A Miniaturised NMR RF Probe Design with External Field-locking Channel

Abstract

Temperature drift is an important factor affecting the measurement accuracy of desktop NMR spectrometers, and adding a field-locking coil to the probe to achieve field-frequency interlocking is a common means of suppressing temperature drift. In this paper, a dual-channel miniaturised RF probe with an external field-locking channel is designed based on a laboratory compact Halbach magnet. The coil diameter, height, number of turns, turn spacing and enamelled wire radius were optimized based on the solenoid structure. The optimum solenoid size was obtained with an enameled wire radius of 0.4 mm, a coil diameter and height of 8.2 mm, a turn spacing of 1.6 mm and a number of turns of 5. Based on the simulation results, the detection and field-locking coils were fabricated, and tested in conjunction with the peripheral circuitry. The results show that the crosstalk between the two coils is low, the signal-to-noise ratio of the detection channel is above 50 and the signal-to-noise ratio of the locking channel is above 20. Final field locking experiments were performed and the frequency drift of the overall system after equipping the locking field was approximately 0.2 ppm/h (1 ppm=10-6), verifying that this probe design can be applied in compact Halbach magnet-based NMR analysis facilities.

Keywords

• nuclear magnetic resonance (nmr)
• coil optimization
• dual-channel probe
• locked field