Fig. 1. Digitization of effective-medium metamaterial^[51]: (a) Discretizing and digitizing processes of effective-medium metamaterial; (b) sampling, discretizing, and digitizing a required permittivity function using two metamaterial bits as building blocks.

Fig. 2. Digital coding representation of metamaterials^[52]: (a) Digital coding metamaterial; (b) the physical implementations of digital units 0 and 1 and their phase responses; (c), (d) electromagnetic responses under different digital coding sequences, showing different functions.

Fig. 3. Digital metamaterial and programmable metamaterial^[52]: (a) An active digital meta-atom; (b) the phase responses of the active digital meta-atom under the 0 and 1 states; (c) a programmable metamaterial controlled by FPGA; (d) the measured programmable functions under different digital coding sequences.

Fig. 4. Information entropy of information metamaterials ^[62]: (a) The random 0 and 1 coding pattern; (b), (c) the far-field radiation patterns of the random 0 and 1 digital coding metamaterial; (d) the geometric information entropy and physical information entropy of the digital coding sequences from order to disorder.

Fig. 5. Digital convolution theorem based on the information metamaterials^[63]: (a)−(c) Three different digital coding patterns, where (c) is obtained by adding (a) and (b); (d)−(f) the far field patterns of the corresponding digital coding patterns, showing the shift property of radiation beam; (g)−(i) the spectrum shift property in the digital signal processing.

Fig. 6. A reprogrammable microwave holographic imaging system based on 1-bit programmable metamaterial. Different binary holograms are controlled by FPGA to generate different holographic images^[65].

Fig. 7. Real-time digital-metasurface imager^[68]: (a) The machine-learning metasurface imager can be optimized for different kinds of scenes; (b) the illustration of training the reprogrammable imager; (c) the map of 2-bit coding digital metasurface, and the illustration of real-time imaging a moving person behind a wall, as well as measurement results.

Fig. 8. Schematic description of the new-architecture QPSK wireless communication system based on the time-domain digital coding metasurface, which can transmit movies in real time^[73].

Fig. 9. . The self-adaptive metamaterial^[91]: (a) An illustrative example; (b) the closed-loop system of the self-adaptive metamaterial, which includes a programmable metamaterial, an FPGA, a sensor, and a microcontroller unit loaded with the fast feedback algorithm.