Investigation on the near-field cutoff effect in a subwavelength plasma shell with near-zero permittivity.

Although the plasma-induced receiving and radiating near-field cutoff phenomena in the subwavelength regime are found of crucial importance in electromagnetic (EM) signal transmissions and plasma property studies, their mechanisms to a large extent remain unclear and undistinguished. In this paper, in the perspective of field and energy transfer, it is demonstrated that the cutoff in the near-field regime is completely different from that in the geometric optical regime. Results show that, for the receiving mode, epsilon-near-zero (ENZ) plasmas can be treated as a nearly ideal EM fluid, and thus, EM waves are restricted into the plasma channel. For the radiating mode, on the other hand, it is the destructive interference between the electric dipole fields of the antenna and the ENZ plasma that results in vanishing far-field radiation. As an important supplement to the existing cutoff theories, our results not only offer clearer physical insights into the near-field cutoff effect but also provide a helpful reference for cutoff-related practical applications in various frequency bands.