Halbach Array

What is a 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. 

In 1979, American physicist Klaus Halbach discovered this special arrangement of permanent magnets while doing electron acceleration experiments, so we call it “Halbach array”.

The array of 5 cube magnets is shown in Figure A. The arrow represents the N pole of the magnet. In a single magnet, the magnetic field lines around the magnet go out from the N pole back to the S pole. The density of magnetic field lines represents the strength of magnetism. When we arrange the 5 magnets in a alternating way, the magnetic lines of force are scattered on both sides. If we arrange the magnets in Halbach array, the magnetic field lines are concentrated on one side of the magnet.

Halbach array is an ideal structure in engineering. It uses a special arrangement of magnets to enhance the magnetic field in one direction. The goal is to generate the strongest magnetic field with a certain number of magnets.


Figure A

Forms and Applications of Halbach Array

Linear Halbach Array

Maglev trains require on-board magnets with light weight, strong magnetic field, uniform magnetic field and high reliability. The magnets are installed horizontally in the center of the car body with Halbach array, which interacts with the windings in the center of the track to generate propulsion. Halbach array maximizes the magnetic field with less magnet usage, while the other side has less magnetic field, which can prevent passengers from being exposed to strong magnetic fields.

Halbach Array Rings

Halbach Array Rings are a combination of radial and parallel magnets, assembled in accordance with the Halbach Array. If the end effect is ignored, and the permeability of the surrounding magnetically permeable material is regarded as infinite, the above permanent magnet structure eventually forms a one-sided field.

Compared with the traditional motor (Figure B), the motor using Halbach Array (Figure C) can effectively reduce the volume of the motor and improve the power density of the motor due to the large increase in the magnetic field strength on the working side. What’s more, in the traditional permanent magnet motor, due to the inevitable existence of harmonics in the air gap magnetic field, inclined slots are generally used in the stator and rotor structure to weaken its influence. In the Halbach motor, due to the high degree of sinusoidal distribution of the air-gap magnetic field and the small harmonic content, the stator and rotor do not need inclined slots anymore.

Figure B

traditional permanent magnet motor

Figure C

Halbach motor

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