Although touch screens may look much the same on the outside, their inner workings can be very different. There are currently five different types of touch screen in use at the moment. Here is a brief guide to them
A glass panel is covered with a resistive coating, which is topped by a layer of insulation, interspersed with spacer dots and then covered again by a sheet of polyester which is conductive on the inner side (the side touching the insulation). When the polyester outer is touched, it flexes slightly and thus sends an electrical charge to the corresponding location on the glass panel. While resistive touch screens had smartphone users grinding their teeth in frustration, they’re great for applications where robustness matters more than responsiveness and so, for example, is the standard choice for ATMs.
Same basic lines as resistive technology, but the key difference is that instead of a layer of insulation, there is a layer of transparent electrodes, which store an electrical charge. When touched by an electrical current, the electrodes discharge and this is converted into an instruction. Surface capacitive screens are a big step up in image quality as compared to resistive ones and they’re also less prone to scratches, but they are also more expensive to produce.
An integrated circuit chip is placed into the electrode layer and used to generate a 3D electrostatic field. When the screen is touched, the ratio of currents changes and this is measured and used to determine the relevant instruction. Projected capacitive screens offer several advantages over surface capacitive screens. Firstly they can be touched by a lightly-covered finger, which is useful for industries in which people are required to use plastic gloves as standard. Secondly they are much better for processing detailed instructions, they go way beyond pinch and zoom and thirdly, they offer even better image quality. They are, however, even more expensive to produce.
Surface Acoustic Wave
SAW technology uses a grid of ultrasonic waves produced by piezoelectric transducers and receivers located on a glass screen. When the screen is touched, by something soft, like a finger, even gloved, the touch is absorbed causing a change in wavelength which can be measured and translated into instructions. The sensitivity of SAW technology is both a benefit and a drawback in that it means it is capable of immense responsiveness, but that immense responsiveness means that it is very easy to trigger it inadvertently, for example through moisture or dust. SAW technology also offers superb image quality - but at a high price.
Infrared touch screens work similarly to SAW touch screens, except that instead of piezoelectric transducers and receivers, they use infrared rays to create the grid and sensors to detect when the infrared beam is interrupted. While the term infrared may conjure up images of remote controls for indoor use, in actual fact, the robustness of infrared makes it popular for outdoor applications.
Benefits of Infrared technology:
Can be scaled to any size without losing resolution
Calibration stability – no touch point drift
High clarity and light transmission
High chemical, scratch, breakage, and liquid resistance
High sealability from dust and liquids
Touch can be activated by anything including finger, gloved hand, or stylus
High durability since a touch is only interrupting light beams