Review of micro and nano scale 3D printing of electromagnetic metamaterial absorbers: mechanism, fabrication, and functionality

Electromagnetic metamaterial absorbers (MMAs), with pivotal roles in applications such as stealth and communication, have revolutionised the field of absorbing materials by offering unique characteristics unattainable by natural materials through artificially designed unit cell structures. Although many MMAs have been successfully prepared through traditional micro/nano fabrication processes, inherent limitations persist. 3D printing, or additive manufacturing, offers unprecedented design freedom and streamlined production processes for MMAs. This review provides a comprehensive examination of 3D-printed MMAs. It first introduces the fundamental concepts and history of MMAs with a brief description of traditional techniques for MMA fabrication. Subsequently, it elucidates mechanisms governing the loss and absorption of electromagnetic MMAs and traditional absorbing materials, shedding light on the design principles. Next, this review centres on 3D printing modalities employed to fabricate MMAs by categorising the processes into one-step and two-step manufacturing that leverage the unique advantages of 3D printing. Moreover, it also delves into innovative 4D-printed MMAs, showcasing the potential of dynamically adjustable MMAs. In the end, potential future research directions are discussed by taking into consideration of current concerns. This review underscores the transformative impact of 3D-printed MMAs, paving a new avenue for future innovations in electromagnetic engineering.