## 2 Materials and Methods
### Acoustic Solutions for Banasa Airport
#### 2.2.2 Design of Sound-Absorbing Panels  
The novel design of the resonance-absorbent screen will target the area of interest between 1600 Hz and 4000 Hz. The new design will incorporate the benefits of traditional barriers and resonance-absorbent structures for optimal performance. The resonance-absorbent structures consist of interconnected resonators, created by perforating holes in a plate mounted at a specific distance from a rigid wall, as shown in \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & **16 Hz** & **31.5 Hz** & **63 Hz** & **125 Hz** & **250 Hz** & **500 Hz** & **1 kHz** & **2 kHz** & **4 kHz** & **8 kHz** \\ \hline Lw1 & 91.4 & 102.6 & 108.4 & 113.7 & 114.7 & 115.1 & 117.1 & 124.9 & 121.3 & 116.7 \\ \hline Lw2 & 93.5 & 104.6 & 106.6 & 116.0 & 116.4 & 116.4 & 116.9 & 125.1 & 123.8 & 119.0 \\ \hline Lw3 & 93.4 & 103.1 & 108.6 & 116.2 & 115.9 & 116.3 & 115.1 & 121.3 & 119.7 & 115.3 \\ \hline Lw4 & 96.1 & 102.9 & 111.4 & 116.8 & 119.3 & 119.5 & 115.2 & 118.8 & 117.6 & 115.9 \\ \hline Lw5 & 95.8 & 103.0 & 110.2 & 117.4 & 118.3 & 117.6 & 112.7 & 113.7 & 115.6 & 115.4 \\ \hline Lw6 & 96.2 & 104.6 & 110.3 & 115.9 & 118.0 & 116.9 & 111.8 & 110.1 & 112.6 & 116.1 \\ \hline Lw7 & 96.4 & 103.9 & 111.8 & 117.8 & 118.3 & 116.6 & 110.6 & 108.8 & 108.3 & 117.0 \\ \hline Lw8 & 97.6 & 104.3 & 112.9 & 117.6 & 118.3 & 117.4 & 114.7 & 110.5 & 110.5 & 118.3 \\ \hline Lw9 & 98.2 & 105.4 & 114.6 & 121.4 & 122.3 & 121.3 & 119.3 & 115.7 & 116.6 & 126.4 \\ \hline Lw10 & 97.9 & 104.6 & 114.1 & 121.0 & 123.5 & 123.3 & 124.1 & 121.0 & 119.8 & 129.2 \\ \hline Lw11 & 100.3 & 104.8 & 114.2 & 120.9 & 123.9 & 121.6 & 120.5 & 118.1 & 118.8 & 125.6 \\ \hline Lw12 & 100.8 & 106.4 & 118.0 & 123.4 & 122.9 & 121.5 & 120.5 & 117.3 & 119.6 & 123.6 \\ \hline \end{tabular}
\end{table} 
Table 2: The \(1/1\) octave sound power spectrum for maximum mode, shown in dB. Figure 11: Noise polar diagrams for maximum mode. The frequency band of such a system can be calculated using Equation (1) [40]:  
\[\Delta\mathrm{f}=4\pi\frac{\mathrm{f}_{0}}{\lambda_{0}}\mathrm{D} \tag{1}\]  
where:  
* D is the distance of the plate from the rigid wall;
* f\({}_{0}\) is the frequency of resonance;
* \(\lambda_{0}\) (m) is the wavelength at resonance. The frequency of resonance is established by the size of the resonator's neck and the volume of air in the cavity. By adjusting the distance of the plate from the wall and the density of the porous material in the cavity, the frequency band can be broadened to cover up to three octaves. To ensure low costs for the new absorbent structure, round perforated plates that are widely available on the market were selected and five types of perforated plates were considered for the study, as presented in Table 3.  
To determine the optimal perforated plate for our application and for the established frequency range of interest, the distance between the perforated plate and the unperforated plate was varied from 10 to 100 mm, increasing in increments of 10 mm, and the resonance frequency and bandwidth of each plate were calculated. The results are presented in Table 4. For each scenario, the bandwidth (Hz) was identical. Figure 12: Resonance-absorbent structures. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Thickness (mm)** & **Perforation Diameter** & **Distance between the Centers of the Perforations** \\  & & **(mm)** & **(mm)** \\ \hline plate\_1 & 1 & 2 & 4 \\ \hline plate\_2 & 1 & 3 & 8 \\ \hline plate\_3 & 1 & 8 & 12 \\ \hline plate\_4 & 3 & 3 & 6 \\ \hline plate\_5 & 3 & 4 & 8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The perforated plate types used for the experiments. Based on the above calculations, plate number 1 exhibits the broadest frequency range. To confirm the calculations obtained for plate 1 and acoustically characterize the plate, measurements of the sound absorption coefficient were carried out using an impedance tube (Kundt tube, Figure 13) according to the UNI EN ISO 10534 2 standard [41; 42].