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Information metamaterial: Bridging the physical world and digital world
Metamaterials described by effective medium parameters have shown powerful abilities in controlling the physical properties of electromagnetic waves. In this special topic, we proposed to represent the metamaterials by digital coding elements to reach information metamaterials. On one hand, a single information metamaterial can switch many different functions in real time in programmable manner (e.g. programmable radar and imaging). On the other hand, the digital coding representation of metamaterial builds up a bridge between the electromagnetic physical world and digital world, and hence the digital concepts (e.g. Shannon entropy and convolution) can be used to control the metasurface physics. Owing to the strong capabilities in manipulating waves and digital signals simultaneously and easy integrations with machine-learning algorithms, the information metamaterials have found applications in real-time imaging, automatic target recognition, self-adaptive beam tracing, and new-architecture wireless communications.
Realizing metasurfaces with reconfigurability, high efficiency, and control over phase and amplitude is a challenge. Here, Li et al. introduce a reprogrammable hologram based on a 1-bit coding metasurface, where the state of each unit cell of the coding metasurface can be switched electrically.
Current digital coding metasurfaces are only space-encoded. Here, the authors propose space-time modulated digital coding metasurfaces to obtain simultaneous manipulations of electromagnetic waves and present harmonic beam steering, beam shaping, and scattering-signature control as application examples.
Conventional imagers require time-consuming data acquisition, or complicated reconstruction algorithms for data post-processing. Here, the authors demonstrate a real-time digital-metasurface imager that can be trained in-situ to show high accuracy image coding and recognition for various image sets.