Robust electrical contacts integrating a liquid metal bridge for mechanical switches

Intrinsic roughness of solid surfaces causes a series of inevitable shortcomings in the use of mechanical electrical contacts, among which one of the most fatal is the repulsive electrodynamic force arising from high currents. A large contact force coming from a heavy holding mechanism helps to suppress the repulsive effect whereas the mechanism consumes energy and remains to be challenging for a compact switching device. Here, a liquid metal (LM) bridge is introduced to wet solid electrodes to eliminate contact issues. Four instability patterns induced by the electromagnetic pinch effect are identified to characterize LM bridge’s response to high currents. Simulation results reveal that an inner vortex caused by uneven distributions of current density and electrodynamic volume force leads to the rupture of a necked LM bridge. With a uniform structure, a cylindrical LM bridge is proved to be robust with respect to an impulse current higher than 10 kA, exceeding a commercial compact relay by a factor of more than 10 in terms of current withstand performance. Our research facilitates compact and energy-saving switch equipment and has a potential to realize arbitrary desired levels of high current withstand without the use of a holding mechanism. This paper also offers deep insights into the high current applications of LM from the perspective of fluid related physical mechanisms.

Effect of Geometrical Parameters On Sensitivity And Volume Of Dual Octal Ring

Force transducer is one of the load cell which is used to measure force or weight, pressure etc. various types of transducers are manufacturing for various applications. But most of strain gauge type of transducer is used. In current research, optimization of octagonal type of force transducer design is carried out by maximizing sensitivity and minimizing the volume. Force transducer is analyze with the help of finite element method and find the critical parameters, its effect also as sensitivity and volume. Response surface methodology is used for experimental set up. For performance of all parameters analysis of variance is carried out and multi-objective optimization is also performed.

Influence of the surface DBD parameters on the streaks development in the boundary layer

The effect of the filamentary barrier discharge parameters on the boundary layer streaks generation and instability was studied. The streaks are formed near the constricted discharge channels due to vortices formation driven by spanwise Coulomb volume force. The secondary instability of the streaky structures can lead to the laminar-turbulent transition of the boundary layer. This work demonstrates that supply voltage parametrs affect the period of the constricted channels and thus the streaks transversal period within the boundary layer. For the various streaks periods, different modes of streak instability are shown to dominate.

Prediction and optimization of process parameters of electrospun polyacrylonitrile based on numerical simulation and response surface method

There is a strong coupling relationship between the process parameters of electrospun polyacrylonitrile (PAN) and its fiber diameter. By examining the mechanism of influence, the quality of electrospun products can be significantly improved and controlled. In this study, a novel idea for predicting and optimizing electrospun PAN process parameters was proposed. First, the control equation of the electrospun PAN was established based on the incompressible Navier–Stokes equation, and the volume force (generated via electric field force, gravity, and surface tension) and jet velocity during electrospinning were solved and analyzed via simulation software. Then, grey correlation analysis was used to calculate the correlation among the three process parameters (applied voltage, feed rate, and distance between the needle and collector) of the electrospun PAN, volume force, jet velocity, and average fiber diameter. Subsequently, the effect of simultaneous changes in multiple process parameters on the average fiber diameter was examined based on the response surface method, and a prediction model was established. Finally, the experimental results indicated that the model can predict the average fiber diameter when multiple process parameters are simultaneously changed. The model predicted the average fiber diameter with an error of only 0.28%, and the optimized minimum fiber average diameter was 235.3 nm (the applied voltage was 12 kV, the distance between the needle and collector was 15.6 cm, the feed rate was 0.37 mL/h). This study provides a theoretical basis for the on-line monitoring of the electrospun PAN.

Controlled Synthetic Freestream Turbulence Intensity Introduced by a Local Volume Force

Generating freestream turbulence within the computational domain instead of applying it as a boundary condition requires a method to introduce the turbulent fluctuations at a specific location. A method based on applying local volume forces has been adapted and supplemented with a control loop in order to compensate for alterations of the turbulence structure resulting from the numerical treatment and physical reasons. The criteria for the tuning of the controller have been developed and the performance of the approach has been assessed. The capabilities of the method are demonstrated for the flow around an airfoil at high angle of attack and with massive flow separation.

Separation of Particles Composed of a Solid Solution [Mg2SiO4 -Fe2SiO4] in the Sequence of Fe2+ Concentration Using a Pocketsize Magnetic-Circuit

Magentic separation generally required strong magnetic forces induced in ferromagnetic or strong paramagnetic particles; in order to realize the separation in diamagnetic or weak paramagnetic particles, it was necessary to attach magnetic beads or magnetic ions to induce the strong magnetic force. A method to separate mixture of weak magnetic particles by its concentration of paramagnetic ferrous ion is newly proposed, which does not require the abovementioned magnetic attachments. The efficiently of the new method is experimentally examined using a pocketsize magnetic circuit (4.5 cm x2.0 cm x 1.0 cm) and a piece of cross sectional paper (5.0 cm x1.0cm). The separation is based on a principle that velocity of a translating particle, induced by a magnetic volume force in an area of monotonically decreasing field, is uniquely determined only by its magnetic susceptibility (per unit mass) of the particle; the velocity is independent to mass of particle. By examining the spectra of the separated particles recovered on the cross sectional paper, a histogram on Fe concentration is easily obtained for the particles without the need of consuming them.

Gradient acoustic focusing of sub-micron particles for separation of bacteria from blood lysate

Handling of submicron-sized objects is important in many biochemical and biomedical applications, but few methods today can precisely manipulate this range of particles. We present gradient acoustic focusing that enables flow-through particle separation of submicron particles and cells and we apply it for separation of bacteria from blood lysate to facilitate their detection in whole blood for improved diagnostics. To control suspended objects below the classical 2µm size limit for acoustic focusing, we introduce a co-flowing acoustic impedance gradient to generate a stabilizing acoustic volume force that supresses acoustic streaming. The method is validated theoretically and experimentally using polystyrene particles, Staphylococcus aureus, Streptococcus pneumoniae and Escherichia coli. The applicability of the method is demonstrated by the separation of bacteria from selectively chemically lysed blood. Combined with downstream operations, this new approach opens up for novel methods for sepsis diagnostics.

Control of crossflow-vortex-induced transition by unsteady control vortices

The fundamental mechanisms of a hitherto unstudied approach to control the crossflow-induced transition in a three-dimensional boundary layer employing unsteady control vortices are investigated by means of direct numerical simulations. Using a spanwise row of blowing/suction or volume-force actuators, subcritical travelling crossflow vortex modes are excited to impose a stabilizing (upstream) flow deformation (UFD). Volume forcing mimics the effects of alternating current plasma actuators driven by a low-frequency sinusoidal signal. In this case the axes of the actuators are aligned with the wave crests of the desired travelling mode to maximize receptivity and abate the influence of other unwanted, misaligned modes. The resulting travelling crossflow vortices generate a beneficial mean-flow distortion reducing the amplification rate of naturally occurring steady or unsteady crossflow modes without invoking significant secondary instabilities. It is found that the stabilizing effect achieved by travelling control modes is somewhat weaker than that achieved by the steady modes in the classical UFD method. However, the energy requirements for unsteady-UFD plasma actuators would be significantly lower than for steady UFD because the approach makes full use of the inherent unsteadiness of the plasma-induced volume force with alternating-current-driven actuators. Also, the input control amplitude can be lower since unsteady crossflow vortex modes grow stronger in the flow.