Scattering or “S” parameters are used to define the behavior of electronic networks. For a two port network, there are four S-parameter definitions: S11 is the input port voltage reflection coefficient, S12 is the reverse voltage gain, S21 is the forward voltage gain, and S22 is the output port voltage reflection coefficient. For this system, only S11 and S21 are of concern. The data can be captured using a VNA. The difference between the energy in the incident wave and the sum of the reflected and transmitted wave energies is the amount of energy absorbed – which is radiated as heat. A simple example to illustrate this is an electromagnetic radiated wave (incident wave) that has 1.0 Joules of energy when it hits the shield. It is determined by measurement that 0.3 Joules (30%) of the energy reflects. That leaves 0.7 Joules (70%) of the energy which is either absorbed or transmitted (it goes right through the shield). If 0.2 Joules (20%) of the energy is measured as transmitted, by deduction, 0.5 Joules (50%) of the energy must have been absorbed in the material and lost to system as heat.