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  • 1
    Electronic Resource
    Electronic Resource
    Theory for the multiloop dc superconducting quantum interference device magnetometer and experimental verification (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4088-4098 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359607
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  • 2
    Electronic Resource
    Electronic Resource
    Plasma nitridation process for the fabrication of all-refractory Josephson junctions (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3038-3042 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A process for the fabrication of high-quality, all-refractory Josephson junctions of the type Nb/Six Ny /Nb is described in detail. The junctions have been fabricated using the selective niobium anodization process with a tunnel barrier consisting of an amorphous Si film converted to its nitride by the application of a rf plasma of nitrogen. An attractive feature of these junctions is their comparably low specific capacitance C/A=3.9±0.1 μF/cm2 (for Jc =6 A/cm2 ). Junctions of this type having critical current densities up to Jc =2000 A/cm2 and Vm =16 mV have been fabricated. Excellent magnetic field threshold curves have also been observed for these junctions, indicating that the critical current density is very uniform.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345432
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  • 3
    Electronic Resource
    Electronic Resource
    A 5-MHz bandwidth SQUID magnetometer with additional positive feedback (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3008-3015 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145587
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  • 4
    Electronic Resource
    Electronic Resource
    A broadband picovoltmeter based on the direct current superconducting quantum interference device with additional positive feedback (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3005-3011 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144593
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  • 5
    Electronic Resource
    Electronic Resource
    Linearity of sensitive YBa2Cu3O7−x dc superconducting quantum interference device magnetometers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3382-3386 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linearity of sensitive superconducting quantum interference device (SQUID) magnetometers fabricated from high critical temperature (high-Tc) superconductors and operated in a direct-coupled flux-locked loop with bias reversal was investigated. The system nonlinearity was determined by applying a sinusoidal test signal and measuring the output signal harmonics using a setup which ensures the elimination of nonlinearities arising from the test signal source and the spectrum analyzer. The experimental setup enables the simultaneous measurement of the harmonic distortion of a single magnetometer and of a first-order electronic gradiometer formed by two individual magnetometers. Test signal amplitudes and frequencies were chosen to simulate typical laboratory interferences. An analysis of the results was performed using analytical equations in which the SQUID's inherent nonlinear character is taken into account. At signal frequencies above about 0.1% of the system bandwidth, the system nonlinearity was found to be mainly caused by the nonlinear behavior of the SQUID magnetometers, whereas at low frequencies nonlinearities arising from read-out electronics components predominate. For signal peak-to-peak amplitudes up to 1 μT and frequencies up to 0.5 kHz, total harmonic distortions below about −105 dB for a single sensor channel and −100 dB for an electronic gradiometer were obtained. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371217
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic detection of photogenerated currents in semiconductor wafers using superconducting quantum interference devices (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2863-2865 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A completely noninvasive method is presented for the investigation of semiconductor wafers with high spatial resolution utilizing a superconducting quantum interference device (SQUID) magnetometer system. The method is based on the detection of the magnetic field caused by photocurrents generated in the semiconductor sample using a sensitive SQUID magnetometer. The photocurrents arise when laser light with a photon energy exceeding the band gap of the semiconductor is focused onto the sample surface in a region of a doping gradient. The spatial resolution of this detection method is mainly determined by the size of the excitation focus of about 20 μm. We report on measurements of silicon wafers with small growth-related doping fluctuations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124039
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  • 7
    Electronic Resource
    Electronic Resource
    Low-frequency noise of improved direct-coupled high-Tc superconducting quantum interference device magnetometers in ac and dc magnetic fields (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2821-2823 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed direct-coupled high-Tc superconducting quantum interference device (SQUID) magnetometers based on 30° bicrystal junctions with superior noise performance in dc and ac magnetic fields. These magnetometers are composed of a 100 pH SQUID loop with a linewidth of 4 μm and a pickup coil consisting of 16 parallel, 50-μm-wide loops. The magnetic field noise down to 1 Hz did not increase when the magnetometers were exposed to ac fields with peak-to-peak amplitudes of up to 54 μT or cooled in static magnetic fields above that of the Earth. The best noise at 1 Hz of such a device cooled in 64 μT was 65 fT Hz1/2. The increased noise below 1 Hz when the devices were cooled in a static magnetic field can be quantitatively described by the measured temperature fluctuations assuming a temperature coefficient of the pickup loop area of about 1×10−4/K. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125161
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  • 8
    Electronic Resource
    Electronic Resource
    Low noise YBa2Cu3O7−x SQUID magnetometers operated with additional positive feedback (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1856-1858 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116036
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  • 9
    Electronic Resource
    Electronic Resource
    Practical low-noise integrated dc superconducting quantum interference device magnetometer with additional positive feedback (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 228-230 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have designed and fabricated a low-noise dc superconducting quantum interference device (SQUID) magnetometer that is integrated on a 4×4 mm2 chip. The white flux noise of the magnetometer measured in a flux-locked-loop mode using simple, direct-coupled electronics with additional positive feedback (APF) is 6.4×10−7 Φ0/(square root of)Hz. The corresponding white flux density noise is 3.9 fT/(square root of)Hz. The SQUID flux-to-voltage transfer function with APF is enhanced to 4.7 mV/Φ0 at the optimal working point, thereby significantly reducing the preamplifier contribution to the total noise. A maximum feedback field of 65 nT for frequencies up to 300 Hz and a maximum slew rate of 120 μT/s at 300 Hz have been attained using a two-pole integrator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105974
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  • 10
    Electronic Resource
    Electronic Resource
    Integrated YBa2Cu3O7−x magnetometer for biomagnetic measurements (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1421-1423 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An integrated dc superconducting quantum interference device (SQUID) magnetometer has been fabricated using a YBa2Cu3O7−x–SrTiO3–YBa2Cu3O7−x multilayer process. The magnetometer consists of a 8.3 mm×8.6 mm pickup coil coupled inductively to a small washer-type SQUID with 9 Ω bicrystal junctions via an integrated 101/2-turn input coil. Using simple direct-coupled read-out electronics with additional positive feedback, a noise level of 9.7 fT/(square root of)Hz at 1 kHz and 53 fT/(square root of)Hz at 1 Hz was measured inside a magnetically shielded room. Due to the low noise level biomagnetic heart and brain signals with high quality and the very weak signals of the peripheral nerve system were recorded. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116100
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