High Output Power Research Articles

H Induced Metal‐Insulation Transition Boosts the Stability of High Temperature Polymer Electrolyte Membrane Fuel Cells

High temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) have garnered significant attention due to their expanded range of hydrogen sources and simplified management systems. However, the frequent start‐up and shut‐down (SU/SD) caused fuel starvation operation condition seriously deteriorates the performance and lifetime of the fuel cell. In this manuscript, VO2 was incorporated in the anode to restrain fuel starvation of the electrode. Under the operation condition, the insulative VO2 would reversibly transform into metallic HxVO2 by intercalating hydrogen, and HxVO2 can automatically release hydrogen, which could act as the hydrogen buffer and suppress reverse‐current degradation. After the hydrogen release, the generated insulating VO2 would prevent the side reactions during fuel starvation. Compared to the traditional Pt anode, the electrode with VO2 showed much higher output power and greatly improved durability after fuel starvation. This work demonstrates the in‐situ reversible hydrogen storage/release‐controlled metal‐insulator phase transition strategy to enhance the durability of fuel cells.

(Ultra)wide bandgap semiconductor heterostructures for electronics cooling

The evolution of power and radiofrequency electronics enters a new era with (ultra)wide bandgap semiconductors such as GaN, SiC, and β-Ga2O3, driving significant advancements across various technologies. The elevated breakdown voltage and minimal on-resistance result in size-compact and energy-efficient devices. However, effective thermal management poses a critical challenge, particularly when pushing devices to operate at their electronic limits for maximum output power. To address these thermal hurdles, comprehensive studies into thermal conduction within semiconductor heterostructures are essential. This review offers a comprehensive overview of recent progress in (ultra)wide bandgap semiconductor heterostructures dedicated to electronics cooling and are structured into four sections. Part 1 summarizes the material growth and thermal properties of (ultra)wide bandgap semiconductor heterostructures. Part 2 discusses heterogeneous integration techniques and thermal boundary conductance (TBC) of the bonded interfaces. Part 3 focuses on the research of TBC, including the progress in thermal characterization, experimental and theoretical enhancement, and the fundamental understanding of TBC. Parts 4 shifts the focus to electronic devices, presenting research on the cooling effects of these heterostructures through simulations and experiments. Finally, this review also identifies objectives, challenges, and potential avenues for future research. It aims to drive progress in electronics cooling through novel materials development, innovative integration techniques, new device designs, and advanced thermal characterization. Addressing these challenges and fostering continued progress hold the promise of realizing high-performance, high output power, and highly reliable electronics operating at the electronic limits.

Single-Longitudinal Mode Quadruple Wavelength C+L-Band Erbium-doped Fiber Laser Based on the Pairs of Reflective Fiber Bragg Gratings.

Abstract Flatness of lasing wavelengths of a multi-wavelength fiber laser (MWFL) is an important design constraint that is considered attractive in various applications of photonics and optical communication systems. In this work, we propose a single longitudinal mode (SLM) quadruple wavelength C+L-band Erbium-doped fiber laser (EDFL) with high output power flatness. It is implemented with a short piece of Erbium-doped fiber (EDF) pumped by conventional 980 nm laser diode and four pairs of reflective fiber Bragg gratings (FBGs) through numerical simulations. The reflectivities of FBGs are adjusted such that SLM quadruple wavelengths are obtained at the output of EDFL with flatness of 0.9 dB, optical signal-to-noise ratio (OSNR) of around 42 dB, and linewidths (LWs) in the range of 5.4-7.3 MHz. Slope efficiency (SE) of around 24% is achieved considering the total power of all lasing wavelengths generated. Moreover, the power variation around 0.1 dB for lasing wavelengths of 1540.2 nm and 1605.7 nm is noticed for twelve iterations each repeating after five-minute interval. The proposed SLM quadruple wavelength EDFL has promising application prospects for distributed sensing and optical communication systems due to excellent performance metrics.

