Department of Mechanical Engineering, Virginia Tech, Institute for Advanced Learning and Research, 150 Slayton Avenue, Danville, Virginia 24540, USA.
J Acoust Soc Am. 2010 Sep;128(3):1414-25. doi: 10.1121/1.3365246.
Beamforming is critical to the function of most sonar systems. The conspicuous noseleaf and pinna shapes in bats suggest that beamforming mechanisms based on diffraction of the outgoing and incoming ultrasonic waves play a major role in bat biosonar. Numerical methods can be used to investigate the relationships between baffle geometry, acoustic mechanisms, and resulting beampatterns. Key advantages of numerical approaches are: efficient, high-resolution estimation of beampatterns, spatially dense predictions of near-field amplitudes, and the malleability of the underlying shape representations. A numerical approach that combines near-field predictions based on a finite-element formulation for harmonic solutions to the Helmholtz equation with a free-field projection based on the Kirchhoff integral to obtain estimates of the far-field beampattern is reviewed. This method has been used to predict physical beamforming mechanisms such as frequency-dependent beamforming with half-open resonance cavities in the noseleaf of horseshoe bats and beam narrowing through extension of the pinna aperture with skin folds in false vampire bats. The fine structure of biosonar beampatterns is discussed for the case of the Chinese noctule and methods for assessing the spatial information conveyed by beampatterns are demonstrated for the brown long-eared bat.
波束形成对于大多数声纳系统的功能至关重要。蝙蝠显著的鼻子和耳屏形状表明，基于出入超声波衍射的波束形成机制在蝙蝠生物声纳中起着重要作用。数值方法可用于研究挡板几何形状、声学机制以及由此产生的波束图之间的关系。数值方法的主要优势是：高效、高分辨率的波束图估计、近场幅度的空间密集预测以及基础形状表示的可变性。本文回顾了一种结合了基于亥姆霍兹方程谐和解的有限元公式的近场预测和基于基尔霍夫积分的远场波束图预估的自由场投影的数值方法。该方法已用于预测物理波束形成机制，例如马蹄蝠鼻叶中的半开共振腔的频率相关波束形成以及假吸血蝠通过皮肤褶皱扩展耳屏孔径的波束变窄。讨论了中国夜蝠生物声纳波束图的精细结构，并演示了用于评估波束图所传达的空间信息的方法。
