20 research outputs found
Controlling surface waves with temporal discontinuities of metasurfaces
In this paper, we investigate the scattering of surface waves on reactive
impedance boundaries when the surface impedance undergoes a sudden change in
time. We report three exotic wave phenomena. First, it is shown that by
switching the value of the surface capacitance of the boundary, the velocity of
surface waves can be fully controlled, and the power of reflected and
transmitted surface waves are amplified. Second, we show that when a capacitive
boundary is switched to an inductive one, the surface wave stops completely,
with a "frozen" static magnetic field distribution. The static magnetic fields
are "melt" and restore propagating surface waves when the boundary is switched
back to a capacitive one. Third, we show that temporal jumps of the boundary
impedance couple free-space propagating waves to the surface wave, which is an
analog to a spatial prism. These interesting effects enabled by temporal jumps
of metasurface properties open up new possibilities for the generation and
control of surface waves.Comment: 19 pages, 10 figure
Metasurface-Based Realization of Photonic Time Crystals
Photonic time crystals are artificial materials whose electromagnetic
properties are uniform in space but periodically vary in time. The synthesis of
such materials and experimental observation of their physics remain very
challenging due to the stringent requirement for uniform modulation of material
properties in volumetric samples. In this work, we extend the concept of
photonic time crystals to two-dimensional artificial structures --
metasurfaces. We demonstrate that time-varying metasurfaces not only preserve
key physical properties of volumetric photonic time crystals despite their
simpler topology but also host common momentum bandgaps shared by both surface
and free-space electromagnetic waves. Based on a microwave metasurface design,
we experimentally confirmed the exponential wave amplification inside a
momentum bandgap as well as the possibility to probe bandgap physics by
external (free-space) excitations. The proposed metasurface serves as a
straightforward material platform for realizing emerging photonic space-time
crystals and as a realistic system for the amplification of surface-wave
signals in future wireless communications.Comment: 21 pages, 3 figure
Intelligent Metasurfaces with Continuously Tunable Local Surface Impedance for Multiple Reconfigurable Functions
Electromagnetic metasurfaces can be characterized as intelligent if they are
able to perform multiple tunable functions, with the desired response being
controlled by a computer influencing the individual electromagnetic properties
of each metasurface inclusion. In this paper, we present an example of an
intelligent metasurface which operates in the reflection mode in the microwave
frequency range. We numerically show that without changing the main body of the
metasurface we can achieve tunable perfect absorption and tunable anomalous
reflection. The tunability features can be implemented using mixed-signal
integrated circuits (ICs), which can independently vary both the resistance and
reactance, offering complete local control over the complex surface impedance.
The ICs are embedded in the unit cells by connecting two metal patches over a
thin grounded substrate and the reflection property of the intelligent
metasurface can be readily controlled by a computer. Our intelligent
metasurface can have significant influence on future space-time modulated
metasurfaces and a multitude of applications, such as beam steering, energy
harvesting, and communications.Comment: 10 pages, 8 figure
Floquet–Mie Theory for Time‐Varying Dispersive Spheres
Exploring the interaction of light with time-varying media is an intellectual challenge that, in addition to fundamental aspects, provides a pathway to multiple promising applications. Time modulation constitutes here a fundamental handle to control light on entirely different grounds. That holds particularly for complex systems simultaneously structured in space and time. However, a realistic description of time-varying materials requires considering their material dispersion. The combination thereof has barely been considered but is crucial since dispersion accompanies materials suitable for dynamic modulation. As a canonical scattering problem from which many general insights can be obtained, a self-consistent analytical theory of light scattering by a sphere made from a time-varying material exemplarily assumed to have a Lorentzian dispersion is developed and applied. The eigensolutions of Maxwell\u27s equations in the bulk are discussed and a dedicated Mie theory is presented. The proposed theory is verified with full-wave simulations. Peculiar effects are disclosed, such as energy transfer from the time-modulation subsystem to the electromagnetic field, amplifying carefully structured incident fields. Since many phenomena can be studied on analytical grounds with the proposed formalism, it represents an indispensable tool that enables exploration of electromagnetic phenomena in time-varying and spatially structured finite objects of other geometries
Exploration of intercell wireless millimeter-wave communication in the landscape of intelligent metasurfaces
Software-defined metasurfaces are electromagnetically ultra-thin, artificial components thatcan provide engineered and externally controllable functionalities. The control over these functionalities isenabled by the metasurface tunability, which is implemented by embedded electronic circuits that modifylocally the surface resistance and reactance. Integrating controllers within the metasurface able them tointercommunicate and adaptively reconfigure, thus imparting a desired electromagnetic operation, opens thepath towards the creation of an artificially intelligent (AI) fabric where each unit cell can have its own sensing,programmable computing, and actuation facilities. In this work we take a crucial step towards bringing theAI metasurface technology to emerging applications, in particular exploring the wireless mm-wave intercellcommunication capabilities in a software-defined HyperSurface designed for operation in the microwaveregime. We examine three different wireless communication channels within the landscape of the reflectivemetasurface: Firstly, in the layer where the control electronics of the HyperSurface lie, secondly inside adedicated layer enclosed between two metallic plates, and, thirdly, inside the metasurface itself. For each casewe examine the physical implementation of the mm-wave transceiver nodes, we quantify communicationchannel metrics, and we identify complexity vs. performance trade-offs.Peer ReviewedPostprint (published version