Biomechanical analysis of a cricket filiform hair socket under low velocity air currents
Joshi, Kanishka Bhuwanchandra
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Filiform hairs of crickets are of great interest to engineers because of the hairs' highly sensitive response to low velocity air currents. In this study, the cercal sensory system of a common house cricket is analyzed. The sensory system consists of two antennae like appendages called cerci that are situated at the rear of the cricket's abdomen. Each cercus is covered with 500-750 flow sensitive hairs that are embedded in a complex viscoelastic socket that acts as a spring and dashpot system and guides the movement of the hair. When a hair deflects due to the drag force induced on its length by a moving air-current, the spiking activity of the neuron that innervates the hair changes and the combined spiking activity of all hairs is extracted by the cercal sensory system. The hair has been experimentally studied by researchers though its characteristics are not fully understood. The socket structure has not been analyzed experimentally or theoretically from a mechanical standpoint, and the characterization that exists is mathematical in nature and only provides a very rudimentary approximation of the socket's spring nature. This study aims to understand and physically characterize the socket's behavior and interaction with the filiform hair by presenting and proving new hypotheses about the hair and socket behavior. The operating principles of the socket can be used for the design of highly responsive MEMS devices such as fluid flow sensors or micromanipulators. A three dimensional computer aided design (CAD) model was first created using confocal microscopy images of the hair and socket structure of the cricket, and then finite element analyses based on the physical conditions the insect experiences were simulated. The results show that the socket acts like a spring but due to its constitutive non-standard geometric shapes, it deforms like a thin membrane at times or like a plate in bending at other instances. It was also determined that the socket provides far greater resistance to hair movement than what has been previously postulated and computed by researchers.