Electrically switchable metamaterials

The control of electromagnetic radiation lies at the core of many modern technologies. Naturally occurring materials provide only limited electromagnetic response, insufficient for emerging technologies with increasingly demanding requirements. Metamaterials/metasurfaces overcome such an obstacle by realizing exotic electromagnetic properties and enhanced functionalities through a designer approach for the control and manipulation of the amplitude, phase and polarization. However, once fabricated, their properties are fixed, which limits the scope of applications. Actively switchable and frequency tunable metamaterials using an external stimulus are highly desirable in order to accomplish a reconfigurable response and signal modulation for communication, imaging, sensing, and adaptive optics, to name a few. During the past years, hybrid metamaterials realizing active and dynamic properties have attracted intensive research interest, where materials/structrures under consideration include varactor diodes, semiconductor Schottky structures, liquid crystals, phase transition materials, grapheme, transparent conducting oxides, and MEMS, and the tuning knobs can be optical excitation, electric field, magnetic field, currents, and temperature. Each of these approaches has their advantages and limitations. Of particular interest and relevance is the electrically switchable metamaterials that can provide a practical solution in real world applications, which require large modulation depth, fast modulation speed, selective wavelength response, and compatibility with existing integrated electronics and photonics. In this presentation I will introduce the concept and overview the progress of active metamaterials/metasurfaces, including the design principle, functional material integration, structure fabrication, and accomplished functionalities, with a focus on the electrical approach.