Abstract
The evolutionary arms-race between bats and moths has led to fascinating adaptations on both sides.In particular, the moths’ fur and wing scales create a remarkable absorptive stealth coating, providing them with ‘invisibility’ against the biosonar of bats.
However, the strong absorption becomes disadvantageous when moths are resting on reflective substrates, as their outline should become apparent to bats as a moth-shaped hole.
This thesis investigates the acoustic camouflage in resting moths by performing echo measurements and tomographies.
For this, an existing custom tomography scanner was reimplemented and improved in a measurement and data analysis pipeline, which streamlines the experiments with a high degree of automation.
A comparison of different acoustic parameters of moth echoes on a smooth and rough substrate reveals that moths are less detectable to bats when resting on rough substrates like bark.
Further, their resting position (tent-shaped wings or flat against the substrate) affects their acoustic ‘visibility’, which indicate different camouflage strategies by moths.
Unpublished data by Thomas R Neil suggests, that moths might behave like acoustic carpet cloaks.
This is investigated from a theoretical perspective by applying transformation acoustics and homogenization theory to the moths’ geometry and wing metamaterial.
The results indicate that a high anisotropy in the moth wings would be needed to successfully create the carpet cloak illusion, which seems unlikely in context of the anisotropies expected in the moth wing.
Lastly, the transformation acoustics method is applied in the context of closed cavities to investigate a new aspect of carpet cloaks: isospectral illusions.
| Date of Award | 1 Oct 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Marc W Holderied (Supervisor) & Bruce W Drinkwater (Supervisor) |