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Applied Superconductivity, IEEE Transactions on

Issue 3 • Date Sept. 2006

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Displaying Results 1 - 14 of 14
  • Table of contents

    Page(s): c1
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  • IEEE Transactions on Applied Superconductivity publication information

    Page(s): c2
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  • High-Temperature Superconducting Coplanar Left-Handed Transmission Lines and Resonators

    Page(s): 1893 - 1897
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    This paper implements wideband, low-loss, and via-free left-handed transmission lines (LH-TLs) using superconductor thin films. Introducing superconductors greatly reduces the loss inherited in the constituent series capacitors and shunt inductors of such planar LH-TLs. The measured results agree very well with design expectations. The bandwidth of left-handed characteristics is 4.9-10.9 GHz, with a minimum insertion loss of 0.03 dB at 30 K. Open-ended LH-TL resonators are also characterized at the different harmonics; of special interest are those with zero or negative phase constants, which are not possible when using any conventional transmission lines. Temperature-dependence measurements of the LH-TLs reveal the effect of the superconductor kinetic inductance View full abstract»

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  • On Gradiometer Imbalance

    Page(s): 1898 - 1907
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    We present methods to compute the imbalance in a gradiometer of arbitrary shape due to imperfections in its geometry, eddy currents induced in the radio-frequency interference shield, and screening currents induced in the modules of the superconducting quantum interference devices (SQUIDs). As an example, the methods are applied to evaluate the maximum expected initial imbalance of second- and third-order axial gradiometers in a measuring setup designed for fetal magnetocardiography. Mechanical imperfections in this specific setup appear to have the largest effect: the field imbalance is 2middot10 -2; the first-order gradient imbalance is 10-3 m; the second-order gradient imbalance is 10-4 m2. In the example, the imbalance caused by the other effects is one order smaller View full abstract»

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  • Hard Magnetic Dots for Flux Bias of DC SQUIDs

    Page(s): 1908 - 1912
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    In this paper, we demonstrate that perpendicularly magnetized sub- and micrometer-sized magnetic dots, with a high coercivity and nearly complete remanence, can be used to provide the flux bias for dc superconducting quantum interference devices (SQUIDs). The radius of a submicrometer Co-Pd magnetic dot has been optimized with respect to the surrounding superconducting circuitry to generate the phase shift of approximately pi/2 in it. In this way, it is possible to bias a dc SQUID to the steepest part of its voltage-flux characteristic without using an additional coil and current source. Furthermore, it has been shown that the flux bias can also be achieved using a micrometer-sized Co-Pd dot, upon saturation, by placing a dc SQUID on top of the dot. Given that the underlying principles of flux biasing do not require any particular superconducting pairing scheme (s- or d-wave), these hybrid superconductor/ferromagnet structures can be used as to design a dc SQUID with a complete flux self-biasing View full abstract»

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  • On the Utilization of Magnetic Vector Potential for a Description of a Superconducting Transmission Line

    Page(s): 1913 - 1917
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    We will present and examine an alternative approach to describe the behavior of superconducting transmission lines, and possibly weak link Josephson junction using the magnetic vector potential (A). While the utilization of magnetic vector potential is known in this field since the inception, a device level formulation based on A has not been fully investigated. We will show that for device level formulation, the magnetic vector potential is a mathematically simpler quantity to deal with than the combination of magnetic flux density (B) and electric field intensity (E) and still contains all the electromagnetic information of the junction under construction. In addition, other benefits of this formalism arise when dealing with Lagrangian and Hamiltonian mechanics. In this paper, we present a detailed description of how A can be determined for an infinite weak link Josephson junction with planar geometry. Utilizing the magnetic vector potential formulation, both electric and magnetic fields are calculated, and we show that we obtain the same dispersion relation as other approaches have previously demonstrated. We then discuss the advantages of this formalism. In addition, as an application of the present approach, we solve the Josephson junction's nonstationary equation numerically to get a realization of the actual coupling that occurs across the junction View full abstract»

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  • Characteristics Analysis of a High-Tc Superconducting Power Supply Considering Flux Creep Effect

