# A New Compact Octagonal Shape Perfect Metamaterial Absorber for Microwave Applications
## 3 Results and Discussions
### Analysis of Design Structure with Resonator's Number  
The absorption of electromagnetic energy also is contingent on the resonator's number used in the structure. Effect of resonator's number on the substrate material of the PMA has been analyzed. The effect of absorption is shown in Figure 10. The absorption peaks of the structure are 58.35% at 7.54 GHz and 91.97% at 10.89 GHz for two inner resonators. Similarly, the peaks of the absorption are 81.77% at 10.99 GHz for inner and outer resonators. Moreover, absorption peaks are 98.99% at 8.10 GHz and 68.97% at 11.43 GHz, respectively, for two outer resonators. Furthermore, 99.64% at 8.08 GHz and 99.95% at 11.41 GHz, respectively, for three metallic resonators. The maximum absorption peaks are 99.64% at 8.08 GHz and 99.95% at 11.41 GHz, for three metallic resonators.  
The absorption values have been different due to the number of metallic resonators. The PMA with three metallic resonators has shown the maximum peak. However, the minimum peak and single absorption peak have been achieved from metallic resonator with the combination of inner and outer resonators. Hence, the variation of absorption has occurred for different ring's number.  
Table 1 demonstrates the comparisons with proposed PMA and another reported PMA. The compared parameters of PMA have been considered here, for example, design structure, size of unit cell structure, applicable band, absorption rate, and year published. [PERSON] et al. [21] proposed modified square-shape structure with 8 \(\times\) 8 mm\({}^{2}\) size and obtained absorption of 95.81% in Table 1. Likewise, other authors, [PERSON] et al. in [22], suggested a U-shape absorber for multiband application. On the other hand, authors have achieved 98% absorption with 15 \(\times\) 15 mm\({}^{2}\) size of design structure. [PERSON] et al. [23] exhibited an O-shape with 12 \(\times\) 12 mm\({}^{2}\) dimension of unit cell structure for X-band application. However, Authors obtained absorption of 98.90%. In [17] an S-shape  
Figure 9: Absorption of the design structure for different resistive load.  
metamaterial absorber was analysed using various substrate materials and different propagation axis of electromagnetic wave. In contrast, authors have obtained a small amount of absorption. [PERSON] et al. recommended L-shape structure with 9 \(\times\) 9 mm\({}^{2}\) dimension for X- and Ku-band operations and attained absorption of 95%. In addition, the authors, [PERSON] et al. [24] suggested modified S-shape structure with 16 \(\times\) 16 mm\({}^{2}\) dimensions and achieved absorption of 90%. The compact octagonal shape PMA has been analysed and attained higher absorption (98.97%) with compact size of unit cell (10 \(\times\) 10 mm\({}^{2}\)) in this paper. The proposed metamaterial has attained compactness and high absorption comparing mentioned references that are suitable for the microwave regime. In addition, the compact size of the design structure is feasible for X band application. Hence, the manufacturability and robustness of the properties of our design structure are very good for commercial adoption.