Negative refractive index metamaterials

a negative index of refraction over a band of microwave frequencies1. This demonstration of a previously unexploited electromagnetic (EM) property proved the importance of engineered materials and has resulted in an extraordinary amount of continued development by scientists working in optics, electromagnetism, physics, engineering, and materials science. Experimental results revealing new phenomena and potential applications for these artificial materials, more recently termed metamaterials (MMs), have provided the basis for impressive growth in this burgeoning field. EM-MMs exhibit exotic properties not easily achieved using naturally occurring materials. In addition to a negative index (NI) of refraction, properties such as artificial magnetism2, negative permittivity, and negative permeability have been observed in fabricated MM composites; these material properties are either absent from conventional materials or are difficult to achieve over various bands of the EM spectrum3,4. With encouraging results having been demonstrated at microwave frequencies, there has been a determined push to extend MMs to the terahertz, infrared, and visible bands. The pursuit of these higher frequency MMs has led to the establishment of many research programs, conferences, workshops, and significant funding efforts dedicated to understanding and developing MMs. Progress has been rapid: although the entire subject of MMs is relatively new1, the scaling of artificial structures has already been demonstrated from radio frequencies (RFs)5 to millimeter-wave6, Engineered materials composed of designed inclusions can exhibit exotic and unique electromagnetic properties not inherent in the individual constituent components. These artificially structured composites, known as metamaterials, have the potential to fill critical voids in the electromagnetic spectrum where material response is limited and enable the construction of novel devices. Recently, metamaterials that display negative refractive index – a property not found in any known naturally occurring material – have drawn significant scientific interest, underscoring the remarkable potential of metamaterials to facilitate new developments in electromagnetism.