    Page(s): 1918 - 1923
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    This paper describes the characteristics analysis of a high-Tc superconducting (HTSC) power supply considering flux creep effect, and also presents its operational characteristics through experiments. The power supply can be employed to charge an HTSC magnet. An HTSC power supply consists of two heaters, an electromagnet, a Bi-2223 solenoid, and a series-connected Bi-2223 pancake load. The pancake load was fabricated by connecting four double pancake coils in series. In the experiments, two cases of the pumping period, which correspond to 8.5 and 17 s, were used with an electromagnet of 331 mH and a dc heater current of 0.8 A. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the Bi-2223 pancake load. The experimental observations have been compared with the theoretical predictions. In this experiment, the pumping-current has reached about 22.9 A View full abstract»

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  • Analysis of Transient Eddy Currents in MRI Using a Cylindrical FDTD Method

    Page(s): 1924 - 1936
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    Most magnetic resonance imaging (MRI) spatial encoding techniques employ low-frequency pulsed magnetic field gradients that undesirably induce multiexponentially decaying eddy currents in nearby conducting structures of the MRI system. The eddy currents degrade the switching performance of the gradient system, distort the MRI image, and introduce thermal loads in the cryostat vessel and superconducting MRI components. Heating of superconducting magnets due to induced eddy currents is particularly problematic as it offsets the superconducting operating point, which can cause a system quench. A numerical characterization of transient eddy current effects is vital for their compensation/control and further advancement of the MRI technology as a whole. However, transient eddy current calculations are particularly computationally intensive. In large-scale problems, such as gradient switching in MRI, conventional finite-element method (FEM)-based routines impose very large computational loads during generation/solving of the system equations. Therefore, other computational alternatives need to be explored. This paper outlines a three-dimensional finite-difference time-domain (FDTD) method in cylindrical coordinates for the modeling of low-frequency transient eddy currents in MRI, as an extension to the recently proposed time-harmonic scheme. The weakly coupled Maxwell's equations are adapted to the low-frequency regime by downscaling the speed of light constant, which permits the use of larger FDTD time steps while maintaining the validity of the Courant-Friedrich-Levy stability condition. The principal hypothesis of this work is that the modified FDTD routine can be employed to analyze pulsed-gradient-induced, transient eddy currents in superconducting MRI system models. The hypothesis is supported through a verification of the numerical scheme on a canonical problem and by analyzing undesired temporal eddy current effects such as the B0-shift caused by activ- - ely shielded symmetric/asymmetric transverse x-gradient head and unshielded z-gradient whole-body coils operating in proximity to a superconducting MRI magnet View full abstract»

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  • Inductive Superconducting Fault Current Limiters With Y123 Thin-Film Washers Versus Bi2223 Bulk Rings as Secondaries

    Page(s): 1937 - 1942
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    We present the comparison between the performance of an inductive superconducting fault current limiter operating with bulk Bi1.8 Pb0.26Sr2Ca2Cu3O 10+x rings or Y1Ba2Cu3O7-delta thin-film washers as secondaries. We have measured the impedance offered by the limiter under current faults and the recovery time once the faults are cleared. Our results show that the use of thin films can improve the impedance response of these devices and especially their recovery time, which can be about two orders of magnitude shorter than that of bulk samples View full abstract»

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  • Fast Resonance Frequency Optical Modulation in Superconducting Stripline Resonator

    Page(s): 1943 - 1950
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    Fast resonance frequency optical modulation of a superconducting stripline resonator is investigated. The experiments are performed using a novel device which integrates a hot electron detector (HED) into a superconducting stripline ring resonator. Frequency modulation is demonstrated by both applying dc current or voltage to the HED, and by applying optical illumination, with modulation frequencies of up to 4.2 GHz. Potential applications for such a device are in telecommunication, quantum cryptography, and biofluorescence View full abstract»

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  • IEEE order form for reprints

    Page(s): 1952
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  • IEEE Transactions on Applied Superconductivity upcoming special conference issues

    Page(s): c3
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  • IEEE Transactions on Applied Superconductivity Information for authors

    Page(s): c4
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Aims & Scope

IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Meet Our Editors

Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde