While this invention would not be heralded as one of the most important inventions of the 20th Century, it sure is one of those inventions without which the age of information technology (on which the 21st century is dependent) and more importantly, the smartphone revolution would not have happened. Quite a lot of us can still remember the iconic moment when Steve Jobs slid the first iPhone out of his pocket and unveiled it to the whole planet which gasped in awe. That was 10 years ago to the month. In the 10 years, smartphones- particularly the ones running Android- have gone to capture the global market and have found their niche in the palms of close to 2 Billion humans. That’s  a small computer in the hands of almost 1/3rd of the planet’s population.

And the one major technology that made this happen is the technology of Touchscreens.

Touchscreens have been around in several forms for the past few decades although the kind of touchscreens that are at the cutting edge and the ones we use today are the capacitive type of touchscreens.

So, How do these ubiquitous little screens work?   

The two most commonly used systems are resistive and capacitive touch screens. 

1. Resistive:

These are the most basic and common touch screens, the ones used at ATMs and supermarkets, that require an electronic signature with that small grey pen. These screens literally “resist” your touch; if you press hard enough you can feel the screen bend slightly. This is what makes resistive screens work – two electrically conductive layers bending to touch one another, as in this picture:

One of those thin yellow layers is resistive and the other is conductive, separated by a gap of tiny dots called spacers to keep the two layers apart until you touch it. (A thin, scratch-resistant blue layer on top completes the package.) An electrical current runs through those yellow layers at all times, but when your finger hits the screen the two are pressed together and the electrical current changes at the point of contact. The software recognizes a change in the current at these coordinates and carries out the function that corresponds with that spot.

Resistive touch screens are durable and consistent, but they’re harder to read because the multiple layers reflect more ambient light. They also can only handle one touch at a time – ruling out, for example, the two-finger zoom on an iPhone. That’s why high-end devices are much more likely to use capacitive touchscreens that detect anything that conducts electricity.

2. Capacitive:

Unlike resistive touch screens, capacitive screens do not use the pressure of your finger to create a change in the flow of electricity. Instead, they work with anything that holds an electrical charge – including human skin. (Yes, we are comprised of atoms with positive and negative charges!) Capacitive touch screens are constructed from materials like copper or indium tin oxide that store electrical charges in an electrostatic grid of tiny wires, each smaller than a human hair.

There are two main types of capacitive touch screens – surface and projective. Surface capacitive uses sensors at the corners and a thin evenly distributed film across the surface (as pictured above) whereas projective capacitive uses a grid of rows and columns with a separate chip for sensing, explained Matt Rosenthal, an embedded project manager at Touch Revolution. In both instances, when a finger hits the screen a tiny electrical charge is transferred to the finger to complete the circuit, creating a voltage drop on that point of the screen. (This is why capacitive screens don’t work when you wear gloves; cloth does not  conduct electricity, unless it is fitted with conductive thread.) The software processes the location of  this voltage drop and orders the ensuing action.

Source credits: ScienceLine