Effect of Niobium Cylinder on Output of the 3D SQUID Gradiometer

Because of the large ambient noise in biomagnetic measurements, it is usually necessary to use a gradiometer to reduce the noise. In order to prevent noise coupling into the SQUID from the on-chip input coil, it is also necessary to cover the chip with a niobium Cylinder. This article focuses on the possible impact of introducing a niobium cylinder on the output of a SQUID gradient meter and how to reduce this effect. Obtained by simulation rules and conclusions, and then design experimental verification conclusion. In this paper, the effect of the niobium tube on the output is equivalent to unbalance degree. Changing the relative position of the niobium tube makes the equivalent imbalance of the SQUID gradient meter coil less than which caused by manual winding.