_ wrote:
I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

The only practical effect would be to isolate the steel from the magnets
for as long as the magnets move in relation to the aluminum. Any
paramagnetic effect of the aluminum will be negligible, if I'm even
correct in remembering that Al is paramagnetic at all. Strong magnets
working against aluminum _will_ generate eddy currents as a consequence
of motion, and you can use that to generate drag. Strong magnets
working against steel will generate an attractive force, eddy currents,
and some hysteresis force that'll work even when the relative motion has
ceased.

Without knowing why your clutch uses steel instead of something else,
and how you propose to mount the aluminum, I couldn't say what the
effect will be.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" gives you just what it says.
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