Electromagnetic Scattering by Arbitrarily Oriented Core-Shell Isotropic-Gyrotropic Cylinders and Active Switching of Terahertz Radiation

In this work, we solve the problem of plane wave electromagnetic scattering by arbitrarily oriented core-shell cylinders, featuring anisotropic properties in the coating. In particular, the core consists of an isotropic material, while the shell is gyrotropic, i.e., it can be of gyroelectric and gyromagnetic type. The plane wave impinges obliquely with respect to the cylinders’ axis. This problem cannot be solved in the traditional manner using a straightforward application of the separation of variables because the z-components of the electric and magnetic field do not satisfy homogeneous Helmholtz equations, as is the case for purely isotropic cylinders. Instead, we employ a superpotential formalism where the electromagnetic field can be expressed in terms of a scalar superpotential, which satisfies a homogeneous differential equation consisting of two factorized Helmholtz-type operators, each featuring a different wavenumber. In this way, the field components can be expressed analytically in terms of the anisotropic constitutive properties. Both TE and TM oblique incidence are considered. First, the method is validated for normal incidence using the separation of variables method, while the validity for oblique incidence is carried out using COMSOL Multiphysics. Having established the correctness of the solution, we apply it to study active switching of terahertz radiation in a core isotropic-shell gyroelectric cylindrical configuration.