How can a Helmholtz arrangement be used to null out magnetic fluctuations?

[Brainy_Mike]

hey I am pretty sure that if the right amount of current passes through the pair of coils in a helmholtz arrangement, the magnetic field it produces can null out any magnetic fluctuation. but how can you calculate the magnetic field it generates?

thanks a lot
and correct me if there was any inaccurate info above.

 

[James R]

If you're talking about creating a zero-field region, what you need is coils in an anti-Helmhotlz arrangement, where the current in one coil flows in the opposite direction to the current in the other coil. Even then, the field will only be zero in a relatively small region between the coils. However, this arrangement also ensures that near the centre of the coils the first derivatives of the field also go to zero, which can be a good thing, depending on the application.

 

[Brainy_Mike]

thanks, that's pretty helpful, ok this is what I am planning to do:
suspend a rare-earth magnet (small, very strong, neodymium) in a box and attach a small piece of mirror on the magnet, shine a beam of laser light on the mirror. supposedly if the magnets are strong enough, it can interact with the Earth's magnetosphere, which is constantly changing, therefore, the disturbances in the Earth's magnetic field can cause the neodymium to fluctuate. so in theory, if the helmholtz arrangement can generate enough magnetic force by pumping current through it, the magnetic field will null out the disturbances and fluctuations observed in the neodymium magnet. and now I am trying to figure how to set the device up and how to measure the amount of current & magnetic field needed.

any suggestion/help/advice is greatly appreciated!
thanks