A new 19-channel SQUID magnetometer system has been developed for research use in order to measure the neuromagnetic fields originating from cortices of the human brain.The system could function for 6 days with a one-time supply of about 25 L of liquid helium. The system consists of Nb/Al-oxide/Nb SQUID sensors with 2nd-order gradiometers, tank circuits, readout electronics, a liquid helium dewar, a gantry, and a prefabricated shielded room. The gradiometers cover a circular area of 15 cm radius. We used fine stainless steel leads for electric connection between the sensors and room-temperature electronics with low thermal conduction in a low helium consumption dewar. The system could function for 6 days with a one-time supply of about 25L of liquid helium. The system can be thermally cycled for repeated measurements, with an intervening nonusage period at room temperature. The noise characteristics, for both the time and frequency domains, of all channels were measured. From an analysis of the voltage output at the phase-sensitive detector, the flux-origin noise which is generated by external sources was dominant in the white noise frequency. The power spectra of the noise field were below 10 fT/Hz1/2 at 10-100 Hz and below 18 fT/Hz1/2 at 1-10 Hz. Some other peaks of power line frequencies such as 50 Hz and 150 Hz were observed at several channels. Sound-evoked magnetic fields were measured from the temporal area of the head upon application of tone bursts. The evoked fields were recorded with the amplitude of about 250 fTpp. The isofield contours of the peak response showed that the measurement area is large enough to estimate current dipoles. It is confirmed that the system has the ability to measure magnetic fields from the human brain.

We have fabricated and measured step-edge microbridges of on-axis sputter-deposited YBCO films using the steps which exist on the cleaved surface of MgO substrate. The microbridges fabricated over the step behaved as Josephson devices, exhibiting clear Shapiro steps with microwave irradiation at 4.2 K. The critical current of the step-edge microbridge is one to two orders reduced from the critical current of the microbridge that has no steps within the same bridge region. The ICRN product is 0.5-1 mV with normal resistance of 1-4 Ω. The present technique utilizing the cleaved steps of MgO is useful for studying basic characteristics of the weak links with the step-edge structure.

We have fabricated and characterized two types of high-Tc planar SQUID gradiometers having different line width of pickup loops. The device worked in flux-locked loop (FLL) operation even in laboratory environment without any shielding. A magnetic field gradient resolution of a parallel-type device in a lightly shielded room was about 0.5 pT/cmHz1/2 at 1 kHz and 2 pT/cmHz1/2 at 1 Hz. The device was possible to record magnetocardiograms in a shielded room. QRS-complex peaks of about 10 pT PP/4mm are clearly observed. For a mesh-type device, the increase of low frequency noise in the open laboratory environment was less than that for a parallel-type.

Y-Ba-Cu-O films sputter-deposited at about 650 in high oxygen concentration gas are superconductive without heat treatment after the deposition. The films of 700 nm thickness have Tc end of 72 K on SrTiO3 and 65 K on sapphire substrates. Reduced interdiffusion, compared with post-annealed films at high temperatures, between the film and the substrate is confirmed.

We describe here development of a multichannel high-Tc SQUID magnetometer system for measurement of cardiac magnetic fields, aiming at future application of diagnosis of heart diseases. Two types of direct-coupled SQUID magnetometers were fabricated and used: single pickup coil magnetometer having flux dams to suppress the shielding current that would induce flux penetration and the consequent low-frequency noise, and double pickup coil magnetometer having no grain boundary junctions and flux dams on the pickup coil. The superconducting film of both the magnetometers had holes and slots, leaving 5 µm-wide strip lines, to suppress trapping and penetration of magnetic flux vortices in environmental fields. We studied different schemes of active shielding to reinforce the efficiency of field-attenuation of magnetically shielded room (MSR). A feedback-type compensation using a normal detection coil wound around the wall of MSR and a selective cancellation of 50 Hz noise by means of adaptive filter were developed. Such combination of passive and active shielding, based on the use of simple MSR, would be suitable in a practical low-cost magnetometer system for clinical MCG examination. We fabricated a liquid nitrogen cryostat that could contain up to 20 magnetometer-capsules at 4 cm separation in a flat bottom, with a distance of 16 mm between the air and liquid nitrogen. The cryostat was set in a gantry, which had rotational, vertical and horizontal freedoms of movement, in a moderate-shielding MSR that was combined with the developed active shielding. Measurements of MCG were performed for normal subject using eight magnetometers operating simultaneously.

Self-healing breakdowns of anodic Y2O3 films with the thickness of 500 to 2000 have been measured. The measurements reveal that the breakdown is a single-hole type and that the breakdown field, which is closely correlated to the anodizing field, is independent of the Y2O3 thickness. An ionic motion is considered to the effective in initiating the breakdown which forms a conducting channel through the Y2O3 film. The energy of the breakdown spot formation is calculated assuming the thermochemical evaporation process of the substances. It agrees well with the discharged energy of the specimen capacitor at the breakdown.