Air-Flow Sensing Hairs in Crickets and Biomimetic MEMS Sensors

Air flow sensing hairs in crickets, cockroaches and spiders are known to be extremely sensitive, as they work at the thermal noise level. Their design has therefore attracted a lot of attention from the engineer community as potential template for biomimetic fluid flow microsensors. Previous works have regarded the distribution of hair length and corresponding resonances of hairs on the cerci, two appendages at the rear of the animals, in analogy to frequency analyzing devices such as the cochlea.. By contrast, we show here, using analytical modeling and measurements using PIV (Particle Image Velocimetry) that individual filliform hairs are optimal on broad receptive frequency bands. Our model also enables us to tease apart boundary layer effects and effects due to mechanical properties of the base of the hair. The hydrodynamical coupling between hairs is furthermore influencing the response of single hairs, but is exceedingly difficult to measure on real animals. We therefore used biomimetic MEMS hairs designed after cricket hairs to visualize, using PIV, and to model the viscous coupling between tandem artificial hairs. The large extent of hydrodynamical coupling, the high density of hairs and the relatively small size of cerci (ca. 1cm) imply that the whole hair canopy works as an ensemble of loosely coupled oscillators. We discuss how the hydrodynamical coupling influences our understanding of the working of single hairs. This study is one of the very few biomimetic study with full mutual benefits, i.e. one in which biomimetic sensors have also helped us to understand how biological systems function.

Casas J, Steinmann T and  Krijnen G (2010) Why do insects have such a high density of flow-sensing sensors hairs? Insights from the hydromechanics of biomimetic MEMS. J. R. Soc. Interface  7, 1487-1495.

Casas J. Dangles 0. (2010). Physical Ecology of Fluid Flow Sensing in Arthropods.  Annual review Entomology, 55, 505-525.