A New Approach for Extraordinary Transmission through Subwavelength Apertures Using ENNZ Metamaterials E. Baladi 1 , J. G. Pollock 1 , and A. K. Iyer 1 1 ECE Department, University of Alberta, Edmonton, Alberta, Canada ebaladi@ualberta.ca Abstract-Extraordinary transmission (ET) through a square array of subwavelength apertures on a metallic screen has been studied extensively, and has been attributed mainly to the interaction of surface plasmons, or the formation of leaky waves. This work describes a novel approach for achieving ET, in which the subwavelength apertures are treated as below-cutoff circular waveguides. Lining these apertures with epsilon-negative and near-zero (ENNZ) permittivity metamaterials enables the propagation of frequency-reduced guided modes through the apertures, resulting in strong transmission. Experiments in the optical regime have observed unusual transmission of light through arrays of subwavelength holes [1], which was referred to as “extraordinary transmission” (ET), and was found to be caused by the interaction of surface plasmons at interfaces with imperfect metals. The formation of leaky waves on a corrugated perfect metallic surface is another theory explaining ET [2], which also accounts for such phenomena in the microwave frequency regime. More recently, Fabry-Perot (FP) resonances have been shown to yield enhanced transmission through a single hole on a metallic screen, but they occur only once the aperture becomes large enough to support the fundamental propagating mode [3]. The work presented here offers a new mechanism for enhanced transmission through deeply subwavelength apertures, making it truly extraordinary in nature. The holes in a metal film of finite thickness may be described as very short metallic circular waveguides (CWGs). Recently, it was shown that transmission through miniaturized CWGs can be vastly improved through the introduction of thin MTM liners. A passband is introduced well below the natural fundamental cutoff frequency, in the regime in which the MTM liner exhibits epsilon-negative and near-zero (ENNZ) permittivity [4]. Figure 1 shows the variation of the HE 11 - mode cutoff frequency as a function of the liner’s relative permittivity (solid curve), for a representative metamaterial-lined CWG, which reveals the dramatic reduction in cutoff in the ENNZ region. Intersection with the superposed Drude permittivity dispersion profile of a representative MTM liner (dotted curve) indicates the cutoffs of two passbands: one at higher frequencies (a typical, forward-wave passband), and another at significantly lower frequencies (a backward-wave passband). The desired cutoff frequency in the reduced band may be achieved simply by engineering the MTM liner’s dispersion profile. The present work establishes the analogy between transmission through miniaturized MTM- lined CWGs and subwavelength apertures loaded using MTM liners. To enable simple, practical realization of the ENNZ MTM liner using inductively loaded thin-wire media exhibiting a Drude response, the phenomenon is illustrated in the microwave regime. Since the apertures are circular, circular arrangements of thin wires are preferred. Therefore, a printed-circuit implementation for Fig. 1. Variation of the fundamental (HE11) cutoff frequency of the lined CWG versus the liner permittivity (solid curve), intersected with Drude dispersion response for a representative MTM-liner permittivity (dashed curve) (a) (b) Fig. 2. The ENNZ MTM-lined aperture in a metallic screen: a) equivalent homogeneous-liner model b) equivalent practical thin-wire liner model