Optically transparent Millimeter-Wave metasurface for frequency-spatial multiplexed holographic imaging

Restricted by the physical properties of materials, most traditional electromagnetic (EM) metasurfaces cannot achieve transparent stealth in visible spectrum. Although some metasurfaces for holography have been designed, there is no standard method for evaluating the advancement of wavefront manipulation, metasurface design, and algorithms. Here, a novel full space control the complex amplitude of a metasurface with optical transparency (OT) is presented in the millimeter-wave (mmWave) band. Through frequency-multiplexing, two distinct holographic images “HOLO” and “GRAM” with high quality are designed, achieving signal-to-noise ratios (SNR) of 14.6 dB and 14.4 dB, respectively. The $\mathbf{6 4 \times 6 4}$ bi-layered metasurface is composed of glass and PET substrates and three silver mesh layers. By changing the opening size and rotating angle of split rings, phase and amplitude modulations are simultaneously and independently realized at 26.6 GHz and 44.0 GHz.