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一、引言流水式核磁共振(NMR)测场法可以精密测量0.03特斯拉以下的弱磁场和均匀度劣于10~(-4)/cm 的磁场。文献[1][2][3]分别描述了这一方法的特点。该方法需要用较强的磁场(0.5～1 T)对流动水样品进行预极化。本文所研究的方法是;用被测磁场作为流水样品的极化磁场,在测量探头内设置极化器。文献[4]研究的流水式宽范围质子特斯拉计的测量精度指标为3×10~(-5)。本文给出了进一步提高流水式核磁共振测场法测量精密度的途径。实际测量波谱仪超导磁场的精密度达到了1×10~(-8)。二、以被测磁场为极化场的磁场测量系统该测场系统由四部分组成:测量探头(内含极化器)、核磁化强度检测器、射频激励源、循环水系统。对于这种测量系统应当着重研究的问题是:探头内极化器的极化效率η、核磁化强度检测器的特性以及射频激励源的频率稳定度和调节细度。这些因素对测量系统的信噪比和精度有着明显的影响。
I. INTRODUCTION The flow field NMR (NMR) method can measure the weak magnetic field below 0.03 Tesla and the magnetic field whose uniformity is less than 10 ~ (-4) / cm. Literature [1] [2] [3] describes the characteristics of this method. This method requires the pre-polarization of flowing water samples with a strong magnetic field (0.5-1 T). The method studied in this paper is: using the measured magnetic field as the polarized magnetic field of the flowing water sample, setting the polarizer in the measuring probe. The accuracy index of flow-type wide-range proton Tesla meter studied in [4] is 3 × 10 ~ (-5). This article gives ways to further improve the precision of flow-based NMR spectrometry. The actual measurement of superconducting magnetic field spectrometer precision reached 1 × 10 ~ (-8). Second, the measured magnetic field polarization field magnetic field measurement system The measurement system consists of four parts: the probe (including polarizer), nuclear magnetization detector, RF excitation source, circulating water system. The main issues that should be addressed in this measurement system are the polarization efficiency η of the polarizer in the probe, the characteristics of the nuclear magnetization detector, and the frequency stability and fineness of the RF excitation source. These factors have a significant impact on the signal-to-noise ratio and accuracy of the measurement system.