Strategic modal management for enhanced stimulated Raman scattering in optical fibers

Raman fiber lasers have attracted significant attention for their unique ability to generate high-power output at specific wavelengths. Theoretically, the quantum loss associated with the nonlinear Stokes frequency shift in Raman scattering is lower than that from energy level transitions in conventional ytterbium-doped lasers, suggesting that Raman lasers should achieve higher conversion efficiencies. However, in practice, the efficiency of high-power Raman lasers often fails to reach these theoretical limits, with power scaling being impeded by 2 nd order Raman effects. In this article, we delve into the dynamics of stimulated Raman scattering within few-mode fibers, offering an in-depth analysis of the underlying physical mechanisms from multiple perspectives. Our research combines theoretical analysis with experimental research, covering the frequency domain, spatial domain, and nonlinear behavior. The experimental findings indicate that strategically increasing the proportion of higher-order modes in the injected light can enhance the conversion efficiency of the Raman process and effectively suppress higher-order Raman and four-wave mixing nonlinear processes. This study provides profound theoretical insights and practical guidance, contributing significantly to the ongoing development and optimization of Raman laser technology.

Hybrid Particle Size Template Method for Controllable Synthesis of Nitrogen-Doped Multilevel Porous Carbon as High-Rate Zn-Ion Hybrid Supercapacitor Cathode Materials.

Achieving high rate performance without compromising energy density has always been a critical objective for zinc-ion hybrid supercapacitors (ZHSCs). The pore structure and surface properties of carbon cathode materials play a crucial role. We propose utilizing a hybrid particle size (20 and 40 nm) magnesium oxide templates to regulate the pore structure of nitrogen-doped porous carbon derived from the soybean isolate. The multilevel pore structure enhanced ion transport efficiency while also improving the utilization of micropores. Nitrogen doping and oxygen-containing functional groups enhanced the wettability of carbon materials with aqueous electrolytes and facilitated the chemisorption of Zn2+ on the carbon material surface. The nitrogen-doped multilevel porous carbon material (HT-NMPC-1/1) prepared with a 1 : 1 mass ratio of the two templates exhibited a specific capacity of 146.65 mAh g-1 at 0.2 A g-1. Moreover, the Swagelok cells assembled with HT-NMPC-1/1 and Zn foil achieved a high energy density of 121.5 W h kg-1, high power output of 166 W kg-1, and 93.09 % capacity retention after 8000 cycles at 2 A g-1. Therefore, HT-NMPC-1/1 is a highly promising candidate for ZHSCs cathode materials. Furthermore, the novel pore regulation strategy and straightforward preparation method offer valuable reference points for other porous carbon-based functional materials.

Na3.5(MnVFeTi)0.5(PO4)3: A Multi‐Transition‐Metal‐Ion‐Engineered NASICON‐Type Cathodes for Sodium Ion Batteries

AbstractElectrochemically active Na‐superionic conductor (NASICON)‐type cathodes have the structural flexibility to include various transition elements, thus enabling high power outputs benefited by multi‐electron redox reactions. This study amalgamated multiple transition metal ions to construct a new NASICON‐type cathode i. e., carbon coated Na3.5(MnVFeTi)0.5(PO4)3 (NMVFTP/C) for Na‐ion batteries (NIBs). The NMVFTP/C cathode engineered in this study demonstrated stable Na+‐storage capacity, including long‐term cycling stability up to 4000 cycles at 3000 mA g−1 with 96 % capacity retention and a high‐rate output capacity of 85.16 mAh g−1 at 2500 mA g−1. To elucidate the ion transport process within the cathode, density functional theory modeling was employed. The low energy barrier for the diffusion of Na+ in the NMVFTP/C materials was proved to be a key factor supporting our material's superior electrochemical performances.

