Date: Thu, 11 Mar 1999 16:21:07 -0500

Author: rueckner@fas.harvard.edu (Wolfgang Rueckner)

Subject: Re: More non-Barkhausen effects

Post:

>I just discovered another non-Barkhausen effect that's been
>bothering me.
>
>When soft steel is placed into the pickup coil...and with no external
>magnetic field (except that of the earth as Wolfgang pointed out), there
>is an increase in humming. This happens even if the steel isn't moving. I
>think this must be some sort of "yoke" effect...it doesn't happen if
>copper or aluminum is placed in the coil. In other words, it's sort of as
>if there's some sort of very tiny induced current in the loop...from
>electromagnetic fields maybe? and the insertion of the yoke increases the
>induction.
>
>I need to check this out further.
>
> Steve W.


We've used two coils physically together, but wound in opposite directions,
and wired in series, for the pick-up coil. This configuration will cancel
out emf's produced by environmental AC; i.e., it greatly reduces the AC
pick-up. Wolfgang

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