Researchers at North Carolina State University have developed an expandable strain sensor that is highly sensitive and works over wide ranges. This was reported by the press service of the university.
Strain measurement is useful in applications such as devices that measure blood pressure or physical movement. However, sensitive strain gauges that can detect small changes cannot be overstressed. On the other hand, sensors that can be extended to large lengths are generally not very sensitive.
“The sensor we developed is sensitive and can withstand significant deformations,” the engineers say. “An additional feature is that the sensor is very reliable even under overvoltage, which means that it is less likely to break if the applied force accidentally exceeds the measuring range.”
The new sensor consists of a network of silver nanowires embedded in an elastic polymer. The polymer is a pattern of parallel cuts of the same depth, alternating on both sides of the material: one on the left, one on the right, then one on the left, etc.
“This feature – patterned incisions – allows for a wider range of deformities without sacrificing precision,” the authors explain. — The sensor measures voltage by measuring changes in electrical resistance. As the material stretches, its resistance increases. The cutouts on the sensor surface are perpendicular to the stretching direction. This serves two purposes. First, the cutouts allow the sensor to deform significantly. As the notches on the surface are stretched to form a zigzag pattern, the material can withstand significant deformations without breaking. Second, when the slits open, it causes the electrical signal to travel up and down in the zigzag.”
To demonstrate the sensitivity of the new sensors, the authors created a set of devices for measuring blood pressure, as well as a human-machine interface based on them. This sensor was also used to make a three-dimensional touch controller that could be used to control a computer game.