The paper describes a new technique for implementing artificial materials (metamaterials) with unusual electrical properties at microwave frequencies. In particular, theoretical and experimental results are presented for realizing "left-handed" metamaterials which support the fascinating phenomenon of negative refraction of electromagnetic waves. Hence these materials can also be referred to as Negative-Refractive-Index metamaterials. I believe that an important reason for this paper being highly cited is that it was published at a time when there was heated controversy regarding the physics and feasibility of negative refraction. Our paper presented clear experimental evidence confirming negative refraction and went even further to demonstrate for the first time focusing of electromagnetic waves from a left-handed lens. In addition, the new technique proposed for constructing left-handed metamaterials leads to broad frequency bandwidths over which negative refraction and focusing can be achieved, an important attribute that caught the attention of the community. In retrospect, it appears that our paper played a significant role in convincing the scientific community that negative refraction and associated focusing effects are indeed real. Another plausible contributing factor for the interest in our paper is that it is written in a clear and simple way so that people across disciplines can follow.

The paper describes a new paradigm for synthesizing artificial materials with unusual properties at microwave frequencies (multi-gigahertz range). This technique is based on printing a mesh of wire strips above a ground plane (transmission lines) loaded with simple circuit components such as inductors and capacitors. Specifically in the paper it has been demonstrated that this transmission-line approach can be utilized for synthesizing left-handed materials. At the interface of a left-handed material and a conventional dielectric, plane waves bend negatively whereas cylindrical waves are brought to a focus. The properties of these new materials can be harnessed for creating a new generation of antennas and other microwave components with reduced size and enhanced performance for the wireless communication and defense industries.

Our work was inspired by previous work on left-handed materials carried out by David R. Smith and Sheldon Schultz of U.C. San Diego, and John Pendry of the Imperial College in London, U.K. Based on our microwave background we conceived a unique and useful way for constructing left-handed materials. Our key observation was that there is a correspondence between an inductor and negative permittivity and a capacitor and negative permeability. The simultaneous presence of negative permittivity and negative permeability gives rise to a left-handed metamaterial. In such left-handed metamaterials the refractive index also becomes negative, thus reversing Snell’s law, which was established in 1621. What is rather amusing is that this idea struck the first author of the paper during the summer of 2001 when he was relaxing on a sunny Sunday morning in his backyard.

The feasibility of left-handed materials was theoretically proposed by the Russian scientist Victor Veselago in the 1960s. However, it is only recently that people learned how to make such materials. Our paper describes a simple method for constructing such materials by means of loaded printed metallic strips over ground (transmission lines). The resulting transmission-line metamaterials are entirely planar, low loss, and maintain their useful properties over a broad band of frequencies. The new physical phenomena enabled by these left-handed materials can prove very useful for making planar microwave lenses with unprecedented levels of resolution, as well as miniaturized antennas and other wireless-communication devices with enhanced performance and functionality. Several groups around the world, including ours, are presently working towards this goal.