Abstract:

With the widespread use of low-field permanent magnet magnetic resonance (NMR) systems in fields such as food testing and material analysis, 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 amplifier, Current source, Stability