用于脑磁图或超低场核磁共振等生物磁学研究的超导量子干涉器件（SQUID）中的磁场噪声通常受到仪器杜瓦噪声的限制。我们构建了一个宽带，超低噪声系统与一个45毫米直径的超导拾波线圈电感耦合到一个电流传感器SQUID。分别采用镀铝聚酯织物作为超绝热层和氧化铝条作为热屏蔽层，减小了液氦杜瓦中的热噪声。在柏林磁屏蔽室2（BMSR2）的中心放置一个磁力计拾波线圈，在约20 kHz和约2.5 MHz系统带宽之间的白噪声范围内，可实现约150 aT Hz $^{-1/2}$的噪声水平。在较低频率下，分辨率受到屏蔽室墙壁产生的磁场噪声的限制。将BMSR2建模为具有连续μ金属壁的封闭立方体，我们可以定量地再现其测量的场噪声。
英文摘要：
The magnetic field noise in superconducting quantum interference devices (SQUIDs) used for biomagnetic research such as magnetoencephalography or ultra-low-field nuclear magnetic resonance is usually limited by instrumental dewar noise. We constructed a wideband, ultra-low noise system with a 45 mm diameter superconducting pick-up coil inductively coupled to a current sensor SQUID. Thermal noise in the liquid helium dewar is minimized by using aluminized polyester fabric as superinsulation and aluminum oxide strips as heat shields, respectively. With a magnetometer pick-up coil in the center of the Berlin magneti- cally shielded room 2 (BMSR2) a noise level of around 150 aT Hz$^{-1/2}$ is achieved in the white noise regime between about 20 kHz and the system bandwidth of about 2.5 MHz. At lower frequencies, the resolution is limited by magnetic field noise arising from the walls of the shielded room. Modeling the BMSR2 as a closed cube with continuous μ-metal walls we can quantitatively reproduce its measured field noise.
