Technology behind touch screen working

HOW TOUCH SCREEN WORKS:
     
   Touch screen works on one of three principles:-

 1. Resistive system 
 2. Capactive System
 3.Surface Acoustic Wave


RESISTIVE SYSTEM:

It consists of glass panel which is covered with conductive and resistive metallic layer. These two layers are held apart by spacers. Electrical current moves through these two layers.When touch the screen ,voltage difference appeared at that spot, immediately OS recognises coordinates of spot and does it's operation.

CAPACTIVE SYSTEM:

It consists  a layer on galss panel which stores electrical charge. when we touch the screen,it transfers some of charge to user .Thereby capactive layer charge decreases,within short span OS recognises the cordinates where the charge is decreased and applies it operation overthere.

SURFACE ACOUSTIC WAVE( pen tip):

This works with two transducers( one receiver and one transmitter). Electrical signal is sent from one to other transducer.

When user touch the screen ,passing electrical signal is disturbed.

Receiving transducer  recognises wave disturbance and tells to OS, then OS traces the spot and does it's operation overthere.

eg: Smartphones uses pen sticks.