Neodymium Magnetic Field
Surface magnetism is an important technical indicator of magnetic steel products. As the name implies, it is the magnetic induction intensity of the surface. The industry sometimes also popularly calls it the surface magnetic field intensity, that is, the surface field.
For application areas that require the use of spatial magnetic fields, surface magnetism or the magnetic induction intensity value of a specified point is usually used as an important technical requirement. Here, it should be made clear that surface magnetism has a direction. We usually refer to the surface magnetic value perpendicular to the magnetic pole surface.
Can surface magnetism be calculated?
If so, how should it be calculated?
This is a question that everyone is concerned about. Some calculation formulas can be found on the Internet, and many magnetic material manufacturers’ websites also have corresponding calculation programs to facilitate calculations neodymium magnetic field.
However, those who have used them can find that these formulas or tools can only calculate the surface magnetism of cylindrical and rectangular magnets, and they calculate the center surface magnetism. Are other shapes difficult to calculate? Is the highest surface magnetism also difficult to calculate? Yes, it is indeed very difficult and complicated to accurately calculate surface magnetism.
For cylindrical and rectangular magnets, we assume that the magnetic field distribution is ideal and symmetrical, and the center surface magnetism is assumed to be ideally perpendicular to the magnetic pole surface neodymium magnetic field. The magnetic permeability in the air gap is equal to the magnetic permeability of the magnet and is equal to 1.0. Based on the above conditions, there will be a relatively simple calculation method. You can refer to TDK’s calculation formula:
Based on the above formula, an Excel calculator can be made to facilitate calculations. This is also the source of formulas for calculation programs on many websites. However, in actual calculations, you will find that the accuracy of the calculation results seems to be insufficient.
The calculated values of some products are very different from the measured values. Take the N50 D10*10mm magnet as an example. Use a Gauss meter to measure the center position of the magnetic pole surface. We believe that the probe and the magnet are close together and there is no air gap.
Excluding the error of the measuring instrument, the Br calculated by the formula is 14kGs, so the center surface magnetism should be 6261Gs neodymium magnetic field. But in fact, no matter how you measure, it is impossible to reach this value, even if you use N54, it is impossible to reach this value. What is the problem? Is TDK’s formula also inaccurate?
To analyze the above problems, we must understand what the basis for the formula is, and we cannot simply take it as it is. First of all, X in the formula is the distance from the calculation point to the surface of the magnet. Although we always put the probe directly against the surface of the magnet when measuring, the Gaussmeter probe itself does not expose the Hall chip.
There is a protective shell. For example, the Japanese KANETEC Gaussmeter, which is widely used in the industry, has a transparent protective shell of about 0.2mm for the Hall chip of the probe. In addition, after more measurements neodymium magnetic field, you will find that there is a difference between the surface magnetism of the black sheet and the finished product. Why? It is because of the influence of the surface coating of the finished product, such as nickel-copper-nickel coating, which is generally 0.02mm thick on one side.
In addition, nickel itself is a magnetic conductive material, which will shield the magnetic field, so the coating will also cause a decrease in the measured value. In addition, the surface magnetism measured by the neodymium magnetic field Gaussmeter we have always emphasized is not an ideal point, but a small area, and the actual orientation and uniformity of the magnet cannot be perfect.
Therefore, based on the above conditions and a lot of practical experience neodymium magnetic field, X needs an additional compensation of 0.4-0.5mm. If the Pc value is below 3, the compensation is 0.5mm, and if the Pc value is above 3, the compensation is 0.4mm.
The above is an explanation of the compensation of the X value. Another more important point is that the principle of the formula is that the magnetic permeability of the magnet and the air gap are both equal to 1.0. We know that the magnetic permeability of air is 1.000065, which is very close to 1.0, but the magnetic permeability of the magnet is not so ideal. In fact, it is already a very good value to reach 1.02.
Most of the N series and M series NdFeB magnets are more than 1.05 neodymium magnetic field, and some even reach 1.1. Why does the magnetic permeability affect the test data? We still have to return to the demagnetization curve to analyze and understand:
It can be seen from the demagnetization curve that the actual remanence value of the magnet in the open circuit state is not the ideal Br value, but lower than Br, which we call the intrinsic magnetic flux density Bdi neodymium magnetic field. The reason is that the initial state of the blue J-H demagnetization curve is not ideally parallel to the X axis, but inclined, so the Br value must be greater than Hcb, and the recovery permeability μrec=Br/Hcb cannot be 1.0.
