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This study aims to provide a better understanding of how bat bio-sonar operates so that the authors can apply this improved understanding to the design of simple in-air sonar systems based on the same operational principles. It focuses on the effect of component and configuration choices on the generated binaural spectral cues. Configurations composed of conventional receivers are evaluated for varying reflection strengths and compared to a system with artificial pinnae receivers. Localisation performance is quantified by an information-theoretic performance criterion expressing the mutual information carried by a binaural spectrum on the corresponding three-dimensional reflector location. Results show that the narrow beamwidth of conventional transducers limits the localisation information carried by the generated binaural spectra. The more complex spatial sensitivity patterns of organic pinna forms such as that of the Phyllostomus discolor bat species are shown to provide additional spectral cues that greatly improve localisation information transfer. The authors have found that the varying acoustic axis in the head-related transfer function of the pinna has a positive effect, but that the higher peripheral sensitivity around the varying acoustic axis is the driving force behind the artificial pinna's superior localisation performance.