Figure 8.

Frequency synthesis, polarization conversion, and convolution operation. (a) Conceptual illustration of STC digital metasurfaces for frequency synthesis. Reproduced from [121]. (b) The time-modulated waveform with 1-bit, 2-bit, and 3-bit quantized phases and continuous sawtooth wave phases, as well as the corresponding harmonic amplitude distributions. Reproduced from [109]. (c) Conceptual illustration of TDC digital metasurfaces for polarization conversion. Reproduced from [122]. (d) A polarization conversion diagram with some specific collocations of the x- and y-polarized phases, from which the RHCP, LHCP, and cross-LP are successfully synthesized. Reproduced from [122]. (e) Conceptual illustration of TDC digital metasurfaces for convolution operation. Reproduced from [123]. (f) An illustrative example of nonlinear convolution operation at the +1^st harmonic frequency, as it can be observed that the original dual-beam pattern deviates from the normal axis to the angle θ₂ with negligible distortion. Reproduced from [123].