Metamaterials: constitutive parameters, performance, and chemical methods for realization
Electromagnetic metamaterials are artificial materials composed of subwavelength structures to provide unusual effective macroscopic behavior not found in nature. These materials are characterized by constitutive relations which contain a maximum of 36 complex constitutive parameters. With different combinations of positive and negative parameters in the constitutive tensors, striking phenomena and novel applications were discovered. In this Feature Article, I briefly review the experimental progress in the metamaterial, focusing on their constitutive parameters and material performance, e.g. the bandwidth, the loss, and the electrical size with respect to the operating wavelength, etc. The two fabrication approaches: the structure approach that is widely used to construct periodic metamaterial structures, and the chemical approach that is very promising in constructing nano-scaled metamaterial with randomized patterns, are discussed. The practical potential of this field and the possible challenging future work are pointed out in the conclusion.