> > I am looking for a reliable way to detect water,
> > although the sensor is covered with a layer of dirt,
> > oil film, etc.  And the water may be pure or contaminated.
>
> Nuclear Magnetic Resonance perhaps?

Have you worked with NMRI?

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

He said it had to be small...  That implies a low magnetic field,
considering that the magnets I work with weigh in at 17 metric tonnes, and
they're only .35 Tesla, though the gap is fairly large, and for this, your
gap could be quite small.  The higher the field strength, the higher the
output signal.  I assume a permanent maget is the only practical solution
for this application.

The field strength directly affects the frequency of the of the output
signal.  A low field strength means a low frequency, low amplitude signal.
I don't think that anyone makes high kHz low noise figure (>.1dB) high
sensitivity transistors.

The really big question is if there are any ferro-magnetic objects in the
surrounding area.  Anything ferromagnetic would cause some trouble in
keeping the magnet where it was supposed to be.

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

Anyone know where I can get 1 Tesla bar magnets? ;o)

--Brendan

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