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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A dc superconducting quantum interference device (SQUID) magnetometer has been integrated on a 9×9 mm2 chip with eight pick-up loops in parallel to directly form a SQUID inductance of about 0.5 nH. Very simple feedback electronics have been developed which do not require liquid-helium temperature impedance matching circuits or flux modulation techniques. The magnetometer has a typical white noise of 8 fT/(Hz)1/2 and a 1/f corner frequency below 3.5 Hz. With an additional positive feedback circuit at 4.2 K the white noise level has been further reduced to 4.5 fT/(Hz)1/2. Using a two-pole integrator, a 3 dB bandwidth around 0.5 MHz and a maximum slew rate of 3 mT/s at 1.3 kHz have been attained with a ±0.4 μT feedback range.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Partly resistive superconducting quantum interference devices (RSQUIDs) are used in noise thermometry in the liquid helium temperature range. Here we analyze one type of RSQUID that has not been thoroughly investigated until now: the direct current biased with two Josephson junctions and a resistive part connected in series with the junctions and closed by a superconducting ring. The resistive shunted model of the Josephson junctions is used for the analysis. Two cases of the RSQUID ring inductance were analyzed: (i) negligibly small and (ii) small but finite inductance. The expressions for the low frequency output signal, the current–voltage (I–V) characteristics, and the current flowing through the resistive part are obtained. In the dependence of the output frequency versus the dc current passed through the resistive part often an offset is observed experimentally. This phenomenon can be explained as an influence of an asymmetry in the critical currents of the junctions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4088-4098 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical analysis of the multiloop dc superconducting quantum interference device (SQUID) magnetometer fabricated from low-Tc (transition temperature) or high-Tc materials is presented. Using simple analytic formulas, the essential parameters of a multiloop magnetometer can be estimated: the effective area A, the effective SQUID inductance L, the transfer function VΦ, and the flux density noise (square root of)SB. The theoretical predictions are compared with experimental results of seven different low-Tc versions and good agreement is found. Based on the analytical description, a high-Tc magnetometer design with a 7 mm pickup coil and 16 parallel loops giving a sufficiently small SQUID inductance L(approximately-equal-to)145 pH is presented. At T=77 K a voltage swing 2δV(approximately-equal-to)8 μV and a white noise (square root of)SB(approximately-equal-to)8 fT/(square root of)Hz are predicted assuming a critical current I0=20 μA and a normal resistance R=2 Ω per junction and a damping resistance Rd=R across the SQUID inductance. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4737-4740 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simplified theoretical analysis and experimental investigations of a partially resistive superconducting quantum interference device with two quantization loops have been performed. The advantage of this device is an extremely large output signal. It is shown that the output signal oscillates with a period determined by the nonstationary Josephson relation. This device was experimentally compared to the dc resistive superconducting quantum interference device used as a test structure.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3008-3015 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A fast SQUID (superconducting quantum interference device) magnetometer system using the latest multiloop magnetometer W7A with additional positive feedback has been built. A 3-dB bandwidth of 5 MHz has been achieved in a simple direct-coupled flux-locked loop. The feedback range is ±620 Φ0 or ±290 nT, the white-noise level 3.4×10−6 Φ0/(square root of)Hz or 1.6 fT/(square root of)Hz, and the 1/ f corner frequency (approximately-equal-to)7 Hz. Above 1 MHz the noise level increases slightly, approximately with (square root of)SΦ ∝f1/6. At high signal frequencies a slew rate of about 8×105 Φ0/s has been measured. Below the pole frequency of the second integrator (480 kHz) the slew rate increases with decreasing frequency, having a maximum of 3×107 Φ0/s at 7.6 kHz. The total harmonic distortion (THD) decreases strongly with the signal amplitude below the slew rate limit. For a sinusoidal signal with half the maximum amplitude, the THD is (approximately-equal-to)4% at 1 MHz, (approximately-equal-to)0.04% at 100 kHz, and (approximately-equal-to)2.7 ppm (1 ppm=10−6) at 10 kHz. Below about 2 kHz the THD becomes almost frequency independent and lies between 0.4 and 7 ppm for signal amplitudes between 2.5 and 620 Φ0. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A picovoltmeter working at 4.2 K and based on a direct current superconducting quantum interference device (dc SQUID) with additional passive positive feedback for investigating the properties of superconducting thin films, Josephson junctions, and SQUIDs has been developed. It has a large small-signal bandwidth fm(approximately-equal-to)800 kHz, a slew rate of (approximately-equal-to)38 mV/s, a dynamic range of 146 dB, and a voltage resolution of 5 pV/Hz1/2 for a signal source impedance Rs=0 Ω. The noise temperature is (approximately-equal-to)0.6 K for Rs=1 Ω. In this article the dynamics and noise properties of the instrument are discussed.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three magnetometers based on dc superconducting quantum interference devices (SQUIDs) fabricated from YBa2Cu3O7−x have been operated in a magnetically shielded room using a flux-locked loop involving additional positive feedback with bias current reversal. Two of these devices, integrated multiloop dc SQUIDs with outer diameters of 7 mm, achieved white noise levels of 10 fT/(square root of)Hz for bicrystal junctions and 30 fT/(square root of)Hz for step-edge junctions. The third magnetometer involved a flux transformer with a 10×10 mm2 pickup coil connected to a 16-turn input coil which was inductively coupled to a bicrystal SQUID. This device achieved a white noise of 16.2 fT/(square root of)Hz. High quality magnetocardiograms were obtained without signal averaging. © 1996 American Institute of Physics.
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  • 8
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of the noble metals Ag and Au are prospective candidates for application as electrical contacts in high temperature superconductor (HTSC) thin film devices. We present first results on intrinsic stress in Ag and Au films measured during and after their UHV deposition onto YBa2Cu3O7−x thin film substrates. At 110 K film growth proceeds by columnar grain growth with tensile stresses as huge as the tensile strength of the bulk phase. At room temperature and up to 600 K the films grow via island growth developing much smaller film stress. At temperatures above 550 K a compressive stress contribution due to interdiffusion of oxygen from the HTSC substrates into the contact films is observed.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2338-2346 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complete circuit model of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil has been developed. With this model, it is shown that the rf properties of the coupled SQUID can be calculated using only the given parameters of the SQUID. There are no adjustable parameters. The resonant structures in the SQUID characteristics caused by the presence of the input coil have been quantitatively studied. Methods to suppress the resonant structures have also been investigated. It is shown that the present circuit model explains well the experimentally observed rf properties of coupled SQUIDs. The present circuit model is therefore useful for the design of highly sensitive SQUIDs.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1000-1006 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The radio frequency (rf) properties of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil have been studied both experimentally and theoretically using an expanded model of the coupled SQUID. The input coil and washer resonances observed in the measured impedance of the expanded model are shown to be in quantitative agreement with the theory presented previously. When the input coil resonances are suppressed by resistive damping, it is shown that the impedance of the coupled SQUID at low frequencies is determined solely by an effective inductance that is much lower than the SQUID inductance. A simple equivalent circuit of the coupled SQUID for this case is proposed. The rf properties of SQUIDs with gradiometric washer configurations are also discussed. It is shown that the rf properties of these devices can be predicted from the properties of the individual washers.
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