Mapping and estimating magnetic field variations due to a one-sided magnet

Abstract

Homogeneous magnetic fields are desirable in nuclear magnetic resonance (NMR) experiments for detecting the presence of nuclear species accurately. However, some applications such as oil well logging [1], perform NMR experiments in inhomogeneous magnetic fields with lower spatial accuracy [2–5]. Achieving improvements in spatial features requires a better understanding of the field profiles in such inhomogeneous fields. Therefore, in this paper, the magnetic field variations introduced due to a one-sided magnet are simulated and studied. A magnetic and a non-magnetic object are placed in the near field of a permanent magnet. Sections of the magnet's near-field region depicting the field decay and variations along different directions are analyzed. Prior NMR measurements do indicate that minor field variations affect the response of the magnetic moments from region to region leading to undesirable peak broadening in the frequency spectrum. However, field variations can be advantageous if the magnetic field profile is pre-mapped and changes in field profiles by placing known nuclei are pre-estimated. Pre-estimation would lead to a improved understanding of spatial resolution. This technique would also be useful for medical imaging purposes where different methods are utilized to obtain improved spatial resolution and contrast between different tissues/matter.