| Refractive index is determined by permittivity epsilon and permeability mu, where permittivity a is the degree of polarization of a material in response to an electromagnetic field and permeability mu is the degree of magnetization of a material in response to an applied electromagnetic field. If both permittivity epsilon and permeability mu are simultaneously negative, the real part of the refractive index is negative, and the material is called a "negative index (meta)material." The prefix "meta" is used to indicate that such materials are not found in nature since no natural materials have magnetism at optical frequencies. In 1999, from calculation, J. B. Pendry demonstrated an engineered structure which exhibits negative effective permeability at microwave frequency. In 2002, we proposed that magnetic resonance can be excited in coupled nano-rods, and in 2005 we fabricated the world's first metamaterials with a negative index of refraction at 1.5 um (this earned a NASA Nano 50 Award for the top 50 nanotechnologies in 2006). Then in 2007, we designed and fabricated the world's first meta-magnetics for visible wavelengths (491 -- 754 nm). In the same year, we demonstrated a state-of-the-art optical metamaterial with a dual-band negative index of refraction at both 813 nm and 772 nm. In 2008, we pushed this record to 710 nm.;The possible applications of negative index metamaterials have boomed since 1999 due to their unique optical properties. Negative index metamaterials have been proposed to be used for a perfect lens, which has the ultimate resolution beyond the diffraction limit. In 2006, negative index metamaterials were used as a building block for a microwave cloaking device. |
