I've been playing around with projected capacitive touchscreens - specifically, the iPhone's. I've attached a white paper that outlines the details, but the basic idea is as follows:
An iPhone's touchscreen has a dielectric layer sandwiched between a layer of conductors arranged in rows and a layer of conductors arranged in columns. The result is a grid of capacitors that can be independently driven. When a finger (or anything capable of sapping enough charge) comes close enough to these pseudo-capacitors, the field between them is altered, and a touch is registered. ("Close enough" has been tuned to exactly the point at which a finger touches the iPhone's glass screen.)
What I'm wondering is - is it possible to alter these fields in the same way, but from further away than originally intended? Perhaps with a generated E-field? In general, can you alter the mutual capacitance of two conductors with an external field?
Thanks in advance!