Hey guys! Sorry for the late response.
There is one emitter and one receiver on the end of the TLENs, so they cannot be used to detect direction of rotation. You could use two devices to make your own quadrature encoder, though.
We have tested detection through various materials and the results are mixed. We definitely recommend cutting a hole. However, it may be possible to detect through the polycarbonate if the TLEN is spaced back far enough so that it doesn't just detect the polycarbonate itself.
Thanks for the questions and good luck, guys! Please post here or email
engineering@mach-engineering.com if you need any further assistance