Toward a Bio-Inspired Acoustic Sensor: Achroia grisella’s Ear

Gathering insights from nature to develop original solutions for engineering problems is known as bio-inspiration. The examples found in nature are often efficient and beautifully simple. For the particular issue of directional acoustic sensing at small scales, insects provide a myriad of clever adaptations to achieve hearing despite their small body size. Achroia grisella is a nocturnal moth capable of directional hearing of wavelengths significantly longer than its intertympanic distance. Previous studies have shown that directionality for this moth is monoaural and exclusively relies on the shape of the eardrum itself. The work developed a computer model that behaves similar to the moth’s ear, which is then 3-D printed. The model starts from a simplified circular membrane and progresses until it reflects the moth’s tympanum more closely. The approach consists of four steps: considering analytical equations, virtually simulating the model, manufacturing and performing experimental measurements, and finally comparing the outcomes of each. Equations are produced for the simplest geometries, and COMSOL Multiphysics is used for the simulations. The samples are manufactured via 3-D printing and excited with a vibrating piezoelectric chip and a speaker while being measured with a 3-D laser Doppler vibrometer to determine their frequency and directional responses.