In this blog, we'll walk through a complete workflow in Ansys Maxwell to simulate the magnetization of a specific permanent magnet, the N48SH, using only its manufacturer datasheet. We will then validate our results against Maxwell’s built-in material library to demonstrate the accuracy of this powerful technique.
1. The Physics of Magnetization & Our Simulation Model
Before diving into the simulation, let's briefly review the underlying physics. The behavior of a magnetic material is described by its B-H curve, or hysteresis loop. When we first magnetize a material, it follows an "Initial Magnetizing" path from (0,0) up to saturation. Once the external magnetizing field is removed, the magnet's flux density "recoils" to a point in the second quadrant, known as its operating point. This second quadrant, the demagnetization curve, is what defines the magnet's performance in an application.
Hysteresis loop of a typical NdFeB magnet, showing the initial magnetization curve and the second-quadrant demagnetization region.
A permanent magnet in open air will generate a "demagnetizing" field within itself, where the magnetic field (H) opposes the direction of magnetization. The intersection of this self-demagnetizing field and the material's B-H curve determines the magnet's operating point.
Example operating point for an N48 magnet on its demagnetization curve (left). Vector plot of the H-field showing the external field and the internal demagnetizing field of a permanent magnet (right).
To simulate this process, we've created a simple magnetizer model in Ansys Maxwell. It consists of two current-carrying coils and two steel cores that work together to generate and direct a strong, uniform magnetic field (H-field) in the space between them. We will place our unmagnetized N48SH material, a simple rectangular block, in this region to be magnetized.
Simulation showing the current density (J) in the coils and the resulting magnetic field (H) generated between them.
Vector plot showing the magnetic field (H) in and around the entire magnetizer assembly.
2. Creating a Custom Initial Magnetizing Curve
The Ansys Learning Hub features an excellent tutorial on magnetic latching that demonstrates the magnetization of a generic Neodymium magnet.
In this blog, we want to take it a step further and simulate a specific material, the N48SH, using its datasheet, and then validate our results by comparing its final operating point to that of Maxwell's built-in N48 material.
Our first step is to get the material data into Maxwell. The N48SH datasheet provides its demagnetization curve graphically. We can use Maxwell’s powerful SheetScan utility to digitize this curve.
N48SH datasheet from Arnold Magnetic Technologies (left). Using the SheetScan tool in Ansys Maxwell to digitize the B-H curve from the datasheet image (right).
(We have a detailed tutorial on how to use the SheetScan tool, which you can find at this link: Ansys Maxwell: SheetScan - Import Material Characteristic Curves )
Next, we need an initial magnetization curve. The Ansys Learning Hub magnetization workshop files provide a "virgin" (Initial) BH curve for a generic NdFeB magnet. Our goal is to modify this generic curve so that it smoothly connects to the N48SH demagnetization curve we just extracted.
Generic NdFeB virgin BH curve provided in the Ansys Maxwell training materials.
By plotting our extracted N48SH curve and extrapolating it into the first quadrant, we can see how the generic curve needs to be adjusted to line up correctly.
Comparison of the generic initial BH curve (green) and the extrapolated N48SH datasheet curve (blue). Curve after extrapolation is on the right.
Using the BH curve smoother tool, we can modify the generic initial curve (green) to align with the N48SH datasheet curve (blue).
New initial BH curve (green), after being modified to align with the N48SH datasheet curve (blue).
With our modified curve ready, we create a new material in Maxwell called "N48_Unmagnetized" and import our custom initial BH curve.
Defining the new material in Maxwell with the custom nonlinear BH curve.
Finally, and this is a crucial step, we must tell Maxwell that we intend to compute the final magnetized state of our permanent magnet object. This is done by right-clicking on Excitations, selecting Set Magnetization Computation, and checking "Compute magnetized operating points" for our PM object.
Enabling the "Compute magnetized operating points" option for the permanent magnet.
3. Running the Simulations and Evaluating Results
Now we're ready to run the simulation. This is a two-step process using linked magnetostatic analyses.
Step 1: The Magnetizing Event
We run the first simulation with the current applied to the coils. Maxwell solves for the magnetic field and determines the operating point of the PM as it's being driven up the initial magnetization curve by the strong external H-field.
The H-field produced by the coils during the magnetizing event.
Plot showing the operating point during the magnetization event, landing on the virgin BH curve.
Step 2: Simulate The Final Magnetized State
To find the final operating point after the magnetizer is turned off, we create a copy of the first design. In this new design, we do two things:
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Set the current in the magnetizing coils to zero.
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Assign a Permanent Magnet Field to the PM object. This feature links the second simulation to the first, using the computed magnetized state from the first analysis as the source for the permanent magnet's field in the second.
Setting up the Permanent Magnet Field in the second analysis, linking it to the result of the first magnetizing event.
After running this second analysis, we can plot the complete history. The graph below shows the magnet's operating point starting at (0,0), traveling up the green initial magnetization curve during the magnetizing event, and then following a recoil line down to its new, stable operating point in the second quadrant. We've also plotted the BH curve of the N48 material in yellow, showing how the magnet's final state lies on the expected demagnetization path.
Plot showing the full magnetization history: the initial curve (green), the peak point during magnetization, the recoil path, and the final newly magnetized operating point.
Step 3: Validation
For our final step, we'll create a third version of the model, again with zero current. This time, instead of using our custom material, we'll assign the PM the material properties of the built-in N48SH material from Maxwell's library.
Assigning the built-in N48SH material properties for the validation simulation.
By running this third simulation, we can directly compare the operating point of our custom-magnetized PM with the operating point of a standard N48 magnet. As the final plot shows, the two points are nearly identical, validating that our workflow has successfully and accurately simulated the magnetization of an N48SH magnet from its datasheet.
Final comparison plot showing the operating point of our newly magnetized PM (blue circle) is almost identical to the operating point of the built-in N48 material (red dot), validating the accuracy of the workflow.
4. Conclusions
This workflow demonstrates a powerful capability within Ansys Maxwell. By starting with a graphical demagnetization curve from a manufacturer's datasheet, you can create a custom initial BH curve to accurately simulate the entire magnetization process. The two-step linked analysis allows you to first compute the magnetization and then determine the final, stable operating point of the newly created permanent magnet.
The close agreement between our simulated magnet and Maxwell's built-in N48 material validates this approach. This gives engineers the confidence to apply the same technique to virtually any permanent magnet material, enabling high-fidelity simulation and robust design even when a complete set of material data isn't readily available.
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