Fig. 1. Conceptual illustration of the FPRM and its function demonstrations under different operating types. The bias voltages of the PIN diodes embedded into the reconfigurable meta-particle are controlled via FPGA, which can realize synchronous amplitude modulation with almost fixed phase in orthogonal CP channels. First, in both the ON and OFF states of two PIN diodes, arbitrarily polarized incident waves can be completely reflected and absorbed, respectively. In addition, when the PIN diodes are in transition states, the incident polarized waves can be converted to other polarized waves. The built-in zoom-in-view inset illustrates the detailed structure of the reconfigurable meta-particle in the dashed box. The height of the cuboid represents the amplitude of reflection, and the orange cuboids represent the invariant phase of θ.

Fig. 2. Schematic diagram of the meta-particle and its amplitude and phase responses. (a) Perspective view of the meta-particle. (b) Sectional view of the meta-particle with geometric parameters. (c) Equivalent circuits of the PIN diode. Simulated (d) co-polarized reflection amplitude rLL, (e) co-polarized reflection phase φLL, (f) cross-polarized reflection amplitude rRL, and (g) absorption AL when RD1 is varied and RD2 is fixed at 1  MΩ at LCP normal incidence. Simulated (h) co-polarized reflection amplitude rRR, (i) co-polarized reflection phase φRR, (j) cross-polarized reflection amplitude rLR, and (k) absorption AR when RD2 is varied and RD1 is fixed at 1  MΩ at RCP normal incidence. Simulated co-polarized (l) reflection amplitude rLL and (m) phase φLL when RD2 is varied and RD1 is fixed at 1  MΩ at LCP normal incidence. Simulated co-polarized (n) reflection amplitude rRR and (o) phase φRR when RD1 is varied and RD2 is fixed at 1  MΩ at RCP normal incidence.

Fig. 3. Simulated surface current and energy loss distributions of the proposed meta-particle. Surface current distributions of the meta-particle under the normal incidence of (a)–(d) LCP waves at 7 GHz when RD1 is varied and RD2 is fixed at 1  MΩ and (e)–(h) RCP waves when RD2 is varied and RD1 is fixed at 1  MΩ, respectively. Energy loss distributions of the meta-particle under the normal incidence of (i)–(l) LCP waves when RD1 is varied and RD2 is fixed at 1  MΩ and (m)–(p) RCP waves at 7 GHz when RD2 is varied and RD1 is fixed at 1  MΩ, respectively. The color depth and direction of the red arrows represent the surface current intensity and flow direction, respectively.

Fig. 4. Versatile functional demonstration of the proposed meta-particle under full-polarization wave excitation. Simulated co-polarized, cross-polarized reflection amplitudes and absorption of the meta-particle under (a) x-polarized or (b) y-polarized excitation when RD1=RD2=1  MΩ. Simulated co-polarized, cross-polarized reflection amplitudes and absorption of the meta-particle under (c) x-polarized or (d) y-polarized excitation when RD1=RD2=210  Ω. (e) Sketch of the Poincaré sphere representing some exemplary states of linear, circular, and elliptical polarizations and (f) mapping of the ellipticity angle χ and the polarization azimuth angle ψ on corresponding polarization ellipse. (g) Simulated amplitude ratio rLL/rRR and phase difference φLL−φRR when RD1 is varied and RD2 is fixed at 1  MΩ under CP normal incidence at 7 GHz. (h) Simulated amplitude ratio rRR/rLL and phase difference φRR−φLL when RD2 is varied and RD1 is fixed at 1  MΩ under CP normal incidence at 7 GHz. Calculated ellipticity angle χ and polarization azimuth angle ψ when (i) RD1 is varied and RD2 is fixed at 1  MΩ and (j) RD2 is varied and RD1 is fixed at 1  MΩ under CP normal incidence at 7 GHz. (k) Polarization ellipses of the reflected waves at different values of RD1 when RD2 is fixed at 1  MΩ under x-polarized excitation.

Fig. 5. Experimental characterization of the FPRM. (a) Front view and (b) bottom view of the fabricated FPRM’s photographs, where the insets exhibit 3×3 local meta-particles. (c) Experimental setup in microwave anechoic chamber. Measured (d) co-polarized reflection amplitude rLL, (e) co-polarized reflection phase φLL, (f) cross-polarized reflection amplitude rRL, and (g) absorption AL when VD1 is varied and VD2 is fixed at 0 V at LCP normal incidence. Measured (h) co-polarized reflection amplitude rRR, (i) co-polarized reflection phase φRR, (j) cross-polarized reflection amplitude rLR, and (k) absorption AR when VD2 is varied and VD1 is fixed at 0 V at RCP normal incidence. Measured CP reflection amplitudes when (l) VD1=0  V and VD2=0  V and (m) VD1=0  V and VD2=0.86  V under x-polarized excitation or when (n) VD1=0  V and VD2=0  V and (o) VD1=0.86  V and VD2=0  V under y-polarized excitation.