Bioinspired origami tymbals — sound production through elastic instabilities

While conservative design practices in engineering avoid buckling of slender structures, nature shows a variety of novel concepts that benefit from buckling and multistability. For example, tymbal organs are doubly-curved striated membranes found in certain moth species that buckle to produce sound; the sound is used, among other purposes, for the emission of anti-predator ultrasonic signals. It is known that tymbals buckle actively through muscular action in tiger moths and passively through aeroelastic forces in ermine moths. Our experimental studies reveal the mechanisms associated with the buckling of ermine moth tymbals (aeroelastic tymbals), which we replicate using curved folded paper origami.

Using the finite-element (FE) method, we have developed a non-rigid origami model based on our studies of the morphology and function of aeroelastic tymbals. The complexity is reduced by modelling the tymbal striations as folds, where the intersecting folds show local monostability—a desired condition to achieve snap buckling. We use explicit time integration to study the transient response and consequent dynamic snap-through of the origami model. Furthermore, through a coupled structural-acoustic FE model we demonstrate “sound production by snapping” observed in paper origami and in aeroelastic tymbals. Finally, the bio-inspired origami model allows scalability, which enables the possibility of replicating the function for the design of multi-functional, buckling-driven and sound producing devices.