In this paper, a compact terahertz stop band filter is presented, which consists of two parallel metallic surfaces corrugated
with rectangular groove arrays of period a. When a metallic surface is periodically corrugated, surface electromagnetic
modes can be excited by incident terahertz waves. These modes are surface plasmon polaritons with an effective plasma
frequency controlled entirely by the surface geometry. Because of the corrugated grooves and geometry induced highly
confined surface plasmon polaritons, the fundamental mode of the parallel metallic plates splits into two modes and there
is a band gap between the two modes. The band stop filtering functionality is realized by rejecting all frequencies in the
gap. Simulation results calculated by finite element method show that the proposed structure has a band gap ranging
from 0.315c/a to 0.350c/a for groove depth d = 0.5a, groove width l = 0.5a and gap width of the two parallel metallic
surfaces w = 2a. Transmission spectra also show zero transmission within the band gap region where no guided modes
are supported. By varying the gap width w and groove depth d, different filtering bandwidths with different center
frequencies can be achieved.
In this paper, square lattices of air holes were fabricated on a three-layer structure of metal-dielectric-metal using
micromachining technology. The metal-dielectric-metal structure is based on RT/duroid 5870 produced by Rogers
corporation. The square period is 400 μm and the radius of circular hole is 100 μm. The thickness of the structure is
about 863 μm with metal thickness of 39.2 μm and dielectric layer thickness of 785 μm. The loss and dispersion of the
dielectric layer with the dielectric constant of 2.33 are low at microwave frequencies. Terahertz transmission spectra
through the sample were measured by the state-of-the-art THz-TDS system. Experimental results show that there is a
transmittance centered at 1 THz with a wide pass-band exceeding 100 GHz. Transmission spectra calculated by FDTD
method were given for comparisons and showed good agreements with the experimental results. Through analysis, the
extraordinary transmission phenomena are caused by both the Febry-Parot effect and surface plasmon polaritons existing
on the metal arrays.
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