Electrode materials optimize operating voltage and switching speed in micro/nano plasma ultrafast devices

Abstract The trade-off between ultrahigh speed and low operating voltage is a major challenge in the continuous improvement of modern electronics. Although micro/nano plasma devices have demonstrated the potential of picosecond switching speed and high output power, surpassing traditional electronic devices, versatile methods for optimizing the operating voltage and switching speed are highly desired. Here, an optimization scheme based on the work function of the electrode materials is reported, which reduces the operating voltage and improves the switching speed. Compared with traditional methods, such as narrowing gaps or distorting electric fields, this approach offers advantages such as reducing production costs, enhancing consistency, and improving tunability. The experimental results show that using silver as a low-work-function electrode material can reduce the operating voltage by 55% to 180 V and increase the switching speed by 58% to 7.1 V ps−1 compared to platinum, which is equivalent to a 71% reduction in gap size. In addition, the underlying working mechanisms and inherent advantages of the approach are demonstrated, providing new insights for the ultrahigh switching speed and low-power application of micro/nano plasma devices, such as high-speed communication and ultrafast electronics.

A hybrid piezoelectric–electromagnetic body energy harvester: design and experiment validation

Abstract The rapid advancement of electronic devices and wireless sensors has heightened the demand for energy sustainability and portable power solutions. Traditional human energy harvesters have limitations in harvesting energy from ultra-low-frequency human motion due to issues related to unstable energy output and wearing comfort. To address this challenge, a piezoelectric–electromagnetic hybrid energy harvesting (HP-EEH) structure designed for the hip joint area. This innovative design employs magnetically coupled frequency boosting alongside electromagnetic energy capture to achieve high output power. Firstly, the structure and principle of the energy capture device are introduced, and the electromechanical coupling model of the energy harvester is derived using Hamilton’s principle. Furthermore, the system is numerically simulated, and the voltage output characteristics of the piezoelectric unit and the electromagnetic unit are analyzed by using the finite element analysis software. Finally, the experimental setup of the (HP-EEH) is constructed, and the voltage output characteristics are tested for different swinging angles and positions. The results show that two parts of energy can be captured simultaneously under ultra-low-frequency motion conditions. At a swing angle of 50 degrees, the piezoelectric and electromagnetic units achieved maximum output power values of 14.96 µW at 0.8 Hz and 10.4 µW at 1.2 Hz, respectively. Incorporating the output power of the electromagnetic unit aims to address the power consumption requirements of low-power devices better.

Impact of electron velocity modulation on microwave power performance for AlGaN/GaN HFETs

In this study, we demonstrate the effects of electron velocity modulation (Δve/ΔVgs) on the microwave power performance for AlGaN/GaN HFETs. In order to conduct the experiments, AlGaN/GaN HFETs with gate lengths ranging from 500 to 80 nm were fabricated. Electron transport was investigated by coupling a drift-diffusion solver with the Monte Carlo method. As gate lengths (Lg) varied from 500 to 200 nm, the increased polarization Coulomb field scattering led to an increase in Δve/ΔVgs and the stronger electric field (E) increased ve and enhanced the transconductance (gm), which in turn led to a greater power gain (Gp) in the HFETs. The higher power output (Pout) was also due to the increased ve that boosted the saturated output current (Ids,sat). The unique phenomenon that occurs from electron velocity modulation of AlGaN/GaN HFETs at electron densities (ns) < 3.42 × 1012cm−2 can be used as an effective mechanism to enhance the power gain of AlGaN/GaN HFETs.

Improved hole injection for AlGaN-based DUV LEDs with graded-composition multiple quantum barrier insertion layers

The primary impediments to achieving high external quantum efficiency (EQE) and light output power (LOP) in AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) are inadequate hole injection efficiency and pronounced electron leakage. The significant polarization-induced positive charges, originating from the discontinuity in the Al composition between the last quantum barrier (LQB) and electron-blocking layer (EBL), attract electrons, consume holes, and reflect holes back into the p-type region, leading to severe electron leakage and low hole injection efficiency. In this paper, we introduce a graded-composition multiple quantum barrier (GQB) structure at the LQB/EBL interface. We adjust the Al composition in the insertion layer to alter the electrical polarity of the polarization-induced sheet charges, thereby modifying the electric field distribution in the EBL, LQB, and inserted GQB structure. Consequently, holes acquire boosted energy during their migration towards the active region. In addition, we enhance the hole injection and electron confinement ability via reducing the effective valence band barrier height and increasing the effective conduction band barrier height, thus diminishing the possibility of electron leakage from the active region into the p-type region. Therefore, the GQB structure proposed in this study provides a promising approach to improving the optical and electrical performance of DUV LEDs.

