Free induction decay

This non-equilibrium magnetization can be created generally by applying a pulse of radio-frequency close to the Larmor frequency of the nuclear spins.

If the magnetization vector has a non-zero component in the XY plane, then the precessing magnetisation will induce a corresponding oscillating voltage in a detection coil surrounding the sample.

Particularly if a limited number of frequency components are present, the FID may be analysed directly for quantitative determinations of physical properties, such as hydrogen content in aviation fuel, solid and liquid ratio in dairy products (time-domain NMR).

[3] Advances in the development of quantum-scale sensors, particularly NV centres, have enabled the observation of the FID of single nuclei.

In this special case, also the measurement itself contributes to the decay as predicted by quantum mechanics.