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

Abstract

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.

Location of somatosensory-evoked dipoles studied by a SQUID system in a superconducting magnetic shield

“…The first order gradiometers have a diameter of 18 mm and a length of 30 mm. Some information about the SQUID is given in [1][2][3][4]. Fig.…”