The Illustration below schematically describes the processes by which spin system evolves under the RF perturbations starting from the thermal equilibrium situation for the spin system. The magnetization vector component values are indicated for a thernmal equilibrium situation. An effort is also made out to sketch out as to what happens under a single 90 degree RF pulse before and after the pulse and how to describe this situation in terms of the strength of perturbation and duration of perturbation. With these variables what are the conditions for the detectability of the magnetic resonance. the terminology of weak RF field and strong Rf fields with the time scales related to the characteristic spin-lattice and spin-spin relaxations are all inclusive in this scheme. Thus this would be a handy one-page sketch for revising the basics of magnetic resonance after going through the contents of this course and having studied through to understand the effects on spin system
Using one of the Mathematical computer package "Mathcad" the FID function has been generated and this simulated FID time-domain signal has been subjected to FT mathematically to get a frequency domain spevtrum and it is also displayed. The time domain and the frequency domain signals have been tabulated in digitized form for verification excercises during the class room work.