Abstract
Over the past 5 years, digital coding and programmable metamaterials have been developed rapidly since their first exhibition in 2014. The iconic feature of the digital coding metamaterial is using digital codes like “0” and “1” to represent the distinct electromagnetic (EM) responses. This seemingly trivial progress has successfully reform the design theory from the effective medium to coding patterns, bridging the physical world and digital information world. More interestingly, beyond the simple coding on the parameters or patterns, the digital coding metamaterials are more intend to introduce the concept of direct interactions and operations of digital information within EM fields, to realize information processing, transmission or recognition. To accurately exhibit the informational specialties, we classify the coding metamaterials, digital metamaterials and programmable metamaterials, as well as other information-operating metamaterials, as information metamaterials. In this review article, we firstly introduce the digital coding concept, working mechanism, and related design methods. Then, three important theories including the scattering pattern calculation, convolution operation, and entropy of digital coding metamaterials, are discussed in details. Finally we introduce several system-level works based on the information metamaterials, such as the new-architecture wireless communication systems and reprogrammable imaging systems, to show the powerful manipulation capabilities of information metamaterials. As the next generation of information metamaterials, two proof-of-concept smart metamaterials and their advanced architectures are discussed. In the summary, the development track of information metamaterials and future trends are presented.
Highlights
Metamaterials are artificial materials, which are usually composed of periodic or quasiperiodic structures with subwavelength dimensions
Due to the lack of experimental verification, metamaterials have not been put into reality until 20 years ago, when Pendry, Smith and co-workers presented the negative-index metamaterials and successfully realized the metamaterials in microwave frequencies [2,3,4]
This paper aims to review the development of information metamaterials, from the early original concepts to various powerful systems so far
Summary
Metamaterials are artificial materials, which are usually composed of periodic or quasiperiodic structures with subwavelength dimensions. Harmonic beam steering is achieved with the time-varying coding patterns of information metamaterials [77, 78] Such digital coding methods are logically developed into digital communication systems, and two communication systems have been realized based on the programmable metasurfaces [79, 80], from the spatial-beam coding and harmonic-frequency coding directions, proposed by Cui and Zhao et al, respectively [79, 80]. Space-time-coding modulation systems based on information metamaterials In above illustrations, the digital coding and programmable metamaterials are focused on the spatial arrangement of coding patterns As another important dimension, the temporal modulation has attracted great attention in metasurface researches [77, 85, 96, 97]. The relationship between objects and measured data can be described with the following coefficient matrix
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