Direct Current Superconducting Quantum Interference Research Articles

Modeling the direct current superconducting quantum interference device coupled to the multiturn input coil. II

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.

The topographic distribution of the magnetic P100M to full- and half-field stimulation.

Visual evoked magnetic responses were recorded to full-field and left and right half-field stimulation with three check sizes (70', 34' and 22') in five normal subjects. Recordings were made sequentially on a 20-position grid (4 x 5) based on the inion, by means of a single-channel direct current-Superconducting Quantum Interference Device second-order gradiometer. The topographic maps were consistent on the same subjects recorded 2 months apart. The half-field responses produced the strongest signals in the contralateral hemisphere and were consistent with the cruciform model of the calcarine fissure. Right half fields produced upper-left-quadrant outgoing fields and lower-left-quadrant ingoing fields, while the left half field produced the opposite response. The topographic maps also varied with check size, with the larger checks producing positive or negative maximum position more anteriorly than small checks. In addition, with large checks the full-field responses could be explained as the summation of the two half fields, whereas full-field responses to smaller checks were more unpredictable and may be due to sources located at the occipital pole or lateral surface. In addition, dipole sources were located as appropriate with the use of inverse problem solutions. Topographic data will be vital to the clinical use of the visual evoked field but, in addition, provides complementary information to visual evoked potentials, allowing detailed studies of the visual cortex.

Aluminum and boron nuclear quadrupole resonance with a direct current superconducting quantum interference device

We report the application of our dc SQUID (superconducting quantum interference device) spectrometer [C. Connor, J. Chang, and A. Pines, Rev. Sci. Instrum. 61, 1059(1990)] to nuclear quadrupole resonance (NQR) studies of aluminum-27, and boron-11 in crystalline and glassy solids. Our results give e2qQ/h=2.38 MHz and η=0.0 for α–Al2O3 at 4.2 K. For the natural mineral petalite (LiAlSi4O10), we obtain e2qQ/h=4.56 MHz and η=0.47. The quadrupole resonance frequency is 1467 kHz in boron nitride, and in the vicinity of 1300 kHz for various borates in the B2O3⋅xH2O system. The distribution of boron environments in a B2O3 glass gives rise to a linewidth of about 80 kHz in the SQUID detected resonance.