By Henry Lau 劉以軒
Nowadays, touch screens are ubiquitous in our lives. Everywhere we go, there’s always a touch screen: be it at the restaurants or directories or even in your own pocket in the form of a smartphone. It’s something we rely on every minute of our lives. It’s amazing how a piece of glass responds to your touch so quickly and accurately, but have you ever given much thought to why and how it works as it does? This article will dive into the “how” and the “why” on the workings of the touch screen.
In fact, there are two commonly used touch screens. One works based on the principle of resistance. The resistive touch screen actually contains two flexible conductive layers separated by an air gap. The upper outward-facing layer is coated with a thin, scratch-resistant material while the inner layer is braced against a rigid layer, usually glass. When the touch screen is in operation, electrical currents run through these two conductive layers. When you touch the screen, pressure is applied. This pressure dents the upper conductive layer momentarily such that it comes into contact with the lower conductive layer. This brief contact of the layers alters the resistance in the area. Such a change in resistance is readily detected by sensors in the touch screen and the precise location of the touch can be calculated. As such, your touch is registered by the machine and the touch screen can be operated with ease.
However, sometimes these touch screens refuse to budge even after constant prodding. This is because older generations of this touch screen can only register one touch at a time; if you press two different locations at the same time, the sensor will be confused as to where you are actually touching, leading to non-responsiveness. Thankfully, newer models of the resistive touch screen have been upgraded to be able to sense more than one touch at the same time.
The other type of touch screen relies on the principle of capacitance. To start off, capacitance is a property defined as the ability to hold electrical charges. In capacitive touch screens, the topmost layer is made up of a large network of tiny fine wires that are able to hold an electric charge. This network of wires holds electricity at all times. It so happens that human skin is also a capacitor. So when your finger touches the screen, a minute amount of electricity is transferred from the network to your finger. This disturbs the original electrostatic field in the network, which is signaled by a drop in voltage at that precise location. Again, this drop is sensed by the machine and the location registers your touch to perform downstream tasks. As this type of technology relies on the transfer of electricity from the screen to the human finger, it well explains why capacitive touch screens cannot work when we touch it whilst wearing non-conductive materials, such as gloves.
Comparatively, resistive touch screens are less costly to produce than capacitive touch screens. As such, this has made the former more commonly used in society, such as the touch screens at canteens or directories. However, as you may have noticed, those touch screens are not as sensitive to your touch as your own electronic devices. (You only need to compare the canteen ordering machine to your own mobile phone.) This is because handheld devices usually utilize capacitive touch screens, which have a noticeably higher touch sensitivity than resistive touch screens. And besides, capacitive touch screens have a brighter and sharper display than resistive touch screens as the former does not have air gaps in between layers. Due to these pros, capacitive touch screens are becoming more and more popular.
So there you have it, the working principles of touch screens. So next time you play games on your phone or order food on a restaurant tablet, remember it was the magic of touch screens that allowed us to perform such simple but pivotal tasks.
[Editor’s remark: This article describes the two most common types of touch screens. Nevertheless, additional, less commonly used touch screen technologies exist.]
 Dube, R. (2018, November 28). Capacitive vs. Resistive Touchscreens: What Are the Differences? Retrieved from https://www.makeuseof.com/tag/differences-capacitive-resistive-touchscreens-si/
 McCann, A. T. (2012, January 17). Okay, but how do touch screens actually work? Retrieved from https://scienceline.org/2012/01/okay-but-how-do-touch-screens-actually-work/
 Technologies of Touch Screens (Surface Capacitive). (n.d.). Retrieved from https://www.dmccoltd.com/english/museum/touchscreens/technologies/Surface.asp