- Scientists have developed a material that makes an underwater object invisible to sonar detectors, an advance that brings us a step closer to Star Trek-style invisibility cloaks.
- A cloaking device is a fictional stealth technology that can cause objects, such as spaceships or individuals, to be partially or wholly invisible.
- Now, researchers at Pennsylvania State University in the US are taking the introductory steps to make acoustic ground cloaks.
- Metamaterials commonly exhibit extraordinary properties not found in nature, like negative density
- These materials redirect approaching waves around an object without scattering the wave energy, concealing the object from the sound waves.
What about Metamaterials?
- To date, most acoustic metamaterials have been designed to deflect sound waves in air.
- Acoustic cloaking underwater is more complicated because water is denser and less compressible than air.
- These factors limit engineering options, researchers said. After multiple attempts, the team designed a three-foot-tall pyramid out of perforated steel plates.
- They then placed the structure on the floor of a large underwater research tank.
- Inside the tank, a source hydrophone produced acoustic waves between 7,000 Hz and 12,000 Hz, and several receiver hydrophones around the tank monitored reflected acoustic waves.
- The wave reflected from the metamaterial matched the phase of the reflected wave from the surface.
- Additionally, the amplitude of the reflected wave from the cloaked object decreased slightly, researchers said.
- These results demonstrate that this material could make an object appear invisible to underwater instruments like sonar.
- The results show potential to contribute to real-world applications, such as acoustic materials to dampen sound and appear invisible underwater.
