A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. This is achieved by having a spatially rotating pattern of magnetisation.
The rotating pattern of permanent magnets (on the front face; on the left, up, right, down) can be continued indefinitely and have the same effect. The effect of this arrangement is roughly similar to many horseshoe magnets placed adjacent to each other, with similar poles touching.
Characteristics of Halbach Arrays
Halbach arrays can generate large and uniform magnetic field in a certain area, and magnetic field can even exceed the remanence of the magnetic material itself.
Enhance magnetic field on one side and keep the field of other side to a very low level at the same time.
Halbach arrays have excellent performance when a gap exists.
Magnetic field exhibit sine distribution and can also drastically reduces harmonic waves.
Significantly increase the power.
Excellent magnetic shielding effect.
Halbach Array types:
Halbach array magnets can be divided into three types: linear, circular and arc halbach according to different shapes.
1. Linear Halbach Array Magnets
One of the applications for linear halbach magnets is a flexible refrigerator magnet. A refrigerator magnet has strong magnetic field on its working face, while the magnetic field on the other side is close-to-zero.
Many electronic devices also employ the advantage of linear halbach array. Take an iPad for example, they use linear halbach design so that Apple pencil can snap precisely to the point where the charging coils are aligned.
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. Circular Halbach Array Magnets (Ring or Cylinder)
Basically, there are three types of configuration for a halbach ring or cylinder: 1) dipole 2) quadrupole and 3) sextupole. For a dipole (N=1), the arrow of magnetization rotates 60° from one magnet to another. For a quadrupole type, the arrow rotates 90° and sextupole 120°.
In the real application, the magnets are combined with adhesive and mostly fixed and protected by a metal sleeve on the outside. Arc halbach is considered when a single circular assembly is difficult to make. It is a sub-assemblies for circular halbach.
3. Arc Halbach Array Magnets
Arc Halbach arrays are currently mainly used in linear motors. The levitation principle of a maglev train is that the interaction between the moving magnet and the magnetic field generated by the current induced in the conductor generates levitation force, and is accompanied by magnetic resistance.
Improving the buoyancy-to-resistance ratio is the key to improving the performance of the levitation system. This requires the weight of the onboard magnet Light, strong magnetic field, uniform magnetic field and high reliability. The Halbach array is installed horizontally in the center of the car body, and generates a propulsive force with the winding in the center of the track.
The magnetic field is maximized with a smaller amount of magnets, and the other side has less magnetic field, which can avoid passengers being exposed to strong magnetic fields.