Characterization of a PXIe based low-field digital NMR spectrometer

A low-field nuclear magnetic resonance (NMR) instrument is an important tool for investigating a wide variety of samples under different conditions. In this paper, we describe a system constructed primarily with commercially available hardware and control software, capable of single-pulse NMR experiments. Details of the construction of the main B₀ magnet are also included. The operating frequency for demonstration is 460 kHz (10 mT), however, the range of the hardware spans 700 Hz (16 μT) to 25 MHz (0.6 T). Tip angle optimizations are used to find the most narrow usable pulse width for this configuration, and the T₁ of water is measured by single-pulse-saturation-recovery (SPSR) to demonstrate the potential for this system as a relaxometer. Discussions of resonator construction and efficiency, power requirements and programming strategies that would increase the utility of this system are also included. Construction of any low-field NMR system will depend on experimental interests, budget and engineering resources. A survey of other low-field NMR systems from the literature is included to aid the novice or experienced magnetic resonance scientist in consideration of how a low-field spectrometer could be constructed and used in the lab.