Abstract
Abstract Metamaterials have been characterized by effective medium parameters over the past decades due to the subwavelength nature of meta-atoms. Once the metamaterials are fabricated, their functions become fixed or tunable. Recently, the concept of digital metamaterials has been introduced, in which, for instance, the constitutive 1-bit meta-atom is digitalized as “0” or “1” corresponding to two opposite electromagnetic (EM) responses. The digital metamaterials set up a bridge between the physical world and the information world. More interestingly, when the digital meta-atom is programmable, a single metamaterial can be used to realize different functions when programmed with different coding sequences. Moreover, as the states of programmable meta-atoms can be quickly switched, it enables the wave-based information coding and processing on the physical level of metamaterials in real time. For these reasons, we prefer to call digital metamaterials with programmable meta-atoms as “information metamaterials.” In this review article, we introduce two basic principles for information metamaterials: Shannon entropy on metamaterials to measure the information capacity quantitatively and digital convolution on metamaterials to manipulate the beam steering. Afterwards, two proof-of-concept imaging systems based on information metamaterials, i.e. programmable hologram and programmable imager, are presented, showing more powerful abilities than the traditional counterparts. Furthermore, we discuss the time-modulated information metamaterial that enables efficient and accurate manipulations of spectral harmonic distributions and brings new physical phenomena such as frequency cloaking and velocity illusion. As a relevant application of time-modulated information metamaterials, we propose a novel architecture of wireless communication, which simplifies the modern wireless communication system. Finally, the future trends of information metamaterials are predicted.
Highlights
Since the publication of the pioneering works of Pendry et al [1] and Smith et al [2, 3] 20 years ago, metamaterials have received worldwide attention in the fields of science, engineering and military, fundamentally refreshing peoples’ insights into the physical mechanism of electromagnetics (EM)
Afterwards, two proof-of-concept imaging systems based on information metamaterials, i.e. programmable hologram and programmable imager, are presented, showing more powerful abilities than the traditional counterparts
Any two adjacent patches are connected via a PIN diode (BAR 65-02L), and each PIN diode has two operation states controlled by the applied bias direct current (DC) voltage
Summary
Since the publication of the pioneering works of Pendry et al [1] and Smith et al [2, 3] 20 years ago, metamaterials have received worldwide attention in the fields of science, engineering and military, fundamentally refreshing peoples’ insights into the physical mechanism of electromagnetics (EM). Giovampaola and Engheta used the mixture of digital meta-atoms, referred to as metamaterial bits or bytes in [25], to construct the analogy metamaterials In this sense, they performed essentially the analysis and synthesis of digital metamaterials with effective medium theory. Cui et al characterized the metaatoms with the quantized EM responses, which in spirit are closer to the digital concept used in digital circuits and signals [24] In this way, the digital metamaterials could set up a bridge between the physical world and information world. As the digital states of programmable meta-atoms can be quickly switched, a single metamaterial enables the wave-based information coding and processing on the physical level of metamaterials in real time. We elaborate on the information metamaterial in terms of its concept, working mechanism and design strategy
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