This plastic ring system doesn't exactly make the eight-centimeter ball inside less noticeable to the eye—but it does make the ball undetectable to sonar at a specific pitch. Spanish scientists have created the first cloaking device to completely shield a 3-D object from sonar, Science News reported.

Another cool thing about the device: It's one of the simplest invisibility cloaks ever made. Most cloaking devices are made of sophisticated lab-made stuff called metamaterials, which are engineered to have properties that don't appear in nature… you know, like scattering light waves, microwaves or sound waves in such a way that they're invisible to devices that detect those waves. This device, on the other hand, is made of 3-D printed plastic.

The shape of the plastic rings is the secret to its sonar invisibility. Its creators, a team of physicists from Spain, ran computer simulations to find a shape that would scatter sound waves in such a way that they cancel out the scattering by the ball tucked inside. When tested in lab, the rings worked for sound waves of 8.55 kilohertz—"an audible high pitch," Science News reported—aimed at the device from one specific direction.