In 2012, Dr. Yong Zhu and a team at North Carolina State University created highly conductive and elastic conductors made from silver nanowires. At the time, Dr. Zhu said the conductors could be used to create stretchable electronics with applications in wearable, multifunctional sensors. Two years later, the NC State researchers have developed just such a sensor.
By sandwiching an insulating material between two of the silver nanowire-based conductors, the researchers were able to create a device with capacitance, or the ability to store an electrical charge. When the stretchable conductors are pushed, pulled or touched, the capacitance is changed. Measuring this change is what provides the device's sensing capabilities.
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"The technology is based on either physical deformation or 'fringing' electric field changes," says Shanshan Yao, a Ph.D. student at NC State and lead author of a paper on the work. "The latter is very similar to the mechanism used in smartphone touch screens, but the sensors we’ve developed are stretchable and can be mounted on a variety of curvilinear surfaces such as human skin."
The researchers say the sensors have a wide variety of potential applications, ranging from biomedical, military and athletics, to prothetics, robotics and flexible touch displays. They have used the sensors to monitor thumb movement and have also demonstrated the monitoring of knee movements while a test subject is running, jumping and walking.
"The deformation involved in these movements is large, and would break a lot of other sensor devices," says Dr. Zhu. "But our sensors can be stretched to 150 percent or more of their original length without losing functionality, so they can handle it."
The team has also used the technology to map pressure distribution by developing an array of sensors. With a response time of just 40 milliseconds, the sensors also allow strain and pressure to be monitored in real time. This could be particularly important for applications in robotics and prosthetics.
"These sensors could be used to help develop prosthetics that respond to a user’s movement and provide feedback when in use," says Dr. Zhu. "They could also be used to create robotics that can ‘feel’ their environment, or the sensors could be incorporated into clothing to track motion or monitor an individual’s physical health."
The team's paper, "Wearable Multifunctional Sensors Using Printed Stretchable Conductors Made of Silver Nanowires," is published online in the journal Nanoscale.
Source: NC State