Fig. 1. Schematic representation of the designed tunable coding metasurface：（a）illustration of the tunable coding metasurface's structural configuration（When the phase-change material，GSST，is in the amorphous state，the deflection angle varies in response to the presence or absence of CH₂I₂ liquid in the etched hole）；（b）phase distribution in the xy-plane without or with CH₂I₂ liquid in the etched hole，showcasing the tunability of the metasurface

Fig. 2. Metaatom configuration and its tunable characteristics across different phase-change states：（a）schematic illustration of the metaatom with parameters H = 2 μm，P = 1 μm，W ranging from 0 to 1 μm，and L from 0 to 10 μm；（b）four states of the tunable coding metasurface；transmittance and phase shift of amorphous state GSST coding metaatoms when the etched hole is without（c）or with（d）CH₂I₂ liquid；transmittance and phase shift of crystalline state GSST coding metaatoms when the etched hole is without（e）or with（f）CH₂I₂ liquid. This highlights the tunable properties of the coding metaatoms in response to different phase-change conditions

Fig. 3. Deflection function of the tunable coding metasurface：（a）simulated far-field scattering pattern of the etched hole with（blue line）or without（red line）CH₂I₂ liquid at a wavelength of 5.2 μm when GSST is in the amorphous state；For comparison，the scattering pattern of GSST in the crystalline state is also presented in（b）；Phase distribution in the xy-plane with the etched hole containing（c）or lacking（e）CH₂I₂ liquid in the amorphous state of GSST. Phase distribution in the xy-plane with the etched hole containing（d）or lacking（f）CH₂I₂ liquid in the crystalline state of GSST. These results illustrate the deflection characteristics of the tunable coding metasurface under different conditions

Fig. 4. Refractive index changes of CH₂I₂ liquid. Simulated far-field scattering patterns of amorphous state GSST（a~d）and crystalline state GSST（e~h）at refractive indices of the liquid：1.4，1.6，1.9，and 2.0，respectively. These results demonstrate the influence of varying refractive indices of CH₂I₂ liquid on the scattering patterns in both amorphous and crystalline states of GSST

Fig. 5. Broadband tunable coding metasurface. Simulated far-field scattering patterns of the etched hole without liquid（a~d）or with liquid（e~h）in the amorphous state of GSST. Wavelengths considered are 5 μm，5.5 μm，5.7 μm，and 6 μm，respectively. These simulations showcase the broadband tunability of the coding metasurface，highlighting the scattering patterns at different wavelengths