Researchers working for Berkeley Lab and the University of California Berkeley have developed e-whiskers that possess incredibly sensitive, tactile sensory networks, manufactured from a combination of carbon nanotubes and silver nanoparticles. The newly devised e-whiskers detect pressure of just a single Pascal, and could facilitate production of robotic devices with the capacity to interpret specific stimuli within their surrounding environment.
Study leader Ali Javey, a researcher in Berkeley Lab’s Materials Sciences Division and a University California Berkeley professor, explains that the e-whiskers were, of course, inspired by the hair-like projections identified in many mammals and insects. Javey explains that these creatures use such tactile sensors to “feel” the world around them, detecting small changes in the wind, maneuvering around physical barriers and navigating through tight spaces.
Previously, Javey and his research associates have been invested in creating e-skin and other electrical components that interpreted particular stimuli. The electronic skin was composed of “Thin, flexible substrates that mimic certain properties of human skin” and, according to the researchers, paves the way to a new type of human-machine interface technology. In terms of applications, the group suggest the e-skin devices could be of benefit in robotics, health monitoring machines and for smart wallpapers.
Producing the E-Whisker
During their latest project, meanwhile, the team developed a highly flexible “network matrix,” comprised of carbon nanotube paste. Capable of conducting electricity, the matrix of the e-whiskers was impregnated with a thin slither of silver nanoparticles that ensured the matrix offered increased sensitivity to mechanical strain. According to Javey, the composite film is fine-tuned to improve its electrical resistance and strain sensitivity by altering the ratio of carbon nanotubes to silver nanoparticles. He goes on to explain that the film is then “printed” onto fibers that, ultimately, forms the e-whiskers:
“The composite can then be painted or printed onto high-aspect-ratio elastic fibers to form e-whiskers that can be integrated with different user-interactive systems.”
Javey explains that the high strain achieved, in response to the most negligible of pressures, is possible by using elastic fibers that have a small spring constant; the spring constant of the elastic fiber is the value of the change in force it exerts, divided by the change in spring deflection. Through implementation of elastic fibers that have a small spring constant, a highly sensitive tactile sensor network can be produced. The resistivity of the composite films were sensitive to strain “… with a pressure sensitivity of up to ∼8%/Pa for the whiskers”; according to the study authors, this is more than 10 times higher than any previously reported capacitive or resistive pressure sensor.
As the whisker bends, the distance between nanoparticles changes, causing an ensuing change in electrical resistance of the e-whisker. The carbon nanotubes help to maintain electrical conduction when the silver nanoparticles are very far apart, and provide a greater range of sensed pressures. A processor – hooked up to one end of the e-whisker – determines the direction the sensor is being bent and the amount of pressure applied.
Applications of E-Whisker Devices
The team then made a proof-of-concept experiment to illustrate the effectiveness of their design for mapping wind flow. An array of seven vertically positioned e-whiskers were employed to successfully create a 3-dimensional map of the wind. The researchers established that two- and three-dimensional gas mapping was highly accurate using the fabricated e-whiskers.
In reflecting over future applications for their e-whisker devices, the group have suggested the technology could be harnessed to invent wearable sensors for monitoring pulse rate and tactile sensing for spatial mapping of objects within a given environment.
The research paper was published in the Proceedings of the National Academy of Sciences (PNAS), and was entitled Highly Sensitive Electronic Whiskers Based on Patterned Carbon Nanotube and Silver Nanoparticle Composite Films.
By James Fenner