Abstract Due to the fast development of modern high-frequency electronics, great attention has been paid to materials that can shield electromagnetic interference (EMI) and absorb the electromagnetic waves as these materials should be lightweight rather than heavy and highly reflective as the metallic shielding. In this study, a floating catalyst chemical vapor deposition (FCCVD) method was adopted to synthesize grapheneated carbon nanotubes (g-CNTs) in a simple one-step process without the use of any substrate. For assessing some of their electrodynamic properties, g-CNTs were added to an epoxy matrix with mass fractions from 5 to 20 wt% along with pristine CNT fillers. Characterization was made of the EMI shielding performance and complex permittivity through a Vector Network Analyzer in the X-band region (8-12GHz) and Ku-band region (12-18GHz). The total shielding effectiveness (SET) of the composite with 20 wt% g-CNTs was evaluated to be as high as 62.71 dB in Ku band which was much higher than its pristine CNT counterparts at the same loading. This superior attenuation is due to absorption-dominated mechanism (SEA >> SER). The improved performance has been attributed to the unique hierarchical foliates of the g-CNTs that induce a microscopic impedance gradient for reducing surface reflection and the complex 3-dimensional architecture of g-CNTs that acts as the volumetric trap to improve the interfacial polarization and the loss of conduction. Hence, the g-CNT/epoxy composites offer a very promising direction for ultra-efficient electromagnetic attenuation, positioning them as strong candidates for high-frequency telecommunication and portable-electronics applications.
Abstract A dual-chamber gas–liquid phase dielectric barrier discharge (DBD) reactor with tri-electrodes was designed for air-fed nitrogen fixation (NF). Air was activated in the gas-phase discharge chamber to produce NOx, and these NOx species continued to synthesize aqueous nitrate species in the gas–liquid discharge chamber. The effect of electrode configuration, applied voltage, air flow rate, initial solution pH, electric discharge duration on the concentration, selectivity of nitrate/nitrite/ammonia, total nitrogen concentration (TNC) and energy yield of NF was studied. The results showed that the DBD reactor with tri-electrodes efficiently produced microdischarges for N2 fixation of high nitrate selectivity at higher applied voltage. The initial pH of water in lower discharge chamber had little effect on the input power but significantly impacted on the transfer and conversion of gaseous NOx into aqueous nitrate, and a weak alkaline pH was more favorable for total nitrogen accumulation. Meanwhile, the input air flow rate in DBD reactor and the water volume in lower discharge chamber showed an optimum value, and the energy yield of total nitrogen fixation reached a maximum 0.84 g·kWh-1 at an initial solution pH 11 and a water volume of 35 mL. The optical emission spectrum in discharge regions indicated that the nitrogen fixation results at different applied voltage and air flow rate can be attributed to their influence on the production of N2*, N2+, and •OH and the experiments including electron quenching and dry air discharge indicated that NH4+ was mainly produced via the reduction of N2 by hydrated electrons.
Abstract Driven by increasingly demanding applications, research into understanding degradation mechanisms and improving the reliability of edge-emitting quantum-well GaAs-and GaN-based laser diodes has become an important parameter for advancing these devices. This paper presents an overview of results from aging and reliability studies on GaAs-and GaN based laser diodes manufactured at the Ferdinand-Braun-Institute. The results are organized into three main topics: First, semiconductor-related effects, where gradual degradation and sudden failures are analyzed by studying the impact of operating conditions on electro-optical properties, combined with material analysis techniques such as scanning electron microscope, cathodoluminescence, and transmission electron microscope of degraded and failed devices. Second, facet related degradation, where the impact of facet preparation technologies on laser diode degradation behavior is examined. Third, a review of statistical methods aimed at predicting the lifetime of these devices through empirical and physics-based modeling approaches.
Abstract We report polarization-controlled nonlinear dynamics in a weakly optically injected 1550 nm vertical-cavity surface-emitting laser (VCSEL). At a fixed injection ratio of 2%, the frequency detuning between the master laser and the free-running VCSEL is scanned while the injected state of polarization is varied among near-linear, elliptical, and near-circular states. Although injection is weak, injected polarization strongly modifies the competition between the two orthogonal linearly polarized modes of the VCSEL. Near-linearly polarized injection mainly produces polarization switching and four-wave mixing spectral features, whereas elliptically polarized injection expands the region of irregular chaos dynamics. Near-circularly polarized injection gives rise to a comb-like state with nearly equally spaced optical components and discrete RF-noise features. Spin-flip-model simulations qualitatively reproduce the measured state map and suggest that the nearly balanced vectorial coupling of the injected field to the two polarization channels promotes the observed multi-frequency dynamics. These results reveal that polarization provides an efficient control parameter for accessing distinct nonlinear dynamics in VCSELs even under weak optical injection, offering a potential low-power approach for polarization-controlled nonlinear photonic functionalities and the generation of comb-like spectral structures.
Abstract Kilovolt-level flexible wearable electronic systems are in critical demand for advanced applications spanning healthcare, human-machine interaction, and soft robotics. This paper proposes a flexible high-voltage pulsed power supply based on a multi-stage collaborative step-up architecture. Constructed on the flexible substrate, the power supply integrates a front-end DC Boost converter, a solid-state half-bridge pulse modulator, and an input-parallel output-series micro-transformer network. It employs a non-uniform layout strategy that combines the localized concentration of rigid components with serpentine routing to buffer mechanical deformation. Furthermore, multiphysics finite element models encompassing electric, thermal, and solid mechanics fields were established to systematically validate the design rationale. Experimental evaluations demonstrate that the developed prototype delivers microsecond pulses with a peak voltage amplitude of up to 4.5 kV and a rise time of 250 ns. The highly compact prototype features a total footprint of 13.92 cm 2 and a weight of 5.1 g, while sustaining macroscopic bending angles of up to 120°. Notably, the prototype successfully drives a cold plasma load with an active area of 20 cm 2 . This work validates the novel concept of a flexible kilovolt-level pulsed power supply, overcoming the inherent voltage bottlenecks of wearable electronics and providing a critical hardware foundation for frontier applications such as chronic wound healing, deep neuromodulation, and soft robotics. These results demonstrate the feasibility of a flexible kilovolt-level pulsed power platform and provide an implementation pathway for future flexible systems requiring localized high-electric-field excitation.
