PC Case - EMC Cavity Simulation

WIPL-D Software suite offers a remarkable variety of tools and features for efficient simulation of electromagnetic compatibility (EMC) problems. Extremely efficient simulation kernel allows solving electrically large and complex scenarios quickly, with minimum amount of computer resources required. GPU enabled numerical analyses can be performed on inexpensive platforms faster than on traditional CPU workstations. For complex geometries, WIPL-D Pro CAD offers import of native CAD files (from IGES to CATIA). In house meshing algorithm yields simulation models adapted for WIPL-D EM simulation (with both large and small scale details included). Short simulation time means that EMC simulations can be run in large number of frequency points, often required for time domain analysis.

PC Case Simulation

EMC simulation capabilities of WIPL-D software suite will be demonstrated by using an EM simulation of PC case tower. The realistic model of the case outer metallic shell is easily built of available primitives and Boolean operations applied on such in WIPL-D Pro CAD. The tool offers full modeling capabilities and built-in quadrilateral mesher.

Figure 1: PC case tower, WIPL-D Pro CAD model

PC case dimensions are 45 x 40 x 18 cm. Meshed model is shown in the following figure. The meshed model has large regular quads on flat surfaces without details, while it has small quads around details significant for EM simulation. That’s required in order to precisely capture geometry of the problem. Single model offers large to small scale details included, which is easily inspected visually.

The case model will be used for the frequency range of devices inside of it, up to 7 GHz. As illustration of the cavity response, a small fraction of the band will be used (2.5 - 2.75 GHz).

Figure 2: PC case tower, meshed model

First scenario is introduced to illustrate the complexity of EM simulation inside the cavity. We place a wire dipole inside of PC case and inspect its input impedance. It reveals us a resonance for each of the modes of the cavity.

Figure 3: Wire dipole inside the case

Figure 4 illustrates numerous resonances inside the cavity, reflected on the antenna return loss. Resonant frequencies are directly related with geometry of the cave and their density is cube function of frequency.

Figure 4: Resonances inside the case

Simulation is performed on a regular desktop PC configuration comprising of quad core i7 CPU, 4 GB of RAM, but also powered by a Nvidia GeForce GTX card. It requires 9,951 unknown coefficients in the MoM system matrix and simulation time is 20.5 seconds per frequency.

EMC Compatibility Scenario

A more complex compatibility scenario involves putting two microstrip technology filters into PC case and observing the response. The filter itself looks as in the attached image.

Figure 5: Microstrip stub filter

The filter simulation requires 800 unknowns and simulation lasts 6 seconds per frequency.

Figure 6: Filter return loss

The last step is to place two such filters in the case and to compare its results when they are inside the case and in free space. Simulation now lasts around 40 seconds per frequency. The response indicates modification due to the presence of second device and resonances as described above due to the presence of the cavity.

Figure 7: Two filters inside the case

Figure 8: Filter return loss inside the case

Figure 9: Coupling between ports inside the case

PDF application note

If you have a specific problem in mind and you are not sure if WIPL-D software can handle that problem, contact us. We will analyze your needs and try to help, and if our products satisfy your requirements, we will make you the best possible offer for purchase.