![scattered fields cst microwave studio scattered fields cst microwave studio](https://docplayer.net/docs-images/44/18507769/images/page_1.jpg)
26, 1-bit digital metasurface has been presented to construct a field-programmable reflective array antenna. By using the existing digital-controlling technology to actively tune the coding sequences, the digital metasurface could realize real-time wave manipulation. With outside stimuli, the meta-atom could behave different EM responses which can be defined as the coding bits. In order to achieve the dynamical control of the EM functions for digital metasurfaces, lumped elements are required to be integrated into the design of the meta-atom 26. Due to the one-to-one relationship between the coding sequence and EM function, the EM response of digital metasurface is confirmed once one coding sequence is made. Based on this concept, digital metasurfaces have been adopted to manipulate EM radiation or scattering field by designing the coding sequences of digital meta-atoms 24, 25. When such two elements are arranged in proper distributions to construct different metasurface bytes, different EM functions could be expected. For example, two kinds of reflective meta-atoms with 0 and π phase response can use reflection phase as the coding bit, which mimic “0” and “1” elements, respectively.
![scattered fields cst microwave studio scattered fields cst microwave studio](https://agupubs.onlinelibrary.wiley.com/cms/asset/8a11feaa-d670-4797-8e33-6e5cca80645c/rds20519-fig-0002-m.jpg)
The same concept is also suitable for metasurface. Through proper spatial mixtures of such metamaterial bits, metamaterial bytes are constructed, corresponding to different material parameters or EM functions.
![scattered fields cst microwave studio scattered fields cst microwave studio](https://agupubs.onlinelibrary.wiley.com/cms/asset/947ddb84-7465-4d8b-8ef7-90d705e2e83d/rds20628-fig-0001-m.jpg)
Just like a digital circuit, different EM responses of meta-atoms can be digitally coded, producing digital metamaterial bits. Recently, a concept of digital metamaterials has been proposed by Giovampaola and Engheta to manipulate field distribution 23. This kind of the existing metasurfaces can be regarded as “analogously-controlled metasurfaces” by their used phase modulation method. Phase modulation is one of the most important features for metasurfaces, and most of the reported metasurfaces adopt the continuous phase varying cells to achieve wave manipulation. Compared with wave-control devices using traditional geometrical optics method, using metasurfaces can significantly reduce thickness and weight, which provides a promising approach for miniaturization and system integration of optical or microwave components. So far metasurfaces based on the phase discontinuities have been realized in visible 5, 6, terahertz 7, 8 and microwave range 9, 10, 11, causing a great number of intriguing applications, such as wave-front control engineering 12, 13, flat lens 14, 15, spin-orbit manipulation 16, 17, holographic technology 18, 19, and low scattering cross-sections 20, 21, 22 and so on. Due to the production of abrupt phase shift over the wavelength scale, metasurface overthrows the traditional physical relations among the reflected, refracted and incident beams, creating the generalized Snell’s law.
![scattered fields cst microwave studio scattered fields cst microwave studio](https://www.mdpi.com/applsci/applsci-11-08173/article_deploy/html/images/applsci-11-08173-g005.png)
Such metasurface has the capability of generating abrupt phase changes in the incident wavefront, and consequently it could be utilized to achieve arbitrary manipulation of wavefront through ingenious design of discontinuous interfacial phase profile. It is generally composed of different patterned elements on a single layer, which significantly relaxes the fabrication requirement, compared with traditional bulky metamaterials. Metasurface has attracted much interest in recent years, owing to its large flexibility to modulate electromagnetic (EM) wave 1, 2, 3, 4.