Researchers around the globe, including a team at Stanford, are making progress on developing artificial electronic skin that rivals the sensitivity of human skin for use in prosthetic limbs, robots and a range of medical applications.
The latest development in the effort comes from Seoul National University, where engineers turned to the beetle's wing design to create a flexible electronic sensor made from interlocking hairs capable of feeling the lightest of touches. A paper (subscription required) describing their work was published today in Nature Materials. More details about the technology are provided in a Nature News piece:
In [the] sensors, the 'hairs' are sheets of polymer fibres that are 100 nanometres in diameter and one micrometre long, and coated with metal to make them electrically conductive. When the sheets are sandwiched together, the nanohairs are attracted to one another and locked in, just like the beetle hairs. The device is then wired up so that an electrical current can be applied, and covered in a layer of soft, protective polymer.
When the sensor sheet is pressed, twisted or brushed, the squishy, metal-coated hairs change position, generating changes in the sensor’s electrical resistance. The design is sensitive to pressures of just five pascals — gentler than the lightest of touches. By analysing how the resistance changes in response to mechanical stress and then recovers when the stress is removed, [Seoul National University engineer Kahp-Yang Suh, PhD] and his colleagues can distinguish between three types of mechanical strain: pressure, which comes straight down on the sensor; shear, a frictional slide along the surface; and torsion, a twisting motion.
At Stanford, Zhenan Bao, PhD, associate professor of chemical engineering, and colleagues have developed a stretchable, transparent skin-like sensor using carbon nanotubes bent to act as springs. Bao comments on the significance of the Korean researchers' findings in the article:
Human skin can distinguish between these types of strain, but most artificial sensors cannot. “Sensing shear and torsion is difficult,” says Zhenan Bao, a materials scientist at Stanford University in Palo Alto, California, who is developing other flexible strain sensors. Other sensors detect only the total applied force, they can't say anything about its direction, says Suh The methods for teasing out the nature of the strain from the electrical readings in Suh’s sensors need some work, says Bao, but getting this type of information from a flexible sensor is unique.