Another situation is that the B-H line has an inflection point, and the working point of the magnet is below the inflection point, so the actual Bdi will be much lower than Br, so the calculated result will deviate from the actual value, as shown in the figure below, which also explains why the actual center surface magnetism of the N54 20*10*1mm magnet is not only far lower than the theoretical calculated value, but also very unstable.
Combined with the above, correcting Br in the formula to Bdi and appropriately compensating X will be a more accurate calculation formula, but in actual situations Bdi is also difficult to calculate neodymium magnetic field. The best method is to calculate from the graph based on the actual demagnetization curve and Pc value, but this is also cumbersome. It is recommended that you calculate according to the following ideas:
1. First of all, the working point must be above the inflection point of the B-H demagnetization curve and retain an appropriate margin. In this way, special attention should be paid to N materials with a magnetic energy product of more than 45 and thin sheets with a Pc of less than 0.6.
If it is below the inflection point, it means that the magnetism is unstable. Even if Bdi is calculated from the curve to calculate the center surface magnetic fluctuation, the fluctuation will be large neodymium magnetic field. Hcj must be increased to maintain the working point below the inflection point or the BH line does not have an inflection point neodymium magnetic field.
2. Under the premise that the first point can be satisfied, Bdi=Br∙(Pc+1)/(μrec+Pc), μrec is determined according to the actual value, generally 1.08-1.1 for N40 and below, 1.06-1.08 for N40 and above, 1.05-1.06 for M gear, 1.04 for H gear, and 1.03 for others.
The final calculation formulas for the central surface magnetism of the cylindrical (or nearly cylindrical) and rectangular (or nearly rectangular) are:
Note: The above formula is only applicable to permanent magnets with linear demagnetization curves, such as NdFeB, SmCo, and ferrite. For permanent magnets with nonlinear demagnetization curves, such as AlNiCo, FeCrCo neodymium magnetic field, and various soft magnetic materials neodymium magnetic field, this method is not suitable for calculating surface magnetism. In addition, the magnetization direction of obliquely oriented magnets is not perpendicular to the magnetic pole plane, and it is not applicable.
Calculating the surface magnetism of a neodymium magnet typically involves determining the magnetic flux density (B) at the surface of the magnet neodymium magnetic field. Here’s a step-by-step outline of how this can be done:
Understand the Magnetic Properties: Neodymium magnets are usually characterized by their magnetic flux density, often measured in Tesla (T) or Gauss (G). This property indicates the strength of the magnetic field they generate.
Identify the Magnet Dimensions: Measure or obtain the dimensions of the magnet, specifically the surface area where you want to calculate the surface magnetism. Let’s denote the area as AA.
Determine the Magnetic Flux Density (B): The magnetic flux density BB can be found from the magnet’s specifications provided by the manufacturer or by using a Gaussmeter to measure it directly.
Calculate Surface Magnetism: Once you have BB (in Tesla or Gauss) and AA (in square meters or square centimeters, depending on the units of BB), you can calculate the surface magnetism MM using the formula:
If BB is given in Tesla and AA in square meters:
M = B \cdot AM=B⋅A
If BB is given in Gauss and AA in square centimeters:
M = \frac{B \cdot A}{10,000}M=
10,000
B⋅A
(Conversion from Gauss to Tesla: 1 Tesla = 10,000 Gauss)
Example Calculation: Suppose you have a neodymium magnet with a surface area A = 4A=4 cm² and a magnetic flux density B = 1.2B=1.2 Tesla. To find the surface magnetism MM:
M = B \cdot AM=B⋅A
M = 1.2 \, \text{T} \cdot 4 \, \text{cm}²M=1.2T⋅4cm
M = 4.8 \, \text{T} \cdot \text{cm}²M=4.8T⋅cm
If you want the result in Gauss:
M = \frac{1.2 \, \text{T} \cdot 4 \, \text{cm}²}{10,000}M=
10,000
1.2T⋅4cm
M = \frac{4.8 \, \text{Gauss} \cdot \text{cm}²}{10,000}M=
10,000
4.8Gauss⋅cm
M = 0.00048 \, \text{Tesla} \cdot \text{m}²M=0.00048Tesla⋅m
Considerations: Ensure units are consistent throughout your calculations. If the magnet has irregular shapes or varying magnetic fields, more sophisticated methods involving magnetic field mapping or numerical simulations may be required for accurate surface magnetism calculations neodymium magnetic field.
By following these steps, you can determine the surface magnetism of a neodymium magnet based on its magnetic flux density and surface area.
