How do we ensure that IR beams in IR proximity sensors reflect directly back to the sensor?

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I know in a proximity sensor an infrared beam is sent out and it is reflected back to a sensor where it does time calculations. Given the laws of reflection, I would’ve guessed that the IR beam would just reflect in random directions upon hitting anything other than a flat surface perpendicular to the proximity sensor. How is this issue resolved?

Tagging this physics but it could easily be engineering

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4 Answers

Anonymous 0 Comments

There are two techniques. Firstly the laws of reflection assumes a flat surface which will give a perfect reflection. In reality most surfaces are quite rough on the scales of the lightwaves. So there is bound to be some surfaces which are parallel to the sensor. This means some light will always return directly to the sensor, if even just a fraction of what the sensor sent out.

The second technique is to use corner reflectors. These have three flat reflective surfaces perfectly perpendicular to each other. The light hitting one surface will reflect to the other two surfaces and then return perfectly back to the source. So even if the reflector is slightly off the light will return back to the sensor. You may know these corner reflectors as regular reflective devices used on clothing and vehicles to reflect light.

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I know in a proximity sensor an infrared beam is sent out and it is reflected back to a sensor where it does time calculations. Given the laws of reflection, I would’ve guessed that the IR beam would just reflect in random directions upon hitting anything other than a flat surface perpendicular to the proximity sensor. How is this issue resolved?

Tagging this physics but it could easily be engineering

In: 3

4 Answers

Anonymous 0 Comments

There are two techniques. Firstly the laws of reflection assumes a flat surface which will give a perfect reflection. In reality most surfaces are quite rough on the scales of the lightwaves. So there is bound to be some surfaces which are parallel to the sensor. This means some light will always return directly to the sensor, if even just a fraction of what the sensor sent out.

The second technique is to use corner reflectors. These have three flat reflective surfaces perfectly perpendicular to each other. The light hitting one surface will reflect to the other two surfaces and then return perfectly back to the source. So even if the reflector is slightly off the light will return back to the sensor. You may know these corner reflectors as regular reflective devices used on clothing and vehicles to reflect light.

You are viewing 1 out of 4 answers, click here to view all answers.