Date: Thu, 07 Oct 1999 08:26:17 -0400

Author: Gerald Zani

Subject: Re: Barkhausen

Post:

Below is some archived tap-l material about the Barkausen effect. I have one,
and I think that Steve Wonnell and Vacek Miglus have made them. After
reading
the discussions, I recommend that you take some soft iron, either welding rod
or iron nails. The best material is mu metal but that is not easy to get.
Use
thin magnet wire, about 28 gauge or so, and wrap about 1 hundred to 4 hundred
turns around the soft iron to act as a pick up coil. Put a BNC connector on
the ends of the magnet wire pick up coil. Connect the BNC to an audio amp.

Insert it into the core of a coil of large gauge wire that will supply a
changing external magnetic field. Slowly apply a current to the coil to
create
a B field. I would not try moving the soft iron in and out of a perm magnet.
Instead, change the B field by changing the current to coil. There is a
lot of
reading on this demo. It was heavily studied years ago. Go to Dick Berg's
site and find this demo and check what he lists for references. He prob
has 15
references to excellent articles.

There are some subtle tricks that can also be used, such as counter-winding
the
turns of your pick up coil?

you wrote:
>Hi,
> Someone just asked me to set up the Barkhausen Effect. Are there any
>tricks that I should know? I tried it with junk I have but my Bark didn't
>Hausen.
>
-----------------------------------------------------------------------

Date: Wed, 10 Mar 1999 16:50:53 -0500
From: Gerald Zani

Steve,

I made a Barkhausen demo three years ago. I cannot tell you why a tap
Produces such a large audio signal. But it was a real problem to the ear. It
made the demo very disturbing to perform because students would be listening
for the soft sound of the Brakhausen clicks but they would hear the loud tap.

I cured the problem the following way. Using thin magnet wire I wound about
400 turns around a core of short 3" long pieces soft iron from a welding rod.
The two ends of the magnet wire coil are input to the differntial inputs of an
audio amplifier. Hold this with a clamp inside the coil of a larger, high
current (about 8 amps max) surrounding coil. Changing the current through the
surrounding coil will provide the external magnetic field to the iron and the
pick up coil will amplify the clicks.

Increase and decrease the current to the surrounding coil to
produce a changing magnetic field through the soft iron. The domains inside
the iron core make the soft Barkhausen "clicks" and the 400 turn pick up coil
does not get tapped because nothing is moved. This arrangement eliminated the
need to move the soft iron into and out of the field of a permanent magnet.

Jerry


Steve wrote:
>
>Taps:
>
>I've just finished making a Barkhausen effect demonstration. I have a
>400-turn coil of wire clamped between the jaws of a permanent magnet, so
>that the coil axis is perpendicular to the magnetic field for convenience.
>The coils is connected to a stereo amplifier which is connected to a
>speaker, and I made three rods: steel, aluminum, and copper. The
>demonstration works fine: with the volume of the stereo crank up, so that
>a visible buzz (noise, I think) is heard, one can hear the clicking as the
>steel rod is inserted and moved; and there is no clicking when the other
>rods are used.
>
>Here's the catch. When I bump the aluminum or copper rods against the
>side of the coil, I hear a bump through the speaker. In fact, if I tap
>the coil with my fingers (no yoke at all in the coil), I hear the tapping
>through the speaker. The sound is roughly proportional to the strength
>with which I tap. What is causing this extraneous sound? I've got the coil
>pretty much clamped between the magnet poles...so the coil can't be moving
>very much with respect to the magnetic flux. Although I suppose I could be
>causing a high-frequency mechanical vibration that, though minute, induces
>an emf in the coil. Is this right?
>
>Steve W.


Date: Thu, 11 Mar 1999 13:30:11 -0500 (EST)
From: Steve Wonnell

Folks, here's some more details:

I've got a U-shaped permanent magnet--the Pasco variable gap
magnet EM-8641--and a small 400 turn coil of wire. I place the coil of
wire into the gap of the magnet, so that the axis of the coil
is perpendicular to the axis of the magnetic field:

XXXXX
XX XX X = coil
|||| X X |||| || = magnet
|| XX XX || B is pointing to the right or left
|| XXXXX || The coil axis is pointing in or out of page.
|| ||
|| ||
|| ||
|||||||||||||||||

I then close the gap on the magnet so that it clamps the coil into place.
So, I'm using the variable gap magnet as a vise. The coil is connected in
the phonogragh input of a stereo amplifier, and the output of the
amplifier is into a speaker that itself has a power amplifier. Then I
place things into the cavity of the coil, being careful not to touch the
coil. You hear a hum, due I think to the amplifier on account of the
volume being turned up so loud, plus an eerie clicking sound as
iron-containing materials are inserted or moved in the coil. You don't
hear any clicking sounds if aluminum or copper are placed in the coil.
An advantage of this setup is that the only movement or change
is the movement of the object inside the coil.

