Metamaterials, artificially structured materials consisting of periodically arranged subwavelength resonators, can produce unique physical properties not available in naturally occurring or traditionally synthesized materials. They emerged as a rule breaker to challenge the fundamental laws of the field of electromagnetism, and soon became a versatile platform - micro in size but macro in function - for manipulating electromagnetic waves, including for generation, propagation, modulation, and detection at specific frequencies via their physical scalability.

In recent years, research in metamaterials has extended towards achieving tunable, nonlinear, and active functionalities for real-world applications, giving rise to the novel concept of metadevices. A variety of strategies, including mechanical reconfiguration by adjusting the balance of electromagnetic and elastic forces under external stimuli and the incorporation of active materials either as environmental media or as constituent materials, have been proposed to enable such functionalities. Metamaterials and metadevices have therefore become part of a multidisciplinary field involving physics, chemistry, materials science, and engineering.

This Special Issue aims to provide a timely forum for highlighting recent progress in active metamaterials and metadevices, showcasing both fundamental research and applications, as well as sharing advances in theory, numerical modeling, and experiments. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS)
• Semiconductors
• Liquid crystal phase change materials
• Superconductors
• Two-dimensional materials, graphene, and beyond
• Self-assembly of metamaterials
• Hydrogen storage metals