What exactly does a capacitive touch screen need to register input, and how can that signal be produced?
How do those emulate human touch?


Capacitive touch screens don't work from the supposed "aura" that some folk believe emanates from humans - they'll work with dogs, cats, medium sized rodents, pieces of metal and probably wet wood. Maybe they'll also work with high dielectric plastics too.

Capacitance is not given by gods to humans but is firmly routed in the physics of objects and the "styli" or pen has to be held in the hand and therefore a significant capacitive connection to the body is made (whether wireless or otherwise).

I suspect that wireless styli that use batteries may work by sensing the capacitive sensor's AC field and re-injecting some form of antiphase signal - the disruption is likely to be enough to "register" a keypress.