Space‐Frequency‐Domain Gradient Metamaterials

Abstract

of targets, [18][19][20] transmission of multiple vortex modes to enhance the communication capacity, [21,22] generation of multiple beams in space for computational imaging, [23,24] and control of EM waves in a digital manner from the information science perspective. [25][26][27][28][29][30] The phase distributions of metamaterials play the key role in realizing the above unnatural physical phenomena and interesting functionalities, whereas the existing theories and methods are usually focused on the performance of metamaterials with phase gradients in space, so that the frequencydomain properties are rarely explored.Here, we propose the general concept of space-frequency-domain gradient metamaterials in which new degrees of freedom are achieved by introducing frequency-domain phase gradients to the metamaterials. Additionally, we present a theoretical method for obtaining the frequency gradients by using the derivatives of phase gradients over the frequency, which generates frequency-variant uniform phase patterns in the working band. By designing the required space-domain gradients and frequencydomain gradients of metamaterials, we analyzed three kinds of typical applications, including 2D flexible beam scanning, continuous transformations of vortex modes, and generation of multiple beams in space with desired transmission directions and modes based on the new concept and approach. These new features of space-frequency-domain gradient metamaterials are analyzed theoretically and experimentally.

Information Metamaterial Systems

“…In the future, the suggested research topics include but are not limited to New approaches to control the digital states of meta-atoms, such as using MEMS, microfluid, and amplifier ( Chen et al., 2019 ; Ma et al., 2019 ), besides the mainly used PIN diodes in the current stage. New degree of freedom to define the digital information, such as anisotropic coding ( Liu et al., 2016a , Liu et al, 2016 , 2018 ), polarization coding ( Ma et al., 2017 , 2020 ), frequency coding ( Wu et al., 2018 Wu et al., 2017 ), and amplitude-phase coding ( Bao et al., 2018 Luo et al., 2019 ), besides the mainly used space-domain phase coding and space-time-domain phase coding in the current stage. New information theory and signal processing methods on the information metamaterials, besides the information entropy and convolution theorem.…”

“…New degree of freedom to define the digital information, such as anisotropic coding ( Liu et al., 2016a , Liu et al, 2016 , 2018 ), polarization coding ( Ma et al., 2017 , 2020 ), frequency coding ( Wu et al., 2018 Wu et al., 2017 ), and amplitude-phase coding ( Bao et al., 2018 Luo et al., 2019 ), besides the mainly used space-domain phase coding and space-time-domain phase coding in the current stage.…”

Microwave Metamaterials

“…By integrating active elements such as biased diodes, a single MTM unit cell can be used to achieve different codes under the control of different voltage . This technique paves the way toward real‐time reconfiguration of functionalities and further leads to the development of programmable metamaterials . Due to the discretization nature in the description of coding and programmable MTMs, this new category of artificial material is also referred to as digital metamaterials in comparison with analog MTMs.…”

Anisotropic and nonlinear metasurface for multiple functions

“…Besides the above methodologies, multi-functional devices were also proposed based on incident EM waves. Compared with features such as frequency [12,13], intensity [14,15], direction [16], and spin angular momentum [17], the utilization of polarization state has been proved to be a popular method. Under different incident polarization states, a rich number of multi-functional devices were delicately designed, such as beam splitters [18,19], chiral structures [20,21], antenna [22], holographic devices [23,24].…”