Improvements in 3D Automated Shimming Techniques in High-Resolution NMR

TL;DR

This paper presents an improved 3D automated shimming method for high-resolution NMR that uses standard hardware, enhances field homogeneity, and addresses calibration and thermal convection issues.

Contribution

The thesis introduces a novel 3D shimming technique compatible with common NMR hardware, eliminating the need for specialized PFG equipment.

Findings

Successfully tested on Varian UNITY INOVA spectrometers

Calibrated linear transverse shim gradients effectively

First report on thermal convection effects on field mapping

Abstract

Traditionally the improvement of static magnetic field homogeneity of the magnet in Nuclear Magnetic Resonance (NMR) spectroscopy is performed manually, which has many limitations. However, in recent years a number of automated shimming techniques based on Fourier Imaging Technique have been proposed. Existing 3D automated shimming methods require special, Pulsed Field Gradient (PFG) hardware, which is not available on majority of high-resolution NMR spectrometers. The modified technique, presented in this thesis uses the normal NMR hardware provided with the majority of high-resolution NMR spectrometers. The 3D shimming technique described was optimised for use with Varian UNITY INOVA spectrometers and successfully tested with both protonated and deuterated solvents. A method for calibrating linear transverse shim field gradients and correcting any non-orthogonality and imbalance of strengths is proposed. The effect of thermal convection on field mapping was observed and is reported here for the first time.