Is the military experimenting with an invisible tank?

With advancements in British technology, by 2012, the army might spot you while you can't see them. Explore more about invisibility in these images. Adid Katib/Getty Images

In October 2007, the British Ministry of Defence sparked global media attention when it revealed its success in making a tank disappear from the human eye. While the government kept the details under wraps, they did disclose the core concept behind the technology.

The tank is coated with silicon, transforming it into a reflective surface akin to a giant movie screen. Cameras on the tank capture real-time footage of the surroundings, which is then projected onto the surface. During secret trials in October 2007, the only visible feature was the terrain images displayed on the tank's surface.

The British military intends to have the tanks ready for battle by 2012, but this technique faces limitations. Cameras or projectors might fail, and from certain angles, the tank could still be visible. This method, though innovative, involves a smoke-and-mirrors optical illusion. The lead researcher at the British tests has expressed concerns about the technology's effectiveness (Mytour covered this technology in another article on invisibility cloaks).

"The next step is to make the tank invisible without relying on [cameras and projectors]," says physicist Sir John Pendry in an interview with the Daily Mail, "which is complex and challenging, but achievable."

Along with Pendry, universities worldwide and the United States military are investigating the potential of rendering objects invisible with cutting-edge cloaking technology that manipulates light. The U.S. Defense Advanced Research Projects Agency (DARPA), the Pentagon's research branch, has been approved for $15 million over three years to explore

urban obfuscants. This innovative project seeks to create a protective shield for soldiers in urban warfare scenarios. The shield would deploy swiftly in cramped spaces, safeguarding the soldier from enemy gunfire. But DARPA isn't stopping there; this shield could also make the soldier beneath it invisible and possess self-repairing properties, allowing it to mend if a bullet penetrates.

DARPA is likely to succeed in its mission eventually. The fundamental physics are already understood, and once the necessary technology to create the required components is available in the next decade, these cloaking devices will become a reality, leaving the realm of science fiction behind.

But how is this even possible? How can we manipulate light? The answer lies in tiny particles. Turn to the next page to learn more about metamaterials.

Metamaterials

DARPA's bold project aims to develop armor for soldiers that will make them -- along with their shadows -- vanish from sight. Alexander Nemenov/AFP/Getty Images

Researchers are currently investigating the potential of an artificial material known as metamaterials.

Natural materials behave according to the molecules that form them -- the atomic structure of a substance dictates its properties. For example, consider the relationship between wood and light. Wood, like all natural materials, reflects and refracts light, but the extent to which it does so depends on how light’s electromagnetic waves interact with the particles -- such as electrons -- within the wood.

In the case of metamaterials, the overall behavior of the material is determined by the combination of its components, rather than the individual properties of each part. Researchers have discovered that by arranging materials like gold and copper in specific patterns, they can merge the properties of those materials. Unlike natural substances, metamaterials derive their behavior from both the individual properties of the components and how they are assembled.

How do metamaterials make an object invisible? To put it simply, Duke University's David R. Smith offers this explanation: Imagine a fabric woven from thread. In this fabric, light can only travel along the threads, not through the gaps between them. If you pierce the fabric with a pin, light will flow around the hole and continue its path as if the hole wasn’t there. Thus, to the light waves, the hole is nonexistent. If you place an object in the hole, the light will flow around it as well, effectively making the object invisible [source: Technology Review].

Metamaterials, in theory, can do the following: they guide light around an object instead of reflecting or refracting it. As a result, to both the light waves and the human eye that perceives them, the object might as well not even exist. If the metamaterials guide the light waves around the object and return them to their original path, the object would not cast a shadow either. This is one of the objectives of using metamaterials to develop cloaking technology.

Smith is among a group of researchers experimenting with metamaterials to manipulate microwaves -- the electromagnetic waves utilized in radar. To effectively control any type of electromagnetic wavelength, the metamaterial must be smaller than the wavelength itself. As microwaves have wavelengths measured in centimeters, scientists have the technology to craft metamaterials small enough to redirect them around an object. For instance, a stealth bomber coated in the right metamaterial could become undetectable by radar. While the shield would remain visible, the radar wouldn't be able to detect the plane.

Rendering the entire aircraft invisible to the naked eye is a much greater hurdle. For one, we lack the technology to manufacture materials on the minuscule scale needed to manipulate light waves. Light wavelengths are measured in nanometers (one billionth of a meter), and the metamaterials required to block light must be even smaller. Another challenge is that a cloaking device made from metamaterials would need to manipulate light across the entire visible spectrum, since different colors correspond to different wavelengths. Finally, a cloaking device would throw the person inside into darkness, as the light that would normally reach them is diverted around the cloak.

If research and funding for metamaterials continue at their current rate, these challenges could soon be overcome. However, additional issues need to be addressed before the technology becomes practical. One key requirement of the DARPA project is that the device be asymmetrical. This means the wearer should be able to see out while remaining invisible to anyone on the outside. Once these obstacles are overcome, the army of the future might become nearly impossible to detect.

For more details on light, invisibility, and related topics, visit the next page.