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Another Dimension to Touch Screens

A clear composite material could make multitouch screens sensitive to pressure.
April 19, 2011

A British company called Peratech has announced a new technology for touch screens that registers pressure as well as the position of a finger. This could provide new ways of interacting with apps for touch screen mobile phones and tablets.

Transparent touch: Inventor David Lussey displays a sample of QTC Clear.

In addition to adding pressure sensitivity to screens, the company claims that the technology, called Quantum Tunneling Composite (QTC) Clear, could make touch screens thinner, more rugged, and more energy-efficient.

Peratech aims to bridge the gap between the two main touch-screen technologies: capacitive and resistive, says joint CEO Philip Taysom. Capacitive touch screens are found in mobile phones and tablets. They respond quickly to multiple fingers at a time, but rely on a grid of electrodes that constantly draw power when a screen is switched on; the bigger the screen, the more power the capacitive sensors gobble up.

Resistive touch screens were used in some early generation handheld devices, and are commonly found at ATMs and point-of-sale screens. They use less power, which makes them more appealing for larger displays, but they aren’t as responsive or as durable as capacitive touch screens.

Resistive screens are built by sandwiching a thin layer of air between two sheets of relatively soft material. Applying pressure on the screen forces the layers into contact, closing a circuit and registering a touch. It’s a simple approach, but it doesn’t allow for high precision or multitouch. And because the screens are constantly deformed, longevity is an issue.

Taysom claims that QTC Clear has the benefits of both technologies while avoiding the downsides of either. A layer of composite material, composed of electrically conducting particles, is sandwiched between sheets of a rigid material like glass. When a finger or stylus presses the top sheet of glass, the particles in the composite conduct electricity proportional to the pressure applied. And, unlike capacitive screens, the system only draws power when touched.

A QTC Clear screen could be more durable than resistive touch screens. Instead of requiring an air gap of a fraction of a millimeter, as with resistive screens, the company uses a six-micron layer of composite material. “There’s a lot less of a gap,” says Taysom, “and that has a number of significant benefits.”

With such a small gap, the materials used to sandwich the polymer don’t need to be as soft. Glass, which is much harder than the softer materials found in resistive screens, could make the screens more durable. Additionally, says Taysom, less light is lost with the clear polymer than with an air gap, which translates into less power required to light up the screen.

Peratech isn’t the only company developing force-sensitive materials. For years, musical instruments, such as electric pianos, have used a force-sensitive resistor ink, in which microscopic particles conduct electricity in response to varying pressure. In 2009, a startup out of New York University called Touchco that employed transparent force-sensitive resistor ink for touch screens was acquired by Amazon, although no products using the technology have been announced.

Peratech has already licensed earlier, opaque versions of its QTC material. These versions can be found in toys, medical devices, and backpacks with built-in MP3 controls. QTC Clear marks the company’s entry into the display industry.

The technology differs from traditional pressure-sensitive inks, says Taysom, because of the electrical properties of the conductive polymers within the composite. Conductive particles in traditional inks are spherical and come in contact with each other when pressure is applied—as more particles come in contact, the material becomes more conductive. QTC’s conductive particles, in contrast, are spiky and held together in silicon rubber, which is  electrically insulating. Electrons at the tip of the spikes transfer to the tips of other spikes , conducting electricity over a small distance without touching in a process called quantum tunneling. As a result, the composite responds to even very light pressure, says Taysom.

“Pressure-sensitive space is an important place to be,” says Daniel Wigdor, professor of computer science at the University of Toronto. “It adds a third dimension so you can push into the screen and better manipulate things.” Wigdor says the low power capabilities of QTC Clear could benefit smaller screens such as those on tablets.

But QTC Clear requires some pressure to be applied in order to respond. “The best user experience today is offered by capacitive screens,” says Patrick Baudisch, professor of computer science at the Hasso Plattner Institute in Potsdam, Germany. “This sounds like a minor detail, but in reality in matters a lot because it allows users to flick to scroll or pan through documents or Web pages.”

Consumers will soon have a chance to feel for themselves. According to Taysom, Peratech has licensed QTC Clear to manufacturers. He expects the first product to be available by the end of the year.

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