Abstract
MEMS acoustic sensors have been developed to mimic the highly-accurate sound-locating system of the Ormia ochracea fly, which detects sound wavelengths much larger than its hearing organ. A typical ormia-based MEMS directional sound sensor possesses two coupled wings that vibrate in response to sound according to a superposition of its two main resonant modes, rocking and bending. Vibrations are transduced into electronic signals by interdigitated comb finger capacitors at each wing’s end along with a capacitance measuring circuitry. A sensor designed to exhibit resonant modes closely placed in frequency, enhancing their coupling, was operated with a closed cavity behind the wings. Simultaneous and independent measurements of electronic signals generated at each of the single sensor wings were used to determine incident sound direction of arrival (DOA). DOA was found proportional to the phase shift between them and to the difference over the sum of their amplitudes as well. Single sensor phase shift DOA measurement presented a resolution better than 3° for sound pressure levels of 25 mPa or greater. These results indicate that a single sensor operating in closed-cavity configuration can provide hemispherical unambiguous direction of arrival of sound waves which wavelength is much larger than the sensor size.
Highlights
For many animal species, perceiving the direction under which a sensorial stimulus occurs is key for survival and reproduction
A typical Ormia-based micro-electromechanical systems (MEMS) directional sound sensor consists of two wings, connected by a bridge in the middle and the entire structure is connected to a substrate using two torsional legs
A similar linear behavior with slope of 1.4 × 10–2 was observed for the ratio of difference over sum. These results show that either technique can be used in determining the direction of arrival (DOA) of an acoustic wave using a single MEMS sensor and with full angular range between − 90° to + 90°
Summary
For many animal species, perceiving the direction under which a sensorial stimulus occurs is key for survival and reproduction. The process involves parasitism of different species’ male hosts by the larvae deposited on or near them Males give off their location by emitting mating calls, directed to the female individuals of their own species, but those are heard by female individuals of the parasitic species. Miles et al.[9,10] found that the mechanical coupling between two tympana mediated by a semi-rigid cuticle was responsible for bringing those stimuli amplitude and time differences to within reasonable working ranges for the neuronal cells involved, enabling the parasitic fly to acoustically locate the host for its larvae. On the female fly hearing organ, each of the tympanal membranes present exclusive bilaterally-symmetric mechanoreceptive structures, the auditory apodeme and the bulba acustica[8] Those are responsible for the transduction of each tympanal membranes mechanical vibrations into neuronal electrical pulses. Similar transduction mechanism was employed by other research groups[21] in their devices
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