Magnet Homogeneity

General

A homogeneous magnetic field exists when flux lines are parallel and the field is equal in all places. The homogeneous region will be clearly labelled on an assembly drawing during the inquiry stage of your order. American Magnetics defines a 1cm diameter spherical volume, or DSV, with a ±0 .1% variation as standard homogeneity. Homogeneity is also commonly specified as a region along the axis, or as a right cylindrical volume, as shown above.

Example

For a magnet energized to 1T (10kG) and rated at ±0.1% homogeneity. The field within the homogeneity region would not vary more than ±10G within the specified region. (see picture below)

10,000G * 0.1% =10G

NOTE: The same magnet would vary no more ±5G if the same magnet were charged to 0.5T (5kG)

Mössbauer and Bucking Coils

Some experiments such as Mössbauer effect measurements require that the magnetic field be reduced close to one end of a magnet. This is accomplished by adding a bucking coil on one end of the main coil. A typical field profile for a bucking coil magnet peaks slightly off from center of the solenoid and sharply decreases along the axis towards and past the bucking coil, we call this the bucked or compensated region. The field near the end of the bucking coil is reduced to a minimal level (and can be reversed slightly in the negative direction). A minor peak normally occurs before the field decreases continually. The field in the compensated region is kept below your experiment’s requirements, typically less than 200G.

Bucking coils can be incorporated into solenoids, split coils, multiaxis vector magnets, or nuclear demagnetization magnets.

DEFINING HOMOGENEITY

When requesting specific homogeneity requirements, please refer to the table below.

DESIRED FEATURE	HOW TO SPECIFY	EXAMPLE
1cm DSV ±0.1%	specify as standard	standard
Other Spherical Volumes	size of DSV then variation tolerance	1cm DSV ±1.0%
Region Along Axis	region length plus variation tolerance	±3cm ±0.01%
Volumetric Region	region diameter, length, variation tolerance	ø 0.5cm x 3cm volume ±0.01%
Bucking coils	point or region from magnetic center and desired field	<200G 30cm from Magnetic Center
Gradient Coils	Gauss over length, variation tolerance	10G/Inch 1.0% DSV