Radiofrequency transmitter in an NMR experiment: Is there an involvement of (electromagnetic) radio wave?
I finally asked an NMR spectroscopist who was the editor of the Journal of Magnetic Resonance and knows the inside out of NMR spectrometers. He sent a scanned copy of Hoult's paper from 1989. The title explains it all "The magnetic resonance myth of radio waves
." Surprisingly very low citations (15). It is amazing how much nonsense we have been fed with radio waves absorption. Sometimes innocent student questions on these forums can lead to introspection.

Here is the article Radio Waves Myth in NMR. Karl will like it.

The conclusion is that there is no involvement of radio waves, neither in absorption nor in emission (of course). The emission process is easier to understand but the transmission process seems to have confused even the experienced spectroscopists and more MRI people.

This is from another paper of Hoult. "The Origins and Present Status of the Radio Wave Controversy in NMR"


  The origins, history, and present status of the controversy
  surrounding a quantum description of the NMR signal as being due to
  radio waves are traced. With the Principle of Relativity and Coulomb’s
  Law as formal starting points and the minimum of mathematics needed
  for understanding, the derivation of a classical electromagnetic
  theory of signal reception is first given. The agreement between that
  classical theory and a recent NMR experiment is then presented,
  leading to proof that, except for the highest field imaging
  experiments, there is no significant contribution of radio waves to
  the signal.