Touch screens are ubiquitous today. But a common complaint is that the smooth surface just doesn’t feel as good to use as a physical keypad. While some touch-screen devices use mechanical vibrations to enhance users’ experiences of virtual keypads, the approach isn’t widely used, mainly because mechanical vibrations are difficult to implement well, and they often make the entire device buzz in your hand, instead of just a particular spot on the screen.

Now, engineers from three different groups are proposing a type of tactile feedback that they believe will be more popular than mechanical buzzing. Called electrovibration, the technique uses electrical charges to simulate the feeling of localized vibration and friction, providing touch-screen textures that are impossible to simulate using mechanical actuators.

One of these groups, composed of researchers from Disney Research in Pittsburgh, Carnegie Mellon University, and the University of Paris Sud, presented a paper earlier this month at the User Interface Software and Technology (UIST) symposium in New York City. In the paper, they described their approach to electrovibration, called TeslaTouch, in which they modified a commercial touch panel from 3M that uses capacitive sensing – the approach used in most mobile phones and in the iPad.

The touch panel is made of transparent electrodes on a glass plate coated with an insulating layer. By applying a periodic voltage to the electrodes via connections used for sensing a finger’s position on the screen, the researchers were able to effectively induce a charge in a finger dragged along the surface. By changing the amplitude and frequency of the applied voltage, the surface can be made to feel as though it is bumpy, rough, sticky, or vibrating. The major difference is the specially designed control circuit that produces the sensations.

It’s a challenge, says Ivan Poupyrev of Disney Research, to vibrate a screen in a way that makes sense for a user. When an entire device buzzes, it can be more annoying than helpful. There are also technical hurdles and extra costs in making a touch screen mechanically move. The goal, then, was to create a tactile sensation without using any mechanical motion. “It sounds crazy,” Poupyrev says, “but that’s what we’ve done with TeslaTouch.”

Electrovibration was first proposed for touch screens in the 1950s, but the approach didn’t see widespread use because the screens didn’t achieve commercial success until recently. Now, with many researchers looking for ways to improve the now-popular screens, other groups have also rediscovered electrovibration. Nokia recently announced a smartphone prototype that uses the approach. And a Finnish company called Senseg has also implemented electrovibration in touch screens, having closed deals with three companies to incorporate the technology into products that could be available in 2011.

All three groups have filed patents for electrovibration; each outlines a different approach. Currently, the Disney demonstration only provides the feeling of texture when a finger is moving, although the group is working on a way to give feedback to a still finger. Senseg’s technology, however, already provides localized feedback to a nonmoving finger, says Ville Mäkinen, founder of the company.

Another limitation of the Disney prototype is that it provides only a single sensation at a time. However, it is possible to split up the screen in various ways to generate different sensations in different parts of the screen, but the design of such a screen would most likely depend on the specific application.

Nokia is exploring ways to use the tactile feedback as a way to augment communication with another person, says Tapani Ryhänen, Nokia lab director in Cambridge, UK. “There’s a possibility to use this as a type of communication,” he says, “so if I do something on my screen, then you can feel it on your screen.”

While electrovibration can provide a different feel for touch screens, the type of interaction is somewhat limited, says Bic Schediwy, director of research at a touch-screen company called Synaptics. Since some systems only work when a finger is moving, those systems couldn’t simulate a button click, one of the biggest complaints with touch screens. Additionally, he says, in demonstrations of electrovibration systems, it appears that people have varying responses to the induced current, possibly because of varying skin thickness.

At the UIST symposium, the Disney researchers showed a range of demos to illustrate TeslaTouch, including a simulated ice-covered window that changes friction as virtual ice is removed and a racetrack that provides different sensation as a finger traverses varying terrain. On hand to test the system was Patrick Baudisch, professor of computer science at the Hasso Plattner Institute in Potsdam, Germany. While the demos were simple, he says, they were “very convincing.” TeslaTouch may not provide “the basis for getting rid of keyboards or such,” Baudisch says, but “it really enriches the interaction on touch devices.”

Disney’s Poupyrev isn’t sure about what his company plans to do with the technology, but the applications that are most obvious involve honing electrovibration so it could be used to more easily draw and paint on a smooth touch surface. Poupyrev also thinks electrovibration, since it is so easily implemented, could find a home in more unusual applications, such as large surfaces like wallpaper, and conformable materials like cloth.