Researchers created a robotic arm with a “cup” grip that uses ultrasonics sound waves to suspend an object in midair “levitating” , making it suitable for the most delicate and precise tasks.
It works with tiny speakers that emit sound at very carefully controlled frequencies and volumes.
The grip produce a sort of standing pressure wave that can hold an object up or, if the pressure is coming from multiple directions, hold it in place or move it around.
Ultrasonic levitation example:
Another advantage is the acoustic gripper eliminates the need for specific gripper : the ultrasonic gripper can adapt to different shapes and movements.
Source : Ethz