ABSTRACT
Metamaterial was first demonstrated by [54] with the use of split ring resonator (SRR) and metallic wire, among which SRR and metallic wire show the properties of negative permeability (µ) and negative permittivity (ε) at the resonance frequency, respectively. Metamaterial is not a traditionally defined material. It comprises many periodic or non-periodic unit cells. By giving different structure and property to these unit cells, the whole array of unit cells, which is the metamaterial, would show some properties that do not naturally exist. A more clear definition can be found in Figure 2.1 [55], where both x and y axes correspond to the material relative permittivity (εr) and permeability (µr), respectively. Most natural materials lie on the horizontal line in the 1st quadrant (εr > 0, µr > 0) with a relative permittivity larger than 1 and a nearly unity relative permeability. But with metamaterial, by giving different design for unit cells, theoretically we can construct a material located in any of the regions of Figure 2.1 that enables many interesting applications. According to the transmission and reflection property, metamaterial can be categorized into two types: non-resonant-type and resonant-type.
