Modelling of electromagnetic material properties at microwave frequencies

In recent years, electromagnetic interference (EMI) has raised serious issues in terms of the unintentional radiation that disrupts the near proximity equipment from working properly. One solution to reduce the effects of EMI is the use of electromagnetic shielding. Carbon fibre composite (CFC) material is a promising customised product that has entered numerous industrial areas due to its attractive properties like high strength, low weight, and the resistance to chemical substances and corrosion. CFC has started to be used as electromagnetic shields, for example modern computer cases. However, not much is known about its electromagnetic behaviour. This research derives various models for CFC materials for the purpose of achieving better understanding to their interaction with electromagnetic waves at microwave frequencies. Throughout this research, the electrical properties of different materials have been investigated in terms of their shielding effectiveness (SE). The modelling was performed using the transmission-line modelling (TLM) method. The digital filter (DF) technique was used for small structures that are embedded in the system under modelling. In this way, the space mesh can be turned into coarser mesh. While maintaining the same accuracy, this technique has substantially saved on computational resources and has increased the speed of the modelling process. This in turn, has made it more feasible to model large scale practical systems. The formulae of DF cascading were derived to allow modelling systems of multiple embedded structures. Simulated models were validated by comparing them with the corresponding conventional fine mesh results. One-dimensional models were validated with the available analytic solution. Experimental measurements were conducted on panels made of this anisotropic material, which has manifested frequency-dependent characteristics that satisfy Drude model. These measurements have validated the corresponding numerical electromagnetic models. The final product of this study is gaining better knowledge about the electromagnetic behaviour of different materials. This knowledge can help in predicting the shielding performance when these materials are used within large-scale systems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo