For Real Invisibility, Passive Cloaks Just Don't Cut It, Active Is The Way To Go - Study

Scientists have possibly discovered a way of creating an invisibility cloak that can actually make the wearer invisible in multiple wavelengths - opening the possibility of "real" invisibility, like you see in the movies.

Of course, invisibility cloaks have been in development for years now, even with a 3D printable design making its way into the research papers. But there still remain some kinks in the physics that have prevented current designs from achieving the kind of invisibility through technology that Harry Potter enjoyed with magic.

But researchers at the University of Texas at Austin have performed a study of the current methods of "invisibility" and have released their research, which shows promise for a new way forward in the quest for invisibility. The researchers have confirmed that the invisibility cloaks in development now - so-called "passive" cloaks, because they do not require electricity - are a dead end for invisibility to all light, and have proposed an "active" invisibility cloak design that will succeed where previous cloaks have failed.

Study: Passive Too Limited

According to the study (and this is something well known from previous limited successes in creating invisibility cloaks), passive cloaks are too limited in the range of light they can cloak.

Invisibility cloaks are based on metamaterials, which are man-made compositis of materials, which have structures that can bend light (or, scientifically speaking, radiation) around an object.

Bending the light around an object theoretically obscures it from view, as all detection of objects relies on light scattering off of objects. But current designs have only managed to bend a very specific band of light - in the non-visible spectrum - resulting in limited invisibility.

In fact, the materials can basically only make an object invisible to a limited-range radiation detector, like specific microwave detectors. "Several recent studies have indeed shown that a properly tailored metamaterial cover can, in principle, render an object invisible when illuminated by an electromagnetic wave oscillating at the specific frequency of interest," wrote researchers Francesco Monticone and Andrea Alù in the study.

But besides this quite limited "invisibility," passive cloaks have another problem: the more they bend a certain wavelength of light, the more they scatter other wavelengths. This means that, while a passive invisibility cloak can obscure an object from some detection, it actually makes the object stand out more on others. Say, for example, the military used a particular passive cloak to make a plane undetectable by some types of radar; the plane would actually stand out more to other types of detection.

Broad Spectrum Cloaking

The solution to this give-and-take spectrum cloaking/scattering problem is an "active" invisibility cloak, which can bend several wavelengths of light simultaneously. The design is based on current metamaterials, but with advanced integrated circuits (CMOS) negative impedance converters, or NICs, added. NICs are electronic components whose capabilities are still being discovered in the lab, but Alù says that with enough NICs adding negative resistance to a powered cloak, multiple frequencies can be bent without the usual resultant light scattering.

With fast-advancing CMOS circuit technology, active cloaks could be thinner and less bulky than passive cloaks currently are, while creating a cloak that can hide an object from a frequency range many times over broader than current passive cloaking technology. Now, all the researchers have to do is build the active cloak to prove it.