NH₄Hg(SCN)₄ and CeCoIn₅ have s-wave and d-wave pairing symmetries, respectively. The pairing symmetry of κ-(BEDT-TTF)₂-Cu(NCS)₂, however, is still an unsolved matter, showing inconsistent results. In this paper, the penetration depth of κ-(BEDT-TTF)₂Cu(NCS)₂ is shown to be more similar to α-(BEDT-TTF)₂NH₄Hg(SCN)₄ than to CeCoIn₅, suggesting the pairing is nodeless.     

Equations for the Magnetic Field Produced by One or More Rectangular Loops of Wire in the Same Plane

Beginning with expressions for the vector potential, the equations for calculating the magnetic flux density from up to three rectangular loops of wire in the same plane are derived. The geometry considered is the same as that found in some walk-through metal detectors and electronic article surveillance systems. Equations for more or fewer loops can be determined by inspection. A computer program for performing the magnetic field calculation is provided in an appendix.     

封闭空腔结构-声耦合场内辐射声粗糙度的研究

基于结构-声耦合场有限元模型以及改进后的Sethares非谐音心理声学模型,计算封闭空腔边界上声固耦合板受简谐力激励后引起的空腔内部辐射声,分析其在评价点被快速调制时产生的粗糙度,并研究调制音声压级、调制音频率以及耦合板刚度对辐射声粗糙度的影响。为计算封闭空腔内部声辐射被其它声源所快速调制时产生的声粗糙度提供依据和预测方法。     

Asymmetry of the Pinning Force in Thin Nb Films in Parallel Magnetic Field

The pinning force, F _p, is studied in Nb films of different thickness in parallel magnetic field H. The asymmetry in the magnetic field dependence of F _p has been observed for two opposite directions of the transport current. The effect is less pronounced for thin and thick films where, respectively, single vortex pinning and pinning of the internal vortices, is relevant. At intermediate thickness, where the pinning mechanism is mostly caused by surface effects, an asymmetry in the F _p(H) dependence is clearly visible. The different surface barriers that vortices should overcome to enter the sample from opposite sides of the film explain the effect, as confirmed by numerical calculations. These have been obtained by solving the Ginzburg?CLandau equations with asymmetric boundary conditions which take into account the different superconducting properties of the film?Csubstrate and film?Cvacuum interface. Such difference can also explain the reduction of the critical current usually observed in thin films as a function of their thickness.     

Surface and Bulk Magnetic Hysteresis Loops of Co-Rich Glass Covered Microwires

The magnetization reversal process in the surface and volume areas of Co-rich glass covered microwires has been investigated. The value of the helical anisotropy has been determined in two wires with different thickness of glass covering. The dependence of the coercive field on the frequency of the external axial magnetic field was studied in the surface and volume of the microwires     

浅谈磁感应强度和磁场强度

本文由磁场的存在和特斯拉计的检定引出了磁感应强度和磁场强度两个概念,分析了其区别和联系,并由此得出了该二者的正确用法.     

Novel Magnetic Photonic Crystal Structures for Magnetic Field Sensors and Visualizers

Optimized one-dimensional (1-D) magnetophotonic crystals greatly increase the sensitivity of magnetooptical sensors, which are widely used in magnetooptical imaging to observe the magnetic domain patterns in magnetic materials, to observe the vortex states in superconductors, to detect small bits in magnetooptical recording media, to visualize defects in ferromagnetic objects, and to measure the value and spatial distribution of stray magnetic fields. This paper examines the properties of such devices operating in the optimized reflection (doubled Faraday rotation) mode and discusses the use of 1-D magnetophotonic crystals as sensors.     

Ferrite-Piezoelectric Multilayers for Magnetic Field Sensors

A magnetic field sensor based on magnetoelectric effects in a ferrite-piezoelectric layered sample is proposed. Such sensors are passive, provide direct conversion of magnetic fields into an electrical signal, and allow measurements of both ac and dc magnetic fields. A multilayer sample of nickel zinc ferrite-lead zirconate titanate has been used to characterize the sensor response to ac and dc fields, field orientations, frequency, and temperature. The sample shows a linear response for dc fields up to a maximum of 1750 Oe. The sensor output is temperature independent over 273–337 K, but is dependent on frequency of the ac excitation field. Operating at electromechanical resonance for the element enhances the sensor sensitivity by an order of magnitude. For ac magnetic field sensors, the output varies linearly with amplitude.     

