Gupta Anupam K, Webster Dane, Müller Rolf
Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA.
School of Visual Arts, Virginia Tech, Blacksburg, Virginia 24061, USA.
J Acoust Soc Am. 2015 Nov;138(5):3188-94. doi: 10.1121/1.4935387.
Horseshoe bats emit biosonar pulses through the nostrils and diffract the outgoing ultrasonic pulses with baffles, so-called "noseleaves," that surround the nostrils. The noseleaves have complex static geometries and can furthermore undergo dynamic shape changes during emission of the biosonar pulses. The posterior noseleaf part, the lancet, has been shown to carry out anterior-posterior flicking motions during biosonar emissions with average lancet tip displacements of about 1 mm. Here, the acoustic effects of the interplay between the lancet furrows and shape change (lancet rotation) on the emission beam were investigated using the animated digital models obtained from the noseleaves of greater horseshoe bats (Rhinolophus ferrumequinum). It was found that forward lancet rotations increase the amount of sound energy allocated to secondary amplitude maxima (sidelobes) in the beampattern, but only in the presence of the furrows. The interaction between static and dynamic features can be readily quantified by roughness (standard deviation about local mean) of the amplitude distribution of the beampatterns. This effect goes beyond the static impact of the furrows on the width of the mainlobe. It could allow the bats to send out their pulses through a sequence of qualitatively different beampatterns.
菊头蝠通过鼻孔发出生物声纳脉冲，并利用围绕鼻孔的所谓“鼻叶”的挡板对发出的超声波脉冲进行衍射。鼻叶具有复杂的静态几何形状，并且在生物声纳脉冲发射过程中还会发生动态形状变化。已表明鼻叶后部，即柳叶刀，在生物声纳发射过程中会进行前后摆动运动，柳叶刀尖端的平均位移约为1毫米。在此，利用从大菊头蝠（Rhinolophus ferrumequinum）的鼻叶获得的动画数字模型，研究了柳叶刀凹槽与形状变化（柳叶刀旋转）之间的相互作用对发射波束的声学影响。研究发现，柳叶刀向前旋转会增加分配到波束图中二次幅度最大值（旁瓣）的声能数量，但前提是存在凹槽。静态和动态特征之间的相互作用可以通过波束图幅度分布的粗糙度（相对于局部均值的标准偏差）轻松量化。这种效应超出了凹槽对主瓣宽度的静态影响。它可以使蝙蝠通过一系列性质不同的波束图发出脉冲。
