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Apple integrates FTIR pressure sensing with projected capacitive touch

Tue, 05/20/2014 - 7:22am
DisplaySearch

A recent patent application indicates that Apple is working on integrating projected capacitive and FTIR (frustrated total internal reflection) to offer pressure sensing and a new user experience. Per the patent, FTIR is used to detect finger pressure, and projected capacitive determines the touch position. Neither of these touch technologies is new, but the combination is unusual. It is not likely that Apple intends to replace projected capacitive touch technology, which remains critical to Apple products, with FTIR, but it is an indication of the potential for utilizing FTIR technology.

As we covered in the Quarterly Touch Panel Market Analysis, the principle behind FTIR (also called waveguide) is to detect a disturbance in total internal reflection (TIR) and interpret it as a touch signal. TIR occurs as light travels in a medium. When light travels between two separate media with differing indices of refraction (such as glass and air), the path is influenced. Total internal reflection occurs when light beams pass from the medium with a higher index of refraction to the medium with a relatively lower index.

For touch applications, FTIR is implemented by a sensor circuit board around the touch area (display). The board contains multiple infrared LED emitters and receivers. The LED emitters deliver infrared light beams into the cover glass. The cover glass top side has a special coating such that, when a finger touches it, it results in a disturbance which frustrates the total internal reflection. This is detected by the LED receivers. Consequently, the controller can calculate the touch signals based on the data from the emitters and receivers.

Like projected capacitive, FTIR can support an edge-to-edge cover glass design, a critical feature for the consumer devices such as smart phone, tablet PC, or wearable device. Optical imaging technologies such as NextWindow cannot support edge-to-edge. FTIR is cost-effective on larger touch areas. FTIR’s sensor circuits surround the touch area.

FTIR is not as mature as projected capacitive in terms of sensitivity, performance, and user experience. Consequently, although FTIR can be more cost-effective at larger sizes than projected capacitive, it still holds a supporting role (force detection) in this patent.

The combination of multi-touch and force detection opens the door to greater creativity for app developers. Steve Jobs complained that a stylus is redundant and not as convenient as fingers. Nonetheless, Apple applied for many touch-related patents that included active stylus. This patent may be adopted in future Apple products. In the patent, we see that the technology can be applied to both iPhones and iPads.

While projected capacitive dominates from smart watch to all-in-one PC sizes, FTIR is a promising touch technology, especially for larger sizes, or in a supporting role, as in this patent. FTIR may help Apple to improve its touch display capabilities in the large area applications.

For more analysis of this subject, see the DisplaySearch Market Tracker.

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