Discharge characteristic of nanosecond-pulse DBD in atmospheric air using magnetic compression pulsed power generator

Dielectric barrier discharge driven by repetitive nanosecond pulses can offer highly efficient non-thermal plasma at atmospheric pressure and is widely used for plasma applications. In this paper, the discharge is generated using a compact pulsed power generator based on one-stage magnetic compression. The output pulse can be up to 30 kV with a rise time of about 40 ns and a full width at half maximum of 70 ns. The electrical characteristics of the discharge parameters are studied by the measurement of voltage and current waveforms. The effects of applied voltage amplitude, voltage polarity, pulse repetition frequency, and barrier dielectric on discharge characteristics are investigated, respectively. The experimental results show that the discharge current, discharge power and electron density increase with the increase of the applied voltage, and the pulse repetition frequency has a slight effect on the electrical parameters. Moreover, the discharge current is influenced by the dielectric barrier, but it is not varied with the polarity of applied pulses.     

Interesting magnetic properties observed in the 4f ferromagnet NdRu2

We have investigated dc magnetization, magneto-transport and magnetostriction of C15 Laves phase 4f ferromagnetic compound NdRu₂ as a function of temperature and applied magnetic field. We find that the magnetic properties of this compound can not be explained within a simple model based on localized magnetic moment even though Nd based compounds and alloys are usually considered as localized magnetic moment systems. Our experimental results on temperature dependence of magnetization, electrical resistivity and magnetoresistance suggest the existence of spin fluctuations in the paramagnetic state of NdRu₂. This compound shows unusually high and non-linear forced magnetostriction. We conjecture the hybridization of Nd 4f states with valence electrons as one of the possibilities for explaining the experimental results.     

Small-scale portable photovoltaic-battery-LED systems with submersible LED units to replace kerosene-based artisanal fishing lamps for Sub-Saharan African lakes

A technical simulation and economic model was developed for a floating photovoltaic (PV)-battery system powering a submerged light emitting diode (LED) lighting system. The system was designed to provide around the equivalent of 1000 lumens (lm) of light of the existing light fishing technology (a floating pressurised kerosene light) for artisanal light fishers to use for 8 h per night on Lake Victoria and other lakes in the region (Tanganyika, Rukwa, Mweru, Kivu, etc.). The net present cost (NPC) of a technically appropriate PV-battery-LED system was calculated as US$280 over 5 years, five-times less than the existing solar-based technology, a PV-battery-compact fluorescent lamp (CFL) system, and around ten times less than the baseline pressurised kerosene-based technology over the five years. Fishers owning the new PV-battery-LED system outright will likely recoup their initial investment within a year relative to the cost of alternatives, although the upfront capital cost of the new system was higher than the pressurised kerosene and PV-battery-CFL, and found to be practically unaffordable to the subsistence fishers without microcredit. Nonetheless, the technical simulations found that the new system was also able to provide additional lighting services during the day and evening, with little (if any) electrical impact on the system when in use for light fishing during the small hours of moonless nights. This research also demonstrates that the high cost of operating pressurised kerosene lamps precludes them for use in other applications within the community, including in homes. This research suggests that facilitated local development of appropriate new light fishing technology configurations will require training of local individuals to sensitise fishing communities to the new technology, and sustain wider adoption of the more efficient, cost-effective, and safer alternative.     

Magnetic pulse spot welding of bimetals

One of the main parameters in magnetic pulse welding (MPW) is the requirement of certain distance/spacing called “air gap” between the two sheets or tubes to be welded. This work presents means to alleviate this constraint through stamped humps in one of the sheets. The sheets remain in contact all over except at humps where a local air gap is sufficient to generate impact velocity required to produce spot welds using electromagnetic energy. The developed approach has been validated on the heterogeneous assembly of AA1199 aluminum to EN 355 steel. The microstructural analysis revealed that the weld interface is wavy and the waves are in two opposite directions from the center. Quasi-static tension–shear tests validated the joint efficiency of spot welds.     

Tracking control for magnetic-suspension systems with online unknown mass identification

This paper proposes a new nonlinear tracking control scheme with simultaneous unknown mass identification for magnetic suspension systems. Specifically, an amplitude-saturated adaptive control law is developed to achieve stable tracking and accurately estimate the unknown suspended mass simultaneously. The stability is assured with rigorous Lyapunov-based analysis. As far as we know, this is the first continuous control method for magnetic suspension systems with unknown levitated ball mass and actuator saturation, yielding an asymptotic result to achieve simultaneous tracking control and mass identification. Through hardware experiments, we verify the performance of the proposed method and compare it with existing methods.     