I haven't yet found a piece of solid iron...I used low-carbon steel from
the shop, a screwdriver, and a nail...all are loud, visible, and make
eerie sounds.

Originally, I tried Vacek's method below, except that at that time I
wasn't using the stereo amplifier, just a self-amplified speaker. I
picked up scratching noises whenever i rubbed the magnet against
iron...and also when I rubbed the magnet against any other metal!
I thought that might be eddy current phenomenon, except that brushing
the magnet against my fingernails also produced a brushing sound
in the speakers. I think now that I didn't have the sensitivity to pick
up the Barkhausen clicks, but more than enough to pick up these
extraneous sounds...which I'm still a bit baffled by.

Steve

Date: Thu, 11 Mar 1999 13:07:48 -0500
From: Vacek Miglus

Steve,


I am baffled by your location of the magnet. When we do this demo the coil
is just mounted in a stand without any magnet. An iron wire is placed in
the coil and held there with your fingers. Then with a magnet in the your
other hand you approach the wire and hear a "whoosh" from the speaker.
Reverse the magnet and again you hear a whoosh as the magnetic domains
realign.

Of course this will not work with the cooper wire you then use for
comparison.

And also if the iron wire is aligned in one direction moving the magnet
back and forth without reversing the direction also does nothing.

I have found that iron and nickel work well, while steel is just barely
worth doing.

Vacek




Date: Thu, 11 Mar 1999 13:27:30 -0500
From: rueckner@fas.harvard.edu (Wolfgang Rueckner)

No, the sound will not go away. The microphonics will still be picked up
(Earth's field). I might also add, the smaller a diameter you use, the
more "grainy" the effect. That is to say, the sound for thick wires is a
"whoosh" whilst that of a very thin wire is literally discreet "clicks" as
individual domains flip over. Wolfgang


X-Sender: rueckner@pop.fas.harvard.edu



Date: Thu, 11 Mar 1999 16:21:07 -0500
X-PH: V4.2@dark.brown.edu
To: tap-l@listproc.appstate.edu
From: rueckner@fas.harvard.edu (Wolfgang Rueckner)
Subject: Re: More non-Barkhausen effects
Reply-To: tap-l@listproc.appstate.edu
Sender: owner-tap-l@listproc.appstate.edu


>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


Date: Thu, 11 Mar 1999 13:41:02 -0700
X-PH: V4.2@dark.brown.edu
From: Steve Anderson
Subject: RE: More non-Barkhausen effects
To: tap-l
Reply-to: Steve Anderson


X-Mailer: QuickMail Pro 1.5.3 (Mac)



X-MIME-Autoconverted: from quoted-printable to 8bit by
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Sender: owner-tap-l@listproc.appstate.edu


Reply to: RE: More non-Barkhausen effects
> 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.
>

This sounds like it to me. I have a Faraday caged room, but that is the only
place where you can get away from the ubiquitous 60 Hz humm. In a doubly
amplified pick up coil this doesn't sound surprising. Maybe its an ac material
permeability checker?
When I measured the magnetic fields from monitors it had to be done in the
shielded room or the normal power line ac fields were 100 - 1000 times more
than those fields.


Steve Anderson, ET III "B here always"
Physics & Astronomy Dept.
Sonoma State University
707-664-2330 fax 664-3012
steve.anderson@sonoma.edu

Date: Thu, 11 Mar 1999 16:47:54 -0500 (EST)
X-PH: V4.2@dark.brown.edu
From: Steve Wonnell
X-Sender: wonnell@eta
To: tap-l@listproc.appstate.edu
cc: Steve Wonnell
Subject: Re: More non-Barkhausen effects




Reply-To: tap-l@listproc.appstate.edu
Sender: owner-tap-l@listproc.appstate.edu





Two oppositely wound coils: that's an idea.
I'm also coming to the conclusing that my stereo amplifier is
too noisy.

I'm no longer sure that I'm observing the Barkhausen effect.
I hear a "shhhhhhhhhhhh" sound as I insert a nail or steel
rod into the coil, along with an occasional clicking sound.
(This is with the coil inside the magnetic field).
If I move the rod or nail around in the coil, I'll hear other
whoosh or shhhhh sounds. However, if I hold the rod in the
coil, and rotate the rod around its axis, without moving the
axis, I don't hear any sounds. It seems to me that I ought
to hear as much as an effect as if I move the rod back and
forth inside the coil. Has anyone had this experience?

