Listening to Magnetism - Barkhausen e... Science Toys | Science Blog | Log Out | Topics | Search
My Toys | Energy | Moderators | Register | Edit Profile

Scitoys Message Board » I am having trouble building one of the toys » Listening to Magnetism - Barkhausen effect « Previous Next »

Author Message
Top of pagePrevious messageNext messageBottom of page Link to this message

John Harrell (John_h)
New member
Username: John_h

Post Number: 1
Registered: 3-2009
Posted on Sunday, March 22, 2009 - 10:58 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Hi_

I can't get the distinct gieger counter link clicks as described and shown on the video clip. I've tried to faithfuly duplicate the set up - 2-1/2" bolt, 60' magnet wire, Radio Shack amplifier, 0.7x.03.5 inch neodymium magnet (except I don't have a goat). I get a whoshing sound as I move the magnet very slowly or rapidly near the bolt, but not distinct gieger counter clicks. I wound another shorter fatter coil with a 5/16" bolt; still just whooshes. I went out and bought a hardened grade 8 bolt, nut and washers thinking different steel would give diferent results; still just wooshes. The sound is rushing whoosh - perhaps the 'whoosh' is made up a 1000's of 'clicks', but no matter how slowly I move it, it just whooshes.. The setup is sensitive, holding the magnet close it's microphonic, i.e., it works like a microphone if it's spaced off the bolt with something with a little give like some cardboard - so I've created a microphone, but no Barkhausen effect. Ideas?


I'm a big fan of this fantastic site!

regards,
John H
Top of pagePrevious messageNext messageBottom of page Link to this message

Theresa Simmons (Theresa)
Senior Member
Username: Theresa

Post Number: 111
Registered: 1-2008
Posted on Monday, March 23, 2009 - 11:13 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You got the effect.
The particular sound you get will depend on the size of the magnetic domains,
and that will depend on what your metal is made of, and how it was processed
and tempered. If the grain size is small, you get a higher frequency hissing
sound.
Top of pagePrevious messageNext messageBottom of page Link to this message

John Harrell (John_h)
New member
Username: John_h

Post Number: 2
Registered: 3-2009
Posted on Tuesday, March 24, 2009 - 10:49 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Thanks. Any advice on finding steel that will give clicks? I've tried a variety of bolts of different hardnesses. I think clicks would be a cooler demonstration - the whooshing isn't as dramatic.

I'm thinkin' of maybe winding a coil on a bobbin with a hole so I can try a variety of metals.

regards, John H
Top of pagePrevious messageNext messageBottom of page Link to this message

JimS (Jimmy101)
Junior Member
Username: Jimmy101

Post Number: 7
Registered: 2-2007
Posted on Wednesday, March 25, 2009 - 11:00 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You might try using a lower grade of steel, heck, iron might be your best option. Steels tend to have varying degrees of ferromagnetism. Often, the better the steel the less it is attracted to a magnet. Many high grade steels are nearly paramagnetic and are only weakly attracted to a magnet. You can test this with a magnet and a collection of iron/steel objects. Nails are generally pretty low grade steels and are usually very strongly attracted to a magnet. High quality kitchen knives are generall much higher grade steels and a really good knife is often only weakly attracted to a magnet.

I discovered this affect when building the Scitoys Gauss rifle. I purchased some high grade (type 302 stainless) steel ball bearings and then discovered they were only weakly attracted to the magnets. I then acquired some chrome steel (surface chromed, the core is much lower grade steel) ball bearings that were much more strongly attracted to the magnets.

So, rummage around and find a hunk of actual iron instead of steel, or perhaps use a large nail or some other low grade steel. One possibility for low grade steel (besides nails) would be a hunk of rebar. Your local hardware store might have one or two foot long lenghts of 1/2" rebar (used as landscaping spikes) for a buck or so each.
Top of pagePrevious messageNext messageBottom of page Link to this message

Theresa Simmons (Theresa)
Senior Member
Username: Theresa

Post Number: 112
Registered: 1-2008
Posted on Wednesday, March 25, 2009 - 11:48 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

To assist in determining which metals give you the best sound,
wind the coil on a hollow tube. Then you can take it (with the
earphone and magnet) to a hardware store and insert various
bolts and nails and rods into it to find the ones that have nice
loud hisses, and the ones that click, and some in-between for
variety.

Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action:
For those who have trouble spelling, the Google Toolbar (included in the Google Pack) can check and correct the spelling in your posts on this message board and others.

Renewable Energy

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration