Metamaterial absorbers towards broadband, polarization insensitivity and tunability

Recent utilization of metamaterial design idea, which presents unique and designable electromagnetic properties, has been prompting the establishment of new stage of electromagnetic metamaterial absorber (EMMA) researches as well as enabling the possibility of the integration of structure and function. Great advances have been made since the first metamaterial perfect absorber (MPA) demonstrated in 2008. In addition to MPAs, broadband EMMAs, polarization independent and angle insensitive EMMAs and tunable EMMAs have been proposed to enlarge the application range of metamaterials in various situations. With an increasing demand for EMMAs operating at modern complex electromagnetic environment, the trend of high integration of full-band, wide-angle and active frequency tunable is inevitable in the future. From this perspective, a progress report should be given to summarize the progress in stages and to inspire researchers for their future studies. The emphasis of this report is given on the structural designs, absorbing performances, fabrication methods and the mechanisms of EMMA. Outlook and insight on the defect of current studies and future developing trend are also provided.