A High-stability Shimming Current Amplifier Design for Low-field Permanent Magnet NMR Systems

doi:10.11938/cjmr20263206

Abstract

Abstract:

The widespread application of low-field permanent magnet NMR systems in areas such as food testing and material analysis places higher demands on the quality of NMR signals. Magnetic field uniformity is crucial for obtaining high-quality signals, and the performance of the shimming current amplifier directly determines the effectiveness of active shimming. This paper presents a specialized high-stability, low-ripple shimming current amplifier design for high-resolution, low-field permanent magnet NMR systems. The design employs a highly integrated modular architecture, supports multi-channel expansion via controller area network (CAN) communication, and utilizes a self-biased push-pull circuit to achieve bipolar current output from -1 A to +1 A, significantly improving output linearity. To ensure accuracy and stability, differential sensing is applied in the current feedback loop to effectively suppress common-mode noise. The amplifier demonstrates a linear regression coefficient R² > 0.999 999 9 and a 48-hour long-term stability of 5.3 ppm (1 ppm=10^-6), enabling precise current control with excellent linearity and stability, thereby meeting the driving requirements of shim coils in high-resolution, low-field NMR systems.

Key words: low-field NMR, permanent magnet, shimming current amplifier, current source, stability

CLC Number:

O482.53

LU Xingyun, YAO Shouquan, XU Juncheng, JIANG Yu. A High-stability Shimming Current Amplifier Design for Low-field Permanent Magnet NMR Systems[J]. Chinese Journal of Magnetic Resonance, 2026, 43(3): 268-278.

Figures/Tables 11

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序号	命令	功能
1	[SWITCHCH0 <value>]	切换通道0输入源（value=0，切换为Z₀输入；value=1，切换为DAC输入）
2	[SETALL <value>]	设定所有通道输出电流值为（value=0~65535）
3	[SETCH0 <value>]	设定通道0输出电流值（value=0~65535）
4	[SETCH1 <value>]	设定通道1输出电流值（value=0~65535）
5	[SETCH2 <value>]	设定通道2输出电流值（value=0~65535）
6	[SETCH3 <value>]	设定通道3输出电流值（value=0~65535）
7	[GETALL]	查询所有通道当前电流设定值
8	[GETCH0]	查询通道0当前电流设定值
9	[GETCH1]	查询通道1当前电流设定值
10	[GETCH2]	查询通道2当前电流设定值
11	[GETCH3]	查询通道3当前电流设定值
12	[RDATACH0 <value>]	返回通道0当前输出电流值（value=0~65535）
13	[RDATACH1 <value>]	返回通道1当前输出电流值（value=0~65535）
14	[RDATACH2 <value>]	返回通道2当前输出电流值（value=0~65535）
15	[RDATACH3 <value>]	返回通道3当前输出电流值（value=0~65535）