The human finger can discriminate between surfaces patterned with ridges as small as 13 nanometres in amplitude and unpatterned surfaces, a study in Scientific Reports reveals. The finding suggests that the human tactile perception limit may extend to the nanoscale.
Mark Rutland and colleagues produced 16 chemically identical surfaces with wrinkle wavelengths (or wrinkle ‘heights’) ranging from 300 nanometres to 90 micrometres and amplitudes (wrinkle ‘widths’) of between seven nanometres and 4.5 micrometres, as well as two unpatterned surfaces. Human participants were presented with random pairs of surfaces and asked to run their dominant index finger across each one in a designated direction (perpendicular to the groove), before rating the similarity of the two surfaces. The smallest pattern that could be distinguished from the unpatterned surface had grooves a wavelength of 760 nanometres and an amplitude of only 13 nanometres.
The study highlights the importance of two physical parameters - surface friction and wrinkle wavelength - in the tactile perception of fine textures. The research could help to inform the development of the sense of touch in robotics and virtual reality, and the improvement of tactile aesthetics in touch-intensive consumer products, such as phones and tablets.