Measurements of Biomagnetism with a Magnetic Shield for a High-Tc Superconductor

We developed a helmet-sized superconducting magnetic shield for a high-Tc Bi-Pb-Sr-Ca-Cu-O superconductor. The shield is 32 cm in diameter, 60 cm in depth, and 2.5 cm thick. It was experimentally confirmed that the container can reduce a weak magnetic field by ¿100 dB or to 1/100,000. The shielding effect of the superconducting container does not decrease even at frequencies as low as 0.2 Hz. Using equipment consisting of a superconducting container, a cryostat to keep the container at liquid nitrogen temperature, and an rf SQUID gradiometer, we successfully detected the magnetic fields of a human brain. We detected somatosensory magnetic fields by stimulating the tibial nerves of the patient with current pulses.