An Omnidirectionally Invisible Artificial Medium

An invisible solid medium in free space requires itself neither reflects nor refracts lights for all incident angles, which has not been found in nature. In this paper, we show that such a medium can be artificially achieved by constructing a mesoscopic building block with independently controllable electrical and magnetic resonances. By precise dispersion engineering, this building block could have both effective unity permittivity and permeability at a specific frequency. Composites consisting of either loosely or densely arranged such blocks can exhibit omnidirectional invisibility in free space, regardless of the shape. 3D sculpture technology was used to fabricate an electrically large aircraft sample for experimental verification. The measured results show that this artificial medium macroscopically exhibits an air-like electromagnetic response at around 5 GHz. The proposed medium can improve mechanical stability, electrical conduction, and heat dissipation of a system, without disturbing the electro-magnetic design.