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Gesture recognition with ultrasound

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A research team at the Fraunhofer Institute for Photonic Microsystems (IPMS) is using a new class of ultrasonic transducers to reliably detect distance changes, movement patterns and gestures in distances to half a meter. The tiny components are cheap to make, allow for high sound pressure and provide a flexible frequency design for optimal balance of distance and sensitivity.

Gesture controls such as swiping, pinching and tapping have been imposed by the smartphone on many other systems. A wide range of equipment for industrial control or public kiosks use these gestures but need environments free from external disturbances such as noise, dirt and even light. Hence, research has focused on alternatives to provide non-contact, three-dimensional recording of distance, movement and gesture for communication with robots as well as in surgical areas and household systems.

Fraunhofer IPMS scientists have developed an architecture that can generate and receive ultrasound to 300kHz. Reflected sound waves are analysed by measuring how long it takes a wave to travel between a sensor and a reflecting object, or how frequencies shift due to the Doppler effect. Evaluation of the ultrasound provides a spatial resolution for natural movements and gestures in the sub-centimetre range at distances to half a meter. The system promises many advantages over other technologies, such as optical sensors, for example.

“Compared to camera-based systems, our ultrasonic sensors enable the construction of significantly cheaper electronic and software systems due to longer signal transit times. Our transducers are not susceptible to stray light and allow for reliable data acquisition on optically transparent surfaces as well,” said Sandro Koch, Fraunhofer IPMS group leader.

For this development, the researchers implemented a new class of electrostatic micro-electro-mechanical (MEMS) bending actuators. The Fraunhofer IPMS proprietary nano-e-drive (NED) principle relies on the high forces of electrostatic fields in nanometre-sized electrode gaps to allow for mechanical movements with displacements in ranges of several microns.

Fraunhofer researchers expect that high air volume flows that have been converted into high sound pressure will support further development to provide an increased signal-to-noise ratio for low-frequency ultrasonic transducers. The resonance frequency and thus the detection range and spatial resolution can then be defined by the geometry of the NED bending actuators.

The systems are CMOS-compatible and considerably more compact than that of other systems.

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