Power Density Range Research Articles

Effect of Substrate Thinning on Temperature Rise in Ga2O3 Rectifiers

The low thermal conductivity of β-Ga2O3 is a concern for the high-power switching applications envisaged for this ultra-wide bandgap semiconductor. In this work, we examine the effect of substrate thinning to reduce the temperature rise in rectifiers under high power conditions and also reduce the on-resistance. The Ga2O3 substrates on which the rectifiers were fabricated were thinned from the original thickness of 630 μm to a lowest value of 50 μm and transferred to a brass heat sink. Experimentally, we observed that the on-resistance was reduced from 5.66 to 5.17 mΩ.cm2 when thinning to 50 μm, in excellent agreement with simulations. The calculated peak temperature rise was roughly halved for rectifiers on such thin substrates over a broad range of power densities (500–1500 W.cm2), a result supported by thermal imaging.

Enhanced and tunable near-field thermophotovoltaics driven by hybrid polaritons

Near-field thermophotovoltaics (NF-TPV) offers the potential for achieving elevated power density and conversion efficiency by leveraging the amplification of thermal radiation within a nanoscale gap. Here, we propose an NF-TPV device with a sandwich emitter composed of calcite film and graphene layer. The results show that this sandwich configuration can significantly enhance output power, outperforming monolayer-graphene-covered heterostructures and the single calcite film. These are because the sandwich configuration can enhance hybrid polaritons, which are formed by the coupling between surface plasmon polaritons in graphene and hyperbolic phonon polaritons in calcite. In addition, the effects of graphene chemical potentials on the performance of NF-TPV devices are also studied. The tunable power density range of the sandwich structure can be up to 3.26 times that of other structures by altering the chemical potential of graphene. The findings presented here may unpack a promising path for enhancing and manipulating the performance of NF-TPV at the nano- and microscale.

Variation of carrier lifetime with optical excitation power density in micro-LEDs

GaN-based micro-LEDs are applied to visible light communication due to their high modulation bandwidth with reduced chip size. It requires a deep understanding of recombination processes and their impact on the bandwidth, which is mainly determined by the carrier lifetime. We employed confocal time-resolved photoluminescence (TRPL) to characterize the variation of carrier lifetime with optical excitation power density on micro-LEDs. We observed an initial increase followed by a sudden decrease within the power density range of 96.7 kW/cm2 to 546 kW/cm2 on a blue micro-LED with a chip size of 80 µm. We attribute this phenomenon to increased optical excitation power, gradually saturating the defect-dominated non-radiative recombination centers, with radiative recombination processes gradually taking over. We compared the power density at the inflection point for different regions on the sample and the samples with different sizes and sidewall structures. The power density for the lifetime inflection point at the center of the sample is smaller than that at the edge. We also find that the value is smaller for the sample with a chip size of 40 µm which prompts fewer total defects. The power density for sudden lifetime drop on samples with inclined sidewall structures is also smaller than those with vertical sidewall structures. Furthermore, we find that the excitation power density corresponding to the highest luminous efficiency is higher than that corresponding to the sudden drop at the beginning of the lifetime. This opens up possibilities for simultaneously achieving high modulation bandwidth and high efficiency between the two inflection points.

Tracking of cogging stiffness using the multi-bin SDFT

Due to the high power density and wide speed range, a permanent magnet synchronous motor (PMSM) is commonly used in industry. Efficient production requires optimized motion control of the mechanism driven by the PMSM. Unfortunately, designing the controller is usually based on a model of the mechanism without including parameters originating from the motor. Cogging stiffness originates from the magnetic forces between rotor magnets and stator teeth and is one of these forgotten parameters. The performance is sub-optimal when this stiffness is not considered during control design. The stiffness also changes over time due to changing load conditions such as temperature. Aiming for optimized motion control of high-speed mechanisms, this article proposes to expand the classic motion controller with an on-line stiffness tracker. The tracker is based on the sliding discrete Fourier transform (SDFT). The tracking technique is conceptually analyzed and experimentally validated on a PMSM-driven rod. The classic Welch technique having an update time of at least 100 s is used as a benchmark. With similar accuracy and a much faster update time of 1.25 ms, the stiffness is tracked on-line using SDFT. The developed stiffness tracker is implemented on the provided commercial motion controller, proving its computational efficiency.

