What device operates by sending sound waves through a target to measure the time for the pulses to bounce back?

• A. Ultrasonic sensor
• B. Proximity sensor
• C. Capacitive sensor
• D. Magnetic sensor

Answer: (A)

Measuring distance by timing the round-trip of a sound pulse is the hallmark of an ultrasonic sensor. It emits a high-frequency acoustic pulse, the wave travels to the target and back as an echo, and the controller converts the elapsed time into distance using the speed of sound in the medium. Since the pulse covers twice the distance to the target, the calculation uses distance = (speed of sound × time) / 2. Temperature and air conditions affect the speed of sound, so many systems account for that to stay accurate. This approach is why ultrasonic sensors are great for obstacle detection and parking assist. Other devices in the options use different principles—proximity sensors detect presence without relying on echo time, capacitive sensors respond to changes in capacitance, and magnetic sensors sense magnetic fields—so they don’t measure distance with sound echoes.