Thanks to the smartphone, simple hand movements for operating devices such as swiping, dragging or tapping have become a matter of course. However, this gesture control requires a touchscreen. If this is not available or the hands are not available to operate it, contactless solutions for human-machine communication are required. Assistance systems for speech recognition and interpretation in particular are becoming increasingly popular. However, they are sometimes unsuitable for public areas and only work reliably in quiet environments that are free from external noise. A research group at Fraunhofer IPMS is therefore working on an alternative approach for contactless, three-dimensional detection of distances, movements and gestures for communication with robots, in operating theaters and in household systems.

The scientists have developed a micro-chip architecture that can generate and receive ultrasound up to 300 kHz. The reflected sound waves are then analyzed by measuring, for example, how long the wave has traveled between the sensor system and the reflecting object or how the frequencies have shifted due to the Doppler effect. The evaluation of the ultrasound allows a spatial resolution of natural movements and gestures in the sub-centimeter range over distances of up to half a meter. According to Fraunhofer IPMS, the ultrasonic transducer has an advantage over competing optical sensor methods. Group leader Dr. Sandro Koch explains the advantages as follows: "Compared to camera-based systems, our ultrasonic sensors enable the construction of significantly more cost-effective electronic and software systems due to longer signal propagation times. They are not sensitive to scattered light and allow reliable data acquisition even on optically transparent surfaces. In addition, the systems are CMOS-compatible and considerably more compact and can be produced in large quantities at low cost."

For the development, the researchers are relying on a new class of electrostatic, micro-electromechanical (MEMS) bending actuators, which have been continuously further developed since 2016 for the generation of audible sound in micro loudspeakers and for micropumps. This Fraunhofer IPMS proprietary nano-e-drive principle (NED) uses the high forces of electrostatic fields in nanometer-sized electrode gaps to enable mechanical movements with deflections in the range of several micrometers. Not only the chip surface but the entire component volume is used to generate sound. "Using the chip volume to generate sound makes it possible to manufacture very small components," explains Sandro Koch. "Because hundreds of such components can be placed on a single wafer and several wafers can be processed simultaneously in individual process steps, the manufacturing costs for large quantities are potentially low." For further development, the Fraunhofer researchers expect high air volume flows, which are converted into high sound pressures and consequently provide an increased signal-to-noise ratio for low-frequency ultrasonic transducers. The resonance frequency and thus the detection range as well as the spatial resolution can be defined by the geometry of the NED bending actuators.

According to the researchers, potential fields of application for ultrasound-based, contactless motion detection can be found in automation and safety technology as well as in medical technology, the automotive industry or entertainment and household electronics. Fraunhofer IPMS will be showing how ultrasound can support gesture recognition with an initial functional demonstrator at the Sensor und Test trade fair stand 248 in hall 5.