  Metamaterials are artificially engineered devices that go beyond the
properties of conventional materials in nature. Metamaterials allow the
creation of negative refractive indexes, light trapping with epsilon-near-zero
compounds, bandgap selection, superconductivity phenomena, non-Hermitian
responses and, more generally, to manipulate the propagation of electromagnetic
and acoustic waves. In the past, low computational resources and the lack of
proper manufacturing techniques have limited the attention to 1-D and 2-D
metamaterials. However, the true potential of metamaterials will be ultimately
reached in 3-D configurations, when the degrees of freedom associated to the
propagating direction are finally exploited in design. This is expected to lead
to a new era in metamaterial field, from which future high-speed and
low-latency communication networks can benefit. Here, a comprehensive overview
of the past, present and future trends related to 3-D metamaterial devices is
presented, focusing on efficient computational methods, innovative designs and
functional manufacturing techniques.
