Fingers Can Sense Nano-Wrinkles on Seemingly Smooth Surface

How sensitive are our fingers? Apparently they can detect even nano-wrinkles on a seemingly smooth surface. The findings have important implications for the development of technologies for the visually impaired.

Before now, scientists have been unsure exactly how sensitive our sense of touch really is. In order to find that out, they tested the smallest pattern that a finger could distinguish. When a finger is drawn over a surface, vibrations occur in the finger. People feel these vibrations differently on different substances and the fiction properties of the surface control how hard we press on the surface as we explore it. A high friction surface requires us to press less to achieve the optimum friction force.

"This is the breakthrough that allows us to design how things feel and are perceived," said Mark Rutland, one of the researchers, in a news release. "It allows, for example, for a certain portion of a touch screen on a smartphone to be designed to feel differently by vibration."

In fact, the scientists discovered that the smallest pattern that could be distinguished from the non-patterned surfaces they tested had grooves with a wavelength of 760 nanometers and an amplitude of only 13 nanometers.

"This means that, if your finger was the size of the Earth, you could feel the difference between houses from cars," said Rutland. "That is one of the most enjoyable aspects of this research. We discovered that a human being can feel a bump corresponding to the size of a very large molecule."

The findings could be huge for informing the development of the sense of touch in robotics and virtual reality. For example, a plastic touch screen surface could be made to feel like another material, such as fabric or wood. In addition, this could allow researchers to create differentiation in product packaging, or in the products themselves.

"The important thing is that touch was previously the unknown sense," said Rutland. "To make the analogy with vision, it is as if we have just revealed how we perceive color. Now we can start using this knowledge for tactile aesthetics in the same way that colors and intensity can be combined for visual aesthetics."

The findings are published in the journal Scientific Reports.