I encountered a question about magnetic shielding in the website's worksheet.

The question is:
"Suppose we needed to shield a sensitive electronic instrument from external magnetic fields. How would you suggest we do such a thing? How can we keep stray magnetic fields away from this instrument? "

And It gives the answer:
"Magnetic shielding requires that the instrument be completely surrounded by a high-permeability enclosure, such that the enclosure will 'conduct' any and all magnetic lines of flux away from the instrument."

However, I was thinking about an enclosure made up of material with high reluctance so that it can block any magnetic force. Should this also be a valid answer?

Also, regarding the answer that's given, doesn't an enclosure of high-permeability "conduct" the magnetic force toward the sensitive electronic instrument?

Here's the link to the question (Question 9): http://www.allaboutcircuits.com/worksheets/magnet1.html

Thanks.

 

You shield magnetic fields using a material that is good for shielding: the stuff called "mu metal" is specifically designed for mag shielding.


http://en.wikipedia.org/wiki/Mu-metal


Steel is also good, aluminum is weak. There are tables listing the relative shielding strength of various materials.

Magnetic shield ability is proportional to thickness of the material, unlike shielding for E-field interference.

 

However, I was thinking about an enclosure made up of material with high reluctance so that it can block any magnetic force. Should this also be a valid answer?

Think about this: Air has VERY high reluctance. If this scheme would work, you wouldn't need a shield.

 

Think about this: Air has VERY high reluctance. If this scheme would work, you wouldn't need a shield.

That makes sense.
But whats the difference between reluctance to magnetic flux and resistance to electrical current?

 

That makes sense.
But whats the difference between reluctance to magnetic flux and resistance to electrical current?

They are unrelated. One is is the resistance to magnetic field flow and the other is the resistance to electricity flow.

 

"Magnetic shielding requires that the instrument be completely surrounded by a high-permeability enclosure, such that the enclosure will 'conduct' any and all magnetic lines of flux away from the instrument."

It doesn't actullay need to be completely surrounded. Depends on how strong the disturbing magnetic field is.

Example: Zero Gauss chamber

There are other zero Gauss chambers with multiple layers of MU-metal.

If, for example, you take the magnetic field line concept imagine that they are concentrated in the material of high permeability. So they are actually diverted from where you don't want them. This is different from the common idea of "shielding".