We present highly sub-wavelength magnetic metamaterials designed for operation at radio frequencies (RFs). A dual layer design consisting of independent planar spiral elements enables experimental demonstration of a unit cell size (a) that is ∼700 times smaller than the resonant wavelength (λ0). Simulations indicate that utilization of a conductive via to connect spiral layers permits further optimization and we achieve a unit cell that is λ0/a ∼ 2000. Magnetic metamaterials are characterized by a novel time domain method which permits determination of the complex magnetic response. Numerical simulations are performed to support experimental data and we find excellent agreement. These new designs make metamaterial low frequency experimental investigations practical and suggest their use for study of magneto-inductive waves, levitation, and further enable potential RF applications.

We computationally and experimentally investigate the use of metamaterial resonators as bandpass filters and other components that enable control of guided surface electromagnetic waves. The guided surface electromagnetic wave propagates on a planar Goubau line, launched via a coplanar waveguide coupler with 50 impedance. Experimental samples targeted for either microwave or terahertz frequencies are measured and shown to be in excellent agreement with simulations. Metamaterial elements are designed to absorb energy only of the planar Goubau line and yield narrow-band resonances with relatively high quality factors. Two independent configurations of coupled metamaterial elements are demonstrated that modify the otherwise flat transmission spectrum of the planar Goubau line. By physically shunting the capacitive gaps of the coupled metamaterial elements, we demonstrate the potential for a large dynamic range in transmissivity, suggesting the use of this configuration for highbandwidth terahertz communications.

The study of light coupling to small apertures in metallic fi lms has a long and illustrious history. In 1897 Lord Rayleigh treated the problem by using the concept of effective dipoles. Most recently, researchers have made these apertures periodic, where they exhibited so-called extraordinary optical transmission (EOT) -transmission effi ciencies far in excess of unity at wavelengths greater than the lattice parameter of the surface. This behavior is not predicted by standard aperture theory as developed by Bethe in 1944, [ 1 ] nor was it noticed before fabricational and measurement techniques had advanced to the point that EOT could be observed at optical wavelengths. However, in 1998 Ebbesen et al. [ 2 ] showed EOT in the near-infrared and posited that this stemmed from plasmon coupling between surfaces. Since then, EOT [2][3][4][5] has been studied with increasing detail in both theoretical and experimental capacities. This result led to a fl urry of intense theoretical and experimental research to probe the nature of this extraordinary optical transmission.Babinet metamaterials [6][7][8] may also be described as periodic apertures in metal fi lms. Metamaterials are structured periodic metallic patterns which enable the construction of materials with specifi ed electromagnetic properties, some of which cannot be obtained via naturally occurring materials. [ 9,10 ] Metamaterials exhibit electromagnetic resonances where the resonant wavelength is signifi cantly larger than the physical dimensions of the individual elements. Thus metamaterials are subwavelength media and well described by the optical constants ε and μ . [ 11 ] In transmission metamaterials (scatterers) yield an absorptive like minimum feature at resonance, but are otherwise highly transmissive outside of this band. In contrast Babinet metamaterials (apertures)-made by taking the 'inverse' metamaterial structure-yield opposite behavior and exhibit a transmission maxima near resonance. [ 12,13 ] Here we describe both Babinet metamaterials and EOT by an effective medium theory with plasmons playing a particularly important role. We further show that by utilizing metamaterial shaped apertures, we can augment the EOT effect. Specifi cally, it is demonstrated that Babinet metamaterials exhibit higher transmission effi ciencies at lower frequencies than traditional ellipsoidal and quadrilateral hole designs.Light transmission through patterned metallic surfaces display more complicated scattering, (compared to transmission in bulk metals), which is not easily reconciled with Drude theory. Specifi cally, drilled holes in metals exhibit transmission maxima far below the plasma frequencies of metals, even considering the fi nite hole size by accounting for diffraction. Most research has focused on holes of simple geometry to provide analytical models of the plasmon dispersion, and good progress has been made to accurately describe the transmission properties and clarify the contribution from surface modes. [14][15][16][17] Although there has been some exp...

W. J. Padilla and co‐workers report on page 221 extremely subwavelength extraordinary optical transmission (EOT) using Babinet metamaterial apertures. The front cover image depicts enhanced transmission and the importance of the strong coupling between light and surface and bulk plasmons, where the geometry of the aperture plays a crucial role.