MEMS and sensors

What is the general principle of the sensor a smartphone uses to turn off the screen when your face approaches during a call, preventing accidental touches?

  1. AMeasuring sound loudness
  2. BMeasuring the strength of the Earth's magnetic field
  3. CEmitting infrared light and detecting with a photodetector the strength of light reflected back from an object
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Answer: C. Emitting infrared light and detecting with a photodetector the strength of light reflected back from an object

A proximity sensor emits light from an infrared LED or similar and detects with a photodetector the light reflected back from a nearby object such as a face. If the reflection is strong, it judges the object to be close and, for example, turns off the screen.

  • A. It does not judge the approach of a face by sound level.
  • B. Measuring the Earth's magnetic field is the principle of an electronic compass.
  • C. Correct. It detects proximity from reflected infrared light.
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More MEMS and sensors questions

  1. What is the driving principle of the "comb-drive" structure used as a MEMS actuator?
  2. Which device uses acoustic waves traveling along the surface of a piezoelectric substrate and serves as a high-frequency filter in smartphones and similar?
  3. Which sensor, widely used in motion sensors that turn on lights when a person approaches, uses a material that generates charge when its temperature changes?
  4. Which is an example of MEMS "energy harvesting"?
  5. Which technology builds tiny channels on a chip to perform chemical analysis or testing with small amounts of liquid?