Bimodal sensor processes both touchless and tactile stimuli

Thursday, 21 November, 2019

Bimodal sensor processes both touchless and tactile stimuli

Through the clever use of magnetic fields, scientists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the Johannes Kepler University Linz have developed what is claimed to be the first electronic sensor that can simultaneously process both touchless and tactile stimuli. Prior attempts have so far failed to combine these functions on a single device due to overlapping signals of the various stimuli.

The skin is likely the most functionally versatile part of the body — not only is it able to differentiate between the most varied stimuli within seconds, it can also classify the intensity of signals over a broad range. Now, a research team led by HZDR’s Dr Denys Makarov and Linz’s Professor Martin Kaltenbrunner has managed to produce an electronic counterpart with similar characteristics.

Described in the journal Nature Communications, the new sensor could massively simplify the interplay between humans and machines, providing a seamless interactive platform for virtual and augmented reality scenarios. As noted by Dr Makarov, “Applications in virtual reality are becoming increasingly more complex. We therefore need devices which can process and discriminate multiple interaction modes.”

Current systems work either by only registering physical touch or by tracking objects in a touchless manner. Both interaction pathways have now been combined in the sensor, which has been termed a ‘magnetic microelectromechanical system’ (m-MEMS) by the scientists.

“Our sensor processes the electrical signals of the touchless and the tactile interactions in different regions,” said HZDR’s Dr Jin Ge, first author on the study. “In this way, it can differentiate the stimuli’s origin in real time and suppress disturbing influences from other sources.”

On a thin polymer film, the scientists first fabricated a magnetic sensor, which relies on what is known as the giant magnetoresistance (GMR). This film in turn was sealed by a silicon-based polymer layer (polydimethylsiloxane) containing a round cavity designed to be precisely aligned with the sensor. Inside this void, the researchers integrated a flexible permanent magnet with pyramid-like tips protruding from its surface.

“The result is rather more reminiscent of cling film with optical embellishments,” Dr Makarov said. “But this is precisely one of our sensor’s strengths.”

This is how the sensor remains so flexible: it fits all environments perfectly. Even under curved conditions, it works without losing its functionality. The sensor can thus very easily be placed, for example, on the fingertip; indeed, it is in this manner that the scientists tested their development.

“On the leaf of a daisy we attached a permanent magnet, whose magnetic field points in the opposite direction of the magnet attached to our platform,” Dr Ge said. As the finger approaches this external magnetic field, the electrical resistance of the GMR sensor drops. This occurs until the point when the finger actually touches the leaf. At this moment, it rises abruptly because the built-in permanent magnet is pressed closer to the GMR sensor and thus superimposes the external magnetic field.

“This is how our m-MEMS platform can register a clear shift from touchless to tactile interaction in seconds,” Dr Ge said.

This allows the sensor to selectively control both physical and virtual objects, as one of the experiments conducted by the team demonstrates: on a glass plate with which they furnished a permanent magnet, the physicists projected virtual buttons that manipulate real conditions, such as the room temperature or brightness. Using a finger on which the ‘electronic skin’ had been applied, the scientists could first select the desired virtual function touchless through interaction with the permanent magnet. As soon as the finger touched the plate, the m-MEMS platform switched automatically to the tactile interaction mode. Light or heavy pressure could then be used, for example, to lower or increase the room temperature accordingly.

The researchers have thus cut down an activity that had previously required several interactions to merely one, opening up the potential for applications beyond virtual reality — the electronic skin could also be used, for example, in sterile environments. Surgeons could use the sensors to handle medical equipment without touching it during a procedure, which would reduce the danger of contamination.

“This may sound like a small step at first,” Prof Kaltenbrunner said. “In the long term, however, a better interface between humans and machines can be built on this foundation.”

Image caption: Bimodal electronic skin in front of a virtual reality setting. Image ©HZDR/D Makarov.

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