Analysis, Design, and Optimization of Segment‐Compensated PCB Coil for Multirelay Wireless Power Transfer System

ABSTRACTThis paper proposed a segment‐compensated printed circuit board (PCB) coil for multirelay wireless power transfer (WPT) system. The PCB coil is designed with variable width to improve the system transfer efficiency, and the segmented compensation method is applied to avoid the high voltage stress on resonant capacitors in case of the multirelay WPT system with a low load resistance operating at a constant voltage frequency. The segmented compensation capacitors are integrated into the PCB coil, so as to constitute the compact coupler used in multirelay WPT system. The optimization procedure of the segment‐compensated PCB coil is also provided. The quality factor of the PCB coil can be improved by optimizing the proportional coefficients of width variation. The voltage of capacitors can be reduced by optimizing the number of segments. A physical variable‐width PCB coil with 3 segments is constructed. The experimental prototypes of the three‐coil, four‐coil, and five‐coil WPT systems are built. The experimental results show that the voltage of the segmented compensation capacitors on each coil is almost uniformly distributed and does not exceed 250 V when the input voltage is 50 V and the load resistance is 10 Ω. Compared with the multirelay WPT system using the equal‐width PCB coil, the multirelay WPT system using the PCB coil designed in this paper has higher output power and higher efficiency.

Research on the Advantages and Challenges of Replacing LEDs with Lasers in Functional Near-Infrared Spectroscopy Systems Based on Advanced Signal Processing Algorithms

Abstract: Functional near infrared spectroscopy (fNIRS) has received increasing attention as a non-invasive, portable brain hemodynamic monitoring tool due to its potential for use in natural Settings. Traditional fNIRS systems commonly use light-emitting diodes (LEDs) as light sources, which have become the mainstream choice because of their low cost, easy integration, low heat output, and availability of a variety of near-infrared wavelengths. However, LEDs are limited by their low optical output power and broad wavelength range, which restrict their effectiveness in deep tissue penetration and signal quality. In contrast, Laser Diodes (LD) have the advantages of good monochromaticity and high optical output power, which can provide deeper tissue penetration and higher signal stability. Therefore, this study explores the feasibility of using lasers instead of leds in fNIRS systems and their impact on signal quality and imaging depth. By comparing the performance of LED and laser-based fNIRS systems, it is evident that lasers provide significant improvements in signal quality and imaging depth, although they face challenges in terms of cost, thermal management, and safety. The research in this paper provides an important reference for the future design of fNIRS system, especially in the application scenarios requiring high precision imaging.

Highly Productive Laser Annealing Manufacturing Method Using Continuous Blue WBC (Wavelength Beam Combining) Technique.

Blue laser annealing can be used to obtain a high-mobility thin-film transistor (TFT) through a laser annealing (i.e., LTPS: low-temperature Poly-Si) process. However, the laser annealing process's low productivity (as well as high cost) is an issue because the high output power of blue lasers still needs to be addressed. Therefore, productivity can be improved if blue laser energy is efficiently supplied during the laser annealing process using a continuous wave laser instead of a conventional pulsed excimer laser. We developed a blue laser light source (440 ± 10 nm) using the wavelength beam combining (WBC) method, which can achieve a laser power density of 73.7 kW/cm2. In this semiconductor laser, when the power was increased s by 2.9 times, the laser scanning speed was increased by 5.0 times, achieving twice the productivity of conventional lasers. After laser annealing, the size of the crystal grains varied between 2 and 15 μm, resulting in a crystallization rate of 100% by Raman scattering rsult and low resistivity of 0.04 Ωcm. This increase in production capacity is not an arithmetic increase with increased power but a geometric production progression.

