Abstract
Thin (sub skin-depth) metal layers are known to almost completely reflect radiation at microwave frequencies. It has previously been shown that this can be overcome at resonance via the addition of closely spaced periodic structures on either side of the film. In this work, we have extended the original one-dimensional impedance mechanism to the use of two-dimensional periodic structures both experimentally and analytically using an equivalent circuit approach. The resulting device shows experimentally a low (<5% relative frequency shift) dependence in both angle of incidence and polarisation. We also show that the same principle can be used to transmit through a thicker (∼μm) perfectly conducting film perforated with a non-diffracting (short pitch) array of subwavelength holes with the cut-off frequency above 900 GHz showing resonant transmissivities in the 20–30 GHz range above 40%.
Highlights
Thin metal layers are known to almost completely reflect radiation at microwave frequencies
We show that the same principle can be used to transmit through a thicker ($lm) perfectly conducting film perforated with a non-diffracting array of subwavelength holes with the cut-off frequency above 900 GHz showing resonant transmissivities in the 20–30 GHz range above 40%
For metals with thickness greater than this, the limited penetration of the electric fields results in a zero transmittance while, for thicknesses below the skin depth, the impedance mismatch with respect to free space limits the transmittance to negligible values1
Summary
Thin (sub skin-depth) metal layers are known to almost completely reflect radiation at microwave frequencies.
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