Hisashi Kado

Step-edge junction of YBCO thin films on MgO substrates

The authors have studied the microstructure of YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) thin films epitaxially grown on MgO

Evaluation of a high-performance magnetically shielded room for biomagnetic measurement

A spherical magnetically shielded room called COSMOS and a method for measuring the shielding factor of well-shielded rooms have been developed. A dc-superconducting quantum interference device is used to detect faint magnetic fields, and the detected signals are averaged to increase the signal-to-noise ratio. The measured magnetic shielding factor for COSMOS is 420000 at 1 Hz.

High sensitivity double relaxation oscillation superconducting quantum interference devices with large transfer from flux to voltage

Double relaxation oscillation superconducting quantum interference devices (SQUIDs) (DROSs) based on Nb/AlOx tunnel junctions have been fabricated and characterized. The estimated relaxation frequencies range from 400 MHz up to 14 GHz. Transfer coefficients from flux to voltage of 2 up to 7 mV/φ0 have been obtained. Both the intrinsic flux noise and the performance in a flux‐locked loop with direct‐voltage readout have been determined. Special attention is paid to the effect of damping resistors on the sensitivity of DROSs. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13h at relaxation frequencies above 2–3 GHz for SQUID inductances of about 30 pH. This sensitivity is very close to the theoretical maximum sensitivity of 6h of a comparable standard type dc SQUID. In a flux‐locked loop based on direct‐voltage readout, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34h has been obtained for a DROS with a SQUID inductance of 29 pH.

Four‐channel YBa2Cu3O7−y dc SQUID magnetometer for biomagnetic measurements

A four‐channel YBa2Cu3O7−y thin film dc SQUID magnetometer was fabricated. Biomagnetic measurements were performed by using the four‐channel system at 77 K in a magnetically shielded room. We have successfully measured four‐channel magnetocardiac signals clearly in real‐time mode. The best magnetic field resolution of the four SQUIDs was 370 fT/Hz1/2 at 10 Hz and 200 fT/Hz1/2 in the white noise region.

An integrated DC SQUID gradiometer for biomagnetic application

A first-order off-diagonal gradiometer was fabricated and tested. The gradiometer consisted of two field pickup coils and a planar DC SQUID (superconducting quantum interference device) with two superconducting loops connected in parallel, two multiturn input coils, and a modulation-feedback coil. The size of the pickup coils was 6*6 mm/sup 2/ with a base line of 8 mm. The overall size of the gradiometer was 15*7.5 mm/sup 2/. The resolution of the magnetic field gradient of the gradiometer increased from 11 to 1.8 pT/m square root Hz (the noise limits), corresponding to the frequencies from 1 Hz to 600 Hz. The resolution became nearly white in a frequency range above 600 Hz. The intrinsic balance of the gradiometer was better than 1000 p.p.m. for the field perpendicular to its plane. >

High sensitivity double relaxation oscillation superconducting quantum interference devices

Double relaxation oscillationsuperconducting quantum interference devices(SQUIDs) (DROSs) have been fabricated with estimated relaxation frequencies up to 14 GHz. Both the intrinsic flux noise and the performance in a flux locked loop with direct voltage readout have been studied. In flux locked loop, a noise level of 0.55 μφ0/√Hz corresponding to an energy sensitivity of 34 h has been obtained for a DROS with a SQUIDinductance of 29 pH. The intrinsic sensitivity improves with increasing relaxation frequency, leveling off to a value of 13 h at relaxation frequencies higher than about 3 GHz.

Asymmetric Bias Injection Technique for Drung-Type Superconducting Quantum Interference Devices

An asymmetric bias current injection method is developed to reduce bias-caused noise in Drung-type SQUID (superconducting quantum interference devices) without adding extra coils. A measuring scheme for ∂Φ/∂Ib is tested, and it is demonstrated that the reduction is from 100 to 150 times that attained by the conventional SQUID biasing method. It is revealed that the direction of APF (additional positive feedback) coil winding is important in attaining this reduction.

System integration and trade-offs of SQUID system for biomagnetic applications

Abstract We have been developing SQUID systems for various applications, with special emphasis on systems for biomagnetic applications. In 1987, Koyanagi and Kado fabricated and integrated a SQUID system made entirely of thin-film integrated SQUID. Research and development activities on multichannel SQUID system integration has been undertaken by various groups. The Superconducting Sensor Laboratory (SSL) project was one of the most significant of these activities. Such activities in North America and Europe have mostly been pursued by commercial groups, who have been fabricating commercial systems for end users. However, large-scale system distribution to end users is still impractical because of high costs and the lack of user-friendliness. As former members of the SSL project, some of us at the Kanazawa Institute of Technology began the development of SQUID systems aimed at overcoming previous problems such as high cost and the low level of user-friendliness. In this paper, we describe our concept of system integration and the level of the system’s sophistication.

High sensitivity magnetic flux sensors with direct voltage readout: double relaxation oscillation SQUIDs

The experimental sensitivity of double relaxation oscillation SQUIDs (DROSs) has been compared with theory and with the results obtained by numerical simulations. The experimental sensitivity ranges from 60 to 13h, where h is Plancks constant, for relaxation frequencies from 0.4 up to 10 GHz. For low frequencies the DROS characteristics can be explained by thermal noise on the critical currents. For high frequencies, the voltage-flux characteristics and the sensitivity are limited by the plasma frequency. The cross-over frequency is at 2 GHz, which is about 2% of the plasma frequency of the DROSs.<<ETX>>

Ocular dominance affects magnitude of dipole moment: an Meg study

To investigate whether the ocular dominance affects laterality in the activity of the primary visual cortex, we examined the relationship between the ocular dominance and latency or dipole moment measured by checkerboard-pattern and magnetoencephalography in 11 right-handed healthy male participants. Participants with left-eye dominance showed a dipole moment of 21.5±6.1 nAm with left-eye stimulation and 16.1±3.6 nAm with right, whereas those with right-eye dominance showed a dipole moment of 18.0±5.2 and 21.5±2.7 nAm with left-eye and right-eye stimulation of the infero-medial quadrant visual field, respectively. Thus, the dipole moment was higher when the dominant eye was stimulated, which implies that ocular dominance is regulated by the ipsilateral occipital lobe.