Design and Analysis of an Interior Permanent Magnet Synchronous Motor for a Traction Drive Using Multiobjective Optimization

With the development of new energy industries, the demand for the driving range and power quality of electric vehicle (EV) drive systems is growing rapidly. The drive motor is faced with the challenge of continuously improving power density and performance. This paper proposes a multiobjective optimization method for an interior permanent magnet synchronous motor for a traction drive (IPMSMTD). Based on the flat wire winding technology, the multiobjective optimization design of the IPMSMTD is carried out to improve the motor power density and high-efficiency range, reduce the torque ripple, and suppress the electromagnetic vibration and noise. The structure and size equation of the IPMSMTD are described. The mathematical model considering iron losses is established, and the optimization objectives are determined. Based on the genetic algorithm, a multiobjective optimization mechanism of the magnetic pole structure is established. The operation performance of the motor is analyzed by the finite element simulation and efficiency map. In order to ensure the comprehensive operation index of the IPMSMTD, the vibration noise and modal analysis are carried out, which verifies the rationality of the designed motor and the optimization method.

Review on the impact of cell phone radiation effects on green plants.

The aim of this review is to assess the impact of cell phone radiation effects on green plants. Rapid progress in networking and communication systems has introduced frequency- and amplitude-modulated technologies to the world with higher allowed bands and greater speed by using high-powered radio generators, which facilitate high definition connectivity, rapid transfer of larger data files, and quick multiple accesses. These cause frequent exposure of cellular radiation to the biological world from a number of sources. Key factors like a range of frequencies, time durations, power densities, and electric fields were found to have differential impacts on the growth and development of green plants. As far as the effects on green plants are concerned in this review, alterations in their morphological characteristics like overall growth, canopy density, and pigmentation to physiological variations like chlorophyll fluorescence and change in membrane potential etc. have been found to be affected by cellular radiation. On the other hand, elevated oxidative status of the cell, macromolecular damage, and lipid peroxidation have been found frequently. On the chromosomal level, micronuclei formation, spindle detachments, and increased mitotic indexes etc. have been noticed. Transcription factors were found to be overexpressed in many cases due to the cellular radiation impact, which shows effects at the molecular level.

Laser Melting of Mechanically Alloyed FeNi: A Study of the Correlation between Microstructure and Texture with Magnetic and Physical Properties.

The current study attempts to establish the interrelation between microstructure and magnetic properties induced during laser melting of the FeNi alloy. This study demonstrates the optimization of laser parameters for defect-free, uniform, and chemically homogeneous FeNi alloy synthesis. Mechanically alloyed FeNi (50-50 atom %) powders obtained after 12 and 24 h milling, with average particle sizes of 15 and 7 μm, were used as starting materials. It was found that the optimum range of laser power density for synthesis of dense and defect-free solids is between 1 and 1.4 J/mm2. For laser melting under similar conditions, 12 h milled FeNi powder produces a larger grain (∼100 μm) with a preferred texture of (001), compared to 25 μm grain size in 24 h milled FeNi, with random texture. Smaller grain size is correlated with higher resistance to domain wall movement, resulting in higher coercivity and remanence in the laser-melted samples prepared from 24 h of milled powder. The presence of microtexture in laser-melted samples prepared from 12 h milled powder is related to a higher anisotropy.

Explore the growth mechanism of high-quality diamond under high average power density in the MPCVD reactor

Investigating the mechanism behind the high-efficiency deposition of high-quality diamond has always been a prominent topic in related research. This paper investigates the CH4-H2 plasma characteristics and related chemical reaction kinetics in the average power density range of 18–100 W·cm−3, which is a typical range for large-area diamond film deposition. The number densities of H, CH3 and C2H2 increase linearly with the average power density. C2H2 is the main hydrocarbon in the discharge, and CH3 is the main single-carbon hydrocarbon. The number density and radial uniformity of CH3 and C2H2 increase with the average power density, which is necessary for the high rate and uniform deposition of diamond films. The plasma's optical emission spectra indicate an acceleration in the C2 production rate at high power density. The diamond film deposition experiment demonstrates the efficacy of high average power density in achieving high-quality diamond deposition at a high growth rate.

