I. Definitions of Concepts Related to the Magnetism of Magnets
1. Maximum Energy Product (BH)
The maximum energy product represents the magnetic energy density established by a magnet in the air gap space (the space between the two poles of the magnet). In simple terms, it refers to the static magnetic energy per unit volume of the air gap. Since this energy is equal to the product of the maximum magnetic induction intensity (Bm) and the maximum magnetic field intensity (Hm) of the magnet, it is called the maximum energy product. This parameter is very important for evaluating the magnitude of the magnetic energy that a magnet can provide in practical applications. For example, in the design of equipment such as motors and speakers, the maximum energy
product is a key factor that determines the performance and efficiency of the equipment.
2. Remanence (Br)
Remanence refers to the magnetic induction intensity retained by a permanent magnet after it has been magnetized to technical saturation and the external magnetic field has been removed. This retained magnetic induction intensity is called the residual magnetic induction intensity. For example, when a strong magnetic field is used to magnetize a piece of permanent magnetic material until the magnetic domains inside it are arranged along the direction of the magnetic field as much as possible to reach a saturated state, and then the external magnetic field is removed, the magnetic field intensity remaining inside the material is the remanence. The magnitude of the remanence is directly related to the strength of the magnetism of the permanent magnet itself when there is no external magnetic field assistance.
3. Coercive Force (Hc)
Coercive force is the reverse magnetic field intensity that needs to be applied to reduce the magnetic induction intensity (B) of a permanent magnet that has been magnetized to technical saturation to zero. This parameter measures the ability of a permanent magnet to resist demagnetization. For example, in some environments where there is interference from external magnetic fields, such as around magnetic elements in electronic equipment where there may be alternating magnetic fields, permanent magnets with a high coercive force are not easily demagnetized, thus ensuring the normal operation of the equipment.
4. Magnetic Field
A magnetic field refers to the space where magnetic action is exerted on magnetic poles. A magnetic field is a special substance that is invisible and intangible and can be vividly described by magnetic lines of force. Magnetic poles will be affected by magnetic force in a magnetic field, and the intensity and direction of the magnetic field may vary at different positions.
5. Surface Magnetic Field
The surface magnetic field refers to the magnetic induction intensity at a specified position on the surface of a permanent magnet. It is an indicator for measuring the strength of the magnetism on the surface of a magnet. In some application scenarios where precise control of the position of magnetic action is required, such as surface detection by magnetic sensors, the magnitude of the surface magnetic field is a very important parameter.
II. Types of Magnets
1. Classification and Main Types of Magnetic Steels
Magnets are also called magnetic steels, and the English term is "Magnet". Magnetic steels are mainly divided into two major categories: soft magnetic materials and hard magnetic materials.
2. Types of Soft Magnetic Materials
Soft magnetic materials include silicon steel sheets and soft magnetic cores. Soft magnetic materials are characterized by being easily magnetized and demagnetized, having a relatively high magnetic permeability, and being able to quickly change the magnetization direction in an alternating magnetic field. Therefore, they are mainly used in electrical equipment such as transformers and inductors that require frequent changes in the magnetic field to reduce energy losses.
3. Types of Hard Magnetic Materials and Their Characteristics
Hard magnetic materials include Alnico, SmCo, ferrite, and Nd-Fe-B.
• SmCo Magnetic Steel: It is relatively expensive and has good high-temperature resistance and high magnetic performance. It is widely used in some high-end equipment with high requirements for temperature stability and magnetism, such as certain instruments in the aerospace field.
• Ferrite Magnetic Steel: It is relatively inexpensive and has relatively weak magnetism. However, its advantages are good chemical stability and low cost. It is widely used in some common electronic products with relatively low requirements for magnetism and high sensitivity to cost, such as ordinary speakers.
• Nd-Fe-B Magnetic Steel: It has relatively high performance and strong magnetism. It is widely used in modern industry and electronic products, such as permanent magnet motors and hard disk drives.
• Alnico Magnetic Steel: It has relatively stable performance and a relatively good temperature coefficient, that is, the change in its magnetism with temperature is relatively small. It is suitable for some environments that are relatively sensitive to temperature changes, such as magnetic elements in precision instruments. Users can choose different hard magnetic products according to their different needs.
