Metacrystals: inversely-designed 3D-printed intelligent panels for 6G communications.

Metasurfaces represent a promising platform for improving coverage in future communication systems. Passive designs are especially attractive because they need no power supply and can be manufactured at low cost. However, most passive metasurfaces work well only for one polarization, frequency band, or incidence angle, which limits their practical use. Here we propose passive intelligent panels, termed metacrystals, that overcome these limitations by enabling highly complex multiplexed responses to multiple incident waves simultaneously and independently. This capability is enabled by a compact volumetric architecture that goes beyond conventional metasurfaces by exploiting a finite, yet still modest, thickness to unlock substantially more degrees of freedom. Through simulations and experiments, we demonstrate all-dielectric metacrystals capable of simultaneously controlling anomalous reflection and absorption, both in transmission and reflection regimes. Designed using inverse topology optimization, these metacrystals combine structural integrity, straightforward scalability, and compatibility with low-cost 3D printing for operation up to 100 GHz.