The secret to their success — sound waves. Actually, it's no secret. A growing number of researchers around the world are investigating how sound waves can be used to simulate touch. These sound waves are ultrasonic. That means they’re so high-pitched people can’t hear them. At the same time, they’re strong enough to put pressure on human skin and trigger the sensation of touch. Scientists can change the location and shape of a tactile (touch) illusion by adjusting the sound waves, focusing them on a particular spot.