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Apple's Exploration of Pressure Sensitive Touch Screens Continues
The patent describes a method of determining the force of a user's touch on a capacitive screen using infrared transmit lines from transmitters and receivers positioned under the frame of the cover glass. Capacitive touch combined with light would determine both the position of the finger and distinguish a soft touch from a harder touch, allowing Apple to implement gestures that could vary with force.
Using infrared light to determine where a user touches a screen is a method known as Frustrated Total Internal Reflection, or FTIR. FTIR is essentially a light-based way to detect multitouch, bouncing infrared light off of the touch screen to detect interference from a finger. When combined with capacitive touch, the interference measurements can also deduce force.
FTIR has been used by Microsoft for its Perceptive Pixel products, as noted in Apple's patent application. Microsoft offers several large-screened multi-touch sensing devices that use FTIR and offers a technology called Microsoft PixelSense, which is used in the Samsung SUR40.
As implemented by Microsoft, the FTIR technology, which uses cameras to detect light refracted by pressure, allows multiple people to use the device at once and it also recognizes and distinguishes objects that are not fingers.
Though Apple has not yet built pressure sensitivity into the touch screens of its mobile devices, the company has been looking at various techniques for implementing pressure detection over the last several years. In addition to infrared light, Apple has explored force sensors, spring membranes, and pressure sensitive device casings.
Given Apple's continued interest in pressure sensitive touch screens and competing products that already include pressure sensitivity, such as Microsoft's Surface Pro line of tablets, the implementation of the technology in some form or another seems like a logical step for Apple's future mobile devices.