Magnetoresistance of the Two-Dimensional Electron Gas in GaN Quantum Wells in a Parallel Magnetic Field

We present results for the resistivity of the two-dimensional spin-polarized electron gas as realized in GaN quantum wells at zero temperatures. A parallel magnetic field is used to create a spin-polarized electron gas. We discuss the density dependence of the magnetoresistance for impurity scattering and interface-roughness scattering. Finite width effects of the electron gas on the magnetoresistance are described.     

Method and Devices for Measuring Magnetic Field Parameters

A new method and devices are suggested for measuring constant, variable, or pulsed magnetic field parameters. The method involves transforming electromagnetic energy into elastic vibration energy in the presence of a magnetic field. This makes it possible to carry out measurements under complex conditions, for example at high temperature or with high intensity ionizing radiation.Translated from Izmeritel’naya Tekhnika, No. 3, pp. 35–38, March, 2005.     

金属离子源磁过滤器磁场位形的设计与实验研究

根据磁过滤器对磁场的要求,利用水冷铜管产生的反向磁场,设计一个轴向磁场较弱的磁镜式磁过滤器.由数值模拟和实验研究的结果可知:磁过滤器磁场位形是一个轴向较弱的磁镜式磁场分布;并且在磁过滤器的出口处,磁场强度的均匀性较好;还增强了水冷铜管和磁过滤器壁之间的磁场.由离子束测试实验可知在加反向磁场时离子束的均匀性比没有反向磁场时高很多.     

Quantum (Nano-Scale) Limit in a Parallel Magnetic Field in Layered Q1D Conductors

We show that electron wave functions in a quasi-one-dimensional (Q1D) layered conductor in a parallel magnetic field are always localized on conducting layers. Wave functions and electron spectrum in a quantum limit, where the “sizes” of quasi-classical electron orbits are of the order of nanoscale distances between the layers, are determined. Possible applications of our results to physical properties of Q1D materials in their superconducting and metallic phases are discussed.     

磁悬浮运动平台的磁场分析及优化设计

研制了一种新型磁悬浮平台,该平台定子采用无铁心式的克莱姆绕组,消除了固有齿槽效应,动子采用Halbach 磁阵列结构方式,由于平台输出推力与悬浮的稳定性主要与其气隙磁场的分布情况有直接关系,因此提高气隙磁场的正弦分布是改善其工作特性的难点和重点. 为了改善气隙磁场的分布问题,提出了一个优化磁场分布的目标函数,并采用步长加速法对平台磁场进行了优化设计,大大降低了磁场谐波分量,改善了气隙磁场分布状态. 将优化结果运用到实际的平台中,对该运动平台进行了阶跃响应实验,实验结果表明满足平台需要达到纳米级精度的要求.     

Magnetic Field Stabilization for Magnetically Shielded Volumes by External Field Coils

For highly sensitive magnetic measurements, e.g., a measurement of the neutron electric dipole moment (EDM), the magnetic field has to be stable in time on a level below picoTesla. One of several measures we employ to achieve this uses an external field coil system which can stabilize the ambient external field at a predefined value. Here we report on the construction and characterization of such a system in the magnetic test facility at PSI. The system actively stabilizes the field along the axis of the EDM experiment by means of four coils in a Helmholtz-like configuration. Additional coils serve to compensate for transverse ambient field components. Because of the long integration times in the EDM experiment (about 100 s or more) only slow disturbances have to be corrected for. The performance of the system has been measured using static and moving magnetic sources and suppression factors in excess of 200 have been observed.     

Magnetic Field Analysis and Structure Design of a New Magnetic Wheel for Wall-Climbing Robot

Journal of Superconductivity and Novel Magnetism - According to the working requirements of the wall-climbing robot, a wall-climbing method using a permanent magnet wheel to realize wall surface...     

Magnetic Characterization of MgB2 Bulk Superconductor for Magnetic Field Mitigation Solutions

Magnetic shielding properties of MgB₂ bulk samples synthesized by the SPS (Spark?CPlasma?CSintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB₂-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, J _c , was evaluated. The J _c magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one.