The inkjet-printing technique is regarded as an efficient
method
to fabricate microlens arrays used in digital cameras, medical endoscopes,
displays, optical communication, and light source devices. The diameter,
height, and aspect ratio of the microlens are the major contributors
to these optical properties. Hence, the optical characteristics of
the microlens array can vary with the type of inkjet-printing method.
In this study, by employing electrohydrodynamic (EHD) jet printing
with the drop-on-demand strategy, we fabricated microlenses and microlens
arrays using a UV-curable photopolymer liquid on flexible poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-coated
poly(ethylene terephthalate). By controlling the number of printing
drops, which is regarded as an efficient approach to control the dimension
of the microlens, lenses with diameters of 11.9 ± 0.2 and 24.4
± 0.5 μm and aspect ratio ranging from 0.22 to 0.33 were
constructed. It was found that the focal length (15.44–26.79
μm), numerical aperture (0.39–0.46), and f-number (1.3–1.1) varied with the number of printing drops.
The results demonstrate that the EHD-printed microlenses have a much
shorter focal length, higher numerical aperture, and smaller f-number than the previously reported printed lenses. Hence,
the EHD-printed microlens can be utilized to produce wide-angle-of-view
applications and capture accurate images with insufficient light intensity.
In addition, the proposed EHD-printing method may provide a cost-effective
and simple route for manufacturing microlens arrays.
For effective ocean energy harvesting, it is necessary to understand the coupled motion of the piezoelectric nanogenerator (PENG) and ocean currents. Herein, we experimentally investigate power performance of the PENG in the perspective of the fluid–structure interaction considering ocean conditions with the Reynolds number (Re) values ranging from 1 to 141,489. A piezoelectric polyvinylidene fluoride micromesh was constructed via electrohydrodynamic (EHD) jet printing technique to produce the β-phase dominantly that is desirable for powering performance. Water channel was set to generate water flow to vibrate the flexible PENG. By plotting the Re values as a function of nondimensional bending rigidity (KB) and the structure-to-fluid mass ratio (M*), we could find neutral curves dividing the stable and flapping regimes. Analyzing the flow velocities between the vortex and surroundings via a particle image velocimetry, the larger displacement of the PENG in the chaotic flapping regime than that in the flapping regime was attributed to the sharp pressure gradient. By correlating M*, Re, KB, and the PENG performance, we conclude that there is critical KB that generate chaotic flapping motion for effective powering. We believe this study contributes to the establishment of a design methodology for the flexible PENG harvesting of ocean currents.
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