capacitivetouchscreen
I'm really curious to get an answer for this question. Since I don't know the functioning of a capacitive display and Google didn't help me on this issue, I landed here. 🙂
Are capacitive displays used in most modern phones capable of measuring relative fraction of the finger being touched? For example, if I touch the screen and then apply pressure gently, will the system be able to make out the increase in the surface area of contact?
The reason the stylus worked even through layers of wool is related to the very nature of capacitance: It is not about conduction (except at the electrodes themselves), it is about the insulation between the plates: Wool is about as good a dielectric as dry air, if it is not woven with some metallic fiber.
The way capacitive touch screens typically work is that they sense the change in capacitance that occurs when an earthed body - essentially any large conducting body, such as a human - comes close(r) to the surface electrode. By using a metallic stylus, that "earthed body" is being brought closer, with merely the wool in between.
This capacitance change can be measured in a number of ways. A common approach is to inject a high frequency signal between the sensing electrode and the device's own ground plane, with air (or glass, or some other material) as a dielectric between these two "electrodes". Any other conductor coming into proximity changes the dielectric (i.e. insulation) pattern, thus changing the capacitance, and thereby the pattern of load shown by the capacitor across the native capacitance.
Digitizer or touch screen/panel digitizer.
You can find them as replacements for small LCDs. For example, but these may not be suitable for your multi-touch requirement, and getting application information may be difficult.
They're typically laminated onto the LCD display, and can be removed safely with a controlled temperature hot-air gun (and care, they're usually very thin glass).
Best Answer
A projected capacitance touch screen like the type in your phone is quite capable of creating a reasonably detailed map of the areas of the screen that are covered by your fingers. You could definitely use this to infer the amount of pressure being applied by looking at the contact patch size, and indeed this is apparently how Apple's Force Touch on the watch works (note, the Macbook's new trackpad has actual force sensors on each corner). However, you can probably imagine a lot of issues with making this work reliably, as everyone's fingers are different sizes, and you don't always touch the screen with the same part of your finger.
Another thing is that you can tune the sensitivity of a touch screen so that it can detect objects nearer or further away (which is how glove mode works on some phones) but then you lose the ability to differentiate the actual contact patch of a finger. It may be that Apple is using a sort of analog sensing system where they can infer the contact patch and the part of your finger that is slightly above the surface by actually measuring the amount of projected capacitance rather than just apply a threshold. Unfortunately you would not be able to do anything like this without your own hardware.