Anode surface engineering of zinc-ion batteries using tellurium nanobelt as a protective layer for enhancing energy storage performance

Over the years, zinc-ion batteries (ZIBs) have attracted attention as a promising next-generation energy storage technology because of their excellent safety, long cycling performance, eco-friendliness, and high-power density. However, issues, such as the corrosion and dissolution of the Zn anode, limited wettability, and lack of sufficient nucleation sites for Zn plating, have limited their practical application. The introduction of a protective layer comprising of tellurium (Te) nanobelts onto the surface of Zn anode has emerged as a promising approach to overcome these limitations and improve the electrochemical behavior by enhancing the safety and wettability of ZIBs, as well as providing numerous nucleation sites for Zn plating. In the presence of a Te-based protective layer, the energy power density of the surface-engineered Zn anode improved significantly (ranging from 310 to 144 W h kg−1, over a power density range of 270 to 1,800 W kg−1), and the lifespan capability was extended. These results demonstrate that the proposed strategy of employing Te nanobelts as a protective layer holds great promise for enhancing the energy storage performance of ZIBs, making them even more attractive as a viable energy storage solution for the future.

Beam-profile compensation for quantum yield characterisation of Yb-Tm codoped upconverting nanoparticles emitting at 474 nm, 650 nm and 804 nm.

Upconverting nanoparticles (UCNPs) have found widespread applications in biophotonics and energy harvesting due to their unique non-linear optical properties arising from energy transfer upconversion (ETU) mechanisms. However, accurately characterising the power density-dependent efficiency of UCNPs using the internal quantum yield (iQY) is challenging due to the lack of methods that account for excitation beam-profile distortions. This limitation hinders the engineering of optimal UCNPs for diverse applications. To address this, this work present a novel beam profile compensation strategy based on a general analytical rate-equations model, enabling the evaluation of iQY for ETU processes of arbitrary order, such as ETU2, ETU3, and beyond. The method was applied to characterise the ETU2 and ETU3 processes corresponding to the main emission peaks (474 nm, 650 nm, and 804 nm) of a Yb-Tm codoped core-shell β-UCNP. Through this approach, the transition power density points (which delimit the distinct non-linear regimes of the upconversion luminescence (UCL)), and the saturation iQY values (which are reached at high excitation power densities above the transition points) were determined. The ETU2 process exhibits a single transition power density point, denoted as ρ2, while the ETU3 processes involve two transition points, ρ2 and ρ3. By compensating for the beam profile, we evaluate the iQY of individual lines across a wide dynamic range of excitation power densities (up to 105 W cm-2), encompassing both non-linear and linear regimes of UCL. This study introduces a valuable approach for accurately characterising the iQY of UCNPs, facilitating a deeper understanding of the upconversion and its performance. By addressing excitation beam-profile distortions, this method provides a comprehensive and reliable assessment of the power density-dependent iQY. The results highlight the applicability and effectiveness of this beam profile compensation strategy, which can be employed for a wide range of UCNPs. This advancement opens new avenues for the tailored design and application of UCNPs in various fields, especially for biophotonics.

Nitrogen-sulfur co-doped ZIF-8-derived carbon materials for supercapacitors with low self-discharge

Supercapacitors (SCs) have attracted extensive attention due to the properties of high power density, long cycle life, and high rate performance. However, the high self-discharge is one giant challenge for long-term energy storage applications of SC. Herein, we prepared a high-performance SC with low self-discharge based on nitrogen-sulfur co-doped ZIF-8-derived (NS-PC) materials. The synergistic effects of high-temperature carbonization and nitrogen-sulfur (N-S) doping are systematically investigated. With a carbonization temperature of 900 °C, assisted with N-S doping, the maximum specific capacitance of the NS-PC-900//NS-PC-900 symmetrical SC is 42.7 F g−1, while the power densities range from 650 to 13,000 W kg−1 at the energy densities of 10.04–7.5 Wh kg−1. The specific capacitance remains 95.7 % even after 20,000 charge-discharge cycles. More importantly, the as-prepared NS-PC-900//NS-PC-900 SC exhibits an ultra-low self-discharge rate of solely 0.025 V h−1 within 24 h. This work provides a universal strategy to fabricate high-performance SCs with low self-discharge.

