Superwideband Terahertz Absorber-Based Highly Sensitive Refractive Index Sensor

A circular-slot-inscribed square-shaped metal-free superwideband absorber is presented. It comprises a silicon dioxide substrate sandwiched between the circular-slot-loaded square-shaped and square graphite slabs. It has an overall volume of
$5\times 5\times 6.77\,\,\mu \text{m}$
with an operating frequency spectrum ranging from 5.1 to > 80 THz (> 176.03% for
${A}\ge {90}$
%). The periodicity and substrate thickness are
${\sim }\lambda _{\text {o}} /{12}$
and
${\sim }\lambda _{\text {o}} / {76}$
respectively at 5.1 THz. The proposed absorber’s performance is insensitive to the polarization angle (
$\Phi $
) variations due to symmetric geometry. In addition to this, the incidence angle (
$\theta $
) variations between 0° and 45° also had insignificant effects on the absorption. The presented absorber has advantages of metal-free geometry, polarization angle insensitiveness to
$\Phi $
and
${0}^{\circ }\le \theta \le {45}^{\circ }$
along with compact dimensions over previously reported absorbers operating in terahertz (THz)/infrared frequency ranges. The proposed absorber-based sensor has a peak sensitivity of 9 THz/RIU for refractive index (RI) sensing and 7 THz/RIU for cancer and tuberculosis detection.