Validating Radiated Susceptibility between Measurement and Ansys EMC Plus

When you are developing a product with electronics, including vehicles, you must meet electromagnetic compatibility (EMC) requirements. Some designers now use simulation to predict potential problems ahead of EMC testing. In certain cases, simulation is replacing EMC testing all together.

To increase confidence, there is growing interest in comparing simulation results to EMC testing. EMA recently completed validation testing with our simulation software Ansys EMC Plus. We fabricated our own non-proprietary electronic device and tested it with our partner, the National Institute for Aviation Research (NIAR) at Wichita State University. NIAR is a full-fledged product certification laboratory largely serving the aerospace industry, but is open to a wide range of electromagnetic environmental tests as well as other types of environmental qualification tests.

Experiment Preparation

The goal of this validation experiment is to optimize the correlation between simulation and testing. A good correlation demonstrates greater confidence in the use of simulation.

We decided to focus this experiment on radiated susceptibility. Radiated susceptibility is a measure of how sensitive a device is to external electromagnetic fields. Engineers evaluate a device by exposing it to an external electromagnetic field and then assess its performance to determine if it can operate normally under those conditions. There is no standard for radiated susceptibility, instead it is essentially a pass/fail test. In this case, we modified the test procedure to be more analytical.

What is Ansys EMC Plus?

Ansys EMC Plus is a platform-level electromagnetic modeling and simulation tool that delivers design to validation workflow for EMC. Solver types include Finite-Difference Time-Domain (FDTD), Nexxim Transient Circuit, and Multi-conductor transmission line. Key features and solutions include:

• Modeling cables, harnesses, connectors, chassis, and shields
• Radiated emissions/ immunity
• Conducted emissions/ immunity
• Shielding effectiveness
• Electromagnetic environmental effects (lightning, HIRF, EMP)
• EMI/EMC simulation
• Cable to RF system coupling
• Integration with Ansys optiSLang, Granta, HFSS, and SIWave

In 2024 R2, Windows GPU acceleration became available for Ansys EMC Plus users. Single GPU acceleration on a gaming desktop station is four-to-eight times faster than a typical CPU simulation. We completed a full vehicle simulation of an excavator in about 20 minutes using GPU acceleration. Using CPU, the same simulation took more than three hours to complete on eight cores.

Validation Campaign

Patch Antenna

In this experiment we used a patch antenna made of a printed circuit board (PCB) designed to resonate at a given frequency. Figure 1 shows the EMC Plus simulation model on the left and the physical model on the right. In each image you can see the same trace on the top, the dielectric, and the antenna port.

Fig. 1. Patch antenna used for validation (right) and EMC Plus model (left)

The first test completed was to confirm that the EMC Plus model is radiating at the correct frequencies. The physical model was resonating at 1.7 GHz. To test this, we measured the scattering parameters, or S-parameters, of the patch antenna model in EMC Plus. We found that the first resonance matched almost perfectly in both frequency and magnitude, getting within three to four dBs of our desired results and that of our physical measurement. Figure 2 shows the results. Even at higher frequencies, we see that the frequency range response of the simulation matches the measurement remarkably well.

Fig. 2. Scattering parameter results for the patch antenna

Radiated Susceptibility

We know from antenna reciprocity that antennas emit signals the way they receive them. This patch antenna resonates at 1.7 GHz. To confirm that it receives power at the same frequency we examined the S parameters.

Once confirmed, we moved into radiated susceptibility measurements of the patch antenna by itself. The left side of Figure 3 shows the physical test up at NIAR. The horn antenna sends an electromagnetic field toward the patch antenna, which stand upright about a meter away. We hit the antenna with a constant electric field and measured the power received at the port. Figure 3 shows the same setup in EMC Plus on the right side, it shows a plane wave traveling toward the patch antenna. At the base of the port, we will be measuring the signal received by the patch antenna from the electric field.

Fig. 3. Radiated susceptibility measured (right) vs. simulated (left)

Figure 4 shows the results. We observe a nicely matched trend throughout the full frequency range, especially at the primary peak of 1.7 GHz. Our results are within just a few dBs of the measured results, offering nicely matched frequency responses throughout the remainder of the frequency range.

