  The applications of terahertz metamaterials are being actively explored in
recent times for applications in high-speed communication devices, miniature
photonic circuits, and bio-chemical devices because of their wide advantages.
The toroidal resonance, a new type of metasurface resonance, has been examined
with great interest to utilize its properties in terahertz metasurface
applications. The study reports a proof of concept design of a toroidal
metasurface that experimentally demonstrates logic gate operations in the
terahertz frequency regime by passive tuning of the split ring resonators
compromising the meta-atom design. The amplitude modulation is utilized as a
method of determining the Boolean logic output of the system. The proposed
metasurface could be further optimized for high amplitude modulations, as well
as for active logic gate operations using tunable materials including graphene
and ITO. The proposed metasurface consists of three split-ring resonators, and
the near-field coupling between the adjacent resonators dictates the logic gate
operations. The toroidal excitation in the metasurface is determined by a
multipole analysis of the scattered powers of terahertz radiation. The proposed
metasurfaces experimentally define AND Boolean logic gate at 0.89 terahertz,
and OR Boolean logic gate at 0.97 terahertz. Numerical simulations support the
experimentally obtained results. Additionally, we numerically report the
excitation of NAND gate at 0.87 THz. Such toroidal logic-gate metasurfaces in
the terahertz region could find applications in digitized terahertz circuits
for photonic device applications.
