Capacitive sensing is the underlying technology that powers a variety of touchscreen devices. From the Apple iPhone to hundreds of Android smartphones and tablets, it’s used to create touchscreen functionality. But while most people have a general understanding of how touchscreen devices work — you tap the interface to control it — few know the mechanics behind capacitive sensing.
Capacitive Sensing Explained
In the most basic terms, capacitive sensing refers to technology that’s used to detect and measure an electric current. Also known as capacitance sensing, it features a variety of components that detect changes in electrical current. With this information in hand, a capacitive touchscreen device can determine when and where a user’s touch command occurred, thereby responding with the appropriate action.
The human body is an excellent conductor of electrical. When you touch a capacitive touchscreen device, your finger will absorb some of its electrical current. It’s not enough to cause a noticeable shock, but it is enough to allow the device to identify your touch command. Capacitive touchscreen devices create a small voltage, typically across their upper layer, that your finger will absorb upon touching. This is the principle on which capacitive sensing works.
Capacitive sensing, not surprisingly, requires the use of capacitive sensors. These sensors are responsible for measuring the electrical current and identifying changes in capacitance. A variety of materials are used to create capacitive sensors, some of which include copper, indium tin oxide (ITO) and printed ink. However, all capacitive sensors must be designed with a conductive material. Otherwise, the electrical current won’t travel through them, nor will the device be able to properly identify the user’s touch commands.
Surface or Projected Capacitive Sensing
While all capacitive sensing technologies follow the same basic principle as mentioned above, there are two primary types used in touchscreen devices: surface and projected. Surface capacitance features an insulator layer, which has a single side coated with a conductive material. The device creates voltage to this insulator layer, allowing for a uniform electrostatic field. Touching this creates creates a capacitor by absorbing some of the voltage.
Project capacitive sensing, on the other hand, is a more refined form of capacitive sensing. It differs from surface capacitive sensing by featuring etching on the conductive layer. The etching allows the device to identify even the slightest change in capacitance. Therefore, you can often operate projected capacitive touchscreen devices while wearing thin gloves.