Artificial Dielectrics: Ordinary Metallic Waveguides Mimic Extraordinary Dielectric Media

Consider an electromagnetic wave propagating in the empty space between two parallel metal plates. This situation is often the first example of guided waves encountered by undergraduate students since the solutions (the guided modes) are analytic and easily obtained. And yet, this seemingly simple configuration can give rise to a number of interesting and even counterintuitive phenomena. For the set of modes with the electric field pointing parallel to the surfaces of the two metal plates, the region between the plates, though simply empty space, mimics the properties of a dielectric medium with a wave velocity yp different from c, that of waves in vacuum. The waveguide therefore can be described as an artificial dielectric [1] with an effective refractive index n=c/yp different from unity. In contrast to naturally occurring dielectrics for which n 2 1, n can have a value less than unity. These waveguide-based artificial dielectrics were first introduced in a small body of work by the microwave community about half a century ago. As discussed here, the wavelength scaling that results when moving from the microwave region to the terahertz (THz) region results in more practical structural dimensions. This gives new life to these artificial dielectrics for a variety of novel and exotic applications in THz science and technology.