Special physical human-robot interactions are increasingly needed in the manufacturing industry, in the professional services sector and in healthcare. This requires an improvement in user comfort, especially with regard to communication between humans and machines. Ideally, robots should be able to anticipate human actions and recognize intentions. This requires flexible metamaterials or flat metasurface antennas with highly integrated electronics to detect the near environment. Such surfaces, which envelop a robot like an adaptive, intelligent skin, are being developed by the Fraunhofer Institute for High Frequency Physics and Radar Technology FHR in Wachtberg, together with six partners in the EU project FITNESS (Flexible IntelligenT NEarfield Sensing Skins). Equipped with metasurface antennas, robots will in future be able to scan their surroundings more effectively in the near field and communicate better with their base station in the far field.

Optimization of human-machine interaction

In all developments of human-machine interaction, the safety of workers is paramount. This is where the EU project FITNESS comes in, which aims to optimize communication and interaction between humans and machines with the help of intelligent antenna solutions in the form of novel, electromagnetic meta-material surfaces with integrated electronics. The flexible and stretchable metasurface antennas, which are suitable for emitting surface waves, should be able to scan the immediate vicinity much better than conventional antennas, thereby increasing human safety and robot performance. In addition to Fraunhofer FHR, the following partners from industry and research are involved in the project: Centre National de la Recherche Scientifique CNRS, eV Technologies, Hamburg University of Technology, Université Catholique de Louvain, University of Zagreb Faculty of Electrical Engineering and Computing and L-up. The Belgian University UCLouvain is coordinating the project, which is funded by the European Union under contract number 101098996.

Intelligent antenna skin with sensory and communicative functionality

The metasurface antennas are flat antennas integrated into film-like substrates that adapt to the contours of the robot. Due to their flat structure, these antennas can be bent and stretched and wrapped around the robot like a skin. Alternatively, and depending on the application, they can also be attached only to the robot arm, for example. They are therefore also referred to as "smart skins". "Our future antenna solution is characterized by the fact that it can scan the immediate vicinity as well as detect motion and at the same time is capable of radio-based communication with the base station in the industrial hall," explains Andrej Konforta, Group Manager 3D Printing RF Systems at Fraunhofer FHR. "A solution of this kind has not been available on the market so far."

Small geometries with a high degree of freedom

The novel and innovative antenna solution is designed to enable beamforming – a method for determining the position of sound sources in wave fields – so that the adjustable electromagnetic beam always points to the base station, guaranteeing a stronger, more stable signal and resulting in an increased range. Until now, phased arrays have supported beamforming. "This involves connecting many antennas in a group. The phase of each individual antenna element is variable, which allows the line of sight of the group antenna to be influenced," says the researcher, explaining the technology, which has so far been used primarily in a military context. In conventional group antennas, the antenna elements and their electronics are closely packed. The result: high costs, a lot of heat dissipation and a high susceptibility to errors. Metasurface antennas, on the other hand, could be constructed with far fewer electronics – without losing the properties of conventional construction. The new concept saves costs and allows for smaller, more compact structures. "With meta-material surfaces, we are pursuing a new design concept that enables very small geometries, which allow a high degree of freedom in the design of the radiated fields, but also the best possible extraction of the gesture signals," says Andrej Konforta.

Development of new antenna substrates

Antennas are usually integrated into rigid microwave substrates. Alternatively, there are materials that can also be stretched and thus exhibit a high degree of flexibility. However, these flexible substrates have excessive losses and do not achieve optimal performance in the high-frequency range, as the measurement technology developed by the Fraunhofer FHR researchers has shown. Therefore, the conventional substrates available on the market are not optimally suited for the transmission of high-frequency signals. Based on the results obtained by Fraunhofer FHR, new substrates are being developed at the project partner Hamburg University of Technology (TUHH) as part of the FITNESS project – the local Institute for Applied Polymer Physics (IAPP) is synthesizing stretchable and potentially high-frequency-compatible materials, relying on a mix of polymers as well as polymers with ceramic foreign particles. These will be tested by Fraunhofer FHR during the course of the project. Based on the initial results, an existing measurement setup is currently being optimized, expanded for other frequency bands, and the software for the final setup is being developed. At the same time, the project partners are investigating how the deformation of the stretchable surfaces affects the properties in the near and far field. The long-term plan is to develop self-calibrating metasurface antennas that can independently detect their curvature and shape in order to ensure optimal signal reception and avoid communication problems.

Wide range of applications

In addition to robotics in the production environment, the project partners also see medical technology and robotics as potential fields of application: here, metasurface antennas could serve as an intelligent skin to help devices such as assistant robots to better recognize gestures and interact more strongly with people. The technology could also be used in protective equipment for firefighters or in space suits.

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