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Box 4.2 What Is Inside Your Smart Phone?
The touchscreen of most smartphones uses
either the analogue resistive or the projected
capacitance technology (Figs. 4.19 and 4.20).
In the first case, panels of the screen work by
detecting how much the resistance to current
changes when a point is touched. In this case,
two separate layers are needed where the bottom layer is made of glass and the top layer is
a plastic film. When the plastic film is pressed
it makes contact with the glass completing a
circuit. The voltage of the circuit is measured
to calculate the position of the touch. The circuit is made of a thin film of transparent conductor material, mostly indium trioxide or tin
dioxide. More recent touchscreens use projected capacitance technology where touching the screen with the finger changes the
electrical charge which is sensed. Thus multiple touches are possible and only the
touches of things with charge are sensed;
therefore, the screen will not react when
touched by a pen, a leather cover or the plastic of the smartphone holder in a car.
Nevertheless indium is always required in
touchscreens.
Fig. 4.19 Typical components of a smart phone (Image taken by Fossbytes, https://fossbytes.com/
whats-inside-smartphone-depth-look-parts-powering-everyday-gadget/)
Fig. 4.20 Touchscreen technologies, analogue resistance (left), projected capacitance (right) (after Walker 2012)
4 Changes on Earth as a Result of Interaction Between the Society and Nature