What Kind of Touch Technology Does the iPhone Use?by John Lister
The majority of touch screens use one of two different technologies, resistive or capacitive. These work in very different ways, affecting the way software on the device interprets and uses your commands. The iPhone's capacitive screen brings several advantages particularly suited to a smartphone.
Resistive touch screens work in an extremely simple way. The screen has several different layers, with the top one being slightly flexible. When you press it down with a finger, the top layer touches the one below and completes an electronic circuit. The device can then tell where on the screen you have pressed down. A resistive touch screen can work with a finger or any device, such as a stylus, that can apply pressure. However, it struggles to detect any gestures more complicated than a simple press in a single spot.
Capacitive touch screens including that on the iPhone carry a very small electrical charge. When you touch the screen, the device will notice a change in the charge because your skin conducts electricity at a rate different than that of the glass or other material used in the screen. The charge is so low as to pose no safety or health risk. Because the technology doesn't rely on a screen flexing in the same way as resistive technology, the system is able to detect light contact with the screen in multiple places simultaneously along with movement of the fingers.
Benefits for iPhone
The iPhone's capacitive touch-screen technology means that you aren't limited to simply pressing the screen in one place. The iPhone can detect the difference between your pressing the screen with one, two, three or four fingers. It can also detect gestures such as swiping or pinching. This sensitivity gives you a much wider range of controls for each individual application. It also helps make the user interface much more intuitive. For example, programmers can map your finger swipes to scrolling through a long page, or pulling two fingers apart to zoom in on an image.
Capacitive touch screens such as the iPhone are configured to detect the conductivity level of a human finger. This means that most other objects such as a pen or stylus won't work, limiting the possibilities for applications that rely on precise positioning and movement, such as drawing apps. The iPhone screen also struggles to detect your input if you are wearing ordinary gloves, though you can buy special gloves with a custom fingertip surface designed to operate capacitive touch screens.
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