Is Mu-Metal the Solution for High Permeability Applications?

[Hami Hashmi]

If you had a box made of mu-metal and and a magnetic material inside the box, then took an insulated wire and wrapped outside the mu-metal box and applied a current, then applied a magnetic field outside the box, which one would magnetize the mu-metal, even for a brief amount of time? Also, if the current outside mu-metal will magnetize it, would applying an insulator on top of the mu-metal help?

Also, if mu-metal has such a high permeability, why isn't it used in applications where high permeability is required, like electric motors?

 

[Vanadium 50]

Hami-

It's very hard to help you. You say you understand Maxwwell's equations, but if you did, couldn't you solve this yourself? As it is, I am a bit confused by the exact geometry you are describing (the title seems to contradict the text), but you of course wouldn't be. Also, you have multiple messages that seem interrelated, leaving us to guess exactly what you are trying to accomplish.

 

[berkeman]

As a side note, your thread title does not seem to track what you are asking in your post...

Current applied to mu-metal

In your post questions below, there is no current "applied" to the mu-metal itself...

If you had a box made of mu-metal and and a magnetic material inside the box, then took an insulated wire and wrapped outside the mu-metal box and applied a current, then applied a magnetic field outside the box, which one would magnetize the mu-metal, even for a brief amount of time?

Both magnetic field sources cause B and H fields in the mu-metal box.

Also, if the current outside mu-metal will magnetize it, would applying an insulator on top of the mu-metal help?

Help what? The intensity of the magnetic fields in the mu-metal? If that's what you are asking, the answer is No. Can you say why? (think distance...)

Also, if mu-metal has such a high permeability, why isn't it used in applications where high permeability is required, like electric motors?

Mu-metal materials are useful for shielding applications because they have such a high mu value, so they attract magnetic fields more than low mu materials (and can be used to "guide" those fields around whatever is being shielded). However, the tradeoff with high mu materials is that they saturate sooner, so they are not able to handle as high an energy density as comparatively lower mu (but still moderately-high mu) ferrous materials.

 

[berkeman]

As an addition, search on "netic" and "co-netic" high-mu metal shielding materials That will give you additional insights into the saturation characteristics of high-mu metals.

 

[Hami Hashmi]

A current produces a magnetic field, if a current was applied around mu-metal then a magnetic field would be produced and the mu metal would draw the magnetic field into itself, is that right? But soft iron enhances the field, and both of them have high mu and low solubility. So what is the difference? And metglas has a much higher mu that mu-metal so why isn't it used in shielding applications?

 

[Hami Hashmi]

And @Vanadium 50 I'm sorry if there was any misunderstanding, but i don't understand maxwell's equations. So I wanted to ask someone who does understand so i could get an answer to my question.

 

[Hami Hashmi]

As a side note, your thread title does not seem to track what you are asking in your post...

In your post questions below, there is no current "applied" to the mu-metal itself...

Both magnetic field sources cause B and H fields in the mu-metal box.

Help what? The intensity of the magnetic fields in the mu-metal? If that's what you are asking, the answer is No. Can you say why? (think distance...)

Mu-metal materials are useful for shielding applications because they have such a high mu value, so they attract magnetic fields more than low mu materials (and can be used to "guide" those fields around whatever is being shielded). However, the tradeoff with high mu materials is that they saturate sooner, so they are not able to handle as high an energy density as comparatively lower mu (but still moderately-high mu) ferrous materials.

Ok thanks but my question was that if you wrapped an insulated wire around a box of mu-metal (like an electromagnet but the inside is hollow) and had a magnetic material inside the box, then applied a current through the wire, would there be a magnetic field outside or inside the box? Would the mu-metal be magnetized from the current like soft iron or would it draw the magnetic field into itself?

 

[berkeman]

Ok thanks but my question was that if you wrapped an insulated wire around a box of mu-metal (like an electromagnet but the inside is hollow) and had a magnetic material inside the box, then applied a current through the wire, would there be a magnetic field outside or inside the box? Would the mu-metal be magnetized from the current like soft iron or would it draw the magnetic field into itself?

It would look something like this (because the field lines get concentrated into the shielding material, so they are guided around the interior of the box):

http://www.mdpi.com/sensors/sensors...loy/html/images/sensors-16-01382-g013-550.jpg

 

[berkeman]

Also, keep in mind -- that figure and our discussion so far do not assume any seams or openings in the shielding box. Those will change (and maybe compromise) the shielding effectiveness of the box.

 

[Hami Hashmi]

Yea i meant with no gaps.

 

[Hami Hashmi]

But soft iron enhances the field, and both it and mu-metal have high mu and low solubility. So what is the difference? And metglas has a much higher mu that mu-metal so why isn't it used in shielding applications?

