Difference between FEM and FDTD

Hello all,

I want to know whether there will be difference between results if I use different methods(FEm and FDTD) to solve a particular design (antenna, surface coil etc) in terms of S-parameter and SAR.

I have used ADS for design a surface type coil and again used EMPro for measuring the SAR for the coil.
Since in EMPro I need to use FDTD method to measure SAR instead of FEM. I am unable to get the required s-parameters. But I am able to get around -12dB in FEM in EMPro using FDTD I could get only -1.2dB only.

Can anyone suggest me anything?

If both are sufficiently converged, you should get the same solution using both methods. However, the advantages depends primarily on your geometry. If your geometry is very block-like, FDTD may be a better approach. If there are sharp corners, thick and thin pieces, etc, then FEM may converge faster.

The difference you're seeing is most likely convergence or mesh setup.

Hello PlanarMetamaterials,

Thank you so much for your reply. I have moved to HFSS since I can measure the SAR value using FEM itself in HFSS. I have finished the design. I have finished the simulation also.

Now, I am not aware of the method to find the finite value of the Average SAR from the field plot. Can you help me to find the finite value of the SAR from the plot. Since in EMPro I can get the Average Value of the SAR for the structure automatically along with this plot.

Hi kannangk1990,

This should be possible using the fields calculator. I believe you need to integrate the SAR over your structure and divide by the volume. Some good tutorials on the calculator can be found via google.

Edit: After checking HFSS, I noticed that there is a scalar quantity "Average SAR" (as opposed to the other quantity "Local SAR"). Could this be what you're looking for?

Good Luck

Dear PlanarMetamaterials,

Thanks again for your reply. I will try your idea of using the fields calculator.

The SAR plot I have attached is actually the Average SAR plot. In EMPro, actually along with this kind of plot the Average SAR for the whole volume can also be measured using which we can say whether the particular radiative structure is safe for human exposure or not. In HFSS, I'm not able to get this by default for SAR simulation. Actually, this is the reason for this query.

Thank you.