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Simulation Study of Compound-eyes-structure Carbon and Light Capture Structure of Plant Leaves

Author: LiTeng
Tutor: DingJian；FanTongXiang
School: Shanghai Jiaotong University
Course: Materials Science
Keywords: antireflection compound eyes amorphous carbon lotus leaves light capture
CLC: TB391
Type: Master's thesis
Year: 2012
Downloads: 45
Quote: 0
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Abstract


Reduction of boundary reflection presents vital importance in improving the efficiency of optical applications. Recently, various kinds of biomimetic antireflective structures have been developed with the thought of“learning from the nature”, while there are still insufficiency in the mechanism of antireflection and the effect of structural parameters. A compound eye amorphous carbon has been fabricated via vacuum sintering process, using the corneal layer of Euploea mulciber as the template and the raw material. SEM as well as Raman spectra show that the nano array structure of the original corneal layer has been well retained in the amorphous carbon.Reflection of this material is only 2-3% in the wavelength of 380-750nm, which is more than 70% less than that of the flat plate amorphous carbon. Reflective spectra as well as Poynting vector distribution map has been got through simulations base on 3D finite differential time domain(FDTD) algorithm, which shows that the scattering effect of the nano array and the interference of scattered light contributed to the enhancement of antireflection. Comparisons of the reflective spectra of different models show that the best wavelength range of antireflection is decided by array height, high aspect ratio will improve the antireflection, and that the optimum antireflective effect occurs when the volume ratio of carbon/air is 0.128-0.195.Plant leaves can be taken as the prototype in the designing of artificial photosynthesis reactors. Taking lotus leaf as the object, characterization of the appearance has been made via optical/fluorescence microscopy, confocal laser microscopy, cryo scanning electron microscopy and transmission electron microscopy, based on which a compound light capture model has been concluded, which comprises of the upper epidermis, the palisade mesophyll cells and the spongy mesophyll cells. Simulation based on ray-tracing and 3D FDTD algorithm shows that the upper epidermis can reduce reflection and focus sunlight; the vacuole inside the palisade cells and the space among the the palisade cells functions as light paths; the spongy cells function as a porous absorber of light. Coordination of the three part in shape, size and function will contribute to effectively utilization of sunlight.In this research, experiments together with simulations have been employed to study the optical properties of biomimetic structures and natural structures, so as to provide a reference model for the fabrication of these materials, which is an effective strategy for bioinspired research.

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