Potential for Square Wave Transmitters in Surface NMR

Abstract

An alternative transit strategy for the surface nuclear magnetic resonance technique is presented. The current waveform traditionally used for excitation in surface NMR is described by a sinusoid oscillating at the Larmor frequency for a finite duration (20-40 ms). However, in principle any current waveform whose spectrum contains non-zero energy at the Larmor frequency may be used to perturb the subsurface magnetization. We investigate the utility of square waves and triangle waves for surface NMR excitation. We aim to exploit: 1) the potential to adapt existing time domain electromagnetic (TEM) transmitters for application in surface NMR, and 2) the potential to allow for modulation of the current amplitude during a single pulse independent of the instantaneous transmit frequency. Although a square wave transmitter represents a less efficient use of power compared to a sinusoid, it offers the potential for a single transmitter to be used to conduct both the surface NMR and TEM experiments. Additionally, the use of square waves allows pulse width modulation to be exploited to provide independent control of the current amplitude throughout the pulse improving flexibility in the design of current waveforms feasible in surface NMR.