Floating touch of Sony xperia
The new Xperia sola announcement includes a brand new touch sensor technolog called
floating touch, that lets you interact with the phone without even touching it. This unique user
experience never seen on a smartphone before lets you control the user interface (UI) by simply
letting your finger hover above the screen. 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 after the jump.
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
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 elf-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.