> Cool idea, but it doesn't seem practical.  It's possible that for simply
> detecting the presence of some water it would be far simpler than actual
> NMRI, but I think the field strength wouldl be a concern

[snip]

> Actually, I guess this could be viable, as long as you could get the field
> strength high enough.

Allow me to correct myself.  I just mentioned the idea to the resident
physicist, and we discussed it a bit.

Apparently, this scheme is used in oil wells (which I didn't know).  The
operating frequency for those is around 2MHz, which implies something around
0.05T.  And I was forgetting that to test the amplitude of the signal, you
really don't need to look at the noise figure much.

The scheme that would work well here is something called "inside-out NMR,"
where the magnet, transmitter and reciever coils are all mounted outside the
tank.  I'm not sure on this, but I think that a rare-earth diske drive
magnet should be getting close to the required field strength.  And if you
did it really well, you should be able to use the magnet to hold the probe
onto the tank ;o).

I know a bit about NMRI reciever coil construction, so if you want some
suggestions about how to build the coils... I can probably help out a little
unless someone else here is more experienced :o)

--Brendan

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