Militaries are likely to be very interested in a new cloaking material capable of making submarines completely ‘invisible’ to detection.
One of the most famous science-fiction technologies that many have dreamed of is the ability to cloak a person or object to make it completely invisible.
While we are a long way from achieving this, major breakthroughs of recent years have managed to reach the cusp of cloaking. Now, a new project has managed to cloak underwater craft such as submarines from sound waves.
A team from Pennsylvania State University spoke at the recent Meeting of the Acoustical Society of America about its new material that acts as an underwater acoustic shield.
Amanda Hanford and her team had set out to engineer a metamaterial – which exhibits extraordinary properties not found in nature – to allow the sound waves to bend around the object as if it were not there.
So far, existing metamaterials have been designed to deflect sound waves in air, but trying the same thing underwater is a lot more challenging because water is denser and less compressible than air.
Pyramid of the metamaterial used to cloak underwater objects. Image: Peter Kerrian
After much trial and error, the team managed to construct a metre-tall pyramid out of perforated steel, and placed it on the floor of a large underwater research tank.
Inside the tank, a source hydrophone produced acoustic waves between 7,000Hz and 12,000Hz, and several receiver hydrophones around the tank monitored reflected acoustic waves.
The findings showed that the waves reflected from the metamaterial matched the phase of the reflected wave of the surface. Additionally, the amplitude of the reflected wave from the cloaked object decreased slightly.
These results demonstrate that this material could make an object appear invisible to underwater instruments such as sonar.
“These materials sound like a totally abstract concept, but the math is showing us that these properties are possible,” Hanford said. “So, we are working to open the floodgates to see what we can create with these materials.”