Active Control of the Spoof Plasmon Propagation in Time Varying and Non-reciprocal Metamaterial

Space-Time-Modulated Reconfigurable Metamaterial Based on a Field-Focused Cavity for Nonreciprocal Transmission Control and Frequency Conversion

Lorentz reciprocity is a fundamental physical property limiting advanced wave propagation control. Previously, special materials and magnetic bias were used to break the reciprocity; however, the approaches are limited by the bulky and costly implementation. To achieve nonreciprocity without magnetic bias, space-time-modulated metamaterials have been investigated for far-field wave propagation control. The metamaterial can also support wave propagation based on near-field coupling between the periodically arranged unit cells, i.e., magneto-inductive waves (MIWs). Near-field wave propagation control via the metamaterial has various significant applications; nevertheless, the potential for near-field wave propagation control has not been fully explored. Therefore, it is necessary to investigate the potential of the space-time-modulated near-field metamaterial. This paper demonstrates nonreciprocal MIW propagation control using a space-time-modulated metamaterial. To achieve field manipulation, we propose a tunable unit cell suitable for creating a cavity mode at a deep subwavelength scale (∼λ/103). Spatial field modulation, achieved by breaking the translational symmetry of the unit cells, allows for the creation of reconfigurable waveguides on the metamaterial. Temporal field modulation, achieved by breaking the capacitive symmetry of the varactor, allows for direction-dependent transmission in the waveguide. This spatiotemporal modulation successfully achieves nonreciprocal wave propagation and frequency conversion, investigated under various conditions. The proposed space-time-modulated metamaterial may provide significant advances for a wide range of systems that require dynamic, nonreciprocal, near-field wave propagation control.

Active spoof plasmonics: from design to applications

Spoof plasmonic metamaterials enable the transmission of electromagnetic energies with strong field confinement, opening new pathways to the miniaturization of devices for modern communications. The design of active, reconfigurable, and nonlinear devices for the efficient generation and guidance, dynamic modulation, and accurate detection of spoof surface plasmonic signals has become one of the major research directions in the field of spoof plasmonic metamaterials. In this article, we review recent progress in the studies on spoof surface plasmons with a special focus on the active spoof surface plasmonic devices and systems. Different design schemes are introduced, and the related applications including reconfigurable filters, high-resolution sensors for chemical and biological sensing, graphene-based attenuators, programmable and multi-functional devices, nonlinear devices, splitters, leaky-wave antennas and multi-scheme digital modulators are discussed. The presence of active SSPPs based on different design schemes makes it possible to dynamically control electromagnetic waves in real time. The promising future of active spoof plasmonic metamaterials in the communication systems is also speculated.