How does surface capacitive touchscreen work in detail?

[genxium]

It's pretty easy to find the "working principle" of surface capacitive touchscreen like http://www.elotouch.com/Technologies/SurfaceCapacitive/howitworks.asp

Roughly speaking, I know that

• A surface capacitive touchscreen has a conductive layer to which some electrodes are attached
• The electrodes apply voltage across the layer
• When some conductive material, e.g. finger touches the layer a portion of current is drawn yielding numbers' changes in the sensors attached to the electrodes
• According to the numbers read from sensors, one calculates the touch location

Here're the questions:

• Should the electrodes apply DC or AC signals to the layer?
• How is the "conductive layer" modeled, i.e. is it regarded as a 2D conductive plane ? Or is it regarded as a 3D conductive block? In either case, how to calculate or approximately guess the charge/voltage/current distribution when the layer is idle/touched?
• What are proper sensors to attach to the electrodes, e.g. voltage metres or current metres or sth else? Why?

 

[gtoguy97]

1. The electrodes apply AC signals to the layer.2. The "conductive layer" is typically modeled as a 2D conductive plane. The charge/voltage/current distribution can be calculated with the help of an electrostatic field solver, such as a finite element solver.3. Voltage meters are typically used as sensors. This is because when a finger touches the layer, it affects the capacitance between the electrodes and the conductive layer, causing a change in voltage that can be measured.