ABSTRACT
In some natural materials, macroscopic electromagnetic (EM) parameters can be theoretically derived from atomic or molecular structures, which usually involves tedious work. As has been pointed out in Chapter 1, metamaterials use man-made atoms, that is, meta-atoms, to mimic real materials for the flexible control of EM waves. Then it is quite natural thatwe can borrow the same idea for the calculation. Sometimes, rigorous analysis may be impossible; however, the classical model (e.g., Lorentz model) can be used for numerical optimizations. Moreover, a deep understanding of natural materials helps to improve the metamaterial design and creates new controllable materials. In this chapter, we provide a few theories frequently used in metamaterials and introduce the detailed parameter-retrieval process. It hence lays the theoretical foundationfor the later chapters.
