Papers by Author: Jun Cai

Abstract: To investigate the effective permittivity of composites composed of ellipsoidal inclusions, three-dimension numerical models for ellipsoidal inclusions distributed randomly are built with the finite-element modeling software Comsol Multiphysics. After calculating the effective permittivity for different cases and comparing the results with analytical results from the Maxwell-Garnett mixing rule, we find that the finite-element method has an advantage in detecting details of the interaction among inclusions, which have some impacts on the effective permittivity and could not be accurately taken into account in the analytical model. The finite-element method is expected to solve more complex problems on electromagnetic computation.

Abstract: In order to fabricate biosensors with high sensitivity, the diatom Coscinodiscus excentricus was cultured on a microfluidic chip made with polydimethylsiloxane (PDMS), then the organic matter of diatom cells was removed and only diatom frustules were left, after which the cleaned frustules were bonded onto the bottom of the PDMS micro chamber by ultraviolet irradiation. The overview and the detailed morphology of the frustules in the chamber were analyzed by SEM, and the ultraviolet irradiation bonding mechanism of diatom with PDMS was discussed. Finally, the diatom based microfluidic chip was tested with the fluorescein-labeled protein; and the result showed that the fluorescence intensity of the diatom is 4 times stronger compared with that of the blank regions.

Abstract: Graphite-FeSi absorbents were fabricated by mechanical milling method. The complex permittivity and permeability were measured in frequency 1-4 GHz, and then reflection loss (RL) and shielding effectiveness (SE) were calculated. It was obtained that the graphite was bonded to the surface of FeSi by X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images. The permittivity and permeability could be enlarged as graphite added in the milling process. It was attributed to the excellent conductivity of graphite and interactions of the two particles. The graphite-FeSi composites had a better shielding property (maximum 25.93 dB) in 1-4 GHz as well as the absorbing property at 1GHz than FeSi composites.

Abstract: In order to manufacture the drag reducing morphology replication mold used for biomimetic drag reducing film fabrication, the real shark skin and micro riblets machined with ultrasonic elliptical vibration cutting (UEVC) were used as templates respectively, followed by the casting process. The manufacturing process and the morphology quality of the molds was studied, and the biomimetic drag reducing effect and suitable application field was analyzed. The result indicates that: the bio-replicated forming mold based on shark skin is superior in morphology similarity with the real shark skin; the UEVC mold can achieve simplified riblets with high quality, and is feasible for large area mold manufacture and riblets spacing adjustment. The riblets morphology made with UEVC has wider application field than the shark shin morphology because of its flexibility of spacing adjustment.

Abstract: The nano-composite electroless coating was introduced into bio-limited forming technology for the first time, and the feasibility of the nano-composite electroless coating on microorganism was verified. The composite coated microorganism was analyzed by using optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results showed that stirring method would make significant effect on the content of nano-particles in the composite coating. And compared with mechanical stirring, the magnetical stirring makes the content of Fe in the composite coating increase almost twice. The co-deposition mechanism of the composite coating was also discussed.

Abstract: The connotative meaning and trend of bionic design and manufacturing was analyzed. A new bioforming technology was presented, which will offer a new way to solve the difficulties in manufacturing of bionic micro-nano structures, and the layout of bioforming technology was also plotted. Several different bioforming technologies targeting typical bionic products were introduced. Compared with traditional manufacturing methods, to machine complicated micro/nano shapes, structures, functional interfaces with bioforming technology has more advantages, which showed that bioforming technologies would have great potential applications in energy-saving, environmental protection, and micro/nano fields.

Abstract: Helical structure plays an important role in many fields and the machining quality is important for its applications. In this paper, a kind of functional hollow lightweight metallic micro-helixes based on cells of spirulina was manufactured by bio-limited forming. Then the impurity degree and the un-metallization degree, two important parameters to evaluate the machining quality of the functional micro-helixes in the application to chiral microwave absorbing material were investigated. Numeric models were established and the regularities were researched on how the two parameters are influenced by metallization technology factors. The results showed that the values of these two parameters could be reduced by adjusting the volume of the original deposition solution for 1g filtered wet activated cells, the diluted multiples of the original deposition solution, the temperature of reaction and the time of reaction so as to improve the machining quality.