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  • 1
    Electronic Resource
    Electronic Resource
    Functional imaging of neuronal brain activities: overlay of distributed neuromagnetic current density images and morphological MR images (1993)
    Springer
    European radiology 3 (1993), S. 41-43 
    Details
    ISSN: 1432-1084
    Keywords: MEG ; Superconducting quantum interference device (SQUID) ; MR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neuromagnetic imaging is a relatively new diagnostic tool for examination of electrical activities in the nervous system. It is based on the non-invasive detection of extremely weak magnetic fields around the human body with superconducting quantum interference device (SQUID) detectors. Often the “equivalent current dipole” model is used to describe the centre of the electrical activity. New current density reconstruction methods enable the imaging of the spatial extent and structure of neuronal activities. For practical use in medical diagnosis a combination of the abstract neuromagnetic images with MR or CT images is required in order to match the functional activity with anatomy and morphology. The neuromagnetic images can be overlaid onto three-dimensional morphological images with spatially arbitrarily selectable slices. The matching of both imaging modalities is discussed. On the basis of the detection of auditory evoked magnetic fields, neuromagnetic images are reconstructed with linear estimation theory algorithms. The MR images are used as a priori information of the volume conductor geometry and allow an attachment of functional and morphological properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00173521
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  • 2
    Electronic Resource
    Electronic Resource
    YBa2Cu3O7 ramp-type junctions and superconducting quantum interference devices with an ultrathin barrier of NdGaO3 (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1841-1843 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated ramp-type Josephson junctions and SQUIDs (superconducting quantum interference devices) using an ultrathin barrier layer of NdGaO3 as weak contact between the YBa2Cu3O7 electrodes. The junctions operate up to 82 K, exhibiting current-voltage characteristics of the resistively-shunted-junction type. A normal-state resistance of up to 30 Ω at a junction width of 5 μm and a characteristic voltage in excess of 100 μV at 77 K are obtained. We find hysteretic behavior below 70 K and an intrinsic junction capacitance of about 0.15 μF/cm2 at 4 K. SQUIDs show a transfer function δ V/δ Φ of 50 μV/Φ0 at an inductance of 40 pH at 77 K. Thus we observe excellent Josephson properties at a thickness of the NdGaO3 barrier of 2 nm. © 1994 American Institue of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112860
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  • 3
    Electronic Resource
    Electronic Resource
    Localization of current dipoles with multichannel SQUID systems (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 3053-3060 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Current sources in the human body can be localized by measuring the biomagnetic fields with multichannel SQUID systems. Important system aspects are the noise level, the ambient field suppression, the dynamic range, the reliability, the number of channels, and the arrangement of gradiometers. From the user's point of view the most important quality factor is the accuracy with which a current dipole can be localized. A test procedure is proposed to determine the localization power of the system. A 31-channel-SQUID system is presented together with the results of the test. The crucial parts of the system determining the accuracy are pointed out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144359
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Highly sensitive YBa2Cu3O7 dc SQUID magnetometer with thin-film flux transformer (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2700-2702 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have designed and fabricated a thin-film flux transformer by a YBa2Cu3O7/SrTiO3 (YBCO/STO) multilayer process. The flux transformer consists of a 20-turn input coil of 10 μm linewidth and a single-turn pickup loop surrounding an area of 7.5 by 7.5 mm2. All device levels are patterned by standard photolithography and Ar-ion-beam etching. The flux transformer has been combined in flip-chip configuration with the square washer of a low-noise YBCO dc SQUID. The dc SQUID magnetometer exhibits a magnetic field sensitivity of 1.4 nT/Φ0. The intrinsic white flux noise level of 70μΦ0/(square root of)Hz at 77 K is mainly dominated by the SQUID corresponding to a magnetic field resolution of the magnetometer of 100 fT/(square root of)Hz for frequencies above 40 Hz. At 1 Hz we measured 200 fT/(square root of)Hz. Biomagnetic measurements were performed in a magnetically shielded chamber.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110399
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  • 6
    Electronic Resource
    Electronic Resource
    Origin of 1/f noise in Y1Ba2Cu3O7−x step-edge dc SQUIDs (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2134-2136 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated Y1Ba2Cu3O7−x step-edge junction dc superconducting quantum interference devices (SQUIDs) and characterized their noise performance. The current-voltage characteristics of our SQUIDs are of resistively shunted junction type with critical current densities jc of about 104 A/cm2 and maximum flux to voltage transfer functions δV/δΦ of 20 μV/Φ0 at 77 K. We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the frequency dependent noise in our devices results from critical current fluctuations of the Josephson junctions. A bias current reversing technique is effective in suppressing this noise contribution. A flux noise Φn of 80 μΦ0/Hz1/2 at 1 Hz and 77 K was measured on a dc SQUID with an inductance Ls of 60 pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109450
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