Y. Uchikawa

Neuromagnetic SQUID measurement in a superconducting magnetic shield

A superconducting magnetic shield of high-Tc superconductor Bi(Pb)SrCaCuOx has been constructed whose diameter is 65 cm and length is 160 cm respectively. We have successfully observed somatosensory evoked magnetic fields coming out from human brains in the superconducting magnetic shield stimulating the median nerves of patients by current pulses. We made a 64-channel whole-head SQUID magnetometer of SNS (Superconductor/Normal metal/Superconductor) junctions. The sensitivities of the dc-SQUID of mesoscopic SNS junctions are around 5 fT//spl radic/(Hz) even in rather unfavorable surroundings. The magnetic shield can reduce a magnetic field to around -80 dB or 10/sup -4/ even at as low a frequency as 0.05 Hz.

A 64-channel whole-head SQUID system in a superconducting magnetic shield

A superconducting magnetic shield of high-Tc superconductor Bi(Pb)-Sr-Ca-Cu-Ox has been constructed whose diameter is 65 cm and length is 160 cm. We have successfully observed magnetic fields from somatosensory-evoked human brains in the superconducting magnetic shield by stimulating the median nerves of patients by current pulses. We made a 64-channel whole-head SQUID magnetometer of superconductor/normal metal/superconductor (SNS) junctions which do not show low-frequency telegraph noise. The sensitivities of the dc SQUID mesoscopic SNS junctions are around 5 fT Hz-1/2 even in rather unfavourable surroundings. The magnetic shield can reduce a magnetic field by around -80 dB or a factor of 10-4 even at as low a frequency as 0.05 Hz. Therefore SQUIDs of SNS junctions and a superconducting magnetic shield are a good combination.

Seven-channel RF SQUID with 1/f noises only at very low frequencies

A seven-channel RF SQUID (superconducting quantum interference device) with anodized short weak links has been fabricated. The devices exhibit a sensitivity of 23.6 fT/ square root Hz and a 1/f noise onset of 0.05 Hz at a white noise level of 1.8*10/sup -4/ phi /sub 0// square root Hz. The intrinsic flux noise is estimated from an observed step pattern to be 4.9*10/sup -5/ phi /sub 0// square root Hz. It is shown that Arnold theory explains very well the behavior of Josephson junctions with a critical current density of around 10/sup 4/ A/cm/sup 2/. >

Analysis of MCG measured by high-TC squid with spatial filter method

Magnetocardiogram (MCG) measurement using high-Tc SQUID magnetometer is receiving attention as a diagnostic technique because the instrument is easy to operate and the liquid nitrogen coolant is lower cost compared with the liquid helium used in conventional SQUID magnetometers. We measured of the linear current and MCG of the subjects with healthy and unhealthy hearts using a 16-channel high-Tc SQUID in a prefabricated magnetically shielded room. The spatial filter method (SFM) is used to reduce the errors in the measurement and analyzes of the signal source. The results of the simulation and actual measurement of the subjects with healthy and unhealthy hearts show that the method is useful for the estimation of the signal source.