Many thanks for the messages (on 'RF-radiation') - I am looking forward to more
comments and further discussion!
1. There are answers sort of supporting the use of 'electromagnetic waves' for
describing NMR excitation (where there is a magnetic field there is an electric
field), to those saying that probes are no 'antennas'. The concepts near and far
fields (electric as well as magnetic) seems to be what makes the difference. In
the near field there is 'no coupling' between the magnetic and electric fields
and the probes are 'designed' to produce zero electric oscillating field (to
minimize sample heating) and maximum magnetic oscillating field inside the
probe.
My understanding (based on some comments and Hoult's article entitled "Magnetic
resonance myth of radio waves") is that true 'electromagnetic radiation' is only
present in the far field (several wavelengths from the antenna) where the
electric and magnetic components are 'closely coupled' (phase and magnitude are
fixed). In contrast, in the near field the term 'induction' is more appropriate
(cf., 'nuclear induction' which was used by the early investigators).
2. There is a lot of evidence for disturbances from local radio stations and
transmitters. The most vicious type appears to be erratic function of the field
lock. One solution is to use a Faraday cage.
3. My original question arose from the popular use of 'radio wave photons' and
'electromagnetic radiation' (cf., visual spectroscopy) for exciting nuclear
spins. Not entirely correct then. Finally, I apologise for my ignorance in the
above matters.
73, Peter
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