U.S. new materials to make objects invisible underwater to avoid sonar to achieve (Figure)
University of Illinois Mechanical science and engineering professor Nicholas ? Square (Nicholas Fang)-led research team has successfully demonstrated an acoustic “cloak”, this “cloak” to make the sonar and other underwater objects in front of ultrasound to achieve “stealth” .
[Site January 11, 2011 Roundup] University of Illinois professor of mechanical science and engineering disciplines Nicholas ? Square (Nicholas Fang)-led research team has successfully demonstrated an acoustic ‘cloak “This” cloak “to make sonar and other underwater objects in front of ultrasound to achieve” stealth. ”
make a material around the object will be surround sound, rather than to reflect or absorb sound waves, this material has been proven for many years before it is theoretically possible, but in reality the concept of The realization has become a challenge. Nicholas ? Professor Fang’s research team in the “Physical Review Letters,” published an article detailing the results of the research team, developed the prototype to make the object in front of many types of sound waves to achieve stealth.
this “cloak” the use of negative refractive index material, negative refractive index materials come from the synthetic, designed by the research team’s project structure so that further enhance their properties. Nicholas ? R & D team led by Professor Fang, designed a two-dimensional cylindrical “cloak”, this “cloak” of 16 acoustic coil concentric rings, this structure can generate the sound wave guide. Each ring has a different refractive index, which means that sound waves from outer to inner communication process, its velocity will be changed.
this, Nicholas ? Professor Fang explained, “Basically at this so-called ‘invisibility cloak’ consists of a series array of cavities connected through a channel formed when sound waves spread in the channel when These cavities can reduce the speed of sound As sound waves spread gradually to the direction of the inner circle, its speed will be faster. “As the speed increased energy needs, with the loss of energy, sound waves can only be round ring channel direction and along the “cloak” of outer communication.
researchers took a steel cylinder to the “cloak” of the performance test. The researchers placed the steel cylinder tank, cylinder ultrasonic sound source placed on one side, place a sensor on the other side, then the cylinder placed in the “cloak”, the observed sonar signal the end of the cylinder disappear. In order to clarify its structure was hidden objects in the “cloak” the environment is also affected, the researchers also different shapes, density and other objects barrier was tested. The results show that the structure of the object to be invisible for stealth effect is concerned there is no relationship between the different shapes of objects similar to the stealth effect. Once the object is “cloak” covered or surrounded by, then the scattering effects or shadow effects were greatly reduced.
Nicholas ? Professor Fang team developed the “cloak” a big advantage is that it can mask a wide range of wavelengths of sound, the “cloak” to the frequency of 40 kHz to 80 one thousand He achieved between the ultrasonic acoustic stealth, with the future to further improve the theory, the “cloak” that can cover the frequency range will reach tens of MHz or more.
researchers next plan to expand the application of stealth technology, from the military’s covert operations to the health care field noise. Such as medical ultrasound and widely used in acoustic imaging techniques, such as negative refractive index materials with a bandage or shield can effectively mask interference. (China Shipbuilding Technology and Economy Institute Lei Song)