Researchers at North Carolina State University have developed a stretchable strain sensor that has an unprecedented combination of sensitivity and range, allowing it to detect even minor changes in strain with greater range of motion than previous technologies. Credit: Shuang Wu, NC State University
Flexible strain sensors are useful in applications such as blood pressure monitoring and technologies that track body movement. In typical strain sensors, there is often a trade-off between stretchability and sensitivity, with highly sensitive sensors having a limited range of motion and highly stretchable sensors having lower sensitivity. Researchers at North Carolina state University have demonstrated a new strain sensor design that overcomes these limitations, using a pattern of cuts in polymer material to increase stretchability without sacrificing sensitivity.
The sensor uses a silver nanowire network embedded in an elastic polymer to measure strain by tracking changes in electrical resistance. The team engineered a pattern of cuts with uniform depth and length that are perpendicular to the direction it is stretched and alternate from either side of the polymer material. As a result, when the sensor is stretched, the cuts pull open, creating a zigzag pattern. This allows the sensor to be stretched further without breaking, and changes the conducting path based on the open cuts, allowing for sensitive strain measurements over a wide range of motion.
The researchers demonstrated the application of the sensor by creating multiple wearable devices. This included wearable blood pressure devices and wearable devices for monitoring motion in a person’s back, according to corresponding author Yong Zhu. In addition to health monitoring, the sensor can also be used to create a human-machine interface, which the team demonstrated by incorporating the sensor into a three-dimensional touch controller that was used to control a video game, explained first author Shuang Wu. This research was published in ACS Applied Materials & Interfaces.
“The sensor can be easily incorporated into existing wearable materials such as fabrics and athletic tapes, convenient for practical applications,” said Zhu. “And all of this is just scratching the surface. We think there will be a range of additional applications as we continue working with this technology.”
Zhu added that the sensor is highly robust, even when over-strained, and is unlikely to break even when the applied strain exceeds the sensing range.