1010 nm Directly LD-Pumped 6kW Monolithic Fiber Laser Employing Long-Tapered Yb3+-Doped Fiber

Utilizing long-wavelength laser diodes (LDs) for pumping to achieve high-power fiber laser output is an effective method for attaining high quantum efficiency and excellent thermal management. In this work, we report on a Master Oscillator Power Amplifier (MOPA)-structured long-tapered Yb3+-doped fiber laser directly pumped by long-wavelength laser diodes. By shifting the center wavelength of the pump source to 1010 nm, the heat generation within the fiber laser is effectively controlled, thereby increasing the transverse mode instability (TMI) threshold. Additionally, the use of a long-tapered fiber enlarges the mode area and suppresses stimulated Raman scattering (SRS) effects that typically arise from increased fiber length. As a result, an output of 6030 W is achieved with an optical-to-optical (O–O) efficiency of 83.7%, a SRS suppression ratio exceeding 50 dB, and no occurrence of dynamic TMI. This approach provides a valuable reference for optimizing long-wavelength pumping to suppress nonlinear effects and also holds potential for wide-temperature operational applications.

13 μm emission InAs/AlSb quantum cascade lasers with high slope efficiency and peak output power enabled by diagonal transition design

Long wavelength InAs/AlSb quantum cascade lasers (QCLs) emitting at 13 μm, based on a diagonal transition scheme design through band structure engineering, have been grown and fabricated. This band structure engineering focuses on enhancing transition efficiency and suppressing carrier leakage. Our 3-mm-long, 25-μm-wide InAs/AlSb QCL has achieved a slope efficiency of 210 mW/A and a maximum peak power of 515 mW, despite encountering a substantial waveguide loss of 27 cm−1 and a relatively high threshold of 4.8 kA/cm2, due to the elevated residual doping level. Our InAs/AlSb QCL devices have demonstrated record-breaking performance in terms of slope efficiency, maximum peak power, and injection efficiency. Cavity length analysis suggests that reducing the residual doping by half could pave the way for achieving continuous wave output power in the realm of hundreds of milliwatts at room temperature for our designed 13 μm QCLs.

Simulated investigation of a ku-band relativistic magnetron with modified all-cavity axial extraction at a low magnetic field

Since its invention in 1921 by Hull, magnetrons have undergone rapid development, transitioning from low-power devices to high-power relativistic magnetrons (RMs). However, research on RMs has been predominantly confined to L-X bands until now. To explore the potential of RM in higher frequency bands and align with the trend toward miniaturization of high-power microwave sources, a Ku-band RM has been investigated in this paper. Theoretical analysis dictates the selection of 24 cavities for optimal performance at a low magnetic field. Utilizing a three-dimensional particle-in-cell simulation platform, we demonstrate that the RM can generate a microwave power of 116 MW at a resonant frequency of 13.717 GHz with an electron beam of 126 kV and 2.0 kA, under a magnetic field of 0.22 T, corresponding to a power conversion efficiency of 46%. The integration of a modified all-cavity axial extraction structure in the Ku-band RM allows for a minimized inner radius of the magnetic field system to approximately 25 mm, while maintaining a high-power microwave output.

Design and analysis of a hundred-watt G-band traveling wave tube

In this paper, a hundred-watt level traveling wave tube operating in the G-band is designed and analyzed. A non-semi-arc folded waveguide (FW) slow wave structure (SWS) is adopted to achieve high output power. Compared with the conventional FW, this structure has a higher coupling impedance, which is beneficial for beam–wave interaction. To further improve the efficiency of beam–wave interaction, phase velocity taper technology is adopted in SWS. A diamond pill-box output window is designed for electromagnetic wave input and output in SWS. In addition, the electron optics including a Pierce electron gun and a periodic permanent magnet focusing system are designed for emitting and constraining the electron beam. Using CST PIC solver for simulation, the results show that under a 23 kV and 80 mA electron beam, the maximum output power of the SWS is 132.7 W and the saturated gain is 36.5 dB. The bandwidth for output power greater than 100 W is 12 GHz. A pill-box window is designed and fabricated, and experimentally measured S11 is better than −13 dB and S21 is better than −1.3 dB in 213–229.5 GHz. The electron optics generate 79 mA current at 23 kV voltage.

