Which sensor detects motion traveling across its beams?

Which sensor detects motion traveling across its beams?

• A. Timers
• B. Infrared
• C. Outdoor Photo Sensors
• D. Ultrasonic

Answer: (D)

Motion detectors that rely on a field of beams sense movement by how echoes change as something passes through those beams. An ultrasonic sensor sends out high‑frequency sound waves through its transducer array to cover an area, creating multiple acoustic beams. When a target moves across that field, the timing and strength of the returned echoes from successive beams change, signaling that motion is happening across the beam pattern. This is different from infrared beam systems that detect motion mainly by interrupting light beams, or from sensors that monitor ambient light or rely on timers. So the ultrasonic approach—using multiple beams and changes in the reflected sound as something crosses them—best explains motion traveling across its beams.

Motion detectors that rely on a field of beams sense movement by how echoes change as something passes through those beams. An ultrasonic sensor sends out high‑frequency sound waves through its transducer array to cover an area, creating multiple acoustic beams. When a target moves across that field, the timing and strength of the returned echoes from successive beams change, signaling that motion is happening across the beam pattern. This is different from infrared beam systems that detect motion mainly by interrupting light beams, or from sensors that monitor ambient light or rely on timers. So the ultrasonic approach—using multiple beams and changes in the reflected sound as something crosses them—best explains motion traveling across its beams.