In the course of the project, various species of crickets and bush-crickets were collected and their individual songs recorded. After analysing the songs, laser vibrometry was performed to record the vibratory behaviour of the wings producing the songs. Using this method, a laser beam scans the wing surface set into motion by stimulation with broadband sound. The light reflected from the moving wing carries information about the vibration and can be used to create detailed vibration maps that show which parts of the wing respond to which sound frequency. These vibration maps therefore show the specific resonance, the “tuning” of the wings (see Figure 1, middle row). Following this characterisation of the bioacoustics and biomechanical properties, the wings were imaged using high-resolution microscopy and micro-computational tomography to produce 2D and 3D wing models. These virtual wings served as the basis for the creation of initial computational (finite-element) models which allow to simulate the wings’ vibratory behaviour. Various approaches for implementing the wing morphology and modelling technique were investigated that ultimately resulted in models that were able to satisfactorily simulate the vibrations of real wings (see Figure 1, bottom row). These models include the 2D wing shape, the thickness and distribution of veins crossing the wing and the thickness of the wing membrane itself. Additionally, material properties like density and stiffness for the type of cuticle that forms the wing (a complex compound biomaterial mostly made of chitin) have to be specified.
In a further step, the structure and material properties of the virtual models were altered to study the impact of certain morphological changes on the wing vibrations. Alterations were inspired by evolutionary or developmentally conceivable changes like decreasing or increasing membrane and vein thicknesses and changes in wing or vein stiffness (the latter could be influenced by, for example, water content or an animal’s diet). In general, increases in wing stiffness resulted in expected increases in wing resonance (which would lead to higher-pitched song) but changing the stiffness of the veins also showed that the size and location of the vibrations is influenced by this parameter. Similarly, increasing the vein thickness had a pronounced impact on the vibratory behaviour (higher resonances and more confined vibrations). Interestingly, vein morphology seemed to have a greater impact on wing tuning than membrane morphology, suggesting that small changes in wing venation have the potential to produce significant changes in song frequency and amplitude. Further manipulation of vein morphology showed that an inflation of only one central vein (as seen in certain cricket species with unusually high pitch) can change the harmonic composition of the vibrations and thus song frequency and even its “timbre”. Detailed results are currently being prepared for publication in at least two international scientific journals.
