Horseshoe bats possess a sophisticated biosonar system that helps them to negotiate complex unstructured environments by relying primarily on the sound as the far sense. For this, the bats emit brief ultrasonic pulses and listen to incoming echoes to learn about the environment. The sites of emission and reception in these bats are surrounded by baffle structures called "noseleaves" and "pinnae (outer ears)". These are the the only places in the biosonar system where direction-dependent information gets encoded. These baffle structures in bats unlike the engineering systems like megaphones have complex static geometry and can undergo fast deformations at the time of pulse emission/reception. However, the functional significance of the baffle motions in biosonar system is not known. The current work primarily focuses on: i) the study of the impact of noseleaf dynamics on the outgoing sound waves, ii) the study of the impact of baffle dynamics on encoding of sensory information and localization performance of bats. For this, we take a numerical approach where we use computer-animated digital models of bat noseleaves that mimic noseleaf dynamics as observed in bats. The shapes are acoustically characterized (beampatterns) numerically using a finite element implementation. These beampatterns are then analyzed using an information-theoretic approach. The followings findings were obtained: i) noseleaf dynamics altered the spatial distribution of energy, ii) baffle dynamics results in encoding of new sensory information, and iii) the new sensory information encoded due to baffle dynamics significantly improves the performance of biosonar system on the two target localization tasks evaluated here -- direction resolution and direction estimation accuracy. These results affirm the importance of dynamics in biosonar system of horseshoe bats and point at the possibility of biosonar dynamics as a key factor behind the astounding sensory capabilities of these animals that are not yet matched by engineering systems. Thus, these biosonar dynamic principles can help improve the man-made sensing systems and help close the performance gap between active sensing in biology and in engineering. / Ph. D.

Bats are known for their highly capable biosonar systems which make them be able to navigate and forage in dense vegetation. Their biosonar system consists of one emitter (nose or mouth) and two receivers (ears). Some bat species, e.g. in the rhinolophid and hipposiderid families, have complicated pinna motion patterns. It has been shown that these pinna motion patterns fall into two distinct categories: rigid motions and non-rigid motions. In the current work, the pinna of Pratt's leaf-nosed bat (Hipposideros pratti) was used as a biological model system to understand how a sensor could benefit from variability. Hence, the variability in the rigid pinna motions and in the non-rigid pinna motions has been investigated by tracking a dense set of landmarks on the pinna surface with stereo vision. Axis-angle representations have shown that the rigid pinna motions exhibited a large continuous variation with rotation axes covering 180 degrees in azimuth and elevation. Distributions of clusters of the landmarks on the pinna surface have shown that the non-rigid pinna motions fall into at least two subgroups. Besides, the acoustic impact of the rigid pinna motions have been investigated using a biomimetic pinna. Normalized mutual information between the acoustic inputs with different rotation axes has shown that different rotation axes can provide at least 50% new sensory information. These results demonstrate that the variability in the pinna motions is an interesting concept for sensor, and how the bats approach that needs to be further investigated. / Master of Science / Sensors have been developed for a long time, and they can be used to detect the environments and then deliver the required sensing information. There are many different types of sensors, such as vision-based sensors (infrared camera and laser scanner) and sound-based sensors (sonar and radar). Ultrasonic transducers are one of the sound-based sensors, and they are more stable and reliable in environments where smoke or steam is present. Similar to human-made ultrasonic transducers, bats have developed highly capable biosonar systems that consist of one ultrasonic emitter (nose or mouth) and two ultrasonic receivers (ears), and these biosonar systems enable them to fly and hunt in cluttered environments. Some bats, e.g. rhinolophid and hipposiderid bats, have dynamic noseleaves (elaborate baffle shapes surrounding the nostrils) and pinna (outer ear), and these could enhance the sensing abilities of bats. Hence, the purpose of this thesis has been to investigate this variability to improve the human-made sensors by focusing on the dynamic pinna of the bats. It has been shown that bats have two distinct categories of pinna motions: rigid motions which change only the orientation of the pinna, and non-rigid motions which change also the shape of the pinna. However, the variability within the rigid and non-rigid pinna motions has received little attention. Therefore, the present work has investigated the variability in the rigid pinna motions and in the non-rigid pinna motions. Landmark points were placed on the pinna of certain bats and the pinna motions were tracked by high-speed video cameras. The rigid pinna motions exhibit a large continuous variation in where the pinna is orientated during rotation. Distributions of clusters of the landmarks on the pinna have shown that the non-rigid pinna motions fall into at least two subgroups. The acoustic impacts of the rigid pinna motions have been studied by a biomimetic pinna which reproduced the observed range of the rigid pinna motions. Ultrasonic signals mimicking the bats were emitted to be received by the biomimetic pinna. Based on these signals, it has been shown that different rotation axes and even small changes can provide over 50% new sensory information. These findings give engineers a potential way to improve the human-made sensors.