Residual magnetic interference induced by applied magnetic field pulses inside a conductive shielded room (SR) has been a common issue in ultra-low-field (ULF) nuclear magnetic resonance (NMR). The rapid cutoff of the applied pre-polarizing field (Bp) induces eddy currents in the walls of the SR, which produces a decaying residual magnetic interference that may cause severe image distortions and signal loss. In this study, a pair of cancellation coils (CC) and control electronics were designed for the suppression of the residual magnetic interference in a SR. Simulations show that this method was effective in suppressing the residual magnetic field (Br) after removal of the pre-polarizing magnetic field. Then, a small-scale SR was designed and the effectiveness of this cancellation scheme was experimentally verified. The test results showed a good agreement with the simulation, which indicated that the cancellation scheme was capable of reducing Br field to a much lower level. The scheme proposed in this study provides a solution for suppressing the residual magnetic field in the ULF NMR system. After decoupling the eddy–current field, the effect of the suppression may be further improved by optimization of the cancellation coil in further work.

中文翻译：

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超低场核磁共振导电屏蔽室残余磁干扰的有效抑制

由在导电屏蔽室 (SR) 内施加的磁场脉冲引起的残余磁干扰一直是超低场 (ULF) 核磁共振 (NMR) 中的常见问题。施加的预极化场 (Bp) 的快速截止会在 SR 的壁中感应出涡流，这会产生衰减的剩磁干扰，这可能会导致严重的图像失真和信号丢失。在这项研究中，设计了一对消除线圈 (CC) 和控制电子设备来抑制 SR 中的剩磁干扰。仿真结果表明，该方法可以有效抑制预极化磁场去除后的剩余磁场（Br）。然后，设计了一个小规模的 SR，并通过实验验证了该抵消方案的有效性。测试结果表明与模拟非常吻合，这表明抵消方案能够将 Br 场降低到低得多的水平。本研究提出的方案为抑制超低频核磁共振系统中的剩余磁场提供了解决方案。涡流场解耦后，在进一步的工作中可以通过优化抵消线圈来进一步提高抑制效果。