# Enhancing Absorption Bandwidth through Vertically Oriented Metamaterials
## 5 Unit Cell Containing both a VSRR and PSRR  
In a unit cell containing dual split-ring resonators (DSRR), the resonator gaps are, at first, intentionally placed near each other to strengthen intra-cell coupling. This condition is further ensured by the matching spectral locations of the peak absorption for the individual resonators. In the DSRR unit cell, the geometric dimensions of the unit cell, VSRR, and PSRR remain the same as in the previous geometries. The unit cell geometry, as well as the plot of spectral absorption for all geometries, are illustrated in Figure 4.  
As with the single resonators, the spectral response is heavily dependent on the geometric parameters of the unit cell and resonators. In the case when two resonators are coupled, however, the parameter space gains complexity from parameters that affect the intra-cell coupling (e.g., relative distance between the SRRs), which arises as a result of MPL's capability to place SRRs on multiple surfaces within a single unit cell.  
In this case, a normally incident plane wave produces an absorption curve characterized by a peak absorption (\(A=0.91\)) of the DSRR geometry located at 31.00 THz, with a FWHM value of 9.549 THz. The shift of the peak absorption and increased FWHM clearly indicate coupling between the SRRs. Furthermore, the DSRR response demonstrates that the absorption of the coupled resonators is not simply the cumulative sum of the individual resonators.  
Similar to previous cases, electric and magnetic field profiles are shown in Figure 5. Specifically, Figure 5a,b shows the electric and magnetic field profile for the VSRR (similar to those shown in Figure 2), and Figure 5c,d shows the electric and magnetic field profile for the PSRR (similar to those shown in Figure 3). At peak absorption, the field profiles appear similar to those in the single SRR cases. When compared to the single SRR geometries, however, a significant decrease in peak field amplitude can be seen for both resonators. Additionally, the field profile near the point of highest  
Figure 3: (**top**) Spectral absorption; and (**bottom**) electric and magnetic field profiles in V/m and A/m, respectively, are shown for a unit cell containing a single planar split-ring resonator (PSRR).  
concentration is noticeably altered due to the presence of the other resonator, further demonstrating the intra-cell coupling between them.  
Figure 4: **(left)** The dual split-ring resonator (DSRR) unit cell geometry is illustrated. **(right)** Spectral absorption is plotted for the case of an empty unit cell, a unit cell containing a single PSRR, a unit cell containing a single VSRR, and a unit cell containing both a VSRR and PSRR. Note the widening of the absorption band in the DSRR case.  
Figure 5: The **(a)** electric and **(b)** magnetic field profiles of the VSRR in V/m and A/m, respectively, are plotted at peak absorption. The **(c)** electric and **(d)** magnetic field profiles of the PSRR in V/m and A/m, respectively, are plotted at peak absorption.  
The performance of metamaterials as a function of the incidence angle of the source, \(\theta\), is also of great interest [3; 39; 49; 50; 51]. In Figure 6, spectral absorption is plotted as \(\theta\) is swept from \(0^{\circ}\) to \(70^{\circ}\). Polarization of the source is unchanged as the angle of incidence varies in the YZ plane.  
Similar to individual resonators, the coupled resonators continue to demonstrate intolerance to changes in angle of incidence. As \(\theta\) increases, the spectral location of the peak remains nearly unchanged; the lowest value of the absorption peak experienced over this range is \(A=0.886\).