Is periodicity required for negative index materials?

It has been demonstrated recently by a number of researchers that a periodic arrangement of closely spaced conducting wires and loops gives rise to double negative (i.e., negative permittivity and negative permeability) materials, known popularly as metamaterials, over a certain range of frequencies. While it may be of interest, in practice, to know the effect of material tolerances on the double negative properties, we are also studying the effect of a non-periodic lattice on the dielectric and magnetic properties of metamaterials. Our results indicate that a completely random array of conducting wires, having the same wire density as the periodic case, gives rise to essentially the same dielectric properties.