This paper presents a high-resolution magnetic field mapping system in development that is capable of collecting spatial magnetic field data for NMR magnets. An NMR probe was designed and built with a resonant frequency of 5.73 MHz. The measured Q-factor of the NMR probe is ~191 with a half-power bandwidth in the range of 5.72-5.75 MHz. An RF continuous-wave technique with magnetic field modulation was utilized to detect the power dispersion of water molecules. The zero-crossing frequency of the NMR dispersion signal corresponds to the magnetic field at the center of the water sample. An embedded system was developed to sweep the frequency and record the reflected RF power simultaneously. A numerically controlled digital oscillator is able to provide a precise frequency step as small as 0.02 Hz, which is equivalent to 4.7 e-7 mT for hydrogen atoms. An RF preamplifier was built to supply up to 4 W of RF power to a bidirectional coupler. The coupler supplies RF power to the NMR probe and channels reflect the RF power back to the detection circuit, which detects the reflected RF power from the NMR probe during the frequency sweep. The homogeneity of an NMR magnet can be determined by magnetic field data.

中文翻译：

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配备 NMR 探头的高分辨率磁场测绘系统

本文介绍了一种正在开发的高分辨率磁场测绘系统，该系统能够收集核磁共振磁体的空间磁场数据。设计并构建了谐振频率为 5.73 MHz 的 NMR 探头。NMR 探头的测量 Q 因子约为 191，半功率带宽范围为 5.72-5.75 MHz。利用磁场调制的射频连续波技术来检测水分子的功率色散。NMR 色散信号的过零频率对应于水样中心的磁场。开发了一个嵌入式系统来扫描频率并同时记录反射的射频功率。数控数字振荡器能够提供小至 0.02 Hz 的精确频率步长，相当于氢原子的 4.7 e-7 mT。RF 前置放大器旨在为双向耦合器提供高达 4 W 的 RF 功率。耦合器向 NMR 探头提供 RF 功率，通道将 RF 功率反射回检测电路，检测电路在频率扫描期间检测 NMR 探头反射的 RF 功率。NMR 磁体的均匀性可以通过磁场数据来确定。