Halbach Arrays

In industrial applications, a Halbach Array is most commonly used to produce a magnetic field utilizing permanent magnets arranged in a 90° orientation change between magnetic elements, which amplifies the magnetic force applied. Halbach Arrays, both planar and circular, produce a magnetic field similar to what a powered solenoid (Electromagnet) would create, but without the extra size, cost, and maintenance. Planar Halbach Arrays contain the magnetic field to one side of the array, while a Circular Halbach Array concentrates the magnetic field on the ID or OD. Other iterations exist as well, and although the orientation of “bucking magnets” provides a 45° angle between magnets instead of a 90° iteration, they can be considered “non-traditional” Halbach Arrays.

For Circular Halbach Arrays, the simplest geometry is an arrangement of wedge shape magnets, with various magnetic orientations around a common axis.

Planar Halbach Arrays can be thought of as an unrolled Halbach cylinder.  This variation does not necessarily create a uniform field, but it does create a very strong magnetic field on one working-face.

 

Halbach Array Applications

Planar Halbach Arrays are typically used for:

• Holding
• Fixturing
• Linear coupling applications

Circular Halbach Arrays (on the OD iteration) are used in:

• Rotors for Brushless DC Motors
• Rotors for magnetic couplers
• Rotors for power generations

Circular Halbach Arrays (on the ID iteration) are used to:

• Constrain plasma
• Steer, sort, and accelerate moving charged particles
• Impart oscillations

Halbach Array Design Considerations

Operational Gap

1. Between the work-piece and magnet array for a Planar design
2. In the ID of a Halbach Cylinder
3. Between a Halbach Rotor and the stator

Operational Environment

1. Temperature
2. Rotational speeds
3. Liquids/ gasses

External Demagnetizing Fields

• This is important especially in Halbach Arrays used for Rotors.

Cost

Required Lifetime in Service

Available Room or Volume that Can Be Allotted to the Array

Size of the Array Assembly

• Halbach Arrays depend on the assemblage of magnets, which by their nature attract and repel each other. The size of the array complicates its construction.

Halbach Array Benefits

The most obvious benefit of a Halbach-style Array is that the field produced is very strong when compared to other arrays having the same amount of the magnet alloy. The arrangement essentially increases the efficiency of the magnetic circuit.

The by-product of the design is that there is only one working surface or “working face.”  The one working-face, where the magnetic field resides, is very strong; and the non-working face has essentially no field.  In essence, the magnetic field, which would normally be present on the non-working face, is rerouted to the working-face. This is true for both Circular and Planar style Arrays.

Disadvantages of Halbach Arrays

The primary disadvantage of the Halbach Array geometry is that it is difficult to put together, resulting in potentially higher manufacturing costs than other potential solutions.  This is because all of the magnet elements are repelling each other in a Halbach Array. This can create a variety of assembly issues including: needing to assemble the magnets magnetized, combating the forces during assembly, and ensuring the assembly will “hold together” during its use.

Another disadvantage is that Halbach Arrays may have an issue in high heat applications because the array elements apply a demagnetizing field on each other.  As the operating temperature increases, a magnet is more susceptible to demagnetizing, and the neighboring magnet demagnetization is exacerbated.

Conclusion

Not all applications are good candidates for a using a Halbach Array.  It has been pointed out that the Halbach Array is a more efficient use of magnet alloy, but it is important to consider the difficulty of design and manufacture before implementing a Halbach Array.  There are many opportunities for a Halbach design to improve performance, but the benefit will come with a cost. Working with an experienced magnetic engineering company is essential for determining the right solution for your halbach array applications. Contact Dura Magnetics for magnet application assistance for all array design and to ascertain if a Halbach Array can enhance your magnetic application.