The virtually aided tactile enhancement system (VATES) allows more motion control. (Image Credit: Rongrong Bao.)


Humans rely on the sense of touch to manipulate objects, but that can be restricted due to injuries or wearing gloves. This can be problematic for surgeons who often have trouble manipulating soft tissues while wearing gloves. Astronauts also have issues handling equipment during spacewalks at the International Space Station. Researchers from China have developed an advanced tactile sensor that’s so sensitive it allows the wearer to feel the touch of a flower petal, light brush of a feather, a tiny wire that can’t be seen with the naked eye, and even droplets falling on a finger. The researchers published their findings in the Applied Physics Reviews on February 18, 2020.


The piezoresistive, crack-based sensor was inspired by a spider’s legs that are connected to sensing organs. The pattern of cracks found in the exoskeleton enables the spider to detect the smallest movements in its proximity. Likewise, the ultrathin crack-based strain sensor (UCSS) uses cracks formed in numerous thin layers of flexible polymer film coated with silver. The cracks in the silver coating are responsible for generating parallel channels that conduct electricity, which causes the sensor to become extremely sensitive to movement.


The researchers carried out experiments with the system, which showed that sensors made of thinner layers generated higher sensitivity while thicker layers exhibited a larger sensing range. To create a more balanced effect, researchers designed UCSSs made of 15-micron thick polymer layers and 37-nanometer thick silver coatings.


When the sensor was placed on a glove, researchers discovered it could monitor tiny movements. (Image Credit: Rongrong Bao.)


The team also created a visually aided tactile enhancement system (VATES) by connecting UCSSs to a signal acquisition circuit and readout device. Afterward, they attached USCSSs to a glove, either on the bank of a hand or on a fingertip, which created “electronic skin.” This allowed tiny movements, like the tip of a person’s finger moving across surfaces, to be monitored. Further tests also demonstrated that the UCSSs were able to detect facial movements, like blinking, frowning, and smiling.


They also suggest UCSSs could be implanted in many different applications, including electronic whiskers, which could map wind flow patterns. They could also be used in wearable sensors for heartbeat and pulse detection or to enhance the sense of touch on prosthetics. 


“These results demonstrate the wide applications of our ultrathin strain sensor in e-skin and human-machine interfaces,” said Caofeng Pan of the Beijing Institute of Nanoenergy and Nanosystems at the Chinese Academy of Sciences.


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