From Bat Pinnae to Sonar Antennae: Augmented Obliquely Truncated Horns as a Novel Parametric Shape Model

Biosonar systems operating in air (bats) use intricate baffle shapes for shaping the sonar beam pattern. Because of its relative ease of implementation, beamforming with such baffle shapes is also an attractive solution for enhancing the sonar-sensing capabilities of animats. The work presented here introduces a novel family of parametric, biologically inspired, baffle-shapes for sonar sensors: augmented obliquely truncated horns. The structural features of these shapes are: an obliquely truncated horn, a washboard ripple pattern on its inner surface, and a pin-shaped flap (“tragus”) partially occluding the aperture through which sound enters the baffle. Shapes generated by this model can be completely controlled with 22 parameters. Numerical methods to generate representations of these shapes, evaluate their acoustic properties, and visualize the results are described. The investigated acoustical system properties are: directivity pattern, shape of iso-gain surfaces in three dimensions and gain contours on planar cuts through the spatial distribution of the gain. The last property (cuts) serves as a representation of the shape of a sonar spotlight shone onto an extended target of relatively low curvature. The results demonstrate that ripple and tragus have a profound impact on the functional properties of the baffle shapes. The most prominent effects include breaking of symmetry and generation of side lobes in different frequency bands. The two features have been shown offer the opportunity to shape the spatial distribution of receiver gain into a large number of profoundly different configurations. Evidence of interactions between the features indicates that a combination of both features may generate system properties inaccessible through any one feature alone. The tool-chain of numerical methods used in the present work establishes a foundation for future investigations of performance measures to be used in optimizing the baffle shapes for a particular task.