Cover for IR Height Sensor. Where don't work the Sensor?

[FBG]

I use from a lot time the IR sensors, works well and no problem with the config.
But sometimes when a print fail some remains/waste of filament touch the "little less of the sensor and broken this....

So my idea is do a cover where never a waste of filament touch the leds, but of course, i need "open" the side where the led detect with some material "no detectable for led IR"....

This side "open" with than material i can put than the led detect the bed and not detect this cover?
PMMA transparent will be ok?
PC transparent will be ok?
Ideas?

[dc42]

I'm not sure that any transparent material at all will work, because you will get reflections from both surfaces. If you want to try it, I suggest you try a piece of thin acetate sheet (like the stuff that used to be used with overhead projectors) placed right against the IR diodes and phototransistor.