Material definition after importing STL model

[Richard-666-666]

try.zip
When I import a box-shaped STL model named "patch" and define its material as PEC, the simulation results differ from those obtained by directly using the AddBox function, despite their shapes and materials being exactly the same. Additionally, the following image appears in the background window. Is this a material definition issue or a mesh recognition problem

[thliebig]

I have not looked at your zip, but looking at the data from the image I assume your box is flat, aka 2D sheet?

While this works well for a box object, an STL object is handled differently. These always need a volume and if egdes hit the surface of the volume, it is very undefined what happens. If you want to use STL objects, always oversize them a bit.

[Richard-666-666]

Thank you very much for your reply！

But I still have doubts. Do you mean that when I import a 2D planar image, openEMS can handle it well, but if it is a 3D cube, there will be unknown reactions at the edges and surfaces. If I import a more complex and irregular 3D model, how can I define the size of the enlargement.

[VolkerMuehlhaus]

From my understanding, it's the other way round: your STL for bottom ground has zero thickness, resulting in a 2D sheet instead of a 3D object. This 2D sheets overlaps with the bottom surface of the 3D substrate object.

According to Thorsten, this can lead to unpredictable behaviour.

[Richard-666-666]

I know what you mean!
Then I should give the 2D plane thickness to coincide with the 3D substrate, or lower the 2D to avoid overlapping, which should have a certain impact on the accuracy of the results.