# Graphene and Iron Reinforced Polymer Composite Electromagnetic Shielding Applications: A Review
## 3 Electromagnetic Inferences Theory  
The practice of blocking conducting or radiating electromagnetic waves into sensitive areas is known as EMI shielding [12; 53]. EMI shielding materials have a wide range of applications including commercial and scientific electronics, antenna systems, space explorations, satellite communication, automotive radar, millimetre wave wireless LAN and medical devices [12; 54]. EMI shielding materials also have a wide range of military applications such as stealth in which radar absorbing materials (RAMs) are used to reduce the detectability of the target by cancelling reflections of a radar signal impinging to its surface [12; 55; 56]. Based on the frequency, electromagnetic waves are classified as ionizing and non-ionizing radiations. Ionizing radiations are high frequency electromagnetic waves that include X-rays and gamma rays, whereas non-ionizing radiations are low frequency electromagnetic waves that include microwaves fields, infrared radiation, ultraviolet radiation and radiofrequency [57]. When electromagnetic waves strike the EMI shield, the occurrence can be a reflection, absorption, transmission, and multiple reflections [58; 59; 60; 61; 62] as shown in Figure 2.  
Reflection is considered as a primary shielding mechanism in a homogeneous conductive material, where materials must possess mobile charge carriers to interact with EM waves [58; 60; 62]. Absorption is considered the second most essential mechanism which depends on the shielding thickness. Absorption capacity increases when the material acquires electrical and magnetic dipoles in contact with EM waves. Multiple reflections are the third shielding mechanism which usually decreases if the shield is thinner than the skin depth but could be ignored if it is thicker than the skin depth. When an EM wave passes a conductive material, its strength decreases [48]. Multiple reflections can be secondary reflection and secondary transmission [63]. Eliminating the secondary microwave pollution generated by a strong reflection of electromagnetic shielding material is also important which can be achieved by developing the high efficiency elect  
Figure 2: Schematic illustration of electromagnetic wave strike on protected device. material [64]. The overall shielding effectiveness for a material can be calculated by using Equation (1) [65]:  
\[\mathrm{SE_{overall}=SE_{R}+SE_{A}+SE_{MR}} \tag{1}\]  
where, SE = shielding effectiveness, R = reflection, A = absorption and MR = multiple reflections  
\(\mathrm{SE_{R}}\) is the reflection loss that is linked with impedance mismatching among EM waves and shielding material. Reflection loss can be calculated by using Equation (2) [66]:  
\[\mathrm{SE_{R}=20\log\left|\frac{Z_{in}-1}{Z_{in}+1}\right|} \tag{2}\]  
where, \(Z_{in}\) is the impedance of the absorber. \(\mathrm{SE_{R}}\) is a function of permeability and conductivity which decreases with frequency. EM waves amplitude decreases upon passing through the material where absorption loss occurs. The absorption loss occurs due to material heating and ohmic losses when current is induced. It can be calculated by using Equation (3) [65]:  
\[\mathrm{SE_{A}=20\log e^{\frac{d}{\delta}}} \tag{3}\]  
\[\delta=\sqrt{\frac{2}{\omega\upmu\sigma}} \tag{4}\]  
where, d = material thickness, \(\delta\) = skin depth, \(\upmu\) = permeability, \(\sigma\) = conductivity, \(\omega\) = wave frequency. Upon passing an EM wave through the material, the intensity reduces, which is known as the attenuation constant. \(\mathrm{SE_{A}}\) depends on thickness, permeability, and conductivity. The dependency of both \(\mathrm{SE_{R}}\) and \(\mathrm{SE_{A}}\) on conductivity and permeability shows that the shielding is controlled by absorption rather than the reflection in conducting metals. Besides that, permittivity is also important for enhancing the \(\mathrm{SE_{R}}\) and \(\mathrm{SE_{A}}\)[65].