Star Trek-style invisibility cloaks are a step closer to becoming reality after scientists developed a material that could make submarines invisible to sonar detectors.
The invention deflects sound waves without echoing them back meaning sonar equipment cannot detect it.
The device could lead to military submarines that are invisible to enemy sonar, paving the way for an invisibility cloak that deflects light like the device used by the Starship Enterprise spacecraft in the Star Trek film and TV franchise.
Radar-evading stealth aircraft are a fixture of the world’s air forces but until now underwater craft able to hide from sonar have proved elusive.
Researchers at Pennsylvania State University developed the new material and incorporated it into a three-foot high prototype.
Sonar works by firing soundwaves and listening for their ‘echo’, but the pyramid-shaped prototype was able to redirect approaching waves.
Rather than deflecting off the object, the waves skirted around it without scattering any energy, rendering sonar technology useless.
To create the device, scientists engineered a new type of metamaterial – materials engineered in a lab to produce extraordinary properties not found in nature.
To work, the unit cell – the smallest component of the metamaterial – must be smaller than the acoustic wavelength of the sonar wave.
Study coauthor Dr Amanda Hanford said: ‘These materials sound like a totally abstract concept, but the math is showing us that these properties are possible.
‘We are working to open the floodgates to see what we can create with these materials.’
Until now most acoustic metamaterials have been designed to deflect sound waves in air.
Acoustic cloaking underwater is more complicated because water is more dense and doesn’t compress as well as air, limiting engineering options.
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, they fired acoustic waves between 7,000 Hz and 12,000 Hz at the object and monitored the reflected waves.
They found the phase and amplitude of the waves reflected from the cloaking device matched those reflected by the tank’s surface – rendering the object invisible.
These results demonstrated this material could make an object appear invisible to underwater instruments like sonar, the researchers said.