Enhancement of incorporated ferromagnetic nanoparticles content in nanocomposite electrodeposited coatings by gradient magnetic field

Electrodeposited NiCoMnP coatings incorporating ferromagnetic nanoparticles demonstrate excellent magnetic properties compared with plain metal and alloy. However, improving the weight per cent of ferromagnetic nanoparticles incorporated into nanocomposite coatings is still a challenge. In this paper, a gradient magnetic field has been applied to enhance the nanoparticles’ incorporation during composite electrodepositing. Both experimental and theoretical investigations on the effect of magnetic field on the content of nanoparticles incorporated into nanocomposite coatings were carried out. The results show that gradient magnetic field is favourable for incorporating ferromagnetic nanoparticles into coatings, and uniform or static magnetic field has almost no effect for enhancing codeposition of ferromagnetic nanoparticles into coatings. With gradient magnetic field, a maximum nanoparticles incorporation of 8·08 wt-%BaFe₁₂O₁₉ is observed in CoNiMnP–BaFe₁₂O₁₉ nanocomposite coatings deposited with a BaFe₁₂O₁₉ nanoparticles bath concentration of 40 g L^?1 at a current density of 2 A dm^?2.     

Improve the signal to noise ratio and installation convenience of the inductive coil for wire rope nondestructive testing

Inductive coil is used as the nondestructive testing sensor of a wire rope or a pipe, because of its low cost and high durability. However, the winding structure is complex and difficult to design during the field test. Hundreds or even thousands of turns are needed to improve the signal to noise ratio (SNR) and the data processing is cumbersome. In this paper, based on the theoretical analysis and 3D transient magnetic field simulation, a kind of iron core is presented as coil winding skeleton for the wire rope nondestructive testing. Additional iron core plays a role of magnetism concentration, where the magnetic flux leakage (MFL) path is changed and the MFL of the defect is converged to the core. Therefore, the SNR of the coil which is wound on the iron core is improved, and the coil winding skeleton is simplified with the iron core structure optimization. Meanwhile, the influence of the coil cross-section area on the test result analysis is eliminated, and the influence of the lift-off distance between coil and wire rope on the detection result is also reduced. Finally, it is proved by experiment that the SNR of coil with the iron core proposed in this paper is increased almost six times, which makes it easier for defect analysis.     

Effect of P on glass forming ability,magnetic properties and oxidation behavior of FeSiBP amorphous alloys

The effect of P on the glass forming ability, soft magnetic properties and oxidation behavior of Fe₇₈B₁₃Si_9-xP_x (x = 0–7) amorphous alloys were investigated. It is found that the proper introduction of P, can effectively improve the glass forming ability and stability of supercooled liquid region. Fe₇₈Si₄B₁₃P₅ BMG, which exhibits high saturation flux density of 1.56 T, was readily made into rod sample with a diameter of 1.5 mm under air casting atmosphere. P bearing alloys also exhibit excellent soft magnetic properties containing low coercivity of 1.7–2.7 A/m, and high effective permeability of 8200–12,200. Slight oxidation can further improve the coercivity to a lower value of 1.1 A/m and the higher effective permeability to 11,900 for the alloys with P content no more than 3 at. %. Excessive addition of P may deteriorate the glass forming ability, soft magnetic properties and oxidation behavior. Magnetic domain revealing the magnetization process of the amorphous ribbons were characterized to explain the effect of P on magnetic properties and oxidation behavior.     

Electromagnetic shielding effectiveness and mechanical property of polymer–matrix composites containing metallized conductive porous flake-shaped diatomite

The porous flake-shaped diatomite particles with different micropores diameter were used as forming templates for the fabrication of the conductive core–shell functional fillers by electroless silver plating. The surface morphologies and phase structures of the surface coatings onto diatomite particles with different micropores diameter were evaluated. The effects of micropores diameter on electrical resistivity, electromagnetic shielding effectiveness and mechanical property of polymer–matrix composites containing silver-coated diatomite particles were also investigated in detail. The results show that the micropores onto initial diatomite particles after plating are completely covered with the coating, while the micropores onto diatomite particles with expanding pores are still visible. The expanding micropores onto diatomite particles in certain size range have less impact on the phase structures, electrical resistivity and electromagnetic shielding effectiveness. However, the mechanical properties of composites are improved significantly after expanding micropores by HF acid corrosion.