Invisibility cloaks made of metamaterials have a limited size: The cloaked region is restricted to a few wavelengths due to the spatially varying electromagnetic properties of the artificial, nano- or micro-fabricated composite materials.

Shuang Zhang, University of Birmingham, UK, and co-workers have demonstrated an invisibility cloak that can hide a three-dimensional object, centimeters in dimension. The team used a crystal of calcite – a transparent mineral with birefringent or double-refraction properties. Calcite splits lights on entry, directing it in two different directions, at different speeds and with different polarizations. With this, the team managed to hide macroscopic objects for the first time, and have shown that the size of the cloaking area is not limited by the technology available, only by the size of the calcite crystal.

• Macroscopic invisibility cloaking of visible light
  X. Chen, Y. Luo, J. Zhang, K. Jiang, J. B. Pendry, S. Zhang,
  Nat. Commun. 2011, 2, 176.
  DOI: 10.1038/ncomms1176