A reflectarray optimized through a Generative Adversarial Network (GAN) is demonstrated. This design focuses on the impact of the top layer on the reflection phase and utilizes the correlation between phase distribution and the direction of the reflected beam. Six programmable Subcells are optimized to accommodate two incident angle waves simultaneously. Silicon substrate is exploited making the design compatible with integrated circuits. The far-field analysis indicates that for incident angles of 19.471° and 41.81°, as well as their vicinity, the reflectarray effectively redirects the incoming waves to reflect towards near-normal direction to its surface. This suggests a near independence of the deflection angle from the incident angle within a specific angular range, making the proposed reflectarray a planar THz beam collimator. The proposed Subcells achieve a reflection phase range of 342°. The return losses for the incident angles of 19.471° and 41.81° are 1.9 dB and 1.4 dB, respectively. For a finite reflectarray measuring 15λ×5λ, the pattern gain and fractional bandwidth are reported as 19.44 dB and 24.8% for the incident angle of 19.471°, and 19.17 dB and 29.9% for the incident angle of 41.81°. This denotes an excellent wideband behavior for the proposed single-layer pixelated reflectarray.

The current research paper presents the results of a simulation-based study on all-perovskite tandem multijunction devices using perovskites. The tandem structure considered in this study combines wide bandgap perovskites with 〖CsSnBr〗_3 (bandgap 1.8 eV) as the top cell and Cs_2 AuBiCl_6 (bandgap 1.2 eV) as the bottom cell. . Additional features of this study include the projection of tandem solar cells using lead-free perovskites containing 〖CsSnBr〗_3 and Cs_2 AuBiCl_6 .The effectiveness of the proposed tandem design is evaluated in two steps: first, we simulate a 1.8 eV perovskite-based top cell and tune the conversion efficiency to 9.8%. We then simulate a 1.2 eV perovskite-based bottom cell with a calibrated efficiency of 13.7%. After the standalone Subcell calibration is completed, the tandem configuration is evaluated. The current matching condition between the top and bottom cells is determined by varying the thickness of the absorption layer of both Subcells. The optimal thickness of the top cell is 350 nm and the optimal thickness of the bottom cell is 390 nm. When feeding the top and bottom cells with filtered spectra, the conversion efficiencies are 9.8% and 7.88%, respectively. Overall, the tandem design showed a conversion efficiency of 18.7%

Anisotropic media appear regularly in electromagnetic wave engineering. The finite-difference time-domain (FDTD) method is a robust technique to model such media. However, the value of the time step in the FDTD algorithm is bounded by the Courant-Friedrichs-Lewy (CFL) condition. In this paper, a simple analytical approach is developed using the Gershgorin circle theorem to derive a point-wise closed-form relation for the CFL condition in bounded inhomogeneous anisotropic media. The proposed technique includes objects of arbitrary shapes with straight, tilted, or curved interfaces located in a computational space with uniform or adaptive gridding schemes. Both axial and non-axial anisotropies are considered in the analysis. The proposed method is able to investigate the effect of boundaries and interfaces on the stability of the algorithm. It is shown that in the presence of an interface between two anisotropic media, the von-Neumann criterion is not able to predict the stability bound for specific ranges of the permittivity tensor components and unit cell aspect ratios. Exploiting the proposed closed-form formulations, it is possible to tune the CFL time step and avoid the temporal instability by the wise selection of the gridding scheme especially in curved boundaries where Subcell modelings such as Yu-Mittra formalism are applicable. Some illustrative examples are provided to verify the method by comparing the results with those of the eigenvalue analysis and time-domain simulations.