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When most think of ceramics, they likely picture items like coffee mugs, bathroom tiles, or flower pots. But for Frank Clemens, the leader of Empa’s Laboratory for High-Performance Ceramics, ceramics represent much more. These materials have the potential to conduct electricity, demonstrate intelligence, and even possess tactile capabilities. Together with his team, Clemens is creating innovative soft sensor materials made from ceramics. These advanced sensors have the ability to detect variables such as temperature, strain, pressure, or moisture, making them valuable in both medical applications and the realm of soft robotics.
What exactly are soft ceramics? According to materials scientists like Clemens, ceramics are inorganic, non-metallic substances made from loose particles that undergo a high-temperature process called sintering. The specific materials and their properties can differ widely. However, conventional clay or porcelain is not what you’ll find in Clemens’ laboratory. Instead, his team works with substances like potassium sodium niobate, zinc oxide, and various carbon particles.
These materials are intrinsically stiff. To create flexible sensors, the researchers embed ceramic particles within stretchable plastics. “We utilize highly filled systems,” Clemens explains. “We create a matrix from thermoplastic materials and incorporate as many ceramic particles as we can without losing the elasticity of the matrix.” When this densely filled framework is manipulated—stretched, compressed, or exposed to varying temperatures—the spacing between the ceramic particles alters, which in turn affects the electric conductivity of the sensor. Clemens points out that it’s not necessary to saturate the entire matrix with ceramics; through 3D printing, they can integrate ceramic sensors like “nerves” into pliable components.
Smart and Selective
Creating these soft ceramic sensors is no straightforward task. Typically, soft sensors pick up multiple environmental signals simultaneously, like temperature, strain, and humidity. “To apply them in real-world situations, we need to specify what we’re measuring,” Clemens notes. His team has successfully designed sensors that respond specifically to either pressure or temperature. They have incorporated these sensors into prosthetic hands that can detect when fingers bend and when they come into contact with hot surfaces. This kind of “sensitivity” is advantageous for both robotic tools and human prosthetics.
The Empa team has also progressed to developing a soft “robot skin.” Mimicking human skin, this multi-layered plastic surface reacts to touch and temperature changes. To analyze this sophisticated data, Empa researchers collaborated with scientists from the University of Cambridge to create an AI model trained on about 4,500 data points. This process mirrors human perception, where nerve signals from our skin are interpreted and processed by the brain.
In their latest endeavor, researchers merged the ceramic sensors with artificial muscles. Working alongside teams from ETH Zurich and the University of Tokyo, they developed a bio-hybrid robot that identifies its contraction state using a soft, biocompatible, tissue-integrated piezoresistive sensor. Their findings have been published in the journal Advanced Intelligent Systems.
Ensuring Safe Human-Robot Interaction
Frank Clemens envisions a future where humans and machines can work effectively and safely together. “Current robotic systems tend to be large, heavy, and powerful, which can pose threats to people,” he explains. For robots to become common fixtures in our workplaces, they must be able to respond quickly and sensitively to human touch. “When you accidentally bump into someone, you instinctively withdraw,” says Clemens. “We aim to program robots with a similar reflex.” The researchers are currently seeking industrial partners to collaborate on robotic grip systems. Additionally, soft sensors have notable applications in the medical field; the team recently completed an Innosuisse project with IDUN Technologies, successfully developing flexible electrodes for measuring brain waves.
Yet their journey is far from over: the researchers aim to enhance the sensitivity and intelligence of their soft ceramic sensors. This involves combining new ceramic materials with soft polymers and refining their sensor capabilities. The key to success lies in effectively merging these two components.
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