A patent, 2007/0236466, filed by Apple in May and recently posted on October 11th with the U.S. Patent office proposes a mechanism for detecting both the location and force applied to a touch sensitive display.
The force measurement mechanism utilizes rubber beads between transparent conductive traces. Apparently as the beads deform, a capacitance proportional to the force is generated, a capacitance that can be measured. "When used with a display element (e.g., a LCD or CRT), an input-output unit capable of both location sensing and force sensing operations is provided," the application stated.
The patent was filed on behalf of Apple Computer by the intellectual property firm in Houston of Wong, Cabello, et al, and the inventor is listed as Steve P. Hotelling.
Image file from patent
As Apple moves into new, mouseless UI development with handheld computers, itis possible that new mechanisms like this could form the basis for new interface protocols.