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yexuqing木虫之王 (文学泰斗)
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Photophoretic flight of perforated structures in near-space conditions
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Photophoretic flight of perforated structures in near-space conditions 近地太阳能飞行器来了 ▲ 作者：Benjamin C. Schafer, Jong-hyoung Kim, Felix Sharipov, Gyeong-Seok Hwang, Joost J. Vlassak & David W. Keith ▲链接： https://www.nature.com/articles/s41586-025-09281-8 ▲摘要： 光泳是一种气体（或液体）中悬浮的颗粒被光加热后产生的运动力。人们已经知道这种原理超过百年，但直到近期才开始探索它的实际用途。在地球大气层上层，空气十分稀薄，光泳的力强到足以让小型物体漂浮。但迄今为止，大多数实验都集中在非常小而轻的材料上，将之扩展到更大、更实用的大型设备一直是个挑战。 美国哈佛大学的Benjamin Schafer与合作者研究了一种小型太阳能漂浮装置，由两片薄而多孔的膜通过微小的垂直支撑连接而成。结合计算机建模和实验室实验优化光泳力后，他们制作了一个宽1厘米的圆盘，能够在与高空阳光强度相当的光照下悬浮。他们还提出了一种3厘米宽的版本，计算机模型显示它白天在75公里高空能够携带10毫克的载重（足以支撑包含射频天线、太阳能电池和集成电路的小型通信系统）。 这些发现凸显了光泳飞行作为监测地球大气甚至探索其他行星的工具的潜力。作者认为，现在的火星运输成本每公斤超过10万美元，而相比专门的火星卫星，光泳装置在尺寸、重量和功耗方面均有显著优势，未来可用于执行传感和通信任务。未来的设计可以包含导航系统、增加载荷能力和运行时长，以及执行更大规模的任务。 ▲ Abstract： Lightweight nanofabricated structures could photophoretically loft payloads in near-space. Proposed structures range from microscale engineered aerosols, to centimetre-scale thin disks with variations in surface accommodation coefficients, to sandwich structures with nanoscale thickness that might be extended to metre-scale width. Quantitative understanding of how structural and surface properties determine photophoretic lofting forces is necessary to develop a practical flying device. Here we focus on thermal transpiration as the most promising photophoretic mechanism for lofting large devices and present a hybrid analytical–numerical model of the lofting force on a structure that consists of two perforated membranes spaced a small distance apart. We identify optimal structural parameters, including device size, membrane perforation density and distribution of the vertical ligaments that connect the two membranes, each as a function of atmospheric altitude. Targeting these optimal parameters, we fabricate structures with a heterogeneous ligament distribution, which efficiently compromises between structural rigidity and photophoretic performance. We measure how lofting forces generated by these structures depend on pressure using gases with three different molecular weights. We observed photophoretic levitation of a 1-cm-wide structure at an air pressure of 26.7 Pa when illuminated by 750 W m-2, about 55% the intensity of sunlight. Lastly, we describe the preliminary design of a 3-cm-radius device with 10-mg payload capacity at 75-km altitudes and discuss horizontal motion control, overnight settling, and applications in climate sensing, communications and Martian exploration. 12,433个实用装置的大气悬浮。向上推力由热对流气流通过装置膜上的434个微尺度孔洞产生。回流发生在远离装置的位置。 |
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