Magnetic field attenuation of nonlinear shields

The analysis of shielding performance of planar shields against near field sources is carried out in the time domain to account for the nonlinear behavior of ferromagnetic materials used in low frequency applications. To this end, the Schelkunoff approach for shielding problems has been reformulated in the time domain introducing the transient wave impedances which relates transient electric and magnetic field components and appear in the integrodifferential boundary conditions. The final equation system is solved by means of a numerical procedure based on the finite element method. The obtained results are compared with analytical and measured data in different configurations     

Magnetic field of cylindrical surface currents

Infinite surfaces carrying surface currents with translational symmetry in one direction are considered. When the magnetic field is treated as a bivector quantity rather than an axial vector quantity, its simple relation to the plane visual angle of the surface becomes easy to establish by means of the Biot-Savart law. If the surface with the current divides the space into two parts, the magnetic field is uniform in these parts and has a value proportional to the visual angle     

rf impedance of sintered BSCCO and melt-textured YBCOsuperconductors

The authors present the temperature and field dependence of radio frequency response of sintered BSCCO 110-K phase and melt-textured YBCO with Ag and 211 inclusions. The rf resistance and reactance measurements are carried out using a marginal oscillator operating at 11.9 MHz. Melt-textured samples are found to exhibit insignificant low-field losses and hence are potential candidates for applications at radio frequencies. The field induced loss in sintered BSCCO is described by invoking two kinds of weak links. The rf penetration depth of the materials measured is found to be much larger than the London penetration depth and represents the effective screen depth. More importantly, the authors observed an anomaly in the penetration depth of BSCCO which is explained in terms of an interplay between intragranular and Josephson penetration depths     

Magnetic field characteristics of the low-beta quadrupole magnets, MQXA, for LHC

As a part of the collaboration program between CERN and KEK for the LHC, KEK has developed a superconducting low-beta quadrupole magnet, MQXA. KEK will supply 18 MQXA magnets, and 16 magnets will be installed in total in the four interaction regions. The cold tests of 13 magnets have been completed. Systematic field measurements were performed on these magnets, and these 13 magnets had satisfactory field quality for the requirement of beam optics. This paper describes the magnetic field behavior of the 13 MQXA magnets from the viewpoint of accelerator operation.     

非制冷红外焦平面微桥形变的主要原因及其控制

微桥是微测辐射热计阵列像元的重要部分,经微细加工工艺制成的微桥结构常常发生弯曲变形,从而严重影响器件性能。利用有限元分析方法研究了造成微桥变形的原因。结果表明,重力导致的微桥形变值仅为1.44×10-5μm,而薄膜的本征应力导致的形变值却高达2.108μm,与实际观测值相当。因此,本征应力是造成微桥变形的主要原因。此外,还研究了本征应力梯度导致的形变,并提出了采用在电极的表面再沉积一层SiNx薄膜的方法,使桥腿的形变值由0.587μm明显地减小到0.271μm,有效地控制了本征应力梯度导致的桥腿变形。     

Short-term and long-term mechanical characteristics of BSCCO steel-reinforced tapes

An investigation on short-term and long-term mechanical characteristics of Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ reinforced tapes is presented in this paper. Results of critical current measurements obtained after bending, as well as during application of tensile stress and strain, are shown. Data are processed to provide a threshold model for the bending test, according to which bending on large-diameter mandrels does not provide appreciable damage to superconductor tapes. The values of critical current density derived from tensile stress and strain are investigated by the Weibull cumulative function, showing the existence of two distinct failure modes, determined by different strengths of reinforced tapes. This statistical analysis provides a methodology for a feasible quality control test on superconductive tapes. Long-term behavior evaluation, carried out through life lines derived from tests under different levels of stress and strain, indicate that reinforced tapes show largely improved endurance with respect to nonreinforced ones.     

Plasmon resonances in a quartz nanofilament covered with gold of variable thickness

A two dimensional problem of diffraction of a plane electromagnetic wave by a cylindrical gold shell is considered in the case when the boundaries of the shell are circular cylinders with displaced centers. The influence of the excentricity of the boundaries on the properties of plasmon resonances in the optical band is studied. The near and far fields and scattering spectra are calculated by rigorous methods. It is found that the excentricity of shell’s boundaries gives rise to additional resonances. Analytical theory of scattering for thin shells is developed in the quasi-static approximation. It is shown that, in this case, the scattering and absorption spectra essentially depend on the displacement of the centers of the cylindrical boundaries but are independent of the direction of this displacement.     

An adjoint variable method for sensitivity calculations of multiport devices

Recently, an adjoint variable method (AVM) for sensitivity calculations has been proposed for use with the method of moments solvers. In this paper, we extend this method to be suitable for application to multiport devices. The target objective function is usually represented in terms of the device's S-parameters. Our AVM obtains the sensitivities of the S-parameters with respect to all design variables using only one full simulation with additional overhead. This overhead is usually less than the computation time of a full simulation. An analytical expression for the adjoint excitation is derived, leading to stable sensitivities. The potential of the proposed technique is demonstrated by analyzing low-pass and bandpass filters. The results show very good agreement between the proposed AVM and the conventional finite-difference approach (FDA). Moreover, the AVM is always faster than the FDA. The speed-up factor increases as the size of the problem increases.     

A silicon vidicon target with electronically variable light sensitivity and spectral response

A silicon vidicon target structure is shown in which light sensitivity and spectral response are controlled by varying the band bending and depletion region depth at the light incident surface. Light sensitivity control ratios of over four orders of magnitude are demonstrated, making the new target suitable for use over a wide range of light conditions without the aid of a mechanical aperture. The use of the light control structure as a high-speed electronic shutter with image sampling times as low as several microseconds is also discussed.     

