In the field of magnetic materials, magnetisation saturation is a key factor that is often mentioned yet easily overlooked. Today, let us explore this topic together.
Magnetisation saturation refers to the ratio of the magnetic flux density achieved by a magnet under a specific magnetisation process to the material’s theoretical saturation flux density; it is used to indicate the actual degree to which the magnet has been magnetised. Achieving a saturated magnetisation state is a common requirement in industrial applications to ensure stable magnet performance and resistance to demagnetisation under normal conditions. This is typically categorised into the following three types:
Unsaturated magnetisation: The magnetisation energy does not reach 95% or more of the saturation magnetisation energy. This is suitable for scenarios where magnetic requirements are not high or where adjustable magnetism is required, such as certain temporary magnets or low-power devices.
Saturation magnetisation: The magnetisation energy reaches 1.5–2 times the intrinsic coercive force of the magnetic material. This is suitable for scenarios requiring a strong and stable magnetic field, such as permanent magnet motors, generators, magnetic resonance imaging (MRI) equipment, and loudspeakers.
Over-saturation magnetisation: The magnetisation energy reaches more than three times the intrinsic coercive force. This is primarily used in special environments with extremely high magnetic energy requirements; however, attention must be paid to potential performance fluctuations and material degradation issues.
The selection of magnetisation saturation strength requires a comprehensive consideration of factors such as the characteristics of the magnetic material, the application scenario and equipment conditions. The specific methods are as follows:
Clarify material parameters: Obtain information on the magnetic material’s grade, intrinsic coercive force (Hcj), remanence (Br), dimensions and magnetisation direction. The coercive force varies significantly between different materials; for example, the Hcj of sintered ferrites is approximately 2.5–4 kOe, whilst that of neodymium-iron-boron (N48H) is approximately 14 kOe, and the required magnetisation field strength also differs.
Consider the application scenario: High-performance motors and generators: A strong and stable magnetic field is required; saturation or over-saturation magnetisation should be selected to ensure stable motor torque and power output, whilst reducing noise and vibration. For speakers, saturation magnetisation allows the permanent magnet to achieve its material’s nominal maximum energy product, enhancing sound clarity and sensitivity; the appropriate intensity must be selected based on the speaker’s power and sound quality requirements. Magnetic sensors and relays have relatively low magnetic field strength requirements; saturation magnetisation is sufficient to meet these needs, avoiding performance fluctuations caused by over-saturation.
Consider equipment capabilities: The output magnetic field strength of magnetisation equipment is limited; the appropriate magnetisation intensity must be selected based on the equipment’s maximum magnetic field strength. If the equipment cannot achieve the required intensity, it may be necessary to replace the equipment or adjust the materials and processes. Pay attention to equipment parameters such as pulse width and energy output to ensure compatibility with the magnetic materials, thereby preventing suboptimal magnetisation results due to insufficient energy or overloading.
Conduct simulation or experimental verification: Use magnetic simulation software to model the magnetisation process, predict magnetisation effects under different magnetic field strengths, and optimise magnetisation parameters. In actual production, determine the magnetisation intensity through small-batch trials, testing indicators such as the magnetic material’s remanence, coercivity and magnetic field uniformity to ensure they meet application requirements.
In summary, the selection of the saturation magnetisation intensity requires a comprehensive consideration of multiple factors, including material properties, application scenarios and equipment capabilities. By combining theoretical calculations, simulation and experimental verification, it is ensured that the magnetic material achieves the desired magnetised state and meets practical application requirements.
Achieving saturation magnetisation hinges on the selection of magnetisation equipment and the configuration of magnetisation parameters. Selecting suitable magnetisation equipment is a critical step in ensuring sample performance; it must strike a balance between performance, efficiency, cost and scalability to ensure that permanent magnets acquire the required stable magnetic properties.
