Illusion 'cloak' makes you see what's not there: Copper conducts electricity well and reflects incoming radio waves, giving it a bright radar signature. To alter this behaviour, the team built a device made of 11 concentric rings of circuit boards etched with small metal-lined channels that prevent electromagnetic waves reflecting away. Instead, they guide the waves in a direction that the researchers choose specifically to make the hidden object appear to have different electrical properties.
Placed around a copper cylinder, the arrangement created the illusion that the cylinder was made of a dielectric, a class of materials including porcelain and glass that do not conduct electricity and are more transparent to radio waves.
The illusion only worked when the cylinder was viewed from the side; what's more, the imaginary object it generated was the same size as the original. Future designs would have to account for all three dimensions, and might produce an illusion quite different from the object they disguise.