An engineering study into the bisonar system of fruitbats in the genus rousettus

The history of research into biosonar has a long and fascinating history, beginning with the documented experiments of Lazarro Spallanzani in the late 18th century. It was some 150 years before the mechanism of echolocation was to be demonstrated. Since that discovery, the acuity with which bats can perceive their surroundings has itself become a wonder for scientists and engineers, and furthermore an inspiration for improving human sonar systems. This Thesis provides further understanding of the signals and processes involved, and indeed replicates these in the laboratory. The calls of the echolocating fruit-bat Rousettus aegyptiacus are recorded using a novel design of wireless ultrasonic microphone sensor, which uses biomimetic variable gain to enable both the emitted signal and the return echoes to be recorded from the bat as it echolocates in flight. This demonstrates the complexity of the echoes returning to the bat, indicating the difficulty inherent in decoding these signals to image the bat's surroundings. It is further demonstrated using the finite element analysis (FEA) technique, that Rousettus echolocation signals, when combined with the response of its ear, do not produce obvious monaural spectral cues that could be used to indicate the location of the source. It is interesting to note that this is different to results reported in the literature for some species of microchiropteran bat, indicating that the nature of megachiropteran echolocation may be rather different. There is also the potential to apply biological techniques and signals in engineering systems. This Thesis documents inexpensive, piston-mode electrostatic transducers that have been designed to generate wideband ultrasonic signals in air. A rigorous characterisation of the operation of these transducers is presented, with detailed surface motion and field measurement data. These transducers are used to replicate echolocation calls to investigate bats' ability to detect targets of cross-section considerably smaller than the wavelength of the signals they emit. It is demonstrated that, partially enabled by their aural gain-control mechanism, this feat is made possible by the dynamic range over which bats can operate. In its entirety, this Thesis presents a multi-disciplinary investigation into biosonar systems, and their replication in human engineered systems.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2013

Author dc:creator

• Whiteley, Simon

DOI

10.48730/tmch-br55

Identifier

T13432

OAI identifier oai:identifier

oai:strathclyde:wh246s17n