# A Subcell Finite-Difference Time-Domain Implementation for Narrow Slots on Conductive Panels
## 5 Conclusions  
This paper proposes and evaluates two subcell full-wave alternatives to the classical capacitive Gilbert-Holland DMMA FDTD model for analyzing the coupling through narrow slots on conducting thin panels: a conformal one (CA) and a subgridding (SG) one. The DMMA method exhibits deficiencies when normal propagation and uniformity of the fields around the slot are not fulfilled. On the other hand, SG and CA do not have this limitation, since they consider all the field components around the slot. Therefore, when the polarization or the incidence angle is relevant, subgridding and CA present better results than DMMA. Three test cases are presented:  
* A classical validation consisting of a narrow slot on PEC and conductive panel, where DMMA assumptions of the normal propagation and uniform field distribution across it produce worse results than CA at HF;
* A PEC cage with one of its sides covered either by PEC or conductive panel with a rectangular slot under plane wave incidence. There, the actual robustness of DMMA is shown compared to the full-wave CA method since the cage resonances dominate over the slot ones at HF;
* A real PEC cage with one side, either in PEC or in CFC, in a RC compared with experimental results. Results show a typical EMC real scenario and help the engineer understand the margins in the differences in simulation versus measurements. Results show that DMMA underestimates the SE, especially below the first resonance. This effect does not appear in the well-controlled cage of the previous test case, and we have attributed it to the stochastic nature of the incident waves. For higher frequencies, no clear conclusions can be drawn since the cage resonances clutter the results, and only worst-case margins could be extracted by an EMC practitioner. Next, we will explore the integration of the Conformal Approximation (CA) method and the subgridding technique proposed in this work for Electromagnetic Compatibility (EMC) applications. By combining these two approaches, we aim to effectively address more complex EMC scenarios, especially in conductive structures with overlapping joints. This integration could lead us to develop a stable and computational efficient method, surpassing the limitations of each method individually, and opening up new possibilities for EMC solutions in various engineering and applied sciences contexts. Conceptualization, M.R.C., A.J.M.V., B.P., M.F., D.P., A.R.B., A.G.B. and S.G.G. ; methodology, M.R.C., A.J.M.V., B.P. and A.G.B. ; software, M.R.C., A.J.M.V. and A.G.B. ; validation, M.R.C., B.P., M.F. and D.P. ; formal analysis, M.R.C., A.J.M.V., A.R.B., A.G.B. and S.G.G. ; investigation, M.R.C., A.J.M.V., A.R.B., A.G.B. and S.G.G. ; resources, B.P., M.F., D.P. and S.G.G. ; data curation, B.P., M.F., D.P. and A.G.B. ; writing--original draft preparation, M.R.C., B.P. and S.G.G. ; writing--review and editing, M.R.C., A.J.M.V., M.F., D.P., A.R.B. and A.G.B. ; visualization, A.J.M.V., B.P., M.F. and A.G.B. ; supervision, S.G.G. ; project administration, D.P., A.R.B. and S.G.G. ; funding acquisition, D.P., A.R.B. and S.G.G. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Method** & **CFLN** & **\(\Delta_{\text{min}}\) [mm]** & **\(\Delta_{\text{max}}\) [mm]** &
\begin{tabular}{c} **CPU Gain** \\ **Respect to** \\ **Standard FDTD** \\ \end{tabular} & **Memory** \\ \hline Standard & 0.9 & 1.25 & - & 1.0 & 7.9 \\ \hline CA & 0.9 & 5 & - & 262 & 0.1 \\ \hline DMMA & 0.9 & 5 & - & 262 & 0.1 \\ \hline SG \(N_{\text{sg}}=1\) & 0.67 & 1.25 & 2.5 & 4.2 & 0.68 \\ \hline SG \(N_{\text{sg}}=3\) & 0.67 & 1.25 & 10 & 14 & 0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Efficiency results. **Funding:** Funded by the European Union under GA no 101101961--HECATE. Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or Clean Aviation Joint Undertaking.