Transit time in the base region of drift transistors considering diffusion, recombination, and variable built-in electric field

The present work gives detailed analysis of the transit time of injected minority carriers in the base region of drift transistors, taking into consideration the effect of recombination as well as the variations in the built-in electric field. Some useful impurity-density distributions in the base region are analyzed in detail. Graphs of transit time for these distributions under different conditions are given. The work also includes the distribution that yields minimum transit time for a specified field parameter.     

Magnetic field dependence of spin doublet in GaAs

The spin-up and spin-down transitions of the ground state of the shallow donor electron have slightly different energies in an applied magnetic field. The splitting of the spin doublet increases with increasing magnetic field intensity. High field measurements of the splitting show that the dependence on magnetic field intensity is not only greater than a linear dependence but also greater than a quadratic dependence.     

Thermal cycling and critical current density of BSCCO/Ag-sheathedwire and tape

The effect of thermal cycling between 4.3 K and 298 K within a He atmosphere, and ambient magnetic field, on the J_c of a Bi-2223/Ag-sheathed monocore tape and two Bi-2212/Ag-sheathed multifilament wire straight samples was studied. The J_c of the tape and wire samples did not degrade as a result of thermal cycling. There was also no degradation of J_c of these samples by thermal cycling between 77.4 K and 298 K by immersion in LN₂ within air     

The sensitivity of threshold voltage of ion-implanted MOSFET's to substrate doping and oxide thickness fluctuations

When the gate region of a MOSFET is implanted in order to adjust, the threshold voltage, the sensitivity of the threshold voltage to fluctuations in substrate doping will be affected. It is shown here that when the implanted ion is of the Same impurity type as the substrate, this sensitivity is lower than for a similar, unimplanted structure. However, the converse is found to he true when the implanted ion is of opposite type and the device is operating in a deep-depletion mode. The latter result has obvious importance in view of substrate–doping fluctuations over the surface of a single silicon wafer, and more so between many different wafers. The effect on the threshold voltage of oxide thickness variations is also investigated, and it is found there is a range of implant energy and dose over which the sensitivity can be very small. This is associated, however, with a sharp rise in the sensitivity outside this range.     

Magnetic field and current density imaging using off-line lock-in analysis

In the current paper the application of a custom developed 2-dimenional scanning magnetic field microscope based on tunnel-magnetoresistive sensors and subsequent qualitative and quantitative analysis is described. To improve sensitivity and to enable the detection and evaluation of phase deviations, an off-line lock-in approach was employed by driving the samples under test with an injected current at a fixed signal frequency. Amplitude and phase evaluation was based on simultaneous acquisition of the reference and the measurement signal obtained from the magnetic field sensor. This off-line lock-in approach enables not just the detection but also the estimation of changes in signal phase caused by capacitive, inductive or ohmic coupling of the induced currents. Furthermore assessed magnetic fields were converted into the current density by solving the inverse magnetic problem and post processing of the acquired signals. For verification of the developed set-up the current density distribution was computed from experimentally acquired magnetic fields for a two-wire test structure. In addition quantitative values of the current density were derived for a calibration pattern containing defined structures. Finally, to evaluate the practical relevance a power MOSFET with unknown defect was analysed and an area of unexpectedly increased magnetic field intensity was observed.     

A silicon MOS magnetic field transducer of high sensitivity

A structure has been devised which converts magnetic flux density change to a change in output current. The structure is essentially a P-channel MOST with the drain diffusion split into two halves. A magnetic field normal to the silicon surface deflects device current towards one half-drain. By operating the MOST in the "pinched-off" mode (VDS> VGS-VT) the output impedance is made high, so that large output voltage swings may be obtained. A theoretical study of the voltage and current distributions in the MOST channel has given data on the influence of device geometry on sensitivity. Experimental results indicate a linear relationship between output current and magnetic flux density, and an unexplained nonlinear variation of output with device current. Comparison of experimental results with theory indicates a carrier Hall mobility in the channel of 116 cm²/V.s.     

考虑螺距时椭圆截面螺线管电流磁场的空间分布

用数值模拟方法,分析计算了疏松型椭圆截面螺线管电流的磁场与螺距、长宽比、管内位置的关系。计算结果表明,当螺距较大时,其磁场分布与密绕螺线管电流的磁场分布相差很大,磁场在空间各个方向都有分量,螺距越大,螺线管越短,垂直于螺线管轴线方向的磁场分量越强;但当螺距较小、螺线管越短较强时,其磁场与密绕螺线管电流产生的磁场基本相同,可用密绕螺线管电流的磁场近似。     

Analysis of Vertical Oscillations of a Permanent Magnet Freely Levitated above an YBCO Bulk in an AC External Magnetic Field

The effect of the moving speed of permanent magnet （PM） on levitation force between PM and high temperature superconducting （HTS） bulk is analyzed and described in the PM-HTS levitation system. The PM vibration characteristic in the PM-HTS system is investigated. The PM may collide with the HTS in vibration if the amplitude and frequency of driving force satisfy the relationship Pmin=Afn. When the load of the system is below a threshold, the minimal collision amplitude of the driving force increases with the load increasing, however, it sharply drops to zero when the load exceeds the threshold. With the increase of the initial height of the PM, the threshold load increases, but the minimal driving force which causes a collision between PM and HTS decreases.     

Magnetic field measurements of the LHC-IR MQXA magnets at room temperature

KEK has completed 13 of the 18 MQXA quadrupole magnets supplied for the LHC interaction region. The field measurements at room temperature were performed before and after the cold test. The multipole components by the warm measurements showed a good correlation with those by the cold measurements. It is concluded that field quality of the magnets can be evaluated by the warm measurements.