Development of The Technology of Biomagnetic Measurement Using High-Temperature Superconductor

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Under the aim to develop the technology of biomagnetic measurement using high-Tc superconductor, we made the following studies and obtained the results described.1. Directly coupled magnetometers were fabricated from YBCO films to have a field noise of less than 100 fT/Hz^<1/2>. The magnetometers have fine structures of slots and holes in μm size on the whole superconducting film and flux dams in the lead film that connects the pickup coil to the SQUID, so that entry and trapping of magnetic flux in the superconducting film would be suppressed. As a result, the magnetometers did not exhibit appreciable increase of low-frequency flux-noise when they were cooled in magnetic fields lower than 30 μT or environmental magnetic field was changed to 1-2 μT.2. In order to reduce environmental magnetic field noises, we investigated various techniques of active compensation that is combined with a soft-shielding simple MSR composed 1-2 layers of μ-metal. A novel compensation method was implemented in which a noise-field detection coil was wound around the MSR wall and a Helmholz-type compensation coil was also wound around the MSR. As a method than is useful in multichannel system, a feedback flux in a flux-locked-loop operation of a magnetometer that detects exclusively field noises was supplied to the feedback coil of other signal-sensing magnetometers. Using such compensation techniques with the soft-shielding MSR, 50-60 dB attenuation of the field noise was possible.3. A multichannel magnetometer system for the measurement of magnetocardiographic signal (MCG) was constructed. The system was installed within the above MSR implemented with the active noise compensation. Real-time MCG signals were measured from the human heart of normal subjects in a wide band-width of 1-100 Hz.