Simulations of the Rotor-Stator-Cavity Flow in Liquid-Floating Rotor Micro Gyroscope.

When rotating at a high speed in a microscale flow field in confined spaces, rotors are subject to a complex flow due to the joint effect of the centrifugal force, hindering of the stationary cavity and the scale effect. In this paper, a rotor-stator-cavity (RSC) microscale flow field simulation model of liquid-floating rotor micro gyroscopes is built, which can be used to study the flow characteristics of fluids in confined spaces with different Reynolds numbers (Re) and gap-to-diameter ratios. The Reynolds stress model (RSM) is applied to solve the Reynolds averaged Navier-Stokes equation for the distribution laws of the mean flow, turbulence statistics and frictional resistance under different working conditions. The results show that as the Re increases, the rotational boundary layer gradually separates from the stationary boundary layer, and the local Re mainly affects the distribution of velocity at the stationary boundary, while the gap-to-diameter ratio mainly affects the distribution of velocity at the rotational boundary. The Reynolds stress is mainly distributed in boundary layers, and the Reynolds normal stress is slightly greater than the Reynolds shear stress. The turbulence is in the state of plane-strain limit. As the Re increases, the frictional resistance coefficient increases. When Re is within 104, the frictional resistance coefficient increases as the gap-to-diameter ratio decreases, while the frictional resistance coefficient drops to the minimum when the Re exceeds 105 and the gap-to-diameter ratio is 0.027. This study can enable a better understanding of the flow characteristics of microscale RSCs under different working conditions.

Impact of Laser Intensity Noise on Dual-Comb Absolute Ranging Precision.

Noise in mode-locked lasers has been a central issue for dual-comb metrological applications. In this work, we investigate the laser intensity noise on dual-comb absolute ranging precision. Two different dual-comb schemes based on linear optical sampling (LOS) and nonlinear asynchronous optical sampling (ASOPS) have been constructed. In the LOS scheme, the ranging precision deteriorates with the increase in laser relative intensity noise (RIN). This effect can be corrected by implementing a balanced photo-detection (BPD). In the ASOPS scheme, the experiment shows that the conversion from laser RIN to dual-comb ranging precision is negligible, making a balanced detection unnecessary for ranging precision improvement. The different manners of RIN's impact on absolute ranging precision are attributed to the distinct cross-correlation signal patterns and the underlying time-of-flight (TOF) extraction algorithms.

High speed time-of-flight displacement measurement based on dual-comb electronically controlled optical sampling.

We demonstrate a direct time-of-flight approach that utilizes dual-comb electronically controlled optical sampling (ECOPS) to measure small displacements. ECOPS is enabled by electrically controlling the repetition rate of one laser via an intracavity electric-optical modulator (EOM). The acquisition rate is set by the EOM modulation frequency, which is much higher than commonly used asynchronous optical sampling (ASOPS). In a proof-of-principle experiment, an 80-kHz acquisition rate is obtained with a pair of ∼105 MHz repetition rate Er-fiber lasers. At an average time of 30 ms, a measurement precision evaluated with Allan deviation reaches 26.1 nm for a 40-µm static displacement. In a dynamic measurement, a 500-Hz sinusoidal vibration with 15 µm amplitude has also been identified. The high-precision and high-speed displacement measurement technique can be potentially used in 3D surface profilometry of microelectronic step-structures and real-time monitoring of high frequency mechanical vibrations, etc.

Novel mussel-inspired Ti-6Al-4V surfaces with biocompatibility, blood ultra-drag reduction and superior durability.

In order to develop new Ti-based biomaterials with biocompatibility, blood ultra-drag reduction and superior durability, a novel fabrication combining simple electrochemical and chemical processes was proposed. After being modified by C14H19F13O3Si (FAS), a biocompatible TiO2-SiO2-polydopamine composite surface on Ti-6Al-4V substrate was obtained. The biocompatibility was evaluated using a series of in vitro test, revealing that compared with Ti-6Al-4V alloys, the surfaces exhibited a number of bio-advantages such as anti-platelet aggregation, anti-bovine serum albumin protein adsorption, a lower hemolysis rate (~0.7%) and non-cytotoxicity (the cell viability >88%). The test of human microvascular endothelial cells (HMEC) cultured on the specimens for 48h showed better cell proliferation of the surface. Moreover, we explored the blood dynamic characteristics of titanium alloy substrate biomaterial for the first time, with a focus on the effects of dopamine-reactant concentration on blood flow resistance. The results showed that, compared to titanium alloy material, the TiO2-SiO2 surface modified by 4mg·mL-1 dopamine solution displayed the optimal blood drag reduction characteristics, reaching a 76% drag reduction. After a 2m (800 meshes, 3500Pa) sandpaper abrasion test, the surface still maintained a superior repellency of blood (contact angles>150°, sliding angles<10°). This practical method may expand the applications of biomedical implantation materials.