Maxwell coil

Magnetic field around a Maxwell coil

A Maxwell coil is a device for producing a large volume of almost constant (or constant-gradient) magnetic field.

Description

A constant-field Maxwell coil set consists of three coils oriented on the surface of a virtual sphere^[1]. According to Maxwell's original 1873 design ^[2] each of the outer coils should be of radius $\sqrt{\frac{4}{7}}R$ and distance $\sqrt{\frac{3}{7}}R$ from the plane of the central coil of radius R. The number of ampere-turns of each of the smaller coils should equal exactly $\frac{49}{64}$ of the middle coil.This arrangement removes variations in magnetic field, up to its 6th-order derivative with respect to position, near the centre of the virtual sphere.

A gradient-field Maxwell coil is essentially the same geometry of the 3-coil configuration above, with the central coil removed to leave only the smaller two coils ^[3]. If the current in one of the coils is reversed, a uniform-gradient magnetic field is produced near the centre of the two coils.

References

1. ^ Garrett, Milan Wayne, Journal of Applied Physics, 38(6), pp2563-2586
2. ^ Clerk-Maxwell, James (1873). Treatise on Electricity and Magnetism. Oxford: The Clarendon Press. ISBN 0-486-60636-8.  Page 319.
3. ^ R. Pascone, Manhattan College, T. Vullo and P.T. Cahill, (1993) http://ieeexplore.ieee.org/iel4/1093/8547/00701859.pdf

See also

• Magnetic field
• Helmholtz coil