The Ultrasonic sensor pair (transmitter and receiver) tuned for 40Khz. 16mm Diameter.

Note that the effective working angle is approximately 30° (which is large compared with other types of sensor), with smaller secondary lobes on each side. Measurement will consequently be more accurate within the central cone of 30°, and less accurate towards the sides. This explains why ultrasound sensors are typically mounted on rotating components so that different measurements can be taken using the central section of the viewing cone. Sound is a mechanical, elastic wave spreading through a physical medium in the form of longitudinal or compressional waves. This phenomenon is, for example, put to good use by loudspeakers, which cause a membrane to vibrate, which in turn causes the air to vibrate. Sound spreads more quickly the denser the environment, which explains why sound travels faster underwater than in the air. It also explains why ultrasonic sensors do not work in a vacuum, because sound waves cannot travel in a vacuum. You will therefore never see ultrasonic sensors on space probes or lunar rovers.

The width of this cone (30°) is both an advantage and a disadvantage. It is a disadvantage because any obstacle detected is not located precisely within the detection cone. Measurement of position is therefore relatively imprecise. It is, in contrast, an advantage in that it enables the environment to be scanned more effectively, and narrower objects, such as chair legs, will definitely be detected.Many animals can hear ultrasound, such as dogs and bats. Bats also have the special ability to emit ultrasound for the purposes of finding their way around, known as echolocation. This is exactly the principle used by the robots we program. Other animals have this faculty (whales, dolphins, chiroptera (bat family) and some rodents). They use ultrasound not only for finding their way around, but also to pinpoint prey and to communicate.