It’s not uncommon for touchscreens to support multiple points of simultaneous contact. Known as multi-touch, it expands the device’s input capabilities. If offered by a touchscreen, you can typically pinch the screen using two fingers to zoom the display in or out. This is just one of many applications in which multi-touch is used. With that said, only some touchscreens support multi-touch. If you’re hoping to take advantage of this feature, you’ll need to choose the right type of touchscreen.
The most common type of touchscreen technology, capacitive, supports multi-touch. Capacitive touchscreens, of course, use capacitance to detect touch commands. Touching the display with a bare finger or a conductive object causes a change in capacitance. Your finger or the object will essentially draw some of the electrostatic field from the device, resulting in a change in capacitance. The touchscreen will then detect this change in capacitance as a touch command.
There are three different types of capacitive touchscreens, including projected, self and mutual. While they each work in a different way, they all support multi-touch operation. Your finger will draw some of the touchscreen’s electrostatic field, which it uses to detect where each of your touches occurred.
In the past, resistive touchscreens lacked the multi-touch operation of their capacitive counterparts. Thankfully, though, this is no longer a problem. Resistive touchscreens can now be made to support multi-touch operation.
Resistive touchscreens don’t measure capacitance. Rather, they rely on pressure to detect touch commands. Touching the display interface will force the device’s top layer down onto the bottom layer at the area of your touch command. The resistive touchscreen will then respond by registering this area as a touch command. Multi-touch in resistive touchscreens follows this same principle by using pressure to determine where each of your touches occurred.
Surface acoustic wave (SAW) touchscreens also support multi-touch operation. They work by emitting ultrasonic waves — sound waves — over the surface of the display interface. There are corresponding sensors placed on the edges of the display interface to read these ultrasonic waves. When you touch the display interface, you’ll disrupt the ultrasonic waves in that area.
Like with resistive touchscreens, most SAW touchscreens designed in the past didn’t support multi-touch operation. In recent years, though, manufacturers have introduced new technologies that allow SAW touchscreens to detect multiple simultaneous points of contact.