## 5 Results  
To assess the effect of the plasma discharge on the metasurface behavior and its possible reconfiguration, we have included the plasma tubes in between a \(8\times 5\) mushroom structure in which its permittivity is modeled using the [PERSON]'s model. For the model, we use four different electron density values, going from \(10\times 10^{11}\) cm\({}^{-3}\) to \(10\times 10^{14}\) cm\({}^{-3}\). The tubes are modeled to have a plasma collision frequency \(\
u_{p}=10^{10}\)\(1/\)s, which are achievable values for plasma tubes used in previous experimentation [34]. The plasma permittivity obtained with these values of \(n_{e}\) and \(\
u_{p}\) are shown in Figure 9.  
Once the plasma tube parameters are defined, we proceed to simulate the metasurface with plasma inserted into the parallel plate condition, with the three different tube positions with respect to the substrate and the top metallic cap of the mushroom (top, middle, and below) and varying the electron density. The simulated trans  
Figure 8: Different configurations of the relative position of the tubes with respect to the substrate and the mushroom cap. (**a**) top of the substrate and mushroom metallic cap; (**b**) half inserted in the substrate, in-line with the mushroom metallic cap; (**c**) below the mushroom metallic cap. Figure 7: Simulation configuration of the metasurface integrating the plasma tubes with its corresponding dimensions. previously described conditions are shown in Figure 10. We can see from the results that, for all the configurations, the discharges produce a shift in the stop-band generated by the mushroom lattice. As expected, we can see the stop-band shift when the electron density takes values of \(10^{13}\) cm\({}^{-3}\) and \(10^{14}\) cm\({}^{-3}\), while, for low values of \(n_{e}\), as the permittivity is close to the unit, its behavior is close to a vacuum condition. It is important to notice that, even if the frequency shift of the stop-band goes towards lower frequencies, the shift is not linear when we look to the assessed values of \(n_{e}\). Another remarkable result is that the frequency reconfiguration is more important when the tubes are placed in the middle configuration, which can be expected as the plasma permittivity will have a more direct interaction with the capacitance that is produced between each patch of the metasurface. We can see that, for the case when \(n_{e}=10^{14}\) cm\({}^{-3}\), the lower cutoff frequency of the stop-band shifts around 2 GHz (from 8 GHz to 6 GHz approx.). We can see a particular behavior for the \(n_{e}=10^{12}\) cm\({}^{-3}\) and \(n_{e}=10^{13}\) cm\({}^{-3}\) cases. For the case when the electron density is \(n_{e}=10^{12}\) cm\({}^{-3}\), we can see that there are important losses in transmission in the lower part of the band, before the stop-band regime. This can be explained with permittivity exhibited by the plasma, which is close to zero, and therefore is close to the plasma oscillation frequency. However, when we go higher in frequency, the permittivity is close to a vacuum behavior, which can be seen in the increment of the transmission coefficient being close to that case scenario. A similar behavior is observed for the case when \(n_{e}=10^{13}\) cm\({}^{-3}\), where its permittivity is close to zero in the higher part of the assessed band, and even if it exhibits a reconfiguration of the lower cutoff frequency of the stop-band, the higher part exhibits higher transmission losses due to the plasma characteristics. Finally, the bottom case has some particular results as it has a lower shift when compared to the middle case, the case when \(n_{e}=10^{12}\) cm\({}^{-3}\) has similar behavior to the lower electron densities cases. These differences can be explained by the fact that the tubes now are an important part of the substrate, which modifies differently the behavior of the metasurface. One last analysis to be done is with respect to the electric field inside the parallel plate structure.