Ultrasonic Sensor

A cheap, short-range sensor that measures distance by emitting ultrasound and listening for its echo.

An ultrasonic sensor emits a pulse of sound above 20 kHz (inaudible to humans) and measures how long the echo takes to return; the speed of sound times half that time gives the obstacle’s distance. It’s cheap, and because it doesn’t depend on light, an object’s color and reflectivity don’t affect the measurement, so it can catch obstacles like glass doors that cameras and lidar often miss — which is why it’s common in car parking sensors and short-range obstacle avoidance on mobile robots. Its drawbacks are a wide beam that can’t resolve fine directional detail, and a range usually limited to a few meters; sound-absorbing materials or steeply angled surfaces produce a weak echo that can go undetected. In cars this is often called an “ultrasonic radar”; Tesla reportedly removed it from some models starting in 2022, switching to a camera-only approach instead.

ExampleWhile backing up, an ultrasonic sensor on the bumper detects an obstacle getting closer behind the car; the warning beep goes from intermittent to rapid, and finally to a continuous tone.

Also called

USS, Ultrasonic Ranging Sensor

Related

Vision-Only Approach · Proximity Sensor · Time of Flight · Obstacle Avoidance · Millimeter-Wave Radar · Transparent & Reflective Object Perception

Sources

Ultrasonic transducer - Wikipedia
Parking sensor - Wikipedia