An invisibility cloak that works in the microwave region of the electromagnetic spectrum has been unveiled by researchers in the US. The device is the first practical version of a theoretical set-up first suggested in a paper published earlier in 2006.
The cloak works by steering microwave light around an object, making it appear to an observer as if it were not there at all. Materials that bend light in this way do not exist naturally, so have to be engineered with the necessary optical properties.
Earlier in 2006, John Pendry, a theoretical physicist at Imperial College London, UK, and colleagues showed how such an invisibility cloak could, in theory, be made (see Physicists draw up plans for real ‘cloaking device’). Now David Smith and colleagues at Duke University in North Carolina, US, have proved the idea works.
In recent years, materials scientists have made rapid progress in making so-called “metamaterials”, which can have exotic electromagnetic properties unseen in nature. These are made up of repeating structures of simple electronic components such as capacitors and inductors.
In 2001, Smith built a metamaterial with a negative refractive index, which bends microwaves in a way impossible for ordinary lenses. Now he has gone one step further.