In all EM simulation, the empty spaces (or volumes) within a model and around a model are important. This is because we are interested in computing and plotting the magnetic and electric fields in these regions. Imagine a magnet lying on a table, there is magnetic field inside the magnet (of course) but there is also a magnetic field in the air region surrounding the magnet and also in the table. In order to capture these fields, one must model these empty spaces as 3D geometry along with the components of interest.
If you are using EMS for SolidWorks, creating air geometry inside SolidWorks is extremely easy (see video linked below). You first have to create a new part in the assembly you want to simulate. Remember that all EMS models have to be SolidWorks assembly to be simulated. In the new part, you can sketch and extrude any arbitrary shape as long as you make sure that this shape sufficiently encloses all the other parts of the assembly. Next you must use the Cavity feature in SolidWorks to subtract out all the inner components. Now your model is ready for EM simulation (see Figure 1). Please note that you are not just limited to a box region as shown in the figure. For some designs which are cylindrical in nature, it is more appropriate to create a cylindrical air geometry (see Figure 2).
Figure 1- Air region created around a C core inductor using SolidWorks cavity feature
Figure 2- One can create a cylindrical air region as well for models that are cylindrical in nature
Video explaining how to create air region in SolidWorks:
When you create the air region, make sure that it is sufficiently big so that the results at the extremities of the air region is negligible compared to the ones closer to the model. For example, plot the magnetic flux density on the boundary faces of the air region and compare those values to the maximum value of the magnetic flux density. Also the magnetic flux density should be fairly uniform in these boundary faces.
This blog post is a part of Learn EMS for SolidWorks series. To learn more about EMS, visit www.emworks.com.