The Earth's Field Nuclear Magnetic Resonance (EFNMR) apparatus consists of three parts.
Conventional high field NMR instruments require an extremely uniform magnetic field for polarization of nuclear spins and the detection of the resultant magnetization.
It is difficult and expensive to make a magnetic field of the required homogeneity (<< 1 ppm in some cases) and so sample sizes are usually quite small. However because the polarization and detection fields are large the resulting signal to noise ratio (S/N) can also be large. EFNMR works because detection takes place in the highly uniform Earth's magnetic field. This means that large samples can be used - partially compensating for the very low detection field. To improve the initial magnetization, a relatively crude electromagnet with a field about 35 times larger than the Earth's field is used to polarize the sample.