A dynamic ultrasonic emitter inspired by horseshoe bat noseleaves

Abstract

The emission of biosonar pulses in horseshoe bats (family Rhinolophidae) differs from technical sonar in that it has dynamic features at the interface to the free field. When the horseshoe bats emit their biosonar pulses through the nostrils, the walls of a horn-shaped baffle (anterior leaf) are in motion while diffracting the outgoing ultrasonic wave packets. Here, biomimetic reproductions of the dynamic emission shapes of horseshoe bats have been studied for their ability to impose time-variant signatures onto the outgoing pulses. It was found that an elliptical sound outlet with rotating baffles that were attached along the direction of the major axis can be well suited for this purpose. Most importantly, concave baffle shapes were found to produce strongly time-dependent devices characteristics that could reach a root-mean-square-difference between beampatterns of almost 6 dB within a rotation angle of 10°. In contrast to this, a straight baffle shape needs to be rotated over 60° for a similar result. When continuously rotated in synchrony with the emitted pulses, the concave biomimetic baffles produced time-variant device characteristics that depended jointly on direction, frequency, and time. Since such device properties are so easily produced, it appears well worthwhile to explore their use in engineering.

Dynamic Substrate for the Physical Encoding of Sensory Information in Bat Biosonar

“…In accordance with (iv), noseleaf and pinna deformations in horseshoe bats have been predicted to produce qualitative beampattern changes [15,17,20]. Similar changes have been demonstrated experimentally with biomimetic reproductions of noseleaves [21] and pinnae [10,22]. In these experiments, the shape deformations resulted in time-variant device characteristics [21,23].…”

“…Similar changes have been demonstrated experimentally with biomimetic reproductions of noseleaves [21] and pinnae [10,22]. In these experiments, the shape deformations resulted in time-variant device characteristics [21,23]. In the frequency domain, the beampatterns typically alternated between a concentration of sensitivity in a single mainlobe and scattering among local maxima (sidelobes) [10,17].…”

“…Data of sufficient quantity and quality for such characterizations is very difficult to obtain from live bats. Therefore, the present work has been based on two types of datasets: numerical estimates derived from detailed digital models of the natural geometries of the noseleaves and pinnae [17,22] and measurements taken from biomimetic physical prototypes (either with full details or simplified) [10,21,24]. In total, four different datasets (Fig.…”

Quantitative approaches to sensory information encoding by bat noseleaves and pinnae

“…Hence, these motions could change the acoustic characteristics of the biosonar emission and reception during a single pulse or a single echo. Indeed, such changes have been predicted by numerical analysis (Gao et al 2011;He et al 2015) and demonstrated with biomimetic physical prototypes Fu et al 2016). Time variant acoustic characteristics would allow the bats to sense their environments through "multiple views" and hence could enhance the quantity -and perhaps also the quality -of the sensory information available to the animals.…”

A comparison of the role of beamwidth in biological and engineered sonar

“…One of the differences between technical and biosonar that has been observed and studied in literature since has been the dynamics of the biosonar system [3,26,25,9]. This has been of particular interest due to the novelty of the idea: bending the biosonar apertures to dynamically alter a sonar signal [3].…”