Steve


On Thu, 11 Mar 1999, Wolfgang Rueckner wrote:

> >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
>

Date: Thu, 11 Mar 1999 16:52:41 -0500 (EST)
X-PH: V4.2@dark.brown.edu
From: Steve Wonnell
X-Sender: wonnell@eta
To: Steve Anderson
cc: tap-l , Steve Wonnell
Subject: RE: More non-Barkhausen effects




Reply-To: tap-l@listproc.appstate.edu
Sender: owner-tap-l@listproc.appstate.edu



I tried putting the coil, but not the whole apparatus, inside a faraday
cage with 1/4" grid (good enough for the radio in a cage demo for the
lowest radio frequencies). No change...I think the background noise is
partly due the amplifier. In fact, there seems to be a small potential
difference at the back of the amplifier...perhaps driving a small current
through the coil...adding the yoke changes the load and hence the current?

I sure wish I had a Faraday caged room. Steve, are your lights, computer,
and other stuff outside of your cage?

Steve W.


On Thu, 11 Mar 1999, Steve Anderson wrote:

> Date: Thu, 11 Mar 1999 13:41:02 -0700
> From: Steve Anderson
> To: tap-l
> Subject: RE: More non-Barkhausen effects
>
> Reply to: RE: More non-Barkhausen effects
> > 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.
> >
>
> This sounds like it to me. I have a Faraday caged room, but that is the
> only place where you can get away from the ubiquitous 60 Hz humm. In a
> doubly amplified pick up coil this doesn't sound surprising. Maybe its
> an ac material permeability checker? When I measured the magnetic
> fields from monitors it had to be done in the shielded room or the
> normal power line ac fields were 100 - 1000 times more than those
> fields.
>
>
> Steve Anderson, ET III "B here always"
> Physics & Astronomy Dept.
> Sonoma State University
> 707-664-2330 fax 664-3012
> steve.anderson@sonoma.edu
>
>


***********************************************************************
Steven K. Wonnell
Physics and Astronomy Department E-Mail: wonnell@pha.jhu.edu
Johns Hopkins University Phone: (410) 516-4696
3400 N. Charles Street Fax: (410) 516-7239
Baltimore, MD 21218-2686 Office: 403 Bloomberg (x0544)


***********************************************************************




Date: Thu, 11 Mar 1999 17:47:59 -0700
From: Jerry DiMarco

Sounds to me like your steel objects have been magnetized. What
happens if you magnetize them strongly, or demagnetize them?

>I tried putting the coil, but not the whole apparatus, inside a faraday
>cage with 1/4" grid (good enough for the radio in a cage demo for the
>lowest radio frequencies). No change...I think the background noise is
>partly due the amplifier. In fact, there seems to be a small potential
>difference at the back of the amplifier...perhaps driving a small current
>through the coil...adding the yoke changes the load and hence the current?

Is the cable going into the phono input shielded? If not, that is a
likely source for the hum...

Jerry


Date: Fri, 12 Mar 1999 10:38:26 +0000
From: John Malone


Hi Steve,
We have a Barkhausen effect demo which I'm very pleased with. We have
a coil (it was alread wound, so I don't know how many turns it is, but
it seems to be many--maybe about like yours). I have it fed
differentially into a microphone mixer, and the output of the mixer is
fed into any sound system. I have three rods (steel, copper, and
aluminum) which I can place into the coil and clamp down with a
non-ferrous clamp. I insert the steel bar into the coil, and then I
bring a strong permanent magnet up to the bar and rotate it so as to
bring first one pole and then the other near the end of the bar. This
orients the magnetic domains in the steel bar first one way, and then
the other. You hear a white-noise-like sound from the speakers as the
domains in the steel bar flip and generate currents in the coil.
Doing this same thing with the copper or aluminum bars inserted into
the coil gives no such sound.
Connecting the coil into the mixer like a low impedence microphone
(differentially, with a shield) seems to help reduce induced noise, and
the mixer gives lots of gain.
I hope this helps.
John Malone
Lecture Demos
Dept. of Physics
Univ. of Virginia



********************************************************
Gerald Zani
Lecture Demonstration Technician
Dept. of Physics #1843
Brown University Phone: (401) 863-3964
Providence, RI 02912 Fax: (401) 863-2024

http://www.physics.brown.edu/users/staff/zani/index.html
http://www.physics.brown.edu/Studies/Demo/

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