How Does the iPhone Touchscreen Work?
The release of the Apple iPhone has sparked mass interest in a type of interface that has been around for a while but is ready for prime time: touchscreens. Apart from making these interactive screens trendy again, the iPhone also broke new ground in terms of responsiveness and the variety of inputs the user can enter, such as placing two fingertips and spreading them to zoom in or out of an image. Not surprisingly, it turns out there is a very ingenious technology involved.
Types of Touchscreens
Five main types of touch-screen technology exist: resistive, surface capacitive, projected capacitive, surface acoustic wave, and infrared, with the first three technologies suiting mobile products, according to Electronic Design magazine. However, they all share three common elements: a sensing mechanism, a control circuit and an interface to the control circuit.
Resistive Touchscreens
Earlier touchscreen devices were of the resistive variety, meaning that users had to exert pressure with their fingernail of stylus to get a proper response. In contrast, the iPhone's technology uses what is known as capacitive technology, which doesn't rely on pressure but instead responds to the electrical properties of your skin, according to Wired blog Gadget Lab. While resistive technology is cheaper to produce than capacitive touchscreens, it can't sense an approaching finger or allow multi-touch inputs.
Surface Capacitive Touchscreens
There are two types of capacitive technology, surface and projected, which are similar yet still have a couple of key differences. Both technologies comprise an outer glass cover and underneath, an inner panel of transparent material, usually made of indium tin oxide, that conducts electricity. The electrical field generated by this panel senses your touch as it distorts the field, according to Apple. The device then transmits this information onto a software application that interprets this touch into actions it shows on the iPhone's LCD screen.
Projected Capacitive Touchscreens
When it comes to projected capacitive technology, we find that the glass panel acts as an insulator, while the conductive panel is actually etched into a grid pattern. Usually two conductive layers are used, one for each axis in the grid (X and Y). The distortions in the electric (or more accurately, electrostatic) field caused by approaching touch inputs can be measured as changes in capacitance, or the degree the panel stores electric charge; hence the word "capacitive."
Multi-Touch
The iPhone uses projected capacitive technology, instead of the simpler surface-capacitive technology. Projected capacitive technology is perfect to discern more than one touch at a time because of its grid configuration. The technology also features a sensing chip that routes touch locations through their X and Y location and offloads the data to the device's main processor. This way, the device can readily recognize actions that require multi-touch input.
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