This ultrasonic radar project is from [mircemk] who uses a small ultrasonic distance sensor attached ... in this project has a range of about a meter, there’s no reason that this principle ...

But for a weekend project, [Vinod.S] took the ultrasonic transmitter and receiver from a distance-meter module and used amplitude modulation to send music ultrasonically from his laptop to a ...

Two non-linear ultrasonic waves can be used to transmit audio signals that can only be heard by a person at a very specific point.