Invisibility Cloaks

In October of 2007, London's Daily Mail, Daily Telegraph and Sun all reported that the British military had conducted an invisibility test. This test involved making 30 foot long, 60 ton Challenger tank disappear in front of a group of observers. Sir John Pendry was believed to have been a leading scientist involved in the experiment but he states that the test never happened. The British Ministry of Defense will not comment on the test but many credible scientists believe that an invisibility cloak is possible.

In the That's Impossible episode entitled "Invisibility Cloaks", the History Channel took a look at this reported experiment and other invisibility claims. Invisibility is looked at as the ultimate camouflage and it has been pursued for hundreds of years. Now it appears that science has made virtual invisibility and perhaps actual invisibility possible.

The barrier to invisibility has always been the difficulty in bending light waves. When we see something, what we are actually seeing is the light waves bouncing off the object and back to our eyes. If the light waves could be bent around an object so that they do not bounce back to the eyes, the object would then be invisible. That's Impossible took a look at how to get around these issues and achieve invisibility.

Tricking the Eye

One early method of achieving invisibility was to trick the eye of the observer. Ninja instructor Shinichi Yoshida explained how ninjas were able to accomplish this as far back as the 6^th century. The ninjas would move in the blind spots of the eye to remain invisible to the observer. Normal range of vision is about 60 degrees in each eye with peripheral vision taking this range out to 100 degrees but when the eye is focused on an object the brain may reduce the field of vision down to as little as 6 degrees. Ninjas would wait for hours until the subjects vision became focused on something in order to make their move. In this manner they could move openly without detection. According to security analyst Tim Brown, modern special forces are trained to utilize these ancient techniques.

Deception Camouflage

During World War II, the British had to protect the vital areas of the port of Alexandria and the Suez Canal from German bombing raids. Churchill turned to professional magician Jasper Maskelyne for aid. The British created the Magic Gang which consisted of set designers, painters, architects and Maskelyne.

To protect the port of Alexandria, the Magic Gang created a fake harbor 3 miles away from the real harbor. The created fake anti aircraft guns, building and even a lighthouse as part of the deception. They blacked out the fake harbor a little less than the real harbor in order to attract the attention of the German bombers. The deception worked well with most bombs hitting the fake Alexandria.

To camouflage the Suez Canal was a lot more difficult. The canal is nearly 120 miles long so it was not feasible to build a fake one. Maskelyne created what he called the "whirling spray" to deceive the Germans. By attaching numerous mini mirrors to spinning searchlights, he was able to make a dazzling light display that made it impossible to distinguish the Suez Canal from the surrounding areas. Most of the German bombs that were aimed at the canal landed miles away.

Radar Invisibility

Most of us are familiar with the current stealth technology that is used by the U.S. Air Force. This technology involves the reduction of sharp edges and special radar absorbent composite materials. Early experiments into radar and electro magnetic invisibility may not have been as successful.

Many people believe that the U.S. Navy was involved in an electro magnetic invisibility experiment that went horribly wrong. This project was referred to as Project Rainbow or the Philadelphia experiment. During World War II, the British navy had used some electro magnetic coils to neutralize German magnetic mines. The Philadelphia experiment is believed to have been an experiment involving electro magnetic coils to divert torpedoes. It is believed that this may have been referenced in an 18 June, 1943 letter from Albert Einstein to Navy Lt. Stephen Brunauer.

The ship reportedly used in the Philadelphia experiment was the destroyer escort USS Eldridge. On 28 October 1943 the Eldridge was anchored at the Philadelphia Naval Yards with a skeleton crew and electrical coils lining its decks. The story goes that at 5:18 p.m., the generators were started and the magnetic coils were charged. A green fog enveloped the ship. The ship disappeared and did not reappear until the generators were turned off. When the ship reappeared some of the crew was missing, some had become deranged and some were partially embedded in bulkheads of the ship. This story can not be proven and it is denied by the Navy but it shows the fascination with different methods of invisibility. Now in the 21^st century it appears that real electromagnetic invisibility has arrived.

Electromagnetic Invisibility

Duke University Professor David Smith has developed a composite material that is capable of bending microwaves around an object. Smith had spent 10 years trying to develop a material capable of achieving this when he stumbled across a paper by Sir John Pendry. This is the same Sir John Pendry that was tied to the invisible British Challenger tank. This article contained information about creating a man made material that could bend light known as metamaterials.

In 2006, Professor David Smith created the first cloaking device utilizing metamaterials. The metamaterial consisted of circuit board materials, gold, copper, and fiberglass. This new metamaterial has electromagnetic properties that can not be found in any other material. Smith made a coil out of this material and is able to conceal object that are placed within the concealment area of the coil. When microwaves approach the concealment area, they are bent around it and restored on the other side. While this does not make the object visually invisible, the ability to make it invisible to microwaves is an important step towards true invisibility.

True Invisibility

UC Berkeley Professor Xiang Zhang has gone a step further and has created a true invisibility cloaking device. This device works only on the microscopic level but is a huge leap forward. Zhang developed a metamaterial that is made up of alternating circuit boards comprised of silver and magnesium fluoride. These circuit boards are then stacked in a manner that is calibrated to oppose the electromagnetic field of incoming light waves. Like two opposing magnets, the metamaterial pushes on the incoming light waves and bends it around the concealed object.

Virtual Invisibility Cloak

Another approach at invisibility is what is known as virtual invisibility. Dr. Susumu Tachi from the University of Tokyo has developed Retro-reflective Projection Technology (RPT). RPT uses a series of projectors and cameras to create the illusion of invisibility. The cloak is made of tiny beads that are covered in retro-reflective material similar to what is used on traffic signs and movie screens. A digital camera catches the images behind the cloaked object. These images are run through a computer and sent back to a combiner (a half silvered mirror). The mirror reflects the image back onto the cloak and the image of the cloak that reflects back to the mirror appears to be invisible. That's Impossible showed some fantastic video of the cloak being tested in an outdoor environment on 1 November 2008. This is the type of technology that Nick Pope, formerly of the British Ministry of Defense, believes may have been used in the British tank experiment.

Conclusions

The Invisibility Cloak episode of That's Impossible showed that invisibility may be achieved in many ways. The most fascinating aspect was just how close we are to achieving true invisibility. Professor Smith thinks that true invisibility cloaks with real world applications could be only months away. When this technology becomes available, the implications could be far reaching. Many applications for counter terrorism and driver/pilot vision could be extremely beneficial. The potential uses by criminals and terrorist are something that one would not want to contemplate.