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

Question

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

Answer 1

Sort of the same way reflective tape works.

if you combine 3 mirrors at 90 degree angels ( think the corner of a box with only 3 sides. )

If you shine a light at this setup, the angle that it leaves the mirrors is the same angle that it enters. Meaning, no matter where the might is at, it will be reflected directly back at it. It’s not 100% effective at a small scale, but it reflects enough IR back at the correct angel for the sensor to see if it’s there.

We left a similar device on the moon so we can shoot lasers at it.

Answer 2

Sort of the same way reflective tape works.

if you combine 3 mirrors at 90 degree angels ( think the corner of a box with only 3 sides. )

If you shine a light at this setup, the angle that it leaves the mirrors is the same angle that it enters. Meaning, no matter where the might is at, it will be reflected directly back at it. It’s not 100% effective at a small scale, but it reflects enough IR back at the correct angel for the sensor to see if it’s there.

We left a similar device on the moon so we can shoot lasers at it.