Broadband light trapping effect and arrays of sub-wavelength textured structures based on the butterfly wing scales are applicable to solar cells and stealth technologies. In this paper, the fine optical structures in wing scales of butterfly Papilio peranthus, exhibiting efficient light trapping effect, were carefully examined. First, the reflectivity was measured by reflectance spectrum. Field Emission Scanning Electronic Microscope （FESEM） and Transmission Electron Microscope （TEM） were used to observe the coupling morphologies and structures of the scales. Then, the optimized 3D model of the coupling structure was created combining Scanning Electron Microscope （SEM） and TEM data. Afterwards, the mechanism of the light trapping effect of these structures was analyzed by simulation and theoretical calculations. A multilayer nano-structure of chitin and air was found. These structures are effective in increasing optical path, resulting in that most of the incident light can be trapped and adsorbed within the structure at last. Furthermore, the simulated optical results are consistent with the experimental and calculated ones. This result reliably confirms that these structures induce an efficient light trapping effect. This work can be used as a reference for in-depth study on the fabrication of highly efficient bionic optical devices, such as solar cells, photo detectors, high-contrast, antiglare, and so forth.
Zhiwu Han Shichao Niu Lufeng Zhang Zhenning Liu Luquan Ren
Morpho butterfly, famous for its iridescence wing scales, has gradually evolved a diversity of functions and has attracted much attention recently. On the other hand, it is known that the wing surface of Morpho butterfly has some complex and so- phisticated structures. In fact, they are composed of an alternating multilayer film system of chitin and air layers, which have different refractive indexes. More importantly, these structures can interact strongly with visible light because the feature size of the structures is in the same order of magnitude with light wavelength. It is noteworthy that it is these optical architectures that cause the excellent multifunction including structural color, antireflection, thermal response, selective vapour response, direc- tional adhesion, superhydrophobicity and so on. This review mainly covers the excellent multifunctional features of Morpho butterfly wings with representative functional structures of multilayer film system, photonic crystal and ridges. Then, the mechanism of the structure-based optical multifunction of Morpho butterfly is analyzed. In order to facilitate mechanism analysis, the models of bionic functional structures are reported, as well as the interaction process between the multiscale structures and the external media It is concluded that these functions of Morpho butterfly wings have inevitable and corre- sponding regularity connection with the structural parameters and the dielectric coefficient of the filled medium. At last, the future direction and prospects of this field are briefly addressed. It is hoped that this review could be beneficial to provide some innovative insoirations and new ideas to the researchers in the fields of engineering, biomedicine, and materials science.
Shichao Niu Bo Li Zhengzhi Mu Meng Yang Junqiu Zhang Zhiwu Han Luquan Ren
An antifogging function surface with simple structure and suitable for large-area production was found inspired by Ephemera pictiventris McLachlan compound eyes.The compound eyes structure,antifogging properties and mechanism were studied by anti-fog test,dyeing test and scanning electron microscopy,and so forth.Then,3D model of the sample was established,and the antifogging mechanism was explained by the Cassie model.Results showed that the compound eyes are composed of hundreds of micron size ommatidia arranged in curved array form,and this structure shows excellent antifogging function.This research may provide new ideas for design of simple structure and micron size antifogging function surface.This work is also expected to be applied to antifogging function surface of astronaut helmets and medical endoscopes,and so forth.
Plant of carnivorous genus Nepenthes alata has evolved specific pitchers to prey insects for survival in the barren habitat, especially its slippery zone. The excellent slippery function has received considerable interest because of its potential applica- tion in antifriction surface design. The surface morphologies of intact and de-waxed slippery zones were characterized using scanning electron microscope and scanning white-light interferometer. Hierarchical structures with anisotropic micro- lunate structure and nano- wax crystals were found on the slippery zone. Due to the hierarchical structures, the slippery zone is hy- drophobic. It shows a significant anisotropic wettability with static contact angles 153.3° and 140.1° in the directions perpen- dicular and parallel to the upward direction （toward the peristome）, respectively. The sliding angles are -3° and -10° in the downward and upward directions, respectively. Crawling experiments indicate that the microscopic surface roughness and the brittleness of the wax crystals may reduce insect attachment in different modes according to the insect mass differences. Moreover, artificial slippery surfaces inspired by the slippery zone of Nepenthes alata were fabricated. Traction experiments quantitatively verified that the friction force of replicated lunate structures with Ra-2.54 μm surface roughness was reduced by about 25% as compared to flat surface with Ra-0.56 μm surface roughness for cricket claws.
Most previous cervical spine finite element(FE) models were validated using in vitro cadaver measurement data from literatures. Although in vitro measurement can provide valuable data for model verification,the in vivo mechanical and physiological conditions of the cervical spine during its natural motions cannot be reproduced in vitro. In this study, a human FE model of skull(C0) and spinal vertebrae(C1–T1) was developed. The in vivo kinematic characteristics of head and neck were obtained from optoelectronic system, and used for the validation of the FE model. The simulation results showed good agreement with the measured data in left/right lateral bending and left/right axial rotation, while discrepancy existed during flexion. The predicted segmental cervical vertebral angles were compared against data from previous in vivo experiment, too. Furthermore, the skin shift data from previous study was used to compensate the experimental measurement during flexion and left/right lateral bending. The results showed the model was successfully validated with the in vivo experimental data.
