Capacitive touchscreens are often preferred over their resistive counterpart because of their superior image quality. As you may already know, capacitive devices identify touch by measuring changes in capacitance. Because the human body is an excellent conductor of electricity, touching the surface of a capacitive device causes a disturbance in its electrical field (capacitance), which the device uses to determine when and where the touch occurred. There are several different types of capacitive touchscreen devices, however, two of which being mutual capacitance and self-capacitance.
Mutual capacitance devices are designed with a grid-like array of traces. A typical devices using this technology, for instance, may feature a 16 by 14 array of traces; thus, creating 224 capacitors. The device works by applying a uniform electrical field over these capacitors. And like other capacitive devices, touching the surface disturbs the electrical field, at which point the device can identify the location of the user’s touch.
Capacitance changes in mutual capacitance devices can be measured at every point of the grid. Using the example previously mentioned, there would be 224 possible points of contact on a device that uses 224 capacitors. One of the key benefits of using mutual capacitance is its support for multi-touch function. With multi-touch function, the device can identify when two or more points of simultaneous contact are made. A common example of multi-touch is the pinch-to-zoom feature found on many smartphones and tablet computers. However, multi-touch can be used for a wide variety of other applications.
On the other hand, a self-capacitance touchscreen device features capacitors that act independently of one another. Like mutual capacitance, it also features a grid-like array of traces. However, the rows and columns function independently. In other words, changes in capacitance is measured on each column or row, typically by a current meter.
Self-capacitance touchscreen devices offer a higher signal strength than their mutual capacitance counterpart, resulting in a higher level of sensitivity. The downside, however, is that they are only able to identify a single point of contact at any time. This means you can not use multi-touch features with a self-capacitance device.
Of course, there are other types of capacitance technology, such as surface capacitance. With this configuration, one side of the insulator layer has a conductive material applied to it. The device then emits a voltage across this layer to create an electrical field, which it uses to identify when and where touch occurs.
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