Shielding a magnetic field

Piano man

Hi everyone,

I have two questions related to magnetic fields.

Firstly, if I have two bar magnets with opposite poles facing each other, ie NS - NS, how do I measure the magnetic field strength at any point between the two magnets?

Secondly, how would I shield the magnetic fields of the bar magnets in a box so they are not detectable outside?

Any help would be appreciated, thanks.

Aromal

Better way to prevent all the magnetic field lines from coming outside of the box is, use a box made up of a super conductor to separate bar magnets. The super conductor plate is able to divert all the field lines.

hms.tech

Use a "Hall Probe" (http://en.wikipedia.org/wiki/Hall_effect_sensor) to measure the magnetic field from the Bar Magnet.

To shield the magnetic field , you could use an iron box to enclose the bar magnets .
(or a thin layer of iron foil would also suffice)

Aromal

hi.hms.tech I dont think a iron box can separate magnetic field lines. I have doubt about it. Can you explain?

Piano man

Thank you for your replies.

Better way to prevent all the magnetic field lines from coming outside of the box is, use a box made up of a super conductor to separate bar magnets. The super conductor plate is able to divert all the field lines.

That sounds useful, though unfortunately I'm restricted in terms of power supply in this setup, so I need to go with the most energy efficient option and avoid a current conductor of any sort if possible.

Use a "Hall Probe" (http://en.wikipedia.org/wiki/Hall_effect_sensor) to measure the magnetic field from the Bar Magnet.

To shield the magnetic field , you could use an iron box to enclose the bar magnets .
(or a thin layer of iron foil would also suffice)

The Hall probe will be useful for measuring, though what I should have written was how do I calculate the field?

Also for the iron box shielding, how do I calculate the change in field strength across the shielding?

Thanks again.

berkeman

Check out the FAQs section of Magnetic Shield Corporation's website:

https://www.magnetic-shield.com/sitemap.html

They mostly sell netic and conetic magnetic shield material and shapes, but the concepts would apply to iron shielding as well.

Piano man

Thanks for that - that will be useful.
However, if I have a shield at a distance from a magnet, how do I calculate the field at that distance?
In a related question, if I have two magnets, how do I calculate the field strength at any point between them - is it merely by superposition or are there other parameters to take into account?

HomogenousCow

I would look into an advanced electrodynamics textbook, there are closed form solutions for what you need, although they will be very very complicated and require a far field approximation.

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Aromal	Better way to prevent all the magnetic field lines from coming outside of the box is, use a box made up of a super conductor to separate bar magnets. The super conductor plate is able to divert all the field lines.

hms.tech	Use a "Hall Probe" (http://en.wikipedia.org/wiki/Hall_effect_sensor) to measure the magnetic field from the Bar Magnet. To shield the magnetic field , you could use an iron box to enclose the bar magnets . (or a thin layer of iron foil would also suffice)

Aromal	Shielding a magnetic field hi.hms.tech I dont think a iron box can separate magnetic field lines. I have doubt about it. Can you explain?

berkeman Mentor	Check out the FAQs section of Magnetic Shield Corporation's website: https://www.magnetic-shield.com/sitemap.html They mostly sell netic and conetic magnetic shield material and shapes, but the concepts would apply to iron shielding as well.

Piano man	Thanks for that - that will be useful. However, if I have a shield at a distance from a magnet, how do I calculate the field at that distance? In a related question, if I have two magnets, how do I calculate the field strength at any point between them - is it merely by superposition or are there other parameters to take into account?

HomogenousCow	I would look into an advanced electrodynamics textbook, there are closed form solutions for what you need, although they will be very very complicated and require a far field approximation.