Abstract
SummaryMetamaterials have great capabilities and flexibilities in controlling electromagnetic (EM) waves because their subwavelength meta-atoms can be designed and tailored in desired ways. However, once the structure-only metamaterials (i.e., passive metamaterials) are fabricated, their functions will be fixed. To control the EM waves dynamically, active devices are integrated into the meta-atoms, yielding active metamaterials. Traditionally, the active metamaterials include tunable metamaterials and reconfigurable metamaterials, which have either small-range tunability or a few numbers of reconfigurability. Recently, a special kind of active metamaterials, digital coding and programmable metamaterials, have been presented, which can realize a large number of distinct functionalities and switch them in real time with the aid of field programmable gate array (FPGA). More importantly, the digital coding representations of metamaterials make it possible to bridge the digital world and physical world using the metamaterial platform and make the metamaterials process digital information directly, resulting in information metamaterials. In this review article, we firstly introduce the evolution of metamaterials and then present the concepts and basic principles of digital coding metamaterials and information metamaterials. With more details, we discuss a series of information metamaterial systems, including the programmable metamaterial systems, software metamaterial systems, intelligent metamaterial systems, and space-time-coding metamaterial systems. Finally, we introduce the current progress and predict the future trends of information metamaterials.
Highlights
Evolution of MetamaterialsSince Sir John Pendry proposed to realize negative permittivity using periodic structure of thin wires in 1996 (Pendry et al, 1996), modern metamaterials have received great progress in the past 20 years and are still in the frontiers of physics, chemistry, material, and information societies
The first stage is for passive metamaterials, which are composed of specially designed artificial structures in periodic or nonperiodic arrays of subwavelength unit cells to reach homogeneous or inhomogeneous effective medium parameters that do not exist in nature or are difficult to achieve in practice
We demonstrated that a 2-bit programmable metamaterial can produce the radiation patterns desired by the machine learning, like the principle component analysis (PCA) (Li et al, 2019a, 2019b)
Summary
Metamaterials have great capabilities and flexibilities in controlling electromagnetic (EM) waves because their subwavelength meta-atoms can be designed and tailored in desired ways. To control the EM waves dynamically, active devices are integrated into the metaatoms, yielding active metamaterials. The active metamaterials include tunable metamaterials and reconfigurable metamaterials, which have either small-range tunability or a few numbers of reconfigurability. A special kind of active metamaterials, digital coding and programmable metamaterials, have been presented, which can realize a large number of distinct functionalities and switch them in real time with the aid of field programmable gate array (FPGA). We firstly introduce the evolution of metamaterials and present the concepts and basic principles of digital coding metamaterials and information metamaterials. We discuss a series of information metamaterial systems, including the programmable metamaterial systems, software metamaterial systems, intelligent metamaterial systems, and space-time-coding metamaterial systems. We introduce the current progress and predict the future trends of information metamaterials
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