What does BHmax mean?
BHmax is the maximum energy product of a permanent magnet material. It indicates how much magnetic energy a magnet can store and deliver. A higher BHmax makes it possible to produce smaller and more powerful magnets.
When describing the performance of a permanent magnet material, technical terms such as remanence (Br), coercivity (Hc), and BHmax often appear. Of these three, BHmax perhaps best illustrates a magnet's overall performance capability.
BHmax stands for the maximum energy product of a magnetic material. It indicates how much magnetic energy a magnet can store and make available for an application.
This property plays a significant role in the development of electric motors, generators, sensors, and other systems that use strong permanent magnets.
What exactly does BHmax mean?
BHmax is an abbreviation for:
B × H (maximum)
Where:
- B stands for magnetic flux density
- H stands for magnetic field strength
The energy product describes the maximum amount of magnetic energy a material can deliver.
The higher the BHmax value, the more magnetic performance is available within the same volume.
Therefore, BHmax is often considered a measure of the "quality" of a permanent magnet material.
Why is BHmax important?
In the design of technical systems, space is often limited.
An electric motor in an electric bicycle, a drone, or a medical scanner must remain as compact as possible while still delivering sufficient performance.
Materials with a high BHmax make this possible.
Because they contain more magnetic energy per unit volume, smaller magnets can be used without losing performance.
The relationship with N35, N42 and N52
The well-known designations N35, N42, N48, and N52 are directly related to the maximum energy product of the material.
The number after the N approximately refers to the BHmax value of the material, expressed in millions of Gauss-Oersted (MGOe).
Examples:
| Magnet grade | BHmax |
|---|---|
| N35 | approx. 35 MGOe |
| N42 | approx. 42 MGOe |
| N48 | approx. 48 MGOe |
| N52 | approx. 52 MGOe |
This means an N52 magnet can store more magnetic energy than an N35 magnet of the same dimensions.
BHmax and magnet strength
A high BHmax does not automatically mean that a magnet is always stronger.
The ultimate performance is also influenced by:
- dimensions
- shape
- temperature
- application
- magnetization
BHmax describes solely the potential of the material itself.
The actual holding force is determined by the combination of material and design.
How is BHmax measured?
BHmax is determined using a hysteresis curve.
This graph shows how a material responds to magnetization and demagnetization.
On this curve, the point at which the product of B and H is maximal is sought.
That point represents the greatest amount of usable magnetic energy that the material can deliver.
What units are used?
BHmax is usually expressed in:
- MGOe (Mega Gauss Oersted)
- kJ/m³ (kilojoules per cubic meter)
Both units describe the same property.
Conversion:
1 MGOe ≈ 7.96 kJ/m³
In Europe, kJ/m³ is often used, while MGOe is still common in the magnet industry.
Why do neodymium magnets have such a high BHmax?
The unique crystal structure of neodymium-iron-boron allows it to store an exceptionally large amount of magnetic energy.
As a result, neodymium magnets have a significantly higher BHmax than traditional ferrite magnets.
This explains why a small neodymium magnet can often deliver the same performance as a much larger ferrite magnet.
BHmax in modern technology
Materials with a high BHmax are used in:
- electric vehicles
- wind turbines
- industrial motors
- robotics
- medical equipment
- consumer electronics
- automation technology
In many of these applications, high energy density is essential for creating compact and efficient systems.
The relationship between Br, Hc and BHmax
The three most important material properties of a permanent magnet are:
Remanence (Br)
Indicates how much magnetism remains in the material.
Coercivity (Hc)
Indicates how well the material resists demagnetization.
BHmax
Indicates the maximum amount of magnetic energy the material can store.
Together, these properties determine the performance of a permanent magnet material.
Conclusion
BHmax is a measure of the maximum amount of magnetic energy that a permanent magnet material can store and deliver. The higher the BHmax value, the greater the energy density of the material.
This property forms the basis of the well-known N35, N42, N48, and N52 classifications and plays an important role in the development of modern technologies that use powerful and compact magnets.
