Common Magnetic Circuit Structures

The usage scenarios of NdFeB permanent magnets can be roughly divided into adsorption, repulsion, induction, electromagnetic conversion, etc. In different application scenarios, the requirements for magnetic fields are also different.

• The spatial structure of 3C products is extremely limited, but at the same time requires a higher adsorption strength. The spatial structure does not allow the size of the magnet to increase, so the magnetic field strength needs to be improved through magnetic circuit design；

• In situations where magnetic field sensing is required, overly divergent magnetic lines of force can cause false touches on the Hall element, and the magnetic field range needs to be controlled through magnetic circuit design;

• When one side of the magnet needs high adsorption strength and the other side needs to shield the magnetic field, if the magnetic field strength of the shielding surface is too high, it will affect the use of electronic components. This problem also needs to be solved through magnetic circuit design.

• Where precise positioning is required and where a uniform magnetic field is required, etc.

As in all the above cases, it is difficult to achieve the use requirements using a single magnet, and when the price of rare earth is high, the volume and amount of the magnet will seriously affect the cost price of the product. Therefore, we can modify the magnetic circuit structure of the magnet to meet different usage scenarios while meeting the adsorption conditions or normal use, while reducing the amount of magnet to reduce costs.

Common magnetic circuits are roughly divided into HALBACH ARRAY, multi-pole magnetic circuit, focused magnetic circuit, added magnetic conductive material, flexible transmission, single-sided magnetism, and magnetic focusing structure. The following introduces them one by one.

HALBACH ARRAY

This is an engineering-approximate ideal structure, the goal is to use the least amount of magnets to generate the strongest magnetic field. Due to the special magnetic circuit structure of the Halbach array, most of the magnetic field loop can circulate inside the magnetic device, thereby reducing leakage magnetic field to achieve magnetic concentration and realize self-shielding effect in the non-working area. After the optimized annular Halbach magnetic circuit design, the non-working area can achieve at least 100% shielding. As can be seen in the figure, the magnetic lines of force of the conventional magnetic circuit are symmetrically divergent, while the magnetic lines of force of the Halbach array are mostly concentrated in the working area, thus improving the magnetic attraction.

Multi-pole magnetic circuit

The multi-pole magnetic circuit mainly utilizes the characteristic that the magnetic lines of force preferentially select the nearest opposite pole to form a magnetic circuit. Compared with ordinary single-pole magnets, the magnetic lines of force (magnetic field) of the multi-pole magnetic circuit are more concentrated on the surface, especially the more poles there are, the more obvious it is. There are two types of multi-pole magnetic circuits, one is the multi-pole magnetization method of a magnet, and the other is the adsorption method of multiple single-pole magnets. The difference between these two methods lies in the cost, and the actual functions are the same. The advantage of multi-pole magnetic circuits in small-pole adsorption is very obvious.

Focusing magnetic circuit

The focused magnetic circuit utilizes a special magnetic circuit direction to concentrate the magnetic field in a small area, making the magnetic field in that area very strong, even reaching 1T, which is very helpful for accurate positioning and local sensing.

Magnetic materials

Magnetic conductive materials utilize the magnetic field loop to preferentially select the path with the smallest magnetic resistance. Using high magnetic conductive materials (SUS430, SPCC, DT4, etc.) in the magnetic circuit can well guide the direction of the magnetic field, thereby achieving the effect of local magnetic concentration and magnetic isolation.

Flexible transmission

The characteristics of flexible transmission are that the attraction and repulsion formed by magnets achieve non-contact flexible transmission, small size, simple structure, torque can be changed according to the volume of the magnet and the size of the air gap, and the adjustable space is large.

Single-sided magnetic

The characteristic of single-sided magnet is that it shields the polarity of one side of the magnet and retains the polarity of the other side. The direct adsorption force is large, but the magnetic force attenuates greatly as the distance increases.

Magnetic structure

The characteristic of the form is that the magnet and iron are arranged relative to each other according to polarity. As the ratio of magnet thickness to iron thickness increases, the thicker the iron thickness, the smaller the divergence of magnetic lines of force. The magnetic concentrating structure can be flexibly designed according to the size of the air gap to achieve the best effect, which can effectively save magnets and evenly distribute the magnetic field along the iron. However, the disadvantage is that the assembly cost is relatively high. The magnetic circuit of a neodymium magnet rod is this structure.