Understanding tympanal mechanics in insect ears

昆虫有奇妙的耳朵。一些昆虫，如蚊子，用头前的触角来探测声音，主要是接近雌性的声音。值得注意的是，我们的研究表明，蚊子的耳朵对振动和人类的耳朵一样敏感，并且含有同样多的振动敏感细胞--16000个。其他昆虫，如蟋蟀、蝗虫和一些稀有的苍蝇，使用带有鼓膜的耳朵。人类的耳朵也有一个鼓膜，用来将声音转化为运动。这种运动反过来被转换成电信号，然后振动敏感细胞将其传递给大脑。因为声音引起的振动非常小，所以这个过程非常微妙。在昆虫身上也发生了类似的过程，但耳朵有时要小100倍。我们和其他人的研究表明，昆虫的耳膜是一种复杂的仪器，经过数亿年的进化，可以提取微弱的声音能量，并将其传递给振动敏感的细胞。特别是，我们发现在蝗虫中，鼓膜至少还有一项额外的功能：对与动物的生命和生存相关的音调频率进行分类。这是机械信息处理的一种形式，甚至在神经元处理之前就发生了。正常的膜振动在纳米范围内，并且在膜表面积上呈行波的形状。我们发现，这一波的时间非常精确，持续时间为百万分之一秒，非常像一场涌向海岸的海啸。有趣的是，这种生物纳米海啸的传播取决于产生它的声音的频率，而不是它的方向。实际上，波的形成为动物提供了对音调的感知。拟议的工作旨在发现允许该波聚集并产生定向频率分解的确切材料属性和膜结构。我们将使用激光光束来监测振动，使用应用于光的多普勒效应来检测膜的运动，分辨率为氢原子直径。我们将首次使用聚焦离子束球磨来改变膜的几何、张力和质量特性，然后探索由此产生的振动行为。离子束研磨使用投射到物体上的原子薄金属离子射流，可以用来切割硬的或软的物体，或向物体添加物质。这项技术从未被用于研究微观和纳米力学。重要的是，数学建模将通过预测改变膜以产生所需效果的最佳方式来指导机理的探索，从而也描绘出膜功能所需的关键物理参数、材料和结构。因为我们使用了三种鼓形昆虫，我们将能够比较和对比该方法的结果和充分性。为什么蝗虫的膜以一种方式振动，而蟋蟀的膜以另一种方式振动，具有不同的信息编码特性，仍然难以捉摸。使用聚焦离子束，我们将尝试增加或删除各自物种的功能，并了解自然选择在昆虫微小耳朵的发育中取得了什么进化成果。从拟议的研究中，我们还将学习如何在技术上使用我们在生物学中观察到的东西来制造更好的麦克风。当目标是制造一毫米或更小的坚固麦克风时，这一点尤其有用。应用的例子涉及能够机载频率和定向处理的助听器麦克风，以及用于最小功率消耗的电子应用的微型麦克风。

Insects have marvelous ears. Some insects, like mosquitoes, use antennae in front of their heads to detect sounds, mainly those of approaching females. Notably, our research has shown the ear of a mosquito is as sensitive to vibrations as the human ear and contains just as many vibration sensitive cells -16,000. Other insect, like crickets, locust and some rare flies use ears equipped with an eardrum, or tympanal membrane. The human ear also has an eardrum that serves to convert sound into motion. This motion is in turn transduced into the electrical signal that vibration sensitive cells then convey to the brain. Because sound-induced vibrations are very small, this process is extremely delicate. In insects, a similar process takes place, but with an ear that is sometimes 100 times smaller. Our research and that of others has shown that the eardrums of insects are sophisticated instruments that evolved for hundreds of millions of years to extract the faint sound energy and deliver it to the vibration sensitive cells. In particular we showed that in locusts the tympanum has at least one additional function: sorting the tone frequencies relevant to the life and survival of the animal. This is a form of mechanical information processing that takes place even before neuronal processing. Normal membrane vibrations are in the range of nanometers and take the shape of a traveling wave across the membrane surface area. We discovered that this wave is exquisitely timed, lasting 100 millionth of a second, strongly resembling a tsunami coming up to a shore. Interestingly, the propagation of this biological nanotsunami depends on the frequency of the sound that creates it, not its direction. The build up of the wave in effect provides the animal with the perception of tones. The work proposed aims at discovering the exact material properties and membrane architecture that allow for that wave to build up and generate directional frequency decomposition. We will use laser beams to monitor the vibrations, using the Doppler effect applied to light, to detect membrane motion with a resolution of the diameter of an atom of hydrogen. For the first time we will use focused ion beam milling to modify the geometry, tension and mass characteristics of the membranes and then explore the resulting vibrational behaviour. Ion beam milling uses an atomically thin jet of metal ions projected onto the object and can be used to either cut through objects, hard or soft, or add matter to that object. This technique has never been used to study micro and nanomechanics. Importantly, mathematical modeling will guide the search for mechanisms, by predicting the best way to alter the membrane to generate desired effects and thereby also delineating the key physical parameters, materials and architecture, that are sufficient and necessary for membrane function. Because we use three species of tympanate insects, we will be able to compare and contrast the results and adequacy of the approach. Why the membrane of the locust is vibrating one way, and that of the cricket another way, with different information coding properties, is still elusive. Using focused ion beams we will attempt to add or remove functions from the respective species, and understand what evolution by natural selection has achieved in the developing the tiny ears of insects. From the proposed research, we will also learn how to make better microphones, using in technology what we have observed in biology. This is especially useful when the goal is manufacture robust microphones a millimeter in size and less. Examples of application pertain to hearing aid microphones capable of on-board frequency and directional processing as well as subminiature microphone for electronic application with minimal power consumption.