# A New Compact Octagonal Shape Perfect Metamaterial Absorber for Microwave Applications
## 3 Results and Discussions  
The simulations of the unit cell structure and array structure are executed using a full-wave frequency domain solver based on the FIT. In simulation, the waveguide port with periodic boundary conditions is applied. In this paper, scattering parameters, absorption of design structure with angular rotation, thickness of substrate materials, thickness of radiated patch and ground materials, effect of the resonator's number, and resistive load have been analysed. The numerical simulation and experimental result of compact octagonal shape PMA has been presented. The numerical simulation and measured absorption A (\(\omega\)) of the design structure has been demonstrated in Figure 3. As is seen from Figure 3, the frequencies of the proposed design are in X-band.  
From Figure 3, the numerical simulation and experimental results are showing agreement with each other. The measured results have been shown the same band when comparing with numerical results in Figure 3. In simulation, the absorption values of the structure are 99.64% and 99.95% at frequencies 8.08 GHz and 11.41 GHz, respectively. However, the values of the absorption are 97.74% at 8.00 GHz, and 98.97% at 11.30 GHz, correspondingly by measurement. Furthermore, the absorption parameter of measured results has been slightly shifted towards the lower frequency and decrease small amount of the magnitude when comparing with simulation results. The small difference can be attributed to fabrication tolerance and open-space measurement procedure.  
Figure 3: Simulated-measured of absorption for the proposed PMA.  
Figure 2: (**a**) The boundary condition of PMA; (**b**) Measurement set of PMA. PEC: perfect electric conductor; PMC: perfect magnetic conductor; EM: electromagnetic.  
The electric field and magnetic field distributions are examined at the resonant frequency of 8.08 GHz to understand the physical mechanism of operation. The field distributions are shown in Figure 4. It is observed that there is high concentration of electric field around the outer side of the rings. The electric field are powerfully coupled with the rings and produce electric response that works as like an electric dipole moment. Hence, the charges of outer surface excite along the external electric field. As a result, a magnetic dipole is induced and it produces a magnetic response that makes a resonant absorption. In addition, high concentration of magnetic field is observed around the upper side and lower side of middle rings. The magnetic fields are strongly coupled with the rings and induce magnetic response that works as like a magnetic dipole moment. Consequently, an electric dipole is induced and produces an electric response that makes a resonant absorption. However, the desired response of electric and magnetic fields occur at this resonant frequency concurrently, resulting in almost complete absorption of the EM wave under the ideal condition (Z (\(\omega\)) = Z0 (\(\omega\))).  
Therefore, the energy of EM is dissipated in the structure, which produces zero transmission and reflection with unity absorption. Moreover, properties are also observed for the second resonance found at 11.41 GHz suppose its approach, as shown in Figure 5. It is seen from Figure 5, the highest concentration of electric filed occurs at the right side of the octagonal resonator. The non-uniform perturbation of field distribution is also investigated. It indicates that the response of electric and magnetic field are similar to 8.08 GHz response with higher intensity. Hence, this approach is higher than the previous one. Hence, this produces higher absorption rate than 8.08 GHz.  
Figure 4: (**a**) Electric field; (**b**) Magnetic field distribution at resonance frequency 8.08 GHz of PMA.  
Figure 5: (**a**) Electric field; (**b**) Magnetic field distribution at resonance frequency 11.41 GHz of PMA.