What is Halbach Array?

A Halbach Array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while reducing the field to near zero on the other side. This was achieved by having a spatially rotating of magnetiztion.

High and uniform magnetic field will be produced by Halbach array in a certain area, and its magnetic field can also exceed the Remanence of the magnetic material itself.

Application:

1.Linear Halbach Arrays:

A series of magnetic rods, magnetized perpendicular to their axes, can be arranged into a Halbach array. This arrangement allows the field to effectively be turned on and off above or below the plane of the rods, depending on the rotation of the rods. Such a device makes an efficient mechanical magnetic latch requiring no power. A detailed study of this arrangement has shown that each rod is subject to a strong torque from its neighboring rods, and therefore requires mechanical stabilization.

Such as the brushless AC motor, voice coils, magnetic drug targeting to high-tech applications, such as wiggler magnets which are used in Particle accelerators and Free-electron lasers.

2. Cylinder Halbach Arrays:

A Halbach cylinder is a magnetized cylinder composed of ferromagnetic material producing (in the idealized case) an intense magnetic field confined entirely within the cylinder, with zero field outside. The cylinders can also be magnetized such that the magnetic field is entirely outside the cylinder, with zero field inside.

Such as brushless AC motors, magnetic couplings and high field cylinders.

• Brushless motors or alternators typically use cylindrical designs in which all the flux is confined to the centre of the bore with the AC coils also contained within the bore. Such self-shielding motor or alternator designs are more efficient and produce higher torque or output than conventional motor or alternator designs.

• Magnetic-coupling devices transmit torque through magnetically transparent barriers (that is, the barrier is non-magnetic or is magnetic but not affected by an applied magnetic field), for instance, between sealed containers or pressurised vessels. The optimal torque couplings consists of a pair of coaxially nested cylinders with opposite +k and −k flux magnetization patterns, as this configuration is the only system for infinitely long cylinders that produces a torque. In the lowest-energy state, the outer flux of the inner cylinder exactly matches the internal flux of the outer cylinder. Rotating one cylinder relative to the other from this state results in a restoring torque.

Advantages of Halbach motors :

1.High power density

Compared with the traditional permanent magnet motor architecture, the superposition of the parallel magnetic field and the radial magnetic field after the decomposition of the Halbach magnetic ring greatly increases the magnetic field strength on the other side, which can effectively reduce the size of the motor and increase the power of the motor density.

2.The stator and rotor no longer requires a chute

In traditional permanent magnet motors,  ramps are generally used on the stator and rotor structures to weaken the influence because of the inevitable presence of harmonics in the air gap magnetic field. However, in the Halbach motor, due to the high degree of sinusoidal distribution of the air gap magnetic field and the small harmonic content, chute is no longer required.

3.The rotor can be made of non-core materials

Because the unilateral magnetic field distribution generated by the self-shielding effect of the Halbach magnet no longer requires the rotor to use magnetic materials to provide access for it, this not only provides a larger choice of selection for the rotor material, but also allows the system to enjoy a lower moment of inertia and a better fast adhesion performance.

4. High utilization rate of permanent magnets 

Due to the directional magnetization of Halbach magnets, the operating point of the permanent magnet is relatively high, generally exceeding 0.9, which improves the utilization rate of the permanent magnet.

5. Concentrated winding can be used

Distributed windings are often used in traditional permanent magnet motors to weaken the influence of harmonic magnetomotive force. In the Halbach motor, due to its high degree of sinusoidal magnetic field distribution and small influence of harmonic magnetic fields, concentrated windings can be used.

The use of Halbach motor magnet arrangement can reduce the torque ripple of the motor, thus greatly reducing the bearing requirements of the motor.

(a) Magnetic field distribution of radial magnet arrangement

(b) Magnetic field distribution of parallel magnet arrangement

(c) Halbach arrangement magnetic field distribution