What is a halbach array
What is a halbach array?
Halbach array is a kind of magnet structure, which is an approximate ideal structure in engineering. The goal is to generate the strongest magnetic field with the smallest number of magnets. In 1979, Klaus Halbach, an American scholar, discovered this special structure of permanent magnet when he did electron acceleration experiment, and gradually improved this structure, and finally formed the so-called “Halbach” magnet.
The array is made up of rare earth permanent magnets. By arranging the permanent magnets with different magnetization directions according to a certain rule, the magnetic lines of force can be converged on one side of the magnet and weakened on the other side, so as to obtain an ideal unilateral magnetic field. Because of its excellent magnetic field distribution characteristics, Haier Buick array is widely used in industrial fields such as nuclear magnetic resonance, magnetic levitation, permanent magnet special motors and so on.
On the left is a single magnet with the north pole all up. From the color, we can see that the strength of the magnetic field is at the bottom and top of the magnet. On the right is a halbeck array with a high magnetic field at the top and a relatively weak field at the bottom. (under the same volume, the magnetic field intensity on the strong side of the halebeck array magnet group is about √ 2 times (i.e. 1.4 times) of that of the traditional single magnet, especially when the thickness of the magnet in the magnetizing direction is 4-16MM.)
The most common example of the Haier Baker array is probably the flexible refrigerator. These thin, soft magnets are usually printed and pasted on refrigerators or the back of cars. Although they are very weak (only 2% – 3% strength) compared with NdFeB, they are widely used due to their low price and practicability.
The form and application of halbach array
Linear type is the most basic form of Halbach array. This kind of array magnet can be regarded as a combination of radial array and tangential array, as shown in the figure below.
Linear Halbach array is mainly used in linear motor. The levitation principle of maglev train is the interaction between moving magnet and magnetic field produced by its induced current in conductor to produce levitation force, accompanied by magnetic resistance. Improving the ratio of buoyancy to resistance is the key to improve the performance of levitation system, which requires light weight, strong magnetic field, uniform magnetic field and high reliability. The Halbach array is horizontally installed in the center of the car body, and acts with the winding in the center of the track to generate the propulsion force, so as to maximize the magnetic field with less magnet consumption, while the magnetic field on the other side is less, so that passengers can avoid being exposed to the strong magnetic field.
The annular Halbach array can be regarded as a ring shape formed by connecting the ends of the linear Halbach array.
In permanent magnet motors, the air gap magnetic field of Halbach array permanent magnet motor is closer to sinusoidal distribution than that of traditional permanent magnet motor. Under the same amount of permanent magnet material, the air gap magnetic density of Halbach permanent magnet motor is higher and the iron loss is smaller. In addition, Halbach ring array is widely used in permanent magnet bearings, magnetic refrigeration equipment and magnetic resonance equipment.
Fabrication and production method of halbeck array
- Method 1: according to the topological structure of the array, the pre magnetized magnet segments are glued together with magnet glue. Because of the strong mutual repulsive force between the magnet segments, the mold should be used to clamp them when they are glued. The manufacturing efficiency of this method is low, but it is easy to realize, so it is more suitable for the laboratory research stage.
- Method 2: firstly, a complete magnet is made by filling or pressing the mold, and then magnetized in a special fixture. The structure of the array processed by this method is similar to the figure below. This method has high processing efficiency and is easy to realize mass production. However, it is necessary to design magnetization fixture and formulate magnetization process.
- Method 3: Halbach type magnetic field distribution is realized by using winding array with specific shape, as shown in the figure below.
Process and effect of self-made halbach array in laboratory ?
Source: China Permanent Magnet Manufacturer – www.rizinia.com