Researchers have demonstrated the potential of new sensors by creating novel health-monitoring machine interface devices
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.
The researchers demonstrated the sensor’s utility by creating new health-monitoring and human to machine interface devices.
Strain is a measurement of how much a material deforms from its original length. For example, if you stretched a rubber band to twice its original length, its strain would be 100%.
Yong Zhu, corresponding author of a paper on the work and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State said: “Measuring strain is useful in many applications, such as devices that measure blood pressure and technologies that track physical movement.
“But to date, there’s been a trade-off. Strain sensors that are sensitive – capable of detecting small deformations – cannot be stretched very far. On the other hand, sensors that can be stretched to greater lengths are typically not very sensitive.
“The new sensor we’ve developed is both sensitive and capable of withstanding significant deformation. An additional feature is that the sensor is highly robust even when over-strained, meaning it is unlikely to break when the applied strain accidentally exceeds the sensing range.”
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greater range of deformation
The new sensor consists of a silver nanowire network embedded in an elastic polymer, a feature that could be utilised for wearable devices and at human to machine interfaces. The polymer features a pattern of parallel cuts of a uniform depth, alternating from either side of the material; one cut from the left, followed by one from the right, followed by one from the left, and so on.
Shuang Wu, who is first author of the paper and a recent PhD graduate at NC State, added: “This feature – the patterned cuts – is what enables a greater range of deformation without sacrificing sensitivity.”
The sensor measures strain by measuring changes in electrical resistance. As the material stretches, resistance increases.
The cuts in the surface of the sensor are perpendicular to the direction that it is stretched. This does two things: first, the cuts allow the sensor to deform significantly, because the cuts in the surface pull open, creating a zigzag pattern, therefore the material can withstand substantial deformation without reaching the breaking point; and second, when the cuts pull open, this forces the electrical signal to travel further, travelling up and down the zigzag.
wearable devices
Zhu said: “To demonstrate the sensitivity of the new sensors, we used them to create new wearable blood pressure devices.
“And to demonstrate how far the sensors can be deformed, we created a wearable device for monitoring motion in a person’s back, which has utility for physical therapy.”
Wu said: “We have also demonstrated a human-machine interface. Specifically, we used the sensor to create a three-dimensional touch controller that can be used to control a video game.”
Zhu concluded: “The sensor can be easily incorporated into existing wearable materials such as fabrics and athletic tapes, convenient for practical applications.
“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.”
Image: 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. It has particular potential in wearable devices and at human to machine interfaces.The new sensor consists of a silver nanowire network embedded in an elastic polymer. The polymer features a pattern of parallel cuts of a uniform depth, alternating from either side of the material: one cut from the left, followed by one from the right, followed by one from the left, and so on. This feature – the patterned cuts – is what enables a greater range of deformation without sacrificing sensitivity. © Shuang Wu/ NC State University.
