## 2 Materials and Methods
### Material Characterizations
#### 2.2.2 Dielectric Testing  
The open-ended coaxial method was used to find the electromagnetic parameters of the polymers. The tested sample diameter was 25 mm, while the thickness was kept at approximately 25 mm, and the sample was measured by touching it to the flat face of a solid material that operating within the frequency range of 1.39-19.22 GHz at room temperature. The measurement system comprised an open-ended coaxial probe (85071E, Keysight, CA, USA) connected to a vector network analyzer. The samples were cured in a small beaker using the same method, as shown in Figure 4a. The cured samples are shown in Figure 4b. The vector network analyzer consisted of a signal source, a receiver, and a display, as shown in Figure 5a,b. The source launches a signal at a single frequency to the material under test. The receiver is tuned to detect the reflected frequency and transmitted signals from the material. The measured response produces the magnitude and phase data at that frequency.  
Figure 4: **(a)** Four cured SE samples in small beakers. **(b)** Four cured PDMS samples being removed from the glass tube.  
Figure 3: A schematic illustration of the sample geometry prior to testing.  
The connected dielectric measurement instrument predictably applies the electromagnetic fields before the measurement process. The measured data are then converted into permittivity or permeability values. The real part of the complex dielectric constant \(\epsilon^{\prime}r\) (\(K\)) is equivalent to the relative permittivity (\(\varepsilon r\)), or the absolute permittivity (\(\varepsilon\)) relative to the permittivity of free space (\(\varepsilon_{0}\)). The real part of permittivity (\(\varepsilon^{\prime}r\)) is the dielectric constant, and the imaginary part is the dielectric loss \(\varepsilon r^{\prime}\). \(\varepsilon^{\prime}r\) is a measure of how much energy from an external electric field is stored in the material. The imaginary part of permittivity (\(\varepsilon r^{\prime}\)) is called the loss factor, which is a measure of how dissipative or lossy the material is to an external electric field.  
\[K=\frac{\varepsilon}{\varepsilon_{0}}=\varepsilon r=\varepsilon^{\prime}r-j \varepsilon r^{\prime\prime} \tag{2}\]  
The conductivity is measured by considering the imaginary part of permittivity \(\varepsilon r^{\prime\prime}\), which represents the mechanisms of electromagnetic losses inside the material due to molecular polarization and electron movement. Hence, the conductivity, \(\sigma\), can be computed as follows [17]:  
\[\sigma(f)=2\pi f\varepsilon r^{\prime\prime}\ (f)\varepsilon_{0} \tag{3}\]  
2.3 Radiation Attenuation Properties: Mean Attenuation Properties and Effective Atomic Number (\(Z_{\text{eff}}\))the tensile strength by reducing the amount of curing agent. PDMS 10.5/0.5 and PDMS 21/1 reduced the stiffness and flexibility of the samples. The PDMS samples were observed to have lower tensile and Young's modulus values with the increasing weight and thickness of the specimens of PDMS 19/3, PDMS 20/2, and PDMS 21/1. This trend showed that lighter samples are consistently stiffer than heavier samples.  
On the other hand, SE did not result in conclusive findings since the graph was not consistent for either Young's modulus or tensile strength (Figures 6 and 7). The Young's modulus of our SE samples was relatively higher, while the tensile strength was in good agreement with that reported in previous studies [15]. However, the thin samples followed the same graph pattern as PDMS. The standard mixing ratio of SE 5/5 was found to be optimum as the elastic modulus was higher compared to those of the other mixing ratios.