 

[Asymptotic]

low solubility

Curious ... how does solubility enter into magnetic properties?

metglas has a much higher mu that mu-metal so why isn't it used in shielding applications?

Several Metglas alloys are suitable for shielding per their Magnetic Materials page.

 

[berkeman]

Curious ... how does solubility enter into magnetic properties?

I'm guessing it is a language translation error...

@Hami Hashmi -- can you please help us with your definition of that word in your application? Thanks.

 

[Hami Hashmi]

Oops i meant susceptibility. But mu-metal is much more common then metglas even though the permeability of metglas is 1.26 while the permeability of mu-metal is 6.3×10^−2 (at the max). So why is this?

 

[Asymptotic]

Oops i meant susceptibility. But mu-metal is much more common then metglas even though the permeability of metglas is 1.26 while the permeability of mu-metal is 6.3×10^−2 (at the max). So why is this?

Had no success finding pricing for metglas materials, but my guess is at least part of the reason is it costs more than mu-metal.

 

[Hami Hashmi]

Ok thanks. But soft iron enhances the magnetic field, and both it and mu-metal have high mu and low susceptibility. So what is the difference?

 

[berkeman]

Ok thanks. But soft iron enhances the magnetic field, and both it and mu-metal have high mu and low susceptibility. So what is the difference?

Have you compared their typical hysteresis curves and the values of the intercepts with the axes?

Also, here is a good website for a mu-metal shielding company that I've used a number of times in the past. They have a good tutorial section at their website, as well as good technical information about their netic and co-netic mu-metal shielding materials:

http://www.magnetic-shield.com/index.html

http://2yh5c119vtjz3yoo8229y5bs.wpengine.netdna-cdn.com/wp-content/uploads/2015/07/hysteresis.jpg

 

[Hami Hashmi]

What is hysteresis? And what does it have to do with magnetic absorption?

 

[berkeman]

What is hysteresis? And what does it have to do with magnetic absorption?

You can read about magnetic hysteresis at Wikipedia or a similar encyclopedia website. If there are parts of that reading that you don't understand, just post a link here to that reading, and ask us about the confusing parts. We are happy to answer those kinds of specific questions.

I mention the B-H curve because it contains a lot of information about the magnetic material. Look at the datasheets for the various materials you are learning about, and look up the terms on the B-H curve (like Br and Hc, etc.). Then tell us what you are finding...

 

[Hami Hashmi]

I did check the wikipedia article but it was a bit to technical for me to understand.

 

[Hami Hashmi]

So both a current and an external magnetic field will cause soft iron to have a magnetic field?

 

[Hami Hashmi]

bump

 

[Hami Hashmi]

The only thing i found is that mu-metal has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses. I searched those terms up but i couldn't understand them. Could anyone explain how mu-metal absorbs magnetic fields in simpler terms?

 

[Vanadium 50]

Hami, impatience with people who you want to help you is seldom effective.

After 23 messages, I have no earthly idea what you are asking. You're jumping from topic to topic (and, unfortunately, from thread to thread). If people can't figure out what you're asking, how can we answer it? One thing I do know - mu metal does not absorb a magnetic field like a paper towel absorbs water. Nothing does.

 

[Hami Hashmi]

Well i want to know what is the difference between mu-metal and soft iron - both have high permeability and low susceptibility and yet mu-metal absorbs a magnetic field and soft iron enhances it. So what i am asking is what is the difference between them and how do they work on an atomic level.

 

[Hami Hashmi]

I read the wiki article on mu metal and it said, "Mu-metal has low magnetic anisotropy and magnetostriction, giving it a low coercivity so that it saturates at low magnetic fields. This gives it low hysteresis losses." I searched those terms up but i couldn't understand them.

 

[berkeman]

Also, here is a good website for a mu-metal shielding company that I've used a number of times in the past. They have a good tutorial section at their website, as well as good technical information about their netic and co-netic mu-metal shielding materials:

http://www.magnetic-shield.com/index.html

@Hami Hashmi -- Did you read through the Application Notes at the website I posted above? They should be very helpful for you, I believe. Here is the direct link:

http://www.magnetic-shield.com/faqs-all-about-shielding.html

 

[Hami Hashmi]

I couldn't find it before but i'll read it now. Thanks.

 

[berkeman]

Great. Yeah, I'm pretty familiar with the company, and have been to their website many times in the past, but it took me a few minutes to find that section again, so I don't blame you for giving up.

I think you will find the information useful. If parts don't make sense, post links to the parts that are not making sense, and ask questions about them. That may be the best way to move forward to help you with your questions.

 

[Hami Hashmi]

Ok, so I found that mu-metal has low coercivity, and because of that it is a good magnetic field insulator. Coercivity is the measure of a material's ability to stay magnetized after a magnetizing field is applied. But soft iron also has low coercivity, so I don't understand that part.