Temporal interfaces by instantaneously varying boundary conditions
- Luca Stefanini ,
- Shixiong Yin ,
- Davide Ramaccia ,
- Andrea Alù ,
- Alessandro Toscano ,
- Filiberto Bilotti
Abstract
Temporal metamaterials have been recently exploited as a novel platform
for conceiving several electromagnetic and optical devices based on the
anomalous scattering response arising at a single or multiple sudden
changes of the material properties. However, they are difficult to
implement in realistic scenarios by switching the permittivity of a
material in time, and new strategies to achieve time interfaces in a
feasible manner must be identified. In this paper, we investigate the
possibility to realize a temporal metamaterial without acting on the
material properties, but rather on the effective refractive index and
wave impedance perceived by the wave during the propagation in an empty
guiding structure by varying the boundaries in time. We demonstrate
analytically and through numerical experiments that suddenly changing
the physical distance between the metallic plates of a parallel-plate
waveguide will induce an effective temporal interface. In addition to
the standard backward and forward scattered fields at different
frequencies due to the temporal interface, we also identify the presence
of a static field necessary to satisfy the continuity of the
electromagnetic field across the interface. The proposed concept can be
extended to temporally controlled metasurfaces, opening an easier path
to the design and realization of novel devices based on time-varying
metamaterials at microwave and optical frequencies.