There are the direction switcher commands. You set them to switch if a particular element is over the sensor. Is there any way to set them to sense Theta or any of the other imaginary elements? Since they are not in the periodic table, I cannot come up with any way to select them. I was unsure if I'm missing something or if this is an added challenge with those elements.
If you're in the main campaign, the "alchemical" or imaginary elements should be in the table. They're off on their own near the bottom.
There's no problem using them in a detection trigger either in any puzzle I've tried (majority has been snipped to hide my highly inelegant solutions)
The extra ResearchNet section, however, does not acknowledge the extra elements at all (except in a sandbox mode). You cannot select them when creating a detection trigger for an existing puzzle, nor can you add them to a puzzle you are trying to design and create. Unfortunately, some of the published user-created puzzles have managed to include them anyway (there is a 3rd party tool apparently that'll work it in) and leave the player stuck. At this point the game is not being updated, so the only way forward - possibly intentionally by whoever made them, since it's not in the puzzle editor - is to work around them. (thanks to Nick who pointed this out in comments)
A partial positive answer for ResearchNet: it's possible to have Greek sensors (and Greek annotations) in production levels, using the following workaround:
- Go to End of the Line, the last boss level of the campaign
- Fill a Sensor reactor with Greek sensors and/or Greek pipe annotations, as Radhil's answer shows
- Copy said reactor to the saved reactors (EotL is the only level that has Greeks and copyable reactors)
- Load the reactor in the desired level and duplicate sensors/annotations at will
No workaround has yet been found for research levels in ResearchNet, to my knowledge, aside from straight up savefile editing.