Virtual buttons and vibrating touch screens

Monday, 25 March, 2019

Virtual buttons and vibrating touch screens

German researchers have developed a film that gives touch screens a third dimension, enabling them to pulse or vibrate on demand.

Professor Stefan Seelecke and his team at the Intelligent Material Systems Lab at Saarland University and at ZeMA (Center for Mechatronics and Automation Technology) in Saarbrücken have created technology that allows buttons to appear and disappear at any point on the touch screen of an IT device. By generating vibrations, pulses or individual jolts that are felt by the user’s fingertip, the screen can guide the user’s finger to a virtual button at any required location on the display. This functionality opens up a whole range of options for computer games, internet searches and satnav devices.

The basis for this new generation of displays is a rather unremarkable looking sheet of silicone film — not a lot unlike a piece of household cling film. As explained by Prof Seelecke, “The material the film is made from is known as a dielectric elastomer.”

The engineers in Prof Seelecke’s team printed an electrically conducting layer onto an extremely thin polymer membrane, which allowed them to apply an electric voltage to the film. Because the film is ‘electroactive’, it contracts in one direction and expands in the other when a voltage is applied to it.

“As a result of electrostatic attractive forces, the polymer film can, for example, be squeezed vertically, causing it to expand outwards,” said Steffen Hau, an engineer working in Prof Seelecke’s team. If the researchers alter the electric field, the film responds by performing complex choreographies and produces tactile signals that range from high-frequency oscillations to pulsing motions like a heartbeat or continuous variable flexing motions.

The team’s prototype system, to be showcased at Hannover Messe from 1–5 April, combines their novel electroactive film with a smartphone’s touch screen. This not only enables virtual buttons to be created on the phone’s screen, it also opens up a whole range of additional screen functions.

Using intelligent algorithms, the Saarbrücken team can transform a piece of polymer into a technical component whose behaviour can be precisely controlled, with Hau explaining, “We use the film itself as a position sensor and this imparts sensory properties to the display. There’s no need for any other sensors.” Furthermore, the research team can precisely assign any change in the position of the film to a change in the film’s capacitance.

“This means that we always know exactly how the film is deforming at any specific moment,” said Hau. “By measuring the capacitance of the dielectric elastomer, we can infer the exact amount of mechanical deformation in the film. By changing the applied voltage, we can precisely control the shape of the film.”

Prof Seelecke revealed that the technology can be manufactured cheaply, as it does not rely on rare earths or copper, as well as being lightweight and consuming very little energy. He and his fellow engineers are now looking for commercial and industrial partners with whom they can develop their system into marketable products.

Image caption: Engineers Sophie Nalbach and Steffen Hau from Stefan Seelecke’s team test the prototype system that will be exhibited at Hannover Messe. Image credit: Oliver Dietze.

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