A class of artificial materials isorefractive with free space

A new class of dispersion-free artificial material that is isorefractive with free space is presented. Materials can be fabricated by composing an array of conducting inclusions in a tenuous host medium that are symmetric with respect to the direction of propagation. Strategies are proposed for both longitudinal and radial propagation. In the presence of the transverse electromagnetic mode, the inclusions are transversely polarized and hence raise the effective relative dielectric constant of the material. The inclusions simultaneously constrict the magnetic field lines, lowering the effective permeability by the same factor. The net effect is to make an artificial material with the same speed of propagation as the host material, but with a lower effective impedance. Such a material can be used to improve aperture efficiency in impulse radiating antennas. Limitations of the materials in-+cluding field enhancement due to the inclusions and skin losses due to finite conductivities are also discussed.