Apple files for a second force-sensitive touchpad patent

It looks like the elves in Cupertino are pretty busy strapping force sensors on the backs of touchpads, because Apple's just filed for a second patent on the tech. Unlike the first application, which described a system of spring membranes, the new patent relies on a second set of conductive traces underneath the standard X / Y array to detect force. As usual, there's no mention of where we might see this stuff pop up, but we're going to go ahead and assume it's for a 3G Newton Circle iPhone Extreme.