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Journal of Physics D: Applied Physics - latest papers

Latest articles for Journal of Physics D: Applied Physics

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  • Numerical simulation of cathode-spot crater and droplet formation with linear and circular motion process
    In this paper, a three-dimensional cathode spot erosion model is proposed to study the development of cathode spot motion process on the surface of copper cathode. The formation and development process of cathode spots motion without external magnetic field is studied. In this model, energy flux density, pressure, and current value are considered as external parameters. The simulation results compared the cathode spot ablation trajectories and temperature distribution under different motion forms and motion velocities. The results indicated that during the spots expansion process, the flow of liquid metal will form a convex structure on the surface of the cathode and a hollow structure inside the cathode. Comparing different motion types, the annular motion significantly increased the roughness of the cathode surface. With the increase of the speed of spots movement, the interaction between the craters is significantly weakened, which will reduce the temperature and the roughness of the cathode surface. The simulation results are consistent with the experimental results.

  • Streamer propagation dynamics in a nanosecond pulsed surface dielectric barrier discharge in He/N2 mixtures
    An atmospheric pressure surface dielectric barrier discharge in helium–nitrogen mixtures is investigated experimentally using phase-resolved optical emission spectroscopy and computationally employing a two-dimensional simulation framework. A good qualitative agreement between experiments and simulations is found. It is shown that by applying microsecond or nanosecond driving voltage waveform pulses, the discharge exhibits filamentary or homogeneous structures. The time evolution/propagation of the homogeneous surface ionization wave for different nitrogen admixtures, pressures, and applied voltage is studied and analyzed. Both, simulations and experiments indicate that for the positive applied voltage pulse, a streamer possessing the typical dynamics of the positive streamer is ignited on the powered side of the electrode. At the same time, on the grounded sides, two streamers are formed: one possessing the dynamics of a negative streamer, which propagates towards the center of the cell of the electrode grid, and a positive one in the opposite direction. It is also shown that the positive streamers on the powered side are partly responsible for the velocity of the negative streamers on the grounded side. Simulations show a deceleration of the negative streamers as soon as two positive streamers collide and then close to the meeting point vanish due to the repulsive electrostatic interactions between them. Additionally, from the time-resolved measurements of the emission signal, the quenching rate constants of the He–I (3 s) 3S1 state by collisions with helium and nitrogen are determined to be cm3 s−1 and cm3 s−1, respectively at K.

  • High permittivity electroluminescence coating for improving flashover strength and visualizing surface defects
    In gas-insulated switchgear, the metallic particles on spacers initiate discharges and significantly reduce flashover strength. It is crucial to sensitively detect surface defects and improve the flashover strength. In this work, a high permittivity electroluminescence coating with ZnS:Cu as fillers and cyanoethyl cellulose (CEC) as polymer matrix was developed to improve flashover strength and visualize surface defects. The dielectric constant, flashover strength, and electroluminescence properties of ZnS:Cu/CEC coatings with different concentrations of ZnS:Cu fillers were tested and the underlying mechanism was investigated. Due to the strong-polarity cyanide group in CEC and the effect of ZnS:Cu fillers on polymer chains, a high-permittivity coating was obtained, which can effectively mitigate the electric field distortion on spacers, and improve the flashover performance. For the basin insulator, maximum increments of flashover strength were realized by doping 12.5 wt% ZnS:Cu fillers, with 11.36%, 31.22%, and 5.83% improvements in air, 0.3 MPa air, and SF6 gas, respectively. Moreover, the electroluminescence coating can effectively indicate the location of defects and the distribution of electric field on the surface of insulators. This paper provides new insight into the electroluminescent materials used in non-destructive self-testing of surface defects and enhancement of flashover strength.

  • Photoluminescence intensity enhancement of nanorod micro-LEDs via localized surface plasmon coupling
    Nano-light-emitting diodes (LEDs) are ideal for ultra-high resolution displays due to their small size and high pixel density. However, traditional photolithography techniques fall short in meeting the requirements for nanoscale LED fabrication. Besides, as the size decreases and the specific surface area increases, non-radiative recombination generated by sidewalls defects becomes a significant issue, affecting the efficiency of nano-LEDs. To address this challenge, a nano-LED array with a single nanorod size of 800 nm was fabricated in this work by using nanosphere lithography and etching technology. Meanwhile, localized surface plasmons (LSPs) coupling technology was employed to enhance the PL efficiency of these nano-LEDs. By comparing with bare nano-LEDs, the PL intensity was boosted by about 43% and 129% when Ag and Ag@SiO2 nanoparticles were added separately. The existence of LSPs coupling process has been further confirmed through time-resolved photoluminescence measurement and finite element simulation analysis of different samples. The results provide compelling evidence for the LSPs coupling technology in enhancing the efficiency of nanoscale LEDs.

  • Programmable metasurface based phase-modulating reflector for 2.4 GHz wireless communications
    This paper presents an innovative programmable metasurface structure that achieves precise phase control within the 2–2.7 GHz frequency range by adjusting the state of varactor diodes embedded in the unit cells. The design employs a single diode, which simplifies the structure, reduces manufacturing costs, and minimizes reflection loss. At 2.4 GHz, the metasurface achieves 1-bit phase responses of 0° and 180°, with a reflection amplitude exceeding 0.72, demonstrating excellent reflective performance. Moreover, as the 2.4 GHz frequency is closely related to wireless communication bands, this programmable metasurface shows significant potential in the field of wireless communication encryption. By integrating dual varactor diodes, the design enables 2-bit phase control with reflection phase angles of 0°, 90°, 180°, and 270°. To validate the design, a 1-bit metasurface structure was fabricated and tested, with experimental results showing a high degree of consistency with simulations, highlighting the potential of this structure in enhancing wireless communication security.