3D and 4D Printing of Electromagnetic Metamaterials

Electromagnetic devices have been widely used in the fields of information communication, medical treatment, electrical engineering, and national defense, and their properties are strongly dependent on the constituent electromagnetic materials. Conversely, electromagnetic metamaterials (EMMs), which are artificially engineered with distinctive electromagnetic properties, can overcome the limitations of natural materials owing to their structural advantages. Three-dimensional (3D) printing is the most effective technique for fabricating EMM devices with different geometric parameters and associated properties. However, conventional 3D-printed EMM devices may lack manufacturing flexibility and environmental adaptability to different physical stimuli, such as electric and magnetic fields. Four-dimensional (4D) printing is an ideal technique for schemes to integrate structural design with intelligent materials environmentally adaptive to external fields, for example, the printed components can change shape under electric stimulation. Given the rapid advancements in the EMM field, this paper first reviews typical EMM devices, their design theories, and underlying principles. Subsequently, it presents various EMM structural topologies and manufacturing technologies, emphasizing the feasibility of combining 3D and 4D printing. In addition, we highlight the important applications of EMMs and their future trends and the challenges associated with functional EMMs and additive manufacturing.