In order to reduce the influence of environmental magnetic field on the test of superconducting single-flux-quantum (SFQ) circuit chip in a liquid helium dewar, a multilayer magnetic shielding structure is designed to provide a clean magnetic field lower than 50 nT and achieve a shielding effectiveness higher than 60 dB. The magnetic shielding structure consists of three cylindrical layers with uniform 1 mm thickness. The first inner layer is made of NbTi which works as a strong diamagnet shell, while the outer two layers are made of permalloy which has high permeability at helium temperature. The superconducting quantum interference device (SQUID) was used to test the shielding performance of the structure under low frequency (0.1–100 Hz) magnetic interference at helium temperature. The results show that the radial and axial shielding effectiveness (SE) are about 80 dB and 68 dB, respectively, indicating that the multilayer structure has good shielding performance and can be used in the testing system of superconducting single-flux-quantum circuitchip.

为降低环境磁场对液氦杜瓦中超导单通量量子（SFQ）电路芯片测试的影响，设计了多层磁屏蔽结构，提供低于50 nT的洁净磁场，实现屏蔽效能高于 60 dB。磁屏蔽结构由三个均匀的 1 mm 厚的圆柱形层组成。第一内层由 NbTi 制成，可作为坚固的抗磁性外壳，而外两层由在氦温度下具有高磁导率的坡莫合金制成。超导量子干涉仪（SQUID）用于测试结构在氦温度下低频（0.1-100Hz）磁干扰下的屏蔽性能。