1.Introduction In recent years,there has been an intense research effort by the international community in the field of“artificial”electromagnetic materials,or“metamaterials.”Metamaterials are engineered structures that induce a tailored arrangement of magnetic and electric dipole moments when excited by an incident electromagnetic field.Under certain conditions,such as when the comprising unit cells are sub-wavelength,metamaterials can be homogenized and described in terms of macroscopic constitutive parameters such as permeability,permittivity,and refractive index.A summary of the early work on“artificial dielectrics”can be found in Ref.[1].In the over 20-year-old field of metamaterials,the desired macroscopic parameters correspond to extreme properties such as negative permittivity,negative permeability,and a negative refractive index.Perhaps the most recognized metamaterial is that which realizes a negative refractive index,originally demonstrated at microwaves and based on a unit cellmade out of a split-ring resonator and a wire[2].In the engineering community,a transmission-line approach was developed for implementing metamaterials with significant advantages,such as reduced transmission losses and wider operating bandwidths[3,4].
展开▼
