The electromagnetic response of H-fractal structures, consisting of self-similar metallic lines or slits in metallic films deposited on silicon substrate, has been investigated in the terahertz region. The subwavelength fractal structure was observed to display electric resonances, with redshift in the resonant frequencies accompanying an increase in either the fractal level or the sample size. The associated increase in sample size is several times smaller than that expected from the scaling rule, indicating the possibility for achieving significantly subwavelength resonances. The very strong terahertz wave confinement in subwavelength regions (about 17 times smaller than the wavelength in vacuum), together with the multifrequency nature of the fractal resonances, characterize our metamaterial unit cell. By measuring both the power transmission and phase shift, we obtain the real and imaginary parts of the effective permittivity for our H-fractal structures in the terahertz regime. Strongly dispersive behavior of the real part of the permittivity is seen at multiple frequencies.

• Received 29 November 2007

DOI:https://doi.org/10.1103/PhysRevB.77.045124