Saraf has demonstrated the sensor on a glass backing, but he says the film could also be made on flexible polymer sheets. Such flexibility would be necessary to wrap the sensor around a robot’s “finger” or the tube of an endoscope (a camera inserted through a small cut that allows surgeons to operate inside the body). Saraf says such an endoscope could take concurrent visual and tactile images, helping surgeons “feel” which tissues the scope is up against.
Srinivasan says an ideal sensor “essentially has to be what skin is: flexible, with the ability to sense dynamically and with high spatial resolution, and physically robust – it shouldn’t break, it shouldn’t wear out.” Human skin obtains highly sensitive tactile readings by having sensors with different strengths. Some cells are good at sensing vibration or movement over time (which is essential for feeling something slipping from your grip); other cells accurately sense a point of pressure smaller than a micrometer.
High touch sensitivity “is extremely important” for robotics, says Robert Platt, a robotics engineer at the NASA-Johnson Space Center who works on the hands for Robonaut, a humanoid robot. To perform the most basic human tasks – dexterous grasping, walking on two legs, climbing, even crawling – robots “need to be cognizant of and controlling the forces they’re applying,” he says. To pick up a glass of water, for example, a robot needs to dynamically sense the forces exerted by its “hand.” Such a task requires high sensitivity – not only being able to feel where on its fingers a stress has been applied, but also in what direction that force is moving. This information can inform the robot whether an object is slipping or not, for example.
The high spatial sensitivity of Saraf’s sensor would not be enough to help a robot hold a glass of water, though, because the sensor can’t tell the direction of pressure. Further research will reveal whether or not nanoparticle layers can sense this kind of tactile information, Saraf says. For now, though, it is “a promising approach,” says NASA’s Platt.