These "invisibility" materials tend to need a negative refractive index, which is normally difficult to achieve, as these reports on special materials reveal.
You can easily experiment with these concepts at visible wavelengths by working under water: then you can get a negative refractive index from any clear material less dense than water - eg: air-filled cavities. Such as the effect within an aquarium that looking along a straight wall you can't see out = total internal reflection (TIR).
Well I guess it is only a matter of time before the Harry Porter cloaks are available.
Although, this technology will have a number of positive applications such as safety (e.g. shielding human beings from dangerous microwave) - I am however more worried about the negative applications. For instance, Harry Porter cloaks would be useful sneaking around and robbing banks. Lol.
How long do you think it will take to find metamaterials for Harry Potter style invisibility cloaks? Invisibility cloaks are created from metamaterials--arrays of free-space resonators that are spaced at the wavelength of the light to be cloaked. The millimeter wavelengths of microwaves can be cloaked with millimeter sized resonators on a printed circuit board. But when you go to infrared wavelengths--measured in microns--you need resonators measured in microns. These researchers say that chalcogenide glass fits the fill by enabling micron-sizes resonators. Next they are looking for the nanometer-sized resonators needed to cloak visible wavelengths. How long do you think it will take to find metamaterials for Harry Potter style invisibility cloaks?