Some of these devices have a glass panel covered with a thin metallic layer that conducts electricity . Both are separated from each other and the whole assembly is covered by a scratch resistant foil. An electric current flows through the two layers, so that when someone touches the screen they come into contact at one point . The change in the electric field is detected and a computer calculates the coordinates. In other computers, a layer that stores an electrical charge is placed on the monitor panel. When it is touched, part of the load passes to the user. The computer can thus calculate where this decrease in current has occurred. The advantage of this method is that 90% of the light of the monitor can be transmitted, compared to 75% of the first.
In another system, called acoustic wave , reflectors placed on the glass bounce an electrical signal sent by a transducer. Another, in charge of receiving the signal, detects if the wave has been altered by the user's touch, which makes it possible to locate where it has occurred.
