Miniature directional acoustic sensors : nature as inspiration

Rights statement
Awarding institution
  • University of Strathclyde
Date of award
  • 2023
Thesis identifier
  • T16717
Person Identifier (Local)
  • 201989379
Qualification Level
Qualification Name
Department, School or Faculty
  • Miniature directional microphones are desirable for applications ranging from smartphones to hearing aids. The most common technique to achieve directional acoustic sensing is the use of microphone arrays of two or more elements, far from each other, with their inputs then being compared. Nevertheless, this is in conflict with the need to reduce the system or microphones’ size. Bigger animals achieve directional hearing in a similar way, with two ears located on opposite sides of the body, an ability known as binaural hearing. Yet smaller animals, like insects, face similar issues to those of miniature microphones. Where inter-ear distance is too short, you cannot rely on comparison for pinpointing the direction of the source. Some small animals have, thus, come up with original solutions to this issue. With bio-inspiration gaining traction in the last few decades, it is not uncommon to look at nature for original design ideas. This thesis looks at Achroia grisella, a small moth capable of seemingly monoaural, i.e. using just one ear, directional hearing. A novel simplified model of the moth’s eardrum is developed to explain if the morphology of its eardrum is enough to confer it with directionality. Eigenfrequency and directionality studies are carried out in the model at the moth scale and it is found to have a directivity pattern that reacts more strongly to sounds coming from the front, with eigenfrequencies appearing at a frequency range that the moth is known to detect. A scaled-up model is 3D printed, approximately ten times bigger in length and width, and 50 times thicker depending on the iteration of the model and sample. Its frequency and directional responses are studied through laser Doppler vibrometry, using sound frequencies under 16 kHz for excitation. The 3D printed samples agree with what is predicted by the model, adjusted for the scaling up, and passive structures are found to respond directionally to an acoustic stimulus.
Advisor / supervisor
  • Reid, Andrew
  • Windmill, James
Resource Type