|dc.description.abstract||So-called CF-FM bats are highly mobile creatures who emit long calls in which much of the
energy is concentrated in a single frequency. These bats face sensor interpretation problems
very similar to those of mobile robots provided with ultrasonic sensors, while navigating in
This dissertation presents biologically inspired engineering on the use of narrowband Sonar
in mobile robotics. It replicates, using robotics as a modelling medium, how CF-FM bats process
and use the constant frequency part of their emitted call for several tasks, aiming to improve
the design and use of narrowband ultrasonic sensors for mobile robot navigation.
The experimental platform for the work is RoBat, the biomimetic sonarhead designed by
Peremans and Hallam, mounted on a commercial mobile platform as part of the work reported
in this dissertation. System integration, including signal processing capabilities inspired by the
bat’s auditory system and closed loop control of both sonarhead and mobile base movements,
was designed and implemented. The result is a versatile tool for studying the relationship
between environmental features, their acoustic correlates and the cues computable from them,
in the context of both static, and dynamic real-time closed loop, behaviour.
Two models of the signal processing performed by the bat’s cochlea were implemented,
based on sets of bandpass filters followed by full-wave rectification and low-pass filtering.
One filterbank uses Butterworth filters whose centre frequencies vary linearly across the set.
The alternative filterbank uses gammatone filters, with centre frequencies varying non-linearly
across the set. Two methods of estimating Doppler-shift from the return echoes after cochlear
signal processing were implemented. The first was a simple energy-weighted average of filter
centre frequencies. The second was a novel neural network-based technique. Each method
was tested with each of the cochlear models, and evaluated in the context of several dynamic
tasks in which RoBat was moved at different velocities towards stationary echo sources such
as walls and posts. Overall, the performance of the linear filterbank was more consistent than
the gammatone. The same applies to the ANN, with consistently better noise performance than
the weighted average. The effect of multiple reflectors contained in a single echo was also
analysed in terms of error in Doppler-shift estimation assuming a single wider reflector.
Inspired by the Doppler-shift compensation and obstacle avoidance behaviours found in
CF-FM bats, a Doppler-based controller suitable for collision detection and convoy navigation
in robots was devised and implemented in RoBat. The performance of the controller is satisfactory
despite low Doppler-shift resolution caused by lower velocity of the robot when compared
to real bats.
Barshan’s and Kuc’s 2D object localisation method was implemented and adapted to the geometry of RoBat’s sonarhead. Different TOF estimation methods were tested, the parabola
fitting being the most accurate. Arc scanning, the ear movement technique to recover elevation
cues proposed by Walker, and tested in simulation by her, Peremans and Hallam, was
here implemented on RoBat, and integrated with Barshan’s and Kuc’s method in a preliminary
narrowband 3D tracker.
Finally, joint work with Kim, K¨ampchen and Hallam on designing optimal reflector surfaces
inspired by the CF-FM bat’s large pinnae is presented. Genetic algorithms are used for
improving the current echolocating capabilities of the sonarhead for both arc scanning and IID
behaviours. Multiple reflectors around the transducer using a simple ray light-like model of
sound propagation are evolved. Results show phase cancellation problems and the need of a
more complete model of wave propagation. Inspired by a physical model of sound diffraction
and reflections in the human concha a new model is devised and used to evolve pinnae
surfaces made of finite elements. Some interesting paraboloid shapes are obtained, improving
performance significantly with respect to the bare transducer.||en