Containing electromagnetic fields??

[Guest shroomy01]

Ok i have a box with essesntially some VERY POWERFUL magnets inside and when i have to move it, it attracts of coarse metal things towards it and i need to know if there is a substance (Cheapish) that will keep the magnetic field stay inside the box.

[YT2095]

putting them in a steel box will lessen this effect on the outside.

you`ll not stop it entirely though, only distance will do that to a level of being un-noticable.

[5614]

There are certain metals which have magnetic field blocking properties.

 

Look up about antiferromagnetic materials (antiferromagnetism) and mu metals... I believe manganese oxide and look at the table on this site:

http://digilander.libero.it/paeng/what_mu_metal.htm

(scroll down a little, there's a table in the middle of the page.

[swansont]

If it's cheap you want, soft iron is the way to go, or steel as YT said. (mu metal isn't cheap)

[JohnB]

Shroomy, I can't help with your question but I have to ask. Have you been to Relto lately?

[YT2095]

here`s a cheap and cheerfull way to do it, get 2 biscuit tins (they`re usualy plated iron) make sure one fits inside the other with a gap of about half inch all around.

you could use polystyrene or wire wool or even cotton wool to maintain this even gap between the 2 tins.

put your magnets inside the inner tin, and you shouldn`t have any problems again

 

btw, with regards to the Thread Title, it`s ordinary magnetism, not ELECTROmagnetism

[swansont]

here`s a cheap and cheerfull way to do it' date=' get 2 biscuit tins (they`re usualy plated iron) make sure one fits inside the other with a gap of about half inch all around.

you could use polystyrene or wire wool or even cotton wool to maintain this even gap between the 2 tins.

put your magnets inside the inner tin, and you shouldn`t have any problems again

 

btw, with regards to the Thread Title, it`s ordinary magnetism, not ELECTROmagnetism [/quote']

 

But of you ground the conductor you have a faraday cage, so you take care of the electric fields, too, and much of the EM radiation that has a wavelength longer than that inter-atomic distances. Except for thermal blackbody radiation, which will be present inside.

[YT2095]

his OP read to me that he was using permanent magnets, and that no oscillation was present to require a grounded cage.

 

I thought his problem was having these strong magnets in a box and if he moved it around by metals prone to magnetic attraction, he`de have to pull them off (pesky paperclips!). a double lined tin container would disperse this field effectively.

[mmalluck]

By blocking a magnetic field, what you're really doing is giving the magnetic lines of force a more attractive path to travel thru rather than random stuff outside of the box.

 

Wrapping the box in any ferric material should help. You want a material with a high permability and a decent cross-sectional area. It's a lot like burying your box within a transformer core.

 

Mu-metal has a very high permability (hencer being called mu-metal) that can take a lot of magnetic field before the material becomes saturated (you can only cram so much magnetic field within a metal object, when it becomes saturated, additional magnetic field has to travel outside of the material). Mu-metal can kind of suck though because it doesn't do well with too much bending. If you bend it too much you destroy the magnetic domains within the material, it's permability falls, and it becomes saturated more easily.

 

The biscut tin idea that YT is talking about adds an air gap to our magentic path. Air by definition is free space and can not saturate. Most of the magnetic field will bunch up around this gap as it leaves one piece of metal and heads towards the next. This can be useful

[Douglas]

I've used mu-metal in the past for magnetic shielding, though I not an expert on it's properties. But it seems to me that if mu-metal is a good magnetic shield and has a high permablility, then the gap in YT's boxes should be filled with high permability toroid cores.

[YT2095]

the gap is simply there to provide the distance and as it`s something about power being halved over the sqr of the distance and stuff, as WELL as providing room for the force concentrations leaving the internal box to be reabsorbed in a more diffuse pattern leaving a near even field disipation on the outer box.

 

nothing fancy (that I know of) I just know it works and that`s my logic

[Douglas]

Yeah, the box within a box idea should work.

 

Talking about magnetic fields (in this case electro magnetic fields), a friend/co-worker of mine built a "field finder", he was selling them to people who worried about homes built near high voltage power lines or computer displays, TV screens etc. As I recall, he measured the electro magnetic field in milligauss in the ELF VLF bands

 

Edited to add....it was also useful in finding electrical wires in the walls of your house.

[YT2095]

It does work, that`s why I presented it as a sollution (I`ve done it)

 

AFAIK those type of detectors only work with AC or pulsed DC (I use something similar here too, for different reasons).

 

a static feild without motion of the device or a magnetometer is practicaly useless tho

[Douglas]

yeah, it only works with AC, but if you rotate the device rapidly, it'll pick up the earths magnetic field, though you'd probably have to rotate it at least 30 cycles per second for it to be accurate. I think the bandwidth of his device was around 30 Hz to 100 KHz

[swansont]

Mu-metal has a very high permability (hencer being called mu-metal) that can take a lot of magnetic field before the material becomes saturated (you can only cram so much magnetic field within a metal object, when it becomes saturated, additional magnetic field has to travel outside of the material).

 

Actually, as the mu gets higher, it saturates more easily, because you are concentrating the field more.

[YT2095]

just a quicky; does the `mu` in Mu metal mean Muons at all?

 

a yes/no ansa will suffice, then we can get back to topic

[5614]

No.

 

Mu as in the greek letter μ

 

(It's the symbol for magnetic permeability)

 

========

 

Mu metals would do the job very well, however they are expensive, which is why it is questionable whether they are worthy of purchasing.

 

[edit] so as not to make another post, the reply to the post below is that yes, it is the same letter.... but 'micro' as you put it is also the letter mu which is also used for magnetic permeability

[YT2095]

Hmmm... μ = Micro to me, but never mind, back to topic now

[swansont]

Mu metals would do the job very well' date=' however they are expensive, which is why it is questionable whether they are worthy of purchasing.

[/quote']

 

Also, as I mentioned earlier, high mu materials saturate easily, so if you are trying to shield a strong magnet, you want a lower permeability anyway, and/or a thicker material, and probably multiple layers.

 

As an example, the shields I designed use 1/16" of one type of mu-metal, and IIRC that is a little more than halfway to saturation in a 1 gauss field (basically the earth's field, rounded up for safety margin)

 

If anyone brought even a weak "real" magnet (i.e. several gauss) nearby, it would saturate the shields. And I would torture them.

[Douglas]

Yeah, µ is the prefix "Micro", also (as said) "permeability", and "amplification factor" from the old vacuum tube days.

[YT2095]

and "amplification factor" from the old vacuum tube days.

 

ah yes! Happy days )

[mmalluck]

Actually, as the mu gets higher, it saturates more easily, because you are concentrating the field more.

 

err, okay, I stand corrected.

[Douglas]

err, okay, I stand corrected.

Since you led me astray, I have to apologize to YT for mentioning putting high permeability toroid cores in the space between the two cans.

[reverse]

Ok i have a box with essesntially some VERY POWERFUL magnets inside and when i have to move it, it attracts of coarse metal things towards it and i need to know if there is a substance (Cheapish) that will keep the magnetic field stay inside the box.

 

oh yes....it's called air.

 

put your box inside a bigger box with expanded foam spacers.

 

fields are pathetic at distance. :

[Guest shroomy01]

 

btw' date=' with regards to the Thread Title, it`s ordinary magnetism, not ELECTROmagnetism [/quote']

 

Not What im Doing

 

Oh and thanks for all these ideas for it these should make it easier and cheaper