A Comparison of Low-Temperature Deposition for SiO2 in PECVD Using SiH4 and TEOS

We have developed a method for depositing SiO2 as an insulating layer at temperatures below 100°C using PECVD. This method has potential applications in the development of flexible displays and organic transistors. We have previously reported on TSV via-hole formation by the Bosch process and TEOS-SiO2 deposition on sidewall by PECVD at 150°C [1]. In this study, we performed PECVD using a power supply frequency of 400 kHz. The deposition temperature was set at 100°C. We compared the deposition rates and the film stress of SiO2 films deposited using SiH4 and TEOS at different RF power densities.Figure 1 shows the relationship between 400 kHz power and the deposition rates. In this power density range, the deposition rate of SiH4 was almost constant at approximately 52 nm/min regardless of power density. On the other hand, the rate using TEOS tended to decrease as the power density increased above 0.28 W/cm2.Figure 2 shows the film stress of each film immediately after deposition and after few days of atmospheric exposure. The minus side of the stress indicates compressive stress. The stress of SiH4 was -50 to -70 MPa immediately after deposition; however, after few days of atmospheric exposure, the stress shifted by approximately -50 MPa at all power densities. On the other hand, in the case of TEOS, the stress did not change at approximately -120 MPa at a power density of 0.18 W/cm2 or higher immediately after deposition; however, after few days of exposure, the amount of change to the compressive stress side became smaller as the power density increased. It has been reported that the change in stress to the compressive side is influenced by moisture in the atmosphere [2]. The small change in stress is considered to mean that the film is denser, and that moisture is less likely to enter the film. The deposition rate is considered to decrease during the process of film densification.In summary, it is thought that by increasing the power density with TEOS-SiO2, a dense film is formed even at a low temperature of 100°C.

Universal Approach to Integrating Reduced Graphene Oxide into Polymer Electronics.

Flexible electronics have sparked significant interest in the development of electrically conductive polymer-based composite materials. While efforts are being made to fabricate these composites through laser integration techniques, a versatile methodology applicable to a broad range of thermoplastic polymers remains elusive. Moreover, the underlying mechanisms driving the formation of such composites are not thoroughly understood. Addressing this knowledge gap, our research focuses on the core processes determining the integration of reduced graphene oxide (rGO) with polymers to engineer coatings that are not only flexible and robust but also exhibit electrical conductivity. Notably, we have identified a particular range of laser power densities (between 0.8 and 1.83 kW/cm2), which enables obtaining graphene polymer composite coatings for a large set of thermoplastic polymers. These laser parameters are primarily defined by the thermal properties of the polymers as confirmed by thermal analysis as well as numerical simulations. Scanning electron microscopy with elemental analysis and X-ray photoelectron spectroscopy showed that conductivity can be achieved by two mechanisms-rGO integration and polymer carbonization. Additionally, high-speed videos allowed us to capture the graphene oxide (GO) modification and melt pool formation during laser processing. The cross-sectional analysis of the laser-processed samples showed that the convective flows are present in the polymer substrate explaining the observed behavior. Moreover, the practical application of our research is exemplified through the successful assembly of a conductive wristband for wearable devices. Our study not only fills a critical knowledge gap but also offers a tangible illustration of the potential impact of laser-induced rGO-polymer integration in materials science and engineering applications.

Investigation of output performance and temperature distribution uniformity of PEMFC based on Pt loading gradient design

Temperature distribution uniformity within the cathode catalyst layer (CCL) and power density are two crucial parameters to characterize the durability and output performance of proton exchange membrane fuel cells (PEMFCs), which are affected by the Pt distribution within the CCL. Therefore, the temperature distribution uniformity within the CCL and the output performance at different operating voltages for a PEMFC with various Pt loading gradient distributions along the in-plane (IP) direction are investigated in this paper. Moreover, a two-dimensional, two-phase, non-isothermal model is developed, and the concepts of high power density range (HPDR) and temperature uniformity index (TUI) are defined in this study. The results indicate that gradient Pt distribution has the opposite effect on output performance and temperature distribution uniformity at low and medium operating voltages; the improvement of one indicator means the deterioration of another. Besides, the optimal output performance is obtained with the uniform Pt distribution at high operating voltages, while the ideal temperature distribution uniformity is achieved by loading more Pt under the channel. Consequently, the output performance and temperature distribution uniformity must be traded off to obtain optimal comprehensive performance of PEMFC at different operating voltages when designing the Pt loading gradient distribution.

