Directional hearing at the micro-scale : bio-inspired sound localization

Student thesis: Doctoral Thesis

Abstract

Miniaturization of sound localization sensors arrays is heavily constrained by the limited directional cues in intensity difference and phase difference available at the microscale. Micro-Electro Mechanical System (MEMS) sound localization sensors inspired by the auditory system of Ormia ochracea offer a potential solution to this problem by the apparent amplification of the available intensity and phase difference between the measurement points. An inherent limitation of these systems is that significant amplification of these cues is only available on or near one of the resonant frequencies of the device, severely limiting it [sic] application as a directional microphone. A lower amplification of directional cues can be achieved across a wide frequency range, forcing designers to compromise the goal of high amplification of directional cues to operate across the audio range. Here we present an alternative approach, namely a system optimized for the maximum amplification of directional cues across a narrow bandwidth operating purely as a sound localization sensor for wide-band noise. In the devices presented in chapter four we present sound-localization sensors where the directional sensitivity is enhanced by increasing the coupling strength beyond the 'dual optimization' point, which represents the collocation of a local maximum in directional sensitivity and a local minimum in non-linearity, compensating for the loss of the desirable linearity of the system by restricting the angular range of operation. Intensity gain achieved is 16.3 dB at 10° sound source azimuth with a linear directional sensitivity of 1.6 dB per degree, while linear directional sensitivity in phase difference gain shows a seven fold increase over the 'dual optimization' point of 8 degrees per degree.In addition, during the course of this work it was discovered that the methods used to calculate the amplified intensity difference between the measurement points introduce unwelcome Cauchy noise which is difficult to reduce. Later iterations of the device demonstrate the process of optimization of a sound localization sensor for the maximum amplification of directional cues across a narrow bandwidth can be used to overcome that error, as well as describing mathematically what appears to have been a commonly encountered but unpublished problem with Ormia inspired directional sensors. In the second part of the thesis, beginning in Chapter 5 the sound localization strategies of another acoustic insect, the lesser wax moth Achroia grisella, is examined. Moths differ somewhat because their ears generally function as simple bat detectors with relatively little directional ability. Those moths that use sound signals for mating communication represent a yet more special case, as these species can localize sound sources but singing and the ability to localize conspecific song evolved well after the origin of hearing. The analyses revealed a novel localization mechanism wherein the geometry and structure of the tympanal membrane of each ear afford sharp sensitivity to sound arriving from a distinct angle. Females can thereby track singing males, but they only do so by following an indirect, curvilinear trajectory regularly interrupted by wide deviations.
Date of Award1 Apr 2016
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsDefence Science and Technology Laboratory DSTL MoD & University of Strathclyde
SupervisorJames Windmill (Supervisor) & Deepak Uttamchandani (Supervisor)

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