A Portable NMR Spectrometer With a Probe Head Combining RF and DC Capabilities to Generate Pulsed-Field Gradients

Abstract

Portable nuclear magnetic resonance (NMR) spectrometers are used in various scientific fields. A vast number of applications are suitable for low-field permanent magnets. However, most of these systems lack the ability of pulsed-field gradients as these require cumbersome additional hardware. We herein report an NMR probe head that incorporates a radio frequency (RF)-coil equipped with pulsed-field gradient capabilities in a single center-tapped solenoid. We developed a circuitry allowing for the application of direct currents without disturbing the RF reception capabilities. Furthermore, we present a System-on-Chip-based NMR spectrometer. Combined with the NMR probe head, it represents a versatile low-cost system capable of field gradient generation. The probe head is characterized in terms of scatter parameters, quality factor, and transversal field homogeneity. We exhibit simulation data of the field gradient and present the required external circuitry. Experimental results show further the dephasing capabilities of the gradient and give insights into the spatial shape. Finally, the system is applied for the mapping of J-couplings in 1-butanol via zero-quantum coherences. A theoretical analysis of the pulse sequence is given for a homonuclear two-spin system. The experimental results demonstrate the potential use of this setup.