A Better, Cheaper Multitouch Interface

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FSR ink has been used for decades, but mostly on musical instruments such as electronic drums or keyboards, Rosenberg says. In making their touch pad, the researchers had to ensure that the pad could detect the exact placement of a finger even though the sensors are a quarter inch apart--something that designers of the electronic instruments didn't need to consider.

Ideally, the researchers wanted to be able to measure to a resolution of 100 dots per square inch, but they didn't want the complications and expense of wiring up such a large number of sensors. So they developed an algorithm that takes the input at each electrode intersection and interpolates the position of an object, even one as small as a stylus tip. It also lets them distinguish between two fingers pressing side by side. The output from the pad is sent to a computer, mapping the intensity and placement of pressure. Currently, data from the entire pad can be collected 50 to 200 times per second.

The simplicity and high resolution of the pad is one of the researchers' main achievements, says Patrick Baudisch, a researcher at the Hasso Plattner Institute, in Germany, and at Microsoft Research. Baudisch is currently collaborating with Perlin's group on the IMPAD project. "The pad gives you an animated pressure picture but has only 20 connectors or so coming out of it," he says. "This sounds like it's not a big deal, but it makes it feasible to use it on very small mobile devices such as our nanoTouch," a screen the size of a credit card that has touch sensitivity on the back and sides.

Bill Buxton, principal researcher at Microsoft, says that the NYU work is "interesting and distinct in a number of ways," including in its ability to sense more than just a finger or a stylus. "You can use whatever best suits the task," he says. Also, he notes that while the prototype is an opaque touch pad, the concept could easily be applied to forthcoming flexible displays, as the ink and the electrodes can be made transparent.

Perceptive Pixel's Jeff Han agrees that capturing information about the amount of force applied to the screen is an important part of a touch interface. However, he notes that integrating such a sensor with a high-fidelity display is the hard part. Making sure that the touch interface and the display play well together is still a significant challenge.

Perlin says that he envisions the technology replacing capacitive touch screens, especially in mobile phones. Hospital beds and wheelchairs could also be equipped with IMPAD screens to indicate when pressure sores might occur. Construction materials could use the technology to monitor stress on buildings, and skinlike outer layers could be made for robots that can detect touch.

The researchers are currently in the first stages of forming a spinoff company to test the commercial possibilities of the technology.