Narrow Results

Micromixer is a kind of microfluidic chip for fast mixing and analysis. Mixing in a micromixer is usually a micron scale. At low Reynolds number, the fluid in the channel is laminar flow, which mainly depends on molecular diffusion as the main mixing mode. Fluid mixing in microchannels is very difficult, especially when the viscosity of the fluid is high. In this paper, we design a novel passive micromixer. The effects of fractal number, Koch fractal channel spacing, microchannel depth and cross-section shape on mixing efficiency were studied. Through a large number of numerical simulations, we continue to optimize the structure of the micromixer and improve the mixing efficiency. Finally, through the continuous optimization of the structure of the micromixer, the mixing efficiency of the micromixer can reach more than 95%.

A compact frequency band reconfigurable dual-mode antenna utilizing both Koch fractal geometry and circular complementary split ring resonators (CSRRs) is presented in this paper. The proposed antenna can be electrically switched into both dual- and single-band resonance modes. A Koch curve derivative novel fractal curve is used to design the patch boundary of the antenna. Two optimized circular CSRRs are loaded inside the antenna geometry to achieve double-band resonance. The antenna operates at both 5.1GHz (upper WLAN band) and 9.6GHz ($X$-band) in dual resonance mode and resonates only at 8GHz ($X$-band) in single resonance mode. A properly biased RF-range PIN diode placed at the slotted ground plane reconfigures the antenna in two operating modes by switching into its ON–OFF states. The antenna is fabricated on cost-efficient epoxy (FR-4) substrate consuming the maximum dimension of $0.34\lambda \times 0.32\lambda$ which is much more compact than the conventional rectangular patch antennas designed for similar bands. Stable radiation characteristics with reduced cross-polarization are achieved at all the resonant bands of the antenna. A prototype of the proposed antenna is fabricated and measured. The simulated results are in good agreement with the measured ones.

In this paper, we focussed on the processing power of CO₂ laser systems and the impact of scanning speed, scanning power and number of scans on the quality of microchannels. We created microchannels which are based on the Koch fractal principle through a flexible and low-cost CO₂ laser system. The processing and manufacturing method of Koch fractal micromixer on polymethyl methacrylate (PMMA) substrate was also studied. The microchannel structure based on the Koch fractal principle can increase the contact area and mixing time of the fluid and improve the mixing efficiency of the micromixer. In the experiment, our speed is 2, 4 and 6mm/s, the number of scans is 2/3/4 times and the power is 4, 8 and 12W. As the power and number of scans increase and the speed decreases, the width and depth of the microchannel are changed more clearly, which contributes to the successful thermal bonding of the Koch fractal micromixer and avoids thermal bonding due to overvoltage. By comparing the experimental data, we found that the width and depth of the channel are ideal when the speed is 2mm/s, the number of scans is 4 and the power is 12W. Because of the lower cost of PMMA, the use of CO₂ laser systems to fabricate microchannels on PMMA substrates will have broad application value, reduce cost and be easier to manufacture.