Tunable UWB/Narrowband Terahertz Metasurface Absorber Through Controlled Relaxation Time

This work presents the design of a polarization-insensitive graphene-based tunable metasurface absorber (TMSA) for a terahertz (THz) regime. The TMSA can provide ultra-wide and narrowband absorptivity response by properly selecting the relaxation time value
$(\tau)$
before fabrication. The TMSA provides a bandwidth (BW) of 193.4% with absorptivity
$(A(f))\geq 90\%$
for
$\tau=0.06$
ps. At the same time, an absorption BW of 6.86% could be achieved from the same design by selecting
$\tau=1$
ps. The thickness of ultrathin TMSA is only 3
$\mu \mathrm{m}$
, corresponding to
$\lambda_{g}/638.87$
, where
$\lambda_{g}$
is guided wavelength computed at 0.1 THz. The periodicity
$(\lambda_{g}/191.66)$
of TMSA is also quite less to ensure effective homogeneity condition. The absorber works well under both transverse electric (TE) and transverse magnetic (TM) polarizations for wide incidence angle
$(\theta)$
. TMSA provide
$A(f)\geq$
90 % for
$\theta\leq 60^{\circ}$
when working as UWB absorber and provide
$A(f)\geq 75\%$
for
$\theta\leq 60^{\circ}$
when working as narrowband absorber. TMSA also provides a shift in the absorption peak from 3.5 to 6.2 THz by varying chemical potential
$(\mu_{c})$
from 0.3 to 1
$\text{eV}$
when
$\tau$
is kept fixed at 1 ps.