Redshifting extraordinary transmission by simple inductance addition

By interpreting the extraordinary transmission phenomenon on the basis of induced surface currents, the potential of engineering Rayleigh-Wood anomalies is shown, or more specifically, moving down the resonant peak away from the Rayleigh-Wood's anomaly. The strategy presented here relies simply on enlarging the path explored by the induced-surface current so as to increase the inductance of the structure, shifting consequently the resonant peak to lower frequencies because of the 1/$L^{1/2}$ dependence. This brings about two important consequences: The aperture is more subwavelength, which opens novel possibilities for realistic metamaterials, and the phenomenon emerges away from the onset of higher-order modes. Numerical as well as experimental results are given at the millimeter-wave regime supporting the initial assumptions.

Figure 1

Unit cell together with parameters and picture of each prototype: (a) normal subwavelength hole arrays and (b) meandering subwavelength hole arrays.

Figure 2

(a) Numerical simulation (dashed) and equivalent circuit (solid) computation for a hole array with square apertures of side $a_m$ $=$ 0.9 connected by meanders, compared to the response of regular hole arrays with $a$ $=$ 0.9 mm (same aperture) and 1.07 mm (same effective area). See rest of parameters in Fig. 1. (Inset) Simplified (lossless and infinitesimally thick) equivalent circuit representation of the type of structures considered. (b) Numerical simulation results of several meanders’ structures for three values of $d_y$ (rest of parameters as stated previously): 3 mm (solid), 3.5 mm (dash-dot), and 4 mm (dotted). (Inset) Frontal view of the surface current magnitude (colors) and electric-field snapshot (arrows) of the meander structure at resonance.

Figure 3

Retrieved constitutive parameters (a) ε${}_r$, (b) μ${}_r$ and normalized admittance (c) $Y$ for wires (green) and meanders (blue): real part (solid curves) and imaginary part (dotted curves). (d) Illustration of induced charge distribution, surface current (red arrows) and electric (green) as well as magnetic field (purple) along the $yz$-cutting plane at the narrow peak appearing nearby the Rayleigh-Wood's anomaly (100 GHz). Notice the enhanced induced field within the aperture.

Figure 4

Numerical (dashed) and experimental transmission coefficient (solid) through subwavelength hole arrays: (a, b) square aperture (wires); (c, d) meandering aperture (meanders). Top panels (a, c) represent magnitude, whereas bottom panels (b, d) phase response. Insets: electric-field distribution along the $yz$-cutting plane at the center of the unit cell ($x$ $=$ 0).