17 Sep 2015


Have you ever wondered why your iPad does not respond to your finger? If you have wondered, then great, but if you have not, then, no problem. Anyways, in either case, it is worth knowing the answer!! To understand the answer to this question, we must first understand what “touchscreen technology” is, and how it works.

Technically ‘touchscreen’ is an input device layered on the visual display unit of an information processing system that enables you to operate the system using your finger, stylus or designed gloves.

In simpler words, it is the technology that helps your finger use your smartphone!

Nowadays, touchscreen technology is not limited to just tablets and smartphones but is instead creatively employed in almost everything from laptops to gaming consoles. It is used in hospitals, heavy machinery and even ATMs.

But, in order to be able to employ touchscreen technology as well as we do in the present, a lot of research and work has been done over the last five decades. And this work, can be traced down to scientist E.A. Johnson who first published his work on touchscreen technology in 1965. A decade later, at CERN the first transparent touchscreen was developed by Frank Beck and Bent Stumpe. In 1972, the University of Illinois filed a patent for the invention of an optical touchscreen, and consequently, further discoveries in the field led to what we possess today in our smartphones, tablets etc.

Now with this much of a background, we can now explore HOW touchscreen works.

There are essentially two main types of touchscreen technologies:

1.      Resistive Touchscreen Technology.
2.      Capacitive Touchscreen Technology

Resistive Touchscreen Technology:

In this technology, there are two layers separated by a very thin space. The front layer has an external hard plastic covering facing outside, and an inside conductive coating.

The layer behind, has a glass covering facing the outside, and a conductive coating on the inside of this layer.

When the front hard plastic coating is touched, the little pressure applied, causes the two internal conductive layers to touch. The device then recognizes which part of the screen the finger/stylus has touched, and accordingly performs its function. 

Capacitive Touchscreen Technology:

Here, unlike before, the pressure applied is not the determinant. Rather, it is the material with which the screen is handled with. 

There is an ITO (Indium Tin Oxide) conducting layer which is horizontally lined with electrodes and has electricity flowing through it. There is another ITO conducting layer beneath. This is vertically lined with sensing wires that monitors the flow of electric current in the first ITO layer.

The wires of these two ITO layer are now perpendicular to one another. These layers are separated only by a thin optical adhesive that helps them remain together intact.

So essentially when we touch the screen of the device with our finger, the electric field is distorted or altered from the first ITO conducting layer due to the conductivity of our finger. This alteration is sensed by the second ITO layer and then the point on the screen that our finger has touched, is identified. Accordingly the device performs its function.

So now the answer to our question is almost self-explanatory. Human nails are a poor conductor of electricity and iPads use capacitive touchscreen technology. So by nature, the nails do not alter the electric field, and so the iPad does not sense it!

I hope this article helps you understand how your tablet or phone responds to your touch!

Some of the references I have provided below can help you understand more about this subject. If you find anything interesting in the field and would like to share it, please post a comment.


1. http://scienceline.org/2012/01/okay-but-how-do-touch-screens-actually-work/
2. https://www.youtube.com/watch?v=SzLoWDkBKXk
3. http://capacitive-resistive-touchscreens.articles.r-tt.com/

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