Color Tuning and Optical Temperature Sensing Properties of Upconversion Emission in Yb3+/Er3+/Tm3+Doped Boro-Zinctellurite Glasses

Zinc borotellurite (B2O3/BaO/ZnO/TeO2) glasses co-doped with Tm3+/Yb3+, Er3+/Yb3+ and tri-doped Tm3+/Er3+/Yb3+ were prepared using the traditional melt quenching method. Optical absorption spectra were measured in the wavelength range of 350 nm-1100 nm at room temperature. The optical bandgap (Eg) and Urbach energy were calculated from Tauc’s plot. Blue and green emissions that can be seen by the naked eye were generated under 975 nm laser light excitation in doped Tm3+/Yb3+ and Er3+/Yb3+ doped glasses. Shifts in both blue and green color coordinates were seen as the excitation power density increased from 0.5 to 15.1 W cm−2. A white light generation was generated in glass doped with Tm3+/Er3+/Yb3+ ions, although a noticeable shift was not observed in both blue and green color coordinates for the same excitation power density range. Temperature sensing properties were investigated using the fluorescence intensity ratio of upconversion green emissions from the two thermally coupled 2H11/2 and 4S3/2 levels of Er3+ ions between 304 K and 443 K. The maximum sensitivity of the glasses doped with Er3+ and Er3+/Yb3+ were found to be 7.2 × 10−3 K−1 and 1.2 × 10−2 K−1 at 429 K, respectively.

Laser-Induced Graphene Formation on Chitosan Derivatives toward Ecofriendly Electronics

Laser-induced graphene (LIG) has aroused a wide range of research interests ranging from micro-nano energy devices to the Internet of Things (IoT). Nevertheless, the non-degradability of most-used synthetic polymer carbon sources poses a serious threat to the environment. In this work, ecofriendly chitosan-based derivatives, including carboxymethyl chitosan (CMCS), chitosan oligosaccharide, and chitosan hydrochloride, are successfully converted into LIGs for the first time via a convenient one-step CO2 laser engraving at ambient air. The obtained LIGs are characterized by a three-dimensional hierarchical porous structure and exhibit good sheet conductivity. The consecutive carbonization and graphitization mechanism of target precursors induced by laser heat accumulation is also deeply discussed. Besides, based on a mechanically reliable LIG/CMCS composite film and tribo-negative acrylic/polyimide anti-layers, two contact-separation mode triboelectric nanogenerators are built and their power densities range from 1.44 to 2.48 mW cm–2. These devices with long cycle life can be used for low-frequency mechanical energy harvesting and commercial capacitance charging, which could be potentially applied in the wireless sensor network nodes. Such a family of chitosan derivatives paves a new route for LIG synthesis and provides new ideas for ecofriendly LIG electronics.

Design and Multiobjective Optimization of Dual-Circulation Cooling System Considering Electro-Thermal Coupling for IPMSM

Benefiting from high power density, high reliability, and wide speed range, interior permanent magnet synchronous motors (IPMSM) have received unprecedented attention. However, due to torque ripple and heat dissipation difficulties caused by the compact structure, the development of IPMSM is not smooth in high-end applications such as electric vehicles. In this article, a dual-circulation cooling system consisting of an external housing water-cooling cycle and an internal rotor-stator air-cooling cycle based on improved magnetic circuit design is innovatively proposed. While the electromagnetic characteristics are substantially improved, the temperature rise problem is also significantly suppressed and weakened. Furthermore, to further optimize multiphysics performance for the IPMSM equipped with this system, an improved multiobjective optimization model considering electro-thermal coupling is studied. Optimization effect is greatly improved by the flexible application of segmented orthogonal experiments, correlation/interaction analysis, and intelligent surrogate model/advanced algorithm. Computational fluid dynamics (CFD) and finite element analysis (FEA) highlight the advantages of proposed dual-circulation cooling system and improved optimization model. Their design rationality, effectiveness, and engineering practicability have been well verified through a series of comparative analyses.

