Magnet:

It is the heart of all types of NMR spectrometers. The sensitivity and resolution of a spectrometer critically depends on the strength and quality of the magnet. Since sensitivity and resolution both increase with field strength, it is advantageous to operate the instrument at highest possible field strength. In addition, the field must be homogeneous, uniform and reproducible. Three types of magnets have been used in NMR spectrometers; these are permanent magnet, electromagnet and super conducting solenoid.

Permanent magnets with strengths that need an oscillator frequency of <100 MHz for bare protons have been used in commercial continuous wave spectrometers. These are very temperature sensitive and require extensive cooling and shielding. However, these are not ideal for extended periods of data accumulation because of field drift problems. The electromagnets are now rarely used in the NMR instruments. The modern high resolution spectrometers use superconducting magnets of T or above. These are simple, small sized and produce high field strength besides having low operating cost. It is very essential that stability of a magnet is maintained at all costs.