Touchscreens are omnipresent, from self-service machines, to our TVs, laptops and smartphones, it’s hard to imagine life without our trusty touch tech. But whilst we’ve been busy tapping away for the last decade or more, lots have people have been working tirelessly behind the scenes to make all this possible. The history of touchscreens is well documented but today we decided to explore some of the tech behind the touch.
The traditional touchscreen technology is analog resistive and it works almost like transparent keyboards coated on top of a screen. This tech features a bendy upper layer of conducting polyester plastic which is fused to a rigid lower layer of glass that’s conductive; this is all separated by a membrane for insulation. When pressure is applied to the screen, the polyester makes contact with the glass and completes a circuit—just like tapping a key on a keyboard. A computer chip inside the screen then works out the coordinates of the place you touched.
Capacitive screens are made from multiple layers of glass with both the inner and outer layers conducting electricity. In effect, the screen behaves like two electrical conductors separated by an insulator, this is also known as a capacitor.
When you start to apply force to the screen the electrical field is altered and capacitive screens can be touched in multiple places at one.
These touchscreens will not work when touched with a plastic stylus, however. That’s because plastic is an insulator and that interferes with your hand affecting the electric field. This type of technology is popular in machines like outdoor kiosks and most smartphones/tablets.
Infrared tech has been around for a long time and features in everything from burglar alarms to mobile phones. Infrared touchscreens adopt a grid pattern of LEDs and photocells that are organised on opposite sides of the screen. The LEDs shine infrared light in front of the screen and this creates an effect similar to a spider’s web.
If you touch the screen at a certain location you will interrupt two or more beams. A microchip inside the screen then formulates where exactly you touched the screen by identifying which beams were interrupted.
Surface Acoustic Wave
Unlike other forms, as the name suggests sound acoustic wave technology detects pressure by using sound as opposed to light. The way it works is that Ultrasonic sound waves are generated at the edges of the screen before being reflected back and forth across the surface. When you apply pressure to the screen the sound beams are interrupted and some of their energy is absorbed. The screen’s microchip then determines where exactly you touched the screen.
Images by KaboomPics / Mercury13