3D Printing Bio-Inspired Microphone Designs Based On Moth Ears

The amazing biology of insects is a result of millions of years of evolutionary development. One of these structures is the ear of the lesser wax-moth (Achroia grisellaThe moths’ mating behaviour involves ultrasonic calls. They can attract bats that hunt them. These moths have evolved directional hearing, which can identify not only a possible mate but also bat call sounds.

What’s most astounding about this is that these moths that only live about a week as an adult can perform auditory feats that we generally require an entire microphone array for, along with a lot of audio processing. This moth’s eardrum or tympanum is what allows them to do this. Instead of a taut, flat surface like in mammals, this moth’s eardrum has intricate 3D structures and pores that appear to do much of the directional process. This is what researchers, including a University of Strathclyde team, have been trying for some time to replicate.

Researchers used a flexible, hydrogel with a piezoelectric substance that converted the acoustic signals into electrical signals. These were then connected to electrical tracks. The 3D features can be printed onto this hydrogel, and then mixed with methanol to form droplets within the curing epoxy resin. These are then expelled leaving the desired pores. One limitation is that currently used printers have a limited resolution of about 200 micrometers, which doesn’t cover the full features of the insect’s tympanum.

This could be useful for anything from cochlear implant to any other application that requires a lot of audio processing to be downsized.

Heading Image: Mapping of displacement of a tympanum in the lesser wax motte (Achroia grimella). (Credit: Andrew Reid) )