What is the inherent problem with ultrasonic proximity sensors?

• A. The blind zone at their sensing face
• B. Limited ambient light tolerance
• C. Slow response time
• D. High power consumption

Answer: (A)

Ultrasonic proximity sensors work by emitting a sound pulse and listening for its echo to judge distance. The key challenge is a blind zone right in front of the sensing face. As the transducer switches from transmitting to receiving, the emitted pulse is still traveling outward, and echoes from objects very close haven’t had time to return. That creates a dead area where the sensor simply can’t detect any object. Once an object is beyond this near field, you get reliable measurements.

Other choices aren’t inherent problems for this type of sensor: ambient light doesn’t affect ultrasound since it uses sound waves, and the speed of response is typically quick enough for most proximity tasks. Power use isn’t the defining issue here.