Scattering Properties of Spherical Time-Varying Conductive Shells

Abstract

The equivalent external noise temperature of timevarying antennas is studied using the concept of cross-frequency effective aperture, which quantifies the intermodulation conversion of external noise across the frequency spectrum into a receiver's operational bandwidth. The theoretical tools for this approach are laid out following the classical method for describing external noise temperature of linear time-invariant antennas, with generalizations made along the way to capture the effects of time-varying components or materials. The results demonstrate the specific ways that a time-varying system's noise characteristics are dependent on its cross-frequency effective aperture and the broadband noise environment. The general theory is applied to several examples, including abstract models of hypothetical systems, antennas integrated with parametric amplification, and time-modulated arrays.

Optical Transitions and Nonreciprocity in Spatio‐Temporally Periodic Layers of Spherical Particles

“…Furthermore, by arranging such temporal slabs in a multilayer architecture, it is possible to build generalized Bragg reflectors or hyperbolic media. [12,[35][36][37][38] Apart from these 1D configurations, novel architectures based on dynamic particles, that is, particles with time-dependent material or geometrical parameters, [39][40][41][42] and periodic or quasiperiodic arrangements of such, offer further possibilities for more sophisticated designs, for example, space-time varying metamaterials [8,11] and metasurfaces, [43][44][45] which expand the boundaries in light control.…”

“…Furthermore, by arranging such temporal slabs in a multilayer architecture, it is possible to build generalized Bragg reflectors or hyperbolic media. [12,[35][36][37][38] Apart from these 1D configurations, novel architectures based on dynamic particles, that is, particles with time-dependent material or geometrical parameters, [39][40][41][42] and periodic or quasiperiodic arrangements of such, offer further possibilities for more sophisticated designs, for example, space-time varying metamaterials [8,11] and metasurfaces, [43][44][45] which expand the boundaries in light control.What is more, optical transitions, which occur in time-varying environments, can give rise to interesting and potentially useful effects, such as frequency conversion and filtering. Photonic transitions, similar to electronic transitions, have been anticipated in time-modulated photonic crystals by Winn et al [46] using coupled mode theory.…”

Floquet–Mie Theory for Time‐Varying Dispersive Spheres

“…[20] A couple of recent studies considered light scattering from finite-sized particles, a sphere and a conductive spherical shell, with time-varying properties. [51,52] However, accommodating dispersion in such models remains a challenge, and, therefore, it was set aside.…”