What are ultrasonic sensors and how are they used in vehicles?

Ultrasonic sensors emit high-frequency sound waves and measure the time for echoes to return, calculating distance to nearby objects. In vehicles, they are primarily used for: Parking assistance (detecting obstacles while maneuvering), rear cross-traffic alert supplements, and low-speed maneuvering. Typically mounted in bumpers (front and rear) with 4-12 sensors providing coverage around the vehicle. Advantages include low cost, good performance for close-range detection, and reliability. Limitations include short range (typically <5 meters), limited object information (distance only), and degraded performance in certain conditions. They complement other sensors for comprehensive coverage.