A Novel Type of Low Frequency Resonance Related to a Hollow Circular Cylinder Formed by an Anisotropic Surface with Helical Conductivity

The problem of diffraction of a circularly polarized plane wave normally incident on an anisotropic circular cylinder with ka¿l has been investigated. The cylinder surface is perfectly conducting along right-hand helical curves with small twirl angle ¿¿1. Provided that ka=¿, a low frequeney resonance has been discovered. The resonance manifests itself by the fact that in the interior of the cylinder, a homogeneous field of surprisingly great magnitude (of the-order of l/(ka)2) arises, with electric and magnetic vectors being of equal magnitude, shifted in phase by ¿/2 and being equally oriented. The vectors are perpendicular to both the cylinder axis and propagation direction of the incident wave. The resonance also causes a finite disturbance of the scattering diagram. When the incident wave is of right-hand circular polarization, the phenomenon is most conspicuous; when the wave is characterized by left-handed rotation, the resonance does not appear. The discovered phenomenon differs fundamentally from the well known electromagnetic analogues of the low frequency Helmholtz´s resonance. The former is characterized by a nontrivial structure and a great magnitude of the interior field. In addition, the scattered field in the case under consderation is circularly polarized.