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
You can split up a reflection in two main types Specular reflection and Diffuse reflection,
Specular reflection is like a mirror all light incoming from one direction is reflected out in another single direction. Diffuse reflection is when light is reflected from a surface in multiple directions like a painted white wall.
So unless you have a perfect mirror with only Specular reflection some will be reflected back to the sensor.
I would assume that IR proximity sensors have limitations in material and will have problems working with a mirror but other materials will reflect enough light back to the sensor.
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.
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.
ELI5
Your buddy Sam is standing in the middle of a dark room. You’re standing over in a corner. You shine a flashlight on Sam.
Can you see Sam from your corner? Sure. Because the light from your flashlight bounced off Sam and back toward you.
But now, put the flashlight down, still aiming at Sam. And walk to another corner. Can you still see Sam?
Yes, because the light from the flashlight bounces off Sam in ALL directions.
The light from the flashlight doesn’t go ONLY back toward the flashlight after bouncing off Sam. It goes in all directions.
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
You can split up a reflection in two main types Specular reflection and Diffuse reflection,
Specular reflection is like a mirror all light incoming from one direction is reflected out in another single direction. Diffuse reflection is when light is reflected from a surface in multiple directions like a painted white wall.
So unless you have a perfect mirror with only Specular reflection some will be reflected back to the sensor.
I would assume that IR proximity sensors have limitations in material and will have problems working with a mirror but other materials will reflect enough light back to the sensor.
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.
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.
ELI5
Your buddy Sam is standing in the middle of a dark room. You’re standing over in a corner. You shine a flashlight on Sam.
Can you see Sam from your corner? Sure. Because the light from your flashlight bounced off Sam and back toward you.
But now, put the flashlight down, still aiming at Sam. And walk to another corner. Can you still see Sam?
Yes, because the light from the flashlight bounces off Sam in ALL directions.
The light from the flashlight doesn’t go ONLY back toward the flashlight after bouncing off Sam. It goes in all directions.
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