Acoustic Cloak Hides Objects In Plain Sound
Professor Nicholas Fang of the University of Illinois has created an acoustic cloak that hides objects from standard sonar waves - and it fits in the palm of his hand.
Underwater stealth technology has been kicking around for a while now and has included using substances like hard rubber to mask submarines from detection as they sneak around in the murky depths. Sonar and detection have always been tricky prospects as they depend not only on sound waves going out from a source, but just what those waves look like when they come back. Deformed waves might not show a sonar operator a specific object, but they'll certainly let them know that something is nearby.
Now, Professor Fang has created a acoustic cloak in the form of a two-dimensional ring; slip it over and object, submerge it and presto - instant invisibility.
The idea behind the cloak is that sound waves approaching the cloak wrap around it rather than be absorbed or reflected, as both of these circumstances would alert a clever sonar operator to a potential problem in the area. The cloak does this by using 16 rings of acoustic circuits, each with a different index of sound refraction, meaning that each ring forces sound to travel at a different speed. As sound waves move toward the center of the circle, the refraction index forces them to speed up, something which requires energy. Once the waves lack the energy to move to a more central ring on the circle, they are channelled around the object along the ring the occupy, making it appear as though they passed straight through.
Constructed of a meta-material, lab tests of the acoustic cloak showed that it was easily able to bend sound waves around a variety of different objects regardless of their shape, and Fang explained that unlike a one-frequency cloak often seen in science fiction, simply changing the output of the sonar would not result in instant detection. Currently, the cloak can hide objects under scrutiny from ultrasonic waves anywhere from 40 to 80 kHz, but Fang hopes to increase that substantially in the near future.
Along with military and soundproofing applications, the Illinois team also hopes to use the device in the medical field as a shield for body parts that interfere with ultrasound scanning during diagnostic treatments.
We could have sworn we heard something.
Source: University of Illinois
Photo Credit: L. Brian Stauffer