How human fingers sense molecules

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Have you ever wondered how acute a person's sense of touch is? Previous work has shown that our fingers can detect bumps as small as 13 nanometers in height. And each of us with our eyes closed will distinguish wood from metal and plastic, because these materials have different textures and absorb the heat of fingers in different ways. But researchers at the University of California, San Diego have found that through touch, humans can sense the difference between two surfaces that differ only in the top layer of molecules.

The team, led by Professor Darren Lipomi, used two silicon wafers, one coated with an oxidized layer dominated by oxygen atoms and the other covered with a carbon-fluorine-based Teflon material. Both plates were smooth and looked pretty much the same.

In the first experiment, a group of 15 volunteers were asked to slide their finger across three plates and guess which one was different from the other two. Participants passed the test 71% of the time.

The second test turned out to be more difficult. Scientists have applied eight transverse stripes of an oxidized and Teflon layer to elongated silicon wafers. In these strips, different materials played the role of "ones" and "zeros" of the binary code, and a letter of the eight-bit ASCII alphabet was encrypted on each plate.

This time, ten of the eleven participants in the experiment, apparently not far from programming, were able to decipher the word Lab (Laboratory) by sliding their finger along the plates. This took them, on average, less than five minutes.

According to the researchers, people can feel these differences due to the different sliding frictional forces that occur when two objects at rest begin to slide relative to each other. It is due to this phenomenon that the creaking of door hinges or the noise of a stopping train is generated.

During the tests, it turned out that the effectiveness of recognizing different surfaces depends on how quickly the finger moves and how hard it presses on the plate.

Lipomi and his colleagues created an "artificial finger with a sensor and pressure transducer," which was passed over various materials. After processing the data with a computer model, they found that for some combinations of speed and pressure, the differences between surfaces become completely elusive.

“Our results show a remarkable human ability to quickly find the right combination of force and speed to perceive the difference between these surfaces,” Lipomi says in a press release. Interestingly, an 'artificial finger' with just one sensor can also sense this difference. nothing to do with the hundreds of nerve endings in our skin, and receptors in the ligaments, joints, wrists, elbow and shoulder that allow people to feel small differences when touched."

The research findings, published in Materials Horizons, are fundamental to the development of technologies such as e-skin, tactile prostheses and tactile virtual reality controls.