Tapered insect (Acheta domesticus) antennae have rapid damped return with minimal oscillation after perturbation

As tactile sensors, antennae must be flexible and responsive while maintaining shape and control of the structure. We evaluated the geometric and mechanical properties of cricket antennae, which we treat as bending cantilever beams. Flexural rigidity (EI) is the mechanical property that most significantly controls bending behavior. We determined that the flexural rigidity decreases steeply (proximal to distal) by evaluating the quasistatic bent shapes in response to obstacle contact at different points along the antennae. This steep decrease in flexural rigidity causes the antennae to bend readily only near the obstacle contact, in contrast to the curvature of a beam with uniform properties and cross-section (which bends closer to the base). This flexural rigidity gradient in the antennae is consistent with the morphology: a decreasing second moment of area calculated from the measured taper and the diminishing wall (cuticle) thickness. Cricket antennae recovered from a single localized perturbation quickly and with minimal to no oscillation, suggesting behavior close to critical damping (fastest return without oscillations). Bending primarily occurred in the portion of the flagellum near the obstacle contact, reducing the length of the flagellum that participated in the oscillating behavior (natural frequency ∼11 Hz). Forced sinusoidal vibrations generated a resonance frequency of ∼30 Hz with imperceptible movement in the proximal part of the flagellum while the distal part vibrated. The results suggest that tapering of an elongated mechanosensor may facilitate a rapid return to its original shape without oscillation, which is an advantageous attribute that may also inform biomimetic applications.