Floating touch™

The Xperia™ sola includes a brand new touch sensor technology, called Floating touch™, that lets you interact with the phone without even touching it. This unique user experience lets you control parts of the user interface (UI) by simply letting your finger hover above the screen. At launch, this feature is implemented in the web browser. Floating touch™ enables the phone to register your finger up to 20mm above the screen. This makes it possible to detect not only the screen coordinates that you are pointing at, but also your finger’s distance from the screen. Erik Hellman, research engineer at Sony Mobile and one of the inventors of the technology, explains more below.

Xperia™ sola.

Erik Hellman:
As part of the team that invented this technology, it’s a great pleasure to see the magic of floating touch™ on a smartphone for the first time now. In the article, I’ll try to explain how this technology works. Like many other smartphones, Xperia™ sola uses capacitive touch sensing to register the user’s input on the screen. The event that occurs when you touch the screen of your smartphone is called touch event. Capacitive touch works by having an X-Y grid of electrodes covering the screen, on which a voltage is then applied. When a finger is near the electrodes, the capacitance changes and can be measured. By comparing the measures from all electrodes you can accurately pinpoint the location of the fingers position.

There are two types of capacitive sensors used for touch screens, mutual capacitance and self-capacitance. Mutual capacitance makes multi-touch detection possible. Self-capacitance generates a stronger signal than mutual capacitance, which allows accurate detection of the finger further away from the sensors. However, with self-capacitance it is not possible to perform multi-touch detection due to an effect called “ghosting”.

The difference between self capacitance and mutual capacitance illustrated. The rings represent the spots where a user touches the screen, while the red X-marks represent the ghosting positions described below.

Mutual capacitance makes multi-touch possible
With mutual capacitance, each intersection of a line in the illustration above forms a parallel plate capacitor. This means that each intersection is a sensor, which allows for true multi-touch since the position of each finger can be exactly measured. However, because the area of the intersection between two lines is very small, the electrical field of the sensor is also small. Since the field of the sensor is so small, the signal from it has a low strength. This makes it poor for sensing very small signals, like when the user’s finger hovers above the screen.

Self capacitance and the ghosting effect
Looking at the graphs above, each X or Y line as whole is a capacitive sensor, in the case of self capacitance. This means that the sensors are larger compared to the mutual capacitance described above. The large sensors create strong signals, which make it possible to detect the user’s finger up to 20 mm above the screen. When a finger is on or just above the screen, the nearest sensor lines are activated (X1, Y0). If two fingers are detected, ghosting positions occurs since four lines activated. As you can see in the graph above, this gives four possible touch positions (all four activated intersections of X1, X3, Y0, Y2 in the illustration), and the correct combination is unknown. This makes multi-touch impossible.

Combining self and mutual capacitance to allow floating touch™
Floating touch™ is solved by running both mutual capacitance and self capacitance, on the same touch screen, at the same time. Mutual capacitance is used for the normal touch sensing, including multi-touch. By running self-capacitance at the same time, we can detect a finger above the surface of the screen. However, since the floating touch™ technology depends on self capacitance, it is not possible to perform multi-touch gestures with the fingers hovering above the screen. However, multi-touch will work fine for the normal touch gestures on the screen.

The technology has been developed in cooperation with Cypress Technologies. By leveraging on the existing capacitive touch sensor, and lowering the threshold for touch registration, it will be possible to differentiate between floating touch™ and “normal” touch. All Android™ applications will work perfectly fine, just like before, and only the apps that explicitly “listen” for floating touch™ events will react to them.

Learn about developer possibilities and the initial implementation of floating touch
In the Xperia sola, this feature is enabled in the built-in web browser, and it will trigger “hover events” that are never before seen on a mobile phone. This kind of use case has previously only been available on a PC when using a standard mouse. All existing websites which reacts to hover events will work with the floating touch™ technology on Xperia™ sola.

This means that web developers can make use of the technology already now through the standard HTML5 hover events that is implemented in the native Android browser of Xperia™ phones. But we have more interesting stuff for developers in the pipeline. In the upcoming Ice Cream Sandwich (ICS) upgrade for Xperia sola, third-party developers will be able to utilise the technology in their own apps using the new open API introduced by Google in ICS to handle hover events.

To show off to your friends, Xperia™ sola will also have live wallpapers that will react to the floating touch™ events, giving them a magic touch.

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