Engineering interfaces to facilitate charge transport pathways in electrospun scaffolds for high-performance, flexible supercapacitors

Understanding and engineering the interface of a polymeric matrix with the ionic conductor offers important insights into the electrochemical charge polarization performance of flexible solid-state supercapacitors. These aspects are captured herewith utilizing chemically identical yet morphologically and interfacially different and distinct non-woven, electrospun polymeric membranes as scaffolds. Three distinct variations achieved through electrospinning namely, bilayered (PU/Ge) and core-shell geometries (PU@Ge and Ge@PU) with polyurethane (PU) and gelatin (Ge) are utilized in both conditions as polymeric electrolyte membranes for flexible supercapacitors. Equally important is the unique graphenic nanoplatelets (GNPs), fabricated through a single-step, template-driven approach, providing synergistic electrode/electrolyte interfaces. We unravel distinct changes in charge transport mechanism brought out by the interplay between surface chemistry and morphology of the electrospun scaffolds. The all-solid-state symmetric supercapacitor devices assembled with GNP@CC electrodes and PU/Ge, PU@Ge or Ge@PU polymeric membrane electrolyte of 1 M H3PO4 or EMIMBF4 are studied.Accordingly, the charge transport is protic and aprotic observed to switch from interfacial driven in the case of PU@Ge with H3PO4 to distinct phase separated ion transport channels in the case of PU/Ge with EMIMBF4. Thereby, a range of energy density (1.03–21.94 Wh kg−1), power density (0.049–99.97 kW kg−1) and scan rate operability (5–10,000 mV s−1) are demonstrated in such devices without any compromise on the cyclability. This study establishes rational design principles for tailoring the ion transport mechanism in a variety of matrices and thereby opens transformative possibilities for realizing high performance energy storage devices.

Electron beam weld penetration depth prediction improved by beam characterisation

Predicting the penetration depth during electron beam welding (EBW) is important, but the accuracy of current predictive models is highly varied, depending on the type and number of data used. This paper develops and compares several penetration depth prediction models for EBW and uniquely compares the influence of the number and type of data used, as well as the measurement and modelling methods. Although accelerating voltage, beam current and welding speed data are essential modelling inputs, additional data for beam focal position and beam shape, measured using a novel 4-slit beam probing method, greatly improve the accuracy of predictions for models based on an empirical equation, a second-order regression and an artificial neural network (ANN). Optimised models predict weld depths that deviate, on average, by less than 5% from measured depths, are valid for very broad linear electron beam power density ranges (86–324 J/mm) and are close to the estimated 4% inherent variability in the process and its measurement. Within this linear electron beam power density range, the ANN yields accurate and reliable depth predictions, demanding as few as 36 welding trials, decreasing the number required for models that do not consider beam focal position and shape, for the same targeted accuracy, by more than 60%. Adding large volumes of virtual data generated by less reliable analytical or regression models did not improve the predictive capability for the ANN developed in this study.

Multi-objective optimization of high torque density spoke-type PM machine for special vehicle drive system

PurposeThis paper proposes a spoke-type fractional-slot concentrated windings (FSCW) permanent magnet (PM) machine for special vehicle driving systems to obtain higher torque and power density, high efficiency and wide field-weakening range. To enhance the efficiencies of multi-objective optimization processes, the respond surface (RS) method and black-hole (BH) algorithm are used.Design/methodology/approachThe spoke-type FSCW PM machine is optimized to meet the requirements of the special vehicle driving system. The combination of the RS and BH algorithm is used to obtain high torque, low torque ripple and high efficiency.FindingsThe optimal spoke-type PM machine is obtained, and it has higher torque density, lower torque ripple, cogging torque and wider magnetic field weakening range. Finally, a 15-kW prototype machine is fabricated and tested to verify the results of the optimization method and finite-element analysis.Originality/valueThis paper designs a high torque density and efficiency spoke-type FSCW PM machine, which is superior for special vehicle driving systems. Meanwhile, the RS model combined with BH algorithm is applied to the field of electrical machine multi-objective optimal design.