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

本文以发展高温超导体生物磁测量技术为目标，进行了以下研究工作，并取得了如下结果：1.用YBCO薄膜制作的直接耦合磁强计的场噪声小于100 fT/Hz^<1/2>。这种磁强计在整个超导薄膜上具有μm大小的槽和孔的精细结构，在连接拾取线圈和SQUID的引线薄膜中具有磁通坝，从而抑制了磁通在超导薄膜中的进入和捕获。结果表明，在低于30 μT的磁场中冷却或将环境磁场改变为1-2 μ T时，磁强计的低频磁通噪声没有明显增加.为了降低环境磁场噪声，我们研究了各种有源补偿技术，结合软屏蔽简单的MSR由1-2层μ-金属。提出了一种新的补偿方法，即在磁共振室壁上绕制噪声场检测线圈，同时在磁共振室上绕制亥姆霍兹型补偿线圈。作为在多通道系统中有用的方法，将专门检测场噪声的磁力计的磁通锁定环操作中的反馈磁通提供给其他信号感测磁力计的反馈线圈。使用这种补偿技术与软屏蔽MSR，50-60 dB的现场噪声衰减是可能的。本文介绍了一种用于心磁图信号（MCG）测量的多通道磁强计系统。该系统安装在上述MSR内，并采用有源噪声补偿。在1-100 Hz的宽频带内，对正常人心脏进行了实时心磁图测量。

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.