Fig. 4. Susceptibility measurements, patch antenna alone

Directivity

Next, we looked at the directivity of the patch antenna. The power levels emitted by PCBs and antenna vary depending on the measurement orientation. Figure 5 shows directivity results on the right. The first test measured the patch antenna at 0°, or directly in front of the patch antenna. This is where the power level is going to be the highest. At 45°, you will see that the power level goes down slightly and at 90° it decreases even further. This demonstrates that changing the angle of incidence for the electromagnetic wave will change the power received at the patch antenna. The bottom left of Figure 5 bottom left shows the onset angle of 45° and 90°.

Fig. 5. Radiated susceptibility measured vs. simulated- Directivity

Figure 6 shows the results of the measurements with the physical results on the left. We are only looking at the primary resonance at 1.7 GHz. Physical measurements clearly show the drop in the magnitude after this frequency. The blue line demonstrates that the face-on position receives the most power. When changing to a 45° angle of incidence (red), we see that the power level drops in magnitude slightly. The 90° line in green also shows a further decrease in power. Our simulated data shows a very similar drop in magnitude between the three different simulations, which shows that we can accurately represent the directivity of an antenna and a PCB. This demonstrates how the power received from different angles of incident can change the power received at the PCB.

Fig. 6. Susceptibility measurements- Patch directivity

Testing in an Enclosure  

We also tested the patch antenna within an enclosure. Testing pieces in a metallic enclosure is useful to understand shielding effectiveness and generally how these pieces will radiate and receive power. Figure 7 on the left shows the setup, including the enclosure. The top left shows the same setup with the horn antenna exciting the PCB, which is inside the enclosure. On the right is the EMC Plus simulation.

Fig. 7. Radiated susceptibility measured vs. simulated- within enclosure

The results again were very promising as seen in Figure 8. The frequency range response matches the physical measurements extremely well. The EMC Plus simulation hit several of the peak frequencies along with the nulls throughout this entire frequency range.

Fig. 8. Susceptibility measurements with an enclosure

Cable Measurements

Additionally, we measured a set of cables just beyond the PCB. On the left side of Figure 9 is a schematic for one of the test setups with a biconical antenna sending an electromagnetic field towards a 3.3 m long cable. Figure 9 also shows the physical setup in the center with the EMC Plus model on the right. The images depict a horizontally polarized electric field directed toward the cable, which stretches between two boxes and has a current probe at the top. This setup allows us to capture both the radiated and conducted effects on the cable.

Fig. 9. Radiated susceptibility schematic vs. test vs. simulation

Figure 10 shows the results. Once again, we see a really impressive frequency range response capturing the simulated results matching the physical measurements across the frequency range.

Fig. 10. Radiated susceptibility results validation

Uncertainty

We must consider uncertainty in both simulation and measurement. In this case, we had our partners at NIAR complete remeasurements on a different day with the exact same units. We also consider a certain level of sensitivity to how things are laid out and variability in the product itself.

Additional Validations

This is the first in a series of validations we will be completing in this campaign. We also intend to look at some more complicated PCBs, including a basic slot antenna and a couple of intentionally poorly designed basic PCBs to validate further and gain a better understanding of how they work. Additional validations in the works include conducted susceptibility and emissions.

Conclusion

In this experiment we validated experimental radiated susceptibility measurements vs. simulation results. We partnered with NIAR to use their environmental test facility which includes EMC labs. The test program was modified to measure quantitative levels for a PCB patch antenna, the antenna within an enclosure, and the antenna in an enclosure connected to cables. We cross validated the radiated emissions from our device to the receiving antenna for both the exciting PCB and cables. Then we were able to do radiated susceptibility for coupling from an antenna to cables connected to a device. The results showed excellent correlation, confirming that EMC Plus would be able to predict if a device will pass or fail standard requirements ahead of manufacturing.

Learn More

You can learn more about this research and EMC Plus in the Solving Electromagnetic Challenges webinar “Validation of EMC Plus Versus Experimental Measurement in an EMC Lab.” You can watch it by clicking here.

EMC Plus is sold exclusively through Ansys, if you are interested in purchasing the software, please reach out to your Ansys channel partner.

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