Defective Microwave Photonic Crystals for Salinity Detection

In this paper, defective microwave photonic crystals (MPCs) are designed to sense the salinity of aqueous solutions. The defective MPC sensors are constructed by two kinds of microwave dielectric layers and one defective salt solution layer. Transfer matrix method (TMM) for lossy medium is developed to calculate the transmittance spectra of the sensors. It is found that the peak transmittance of both the defective resonance within the microwave band gap (MBG) and transmitting modes outside the MBG monotonously decrease with the increase of salinity, while the resonant and transmitting mode frequencies remain unchanged. By comparing the four MPC sensor structures, the first transmitting mode in the upper frequency band outside the MBG of the 15-layer MPC sensor has the largest salinity sensing range from 0 to 40‰ with relative stable detecting sensitivity. The sensing principle is based on the fact that the dielectric loss factor of saline solution is much more sensitive to salinity than the dielectric constant in the microwave frequency band. The sensitivity, quality factor, and salinity detection range of the MPC sensors are calculated and compared. The reported defective MPC sensors are suitable to be used for non-contact salinity detection.

Space Electroosmotic Thrusters in Ion Partitioning Soft Nanochannels

Space electroosmotic thrusters (EOTs) are theoretically investigated in a soft charged nanochannel with a dense polyelectrolyte layer (PEL), which is considered to be more realistic than a low-density PEL. When the PEL is dense, its permittivity is smaller than the one of the electrolyte solution layer, leading to rearrangement of ions in the channel, which is denoted as the ion partitioning effect. It is noted that fluid viscosity becomes high within the PEL owing to the hydration effect. An analytical solution for electroosmotic velocity through the channel is obtained by utilizing the Debye–Hückel linearization assumption. Based on the fluid motion, thruster performances, including thrust, specific impulse, thrust-to-power ratio, and efficiency, are calculated. The ion partitioning effect leads to enhancement of the thruster velocity, while increase of the dynamic viscosity inside the PEL reduces the flow rate of the fluid. Therefore, these performances are further impacted by the dense soft material, which are discussed in detail. Moreover, changes or improvements of the thruster performances from the dense PEL to the weak PEL are presented and compared, and distributions of various energy items are also provided in this study. There is a good result whereby the increase in electric double layer thickness promotes the development of thruster performances. Ultimately, the simulated EOTs produce thrust of about 0 to 20 μN and achieve thruster efficiency of 90.40%, while maintaining an appropriate thrust–power ratio of about 1.53 mN/W by optimizing all design parameters.

Numerical Approach for Differential-Difference Equations having Layer Behaviour with Small or Large Delay using Non-Polynomial Spline

A numerical approach is suggested for the layer behaviour differential-difference equations with small and large delays in the differentiated term. Using the non-polynomial spline, the numerical scheme is derived. The discretization equation is constructed using the first order derivative continuity at non-polynomial spline internal mesh points. A fitting parameter is introduced into the scheme with the help of the singular perturbation theory to minimize the error in the solution. The maximum errors in the solution are tabulated to verify the competence of the numerical method relative to the other methods in literature. We also focused on the impact of large delays on the layer behaviour or oscillatory behaviour of solutions using a special mesh with and without fitting parameter in the proposed scheme. Graphs show the effect of the fitting parameter on the solution layer.

Laser Induced Aggregation of Light Absorbing Particles by Marangoni Convection

Laser induced Marangoni convection can be used to accumulate micro-particles. In this paper, a method is developed to control and accumulate the light absorbing particles dispersed in a thin solution layer. The particles are irradiated by a focused laser beam. Due to the photothermal effect of the particles, the laser heating generates a thermal gradient and induces a convective flow around the laser’s heating center. The convective flow drives the particles to accumulate and form a particle aggregate close to the laser’s heating center. The motion of particles is dominated by the Marangoni convection. When the laser power is high, the vapor bubbles generated by laser heating on particles strengthen the convection, which accelerates the particles’ aggregation.

Brazing of transparent polycrystalline Al2O3 and GH99 with the assistance of (Cu, Ni) solid solution cladding layer

In this study, pure Cu foil was firstly vacuum cladding on the GH99 alloy (GH99) surface to prepare a (Cu, Ni) solid solution layer. By varying the cladding temperatures, (Cu, Ni) solid solution layers with different Ni contents were achieved. The vacuum cladding process was then followed by vacuum brazing of the Cu-coated GH99 to transparent polycrystalline Al 2 O 3 (TPA). Typical microstructure of the TPA/Cu-cladding GH99 brazed joint was characterized. The effects of different cladding temperatures on microstructural evolution and mechanical response of the brazed joints were discussed. By varying the cladding temperature, different thickness of the reaction layer at the braze filler/TPA interfaces can be achieved, which shows a strong correlation with the mechanical performance of the brazed joint. The maximum shear strength of the brazed joint reached 103 MPa when the cladding temperature was 1105 ºC. Compared with the directly brazed joint, shear strength was improved by 472%.