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U. mathematicians discover invisibility process

The idea of becoming invisible crosses nearly everyone's mind at some point. Three mathematicians at the University of Utah have figured out a way to make it possible, albeit not for humans.

"It's one of the few things I have done that I can explain to people," said assistant math professor Fernando Guevara Vasquez. He said the original idea, belonging to the U.'s distinguished mathematics professor Graeme Milton, is one that can likely be used in many different ways, including possibly blocking radar signals from a passing police car.

The new mathematical equation, which as a theoretical work can be used to detect incoming frequencies and then mask objects from being detected, was published online Monday in the journal Optics Express. It might someday be the basis for the development of devices that could shield submarines from sonar waves, planes and vehicles from radar waves, and protect buildings from earthquakes and oil rigs and coastal structures from tsunamis.

"I cannot tell you if somebody is really going to build the devices to make this work, but we have determined that is feasibly possible," Vasquez said.

The numeric possibility has shown that objects can be shielded from actual pulses generated by a multi-frequency source, and not just single-frequency waves, according to Milton.

"It's a brand new method of cloaking," he said. "It is two-dimensional, but we believe it can be extended easily to three dimensions, meaning real objects could be cloaked."

Before now, Milton's calculations allowed for the shielding of small particles, but the new sequence indicates cloaking of larger objects – much like process of cloaking items from visible light used in science fiction movies, games, books and shows – is possible. According to the U. professors, it is the first numerical simulation of cloaking against an incoming broadband pulse.

The mathematicians have tested the method up to 10 feet, but Vasquez said improvised devices of all sizes are practical.

"We just do the math and hope other people do the experiments," Milton said.

In the Optics Express article, it is demonstrated that three cloaking devices together create a "quiet zone" so that "objects placed within this region are virtually invisible" to incoming waves.

Milton says the cloaking devices cause "destructive interference," which also occurs when two pebbles are thrown in a pond. In places where wave crests meet, the waves add up and the crests are taller. Where troughs meet, the troughs are deeper. But where crests impact troughs, the water becomes still, or the waves disappear, because they cancel each other out.

The principle, applied to sound waves, is "sort of like noise cancellation devices you get with headphones in airplanes if you travel first class," he said.

"Our method may have application to water waves, sound and microwaves (radar)," including shielding various structures and vehicles from sonar and radar, respectively and protecting structures from seismic waves during earthquakes and water waves during tsunamis, Milton said. It's all "on the borderline of what's possible."

The only drawback for the new method of detection and non-detection is that incoming wavelengths must be known about, requiring the placement of numerous sensors in various environments. A related study, including work from Vasquez, Milton and U. professor Daniel Onofrei, was also published online last week in Physical Review Letters.

"Even though cloaking from light is probably impossible, it's a fascinating subject, and there is beautiful mathematics behind it," Milton said. "The whole area has exploded. So even if it's not going to result in a 'Harry Potter' cloak, it will have spin-offs in other directions," not only in protecting objects from waves of various sorts, but also "for building new types of antennas, being able to see things on a molecular scale. It's sort of a renaissance in classical science, with new ideas popping up all the time."