Energy harvesting properties for potassium-sodium niobate piezoceramics through synergistic effect of phase structure and texturing engineering

In order to address the energy dilemma and meet environmental protection requirements, it is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs). However, the low output power density has seriously hindered the application of lead-free piezoceramics as high efficiency energy harvesters. To solve above question, the combination of phase structure regulation and texturing technique in the K0.5Na0.5NbO3-xBi0.5Na0.5ZrO3-0.5%wtBiFeO3 (KNN-xBNZ) ceramics was adopted in this work. Because of both the Rhombohedral-Orthorhombic-Tetragonal (R-O-T) multiphases coexistence and texturing engineering, an ultrahigh piezoelectric activity quality factor d33×g33 ∼ 18324 ×10-15 m2·N-1 was achieved in the textured KNN-0.05BNZ (T-KNN-0.05BNZ) ceramics, which is about third times higher than that of random KNN-0.05BNZ (R-KNN-0.05BNZ) (d33×g33 ∼ 6672 ×10-15 m2·N-1) ones. A high output power of ∼ 0.32 mW was also obtained in the T-KNN-0.05BNZ ceramics by cantilever beam-based energy harvester devices under the resonance frequency of 75 Hz and matched RL of 1.2 MΩ, suggesting that the T-KNN-0.05BNZ ceramics have a great potential for application in the PEHs devices. This result also reveals that the combination of phase structure regulation and texturing technique is an effective way to achieved a high energy harvesting performances.

Analyzing the performance of metaheuristic algorithms in speed control of brushless DC motor: Implementation and statistical comparison.

A brushless DC (BLDC) motor is likewise called an electrically commutated motor; because of its long help life, high productivity, smaller size, and higher power output, it has numerous modern applications. These motors require precise rotor orientation for longevity, as they utilize a magnet at the shaft end, detected by sensors to maintain speed control for stability. In modern apparatuses, the corresponding, primary, and subsidiary (proportional-integral) regulator is broadly utilized in controlling the speed of modern machines; however, an ideal and effective controlling strategy is constantly invited. BLDC motor is a complex system having nonlinearity in its dynamic responses which makes primary controllers in efficient. Therefore, this paper implements metaheuristic optimization techniques such as Whale Optimization Algorithm (WOA), Particle Swarm Optimization (PSO), Ant Colony Optimization (ACO), Accelerated Particle Swarm Optimization (APSO), Levy Flight Trajectory-Based Whale Optimization Algorithm (LFWOA); moreover, a chaotic map and weight factor are also being applied to modify LFWOA (i.e., CMLFWOA) for optimizing the PI controller to control the speed of BLDC motor. Model of the brushless DC motor using a sensorless control strategy incorporated metaheuristic algorithms is simulated on MATLAB (Matrix Laboratory)/Simulink. The Integral Square Error (ISE) criteria is used to determine the efficiency of the algorithms-based controller. In the latter part of this article after implementing these mentioned techniques a comparative analysis of their results is presented through statistical tests using SPSS (Statistical Package for Social Sciences) software. The results of statistical and analytical tests show the significant supremacy of WOA on others.

A new Q-band comb-based multi-channel microwave Doppler backward scattering diagnostic developed on the HL-3 tokamak

Abstract The Doppler backscattering (DBS) diagnostic is widely used to measure the localized density fluctuations and the propagation velocity of turbulent structures. Microwave is launched at a frequency that approaches a cutoff layer in the plasma and at an angle that is oblique to the cutoff layer. A new Q-band multichannel DBS system based on a comb generator has been designed and tested for application on the HL-3 tokamak. With the comb generator and heterodyne scheme, the stability and flexibility of the new DBS system are improved. The new DBS diagnostic has a high output power (~ 10 dBm), good power flatness (< 5 dB in Q-band) and frequency stability, and the inter-frequency separation is tunable remotely. This article introduces the system design, laboratory test results, and initial experimental results from the HL-3 tokamak. With the help of the newly developed multichannel DBS, the turbulence information can be studied with high temporal and spatial resolution.