Diffraction of Life - biosonar camouflage, cloaking and concealment

从《哈利·波特》到《星星大战》，隐形衣都是流行文化中的神奇装备。隐身背后的科学已经发展到一个水平，使我们能够在未来的现实生活中隐形斗篷。事实上，几个部分功能性的斗篷已经用所谓的超材料实现了--超材料是由多个元素组成的组件，具有自然界中尚未发现的特性。一个更有前途的领域，为发展一个功能性的隐形装置是不是光，但声音-声学斗篷。由于声波的波长比光波的波长长，因此设计和制造声学超材料以及有效的斗篷更容易。事实上，最先进的声学斗篷现在可以完全隐藏表面上的物体-所谓的地毯斗篷。作为一种超材料，它由部分重叠的穿孔板组成，排列得很像屋顶瓦片。虽然我们知道自然界中没有超材料用于光，但这对声学超材料也是正确的吗？哪种生物需要这样的装置来隐藏自己的声音？我们认为答案在于65年前回声定位蝙蝠和它们的蛾类猎物之间的军备竞赛。一个对付蝙蝠的“生物声纳斗篷”将减少飞蛾的捕食压力，因此提供了大量的进化好处。有趣的是，飞蛾体表的鳞片层与声学地毯斗篷有着惊人的结构相似性。我们假设飞蛾翅膀是自然界设计的声学超材料。我们将调查飞蛾的鳞片是否具有声学特性，可以使飞蛾从回声定位蝙蝠那里隐藏起来。在我们的试点研究中，我们开发了一种“生物声纳可视化器”，可以创建声学图像，揭示身体部位的反射性质。该技术与医学超声成像（断层扫描）密切相关。我们还使用激光扫描仪来测量鳞片层如何响应超声波而振动。从这些初步的数据中，我们发现了一系列令人惊讶的有趣的适应性：首先，（死亡和干燥）蛾翅膀上的鳞片会改变翅膀的反射率四倍。在另一个非常令人兴奋的发现中，我们发现月蛾的长尾反射强烈的回声，这样它们就吸引了蝙蝠的注意力，并远离蛾的身体进行攻击。我们还发现，眼睛的斑点，用于视觉显示，以惊吓接近捕食者，也站在声学。最后，我们有证据表明，飞蛾选择的地方休息，并调整其翅膀的位置，以减少对比度和融入基板声学。这些试验数据清楚地表明，有一个广泛的和有前途的未研究领域的回声适应。类比于视觉伪装，我们介绍了一个全新的研究领域-生物声纳伪装。我们确定了几种可能的伪装策略。一种策略是飞蛾在飞行中反射很少的超声波（隐身），从而减少蝙蝠可以探测到它的距离;另一种策略是模仿休息表面的回声。在这种情况下，蛾休息的树皮上的声音与它的环境相融合。我们的研究将建立什么样的声学特性和声音处理机制已经在蛾的鳞片响应蝙蝠生物声纳进化。自工业革命以来，世界已成为一个嘈杂的地方，人造声音遍布我们的生活栖息地。声污染是人类和动物不适和压力的来源。我们将利用我们对飞蛾翅膀的理解，在可听频率下3D打印具有声学超材料特性的缩放原型。因此，我们为当前对人类语言和舒适度至关重要的低频噪声控制挑战提供了新的生物启发解决方案。

Invisibility cloaks are fantastic devices in popular culture from Harry Potter to Star Wars. The science behind cloaking has been advanced to a level that brings a future real-life invisibility cloak within our reach. In fact, several cloaks with partial functionality have already been realised with so-called metamaterials - assemblies of multiple elements engineered to have properties not yet found in nature. An even more promising field for the development of a functional cloaking device is not for light, but for sound - acoustic cloaks. Because the wavelengths of sound are longer than those of light waves, it is easier to design and build acoustic metamaterials and hence effective cloaks. Indeed, the most advanced acoustic cloak can now completely hide an object on a surface - a so-called carpet cloak. As a metamaterial it consists of partly overlapping perforated plates, arranged much like roof tiles.While we know of no metamaterials for light in nature, is this also true for acoustic metamaterials? Which organism would need such a device to hide itself acoustically? We propose the answer lies in the 65MY old arms race between echolocating bats and their moth prey. A 'biosonar cloak' against bats would reduce predation pressure on the moths and therefore offer substantial evolutionary benefits. Interestingly, the layers of scales on a moth's body surfaces bear remarkable structural resemblance to an acoustic carpet cloak.We hypothesise that moth wings are an acoustic metamaterial engineered by nature. We will investigate whether the scales on the moths have acoustic properties that hide the moth from an echolocating bat. In our pilot study, we have developed a 'biosonar visualizer' that creates acoustic images revealing the reflective nature of body parts. This technique is closely related to medical ultrasound imaging (tomography). We also use a laser scanner to measure how the layer of scales vibrates in response to ultrasound. From these preliminary data we find a surprising range of interesting adaptations: First, scales on a (dead and dried) moth wing change wing reflectivity by a factor of four. In another very exciting discovery, we find that the long tails of Luna moths reflect strong echoes such that they attract the bat's attention and attack away from the moth's body. We also find that the eye spots, used in a visual display to startle an approaching predator, also stand out acoustically. Finally, we have evidence that moths choose the places to rest and adjust their wing position to reduce contrast and blend into the substrate acoustically. This pilot data make clear that there is a wide and promising unstudied field of echoacoustic adaptations. In analogy to visual camouflage, we introduce an entirely novel field of research - biosonar camouflage. We identify several possible strategies for camouflage. One strategy is for the moth to reflect very little ultrasound (cloaking) when in flight, thus reducing the distance over which a bat can detect it. Another strategy involves mimicking the echoes of a resting surface. In this scenario, the moth resting on the bark of a tree is acoustically blending with its environment.Our research will establish what acoustic properties and sound processing mechanisms have evolved in moth scales in response to bat biosonar. Since the industrial revolution, the world has become a noisy place where man-made sounds are pervasive throughout our living habitats. Acoustic pollution is a source of discomfort and stress for humans and animals. We will use our understanding of moth wings to 3D print scaled prototypes with acoustic metamaterial properties at audible frequencies. Thereby we contribute new bio-inspired solutions to current noise control challenges at the low frequencies so important to human speech and comfort.