High Output Power Research Articles

Exploring challenges and potential for a commercially viable piezoelectric energy harvesting system—Can Energy-as-Data concept thrive?

Over the past two decades, piezoelectric energy harvesting systems have undergone extensive research, spanning from materials to devices and electronics. Recently, there has been a notable introduction of the term “self-powered sensors,” which essentially refers to conventional, older passive sensors, associated with piezoelectric (or triboelectric) nanogenerators. Unfortunately, neither approach has yet yielded a successful market example. The primary challenge seems to lie in the intermittent nature of ambient kinetic energy input to these harvesters, despite the high output power density of piezoelectric energy harvesters. This article emphasizes the concept of Energy-as-Data, holding promise for a potentially brighter future for commercializable piezoelectric energy harvesting systems. The key advantage offered by this concept is the substantial extension of battery life through the optimization of data acquisition protocols. This involves transitioning from the traditional passive sensing mode with a high sampling rate to an extremely low duty cycle. This transition allows the harvested energy, accumulated in an energy storage unit over a specific interval, to be translated into critical information regarding kinetic environmental changes during that period. The article also discusses the broader context that necessitates the Energy-as-Data concept, establishing it as one of the few viable pathways to cultivate specialized markets for piezoelectric energy harvesting.

Relative Intensity Noise in a Two‐Section Distributed Bragg Reflector Tapered Laser

The relative intensity noise (RIN) in a two‐section distributed Bragg reflector (DBR) tapered laser emitting around 1060 nm is being studied experimentally. By analyzing the RIN spectra, a resonance frequency and damping is obtained. Herein, the dependence of the resonance frequency and the maximum RIN at the resonance frequency is studied as functions of the ridge waveguide (RW) and tapered section currents independently. The low frequency RIN is approximately −162 dB Hz−1, and the RIN peak at currents providing high output power is as low as −154 dB Hz−1. The observed nonlinearity of the squared resonance frequency with the RW section current is attributed to carrier saturation. The measured high values of the resonance frequency, exceeding 2.5 GHz for RW currents higher than 100 mA at a tapered current of 3 A, indicate gain lever enhancement.

Continuous-wave and Fe2+:ZnSe passively Q-switched mid-infrared lasers based on 2at.% Er3+:CaF2 crystal

A compact high-power 2.8-µm laser with a 2 at.%-doped Er3+:CaF2 crystal was demonstrated, which delivered a maximum output power of 2.848 W with a slope efficiency of 26.3 %. To the best of our knowledge, this is the highest output power among all the reported LD end-pumped Er3+-doped fluoride crystal lasers. Experimentally, the negative thermal lens effect was characterized and the thermal lens optical diopters for two axes were obtained as Mx = -0.21 m−1/W and My = -0.33 m−1/W. In addition, the visible fluorescence spectra of Er3+:CaF2 crystal with and without laser operation were measured and analyzed. With Fe2+:ZnSe as saturable absorber, a passively Q-switched 2.759-µm Er3+:CaF2 laser with an average output power of 75 mW, a peak power of 2.39 W, a single pulse energy of 1.81 µJ, and a pulse width of 755.3 ns was obtained at a repetition rate of 41.55 kHz.

Ultrafast Optical Encoder Using Photonic Crystal Ring Resonator

ABSTRACT In this paper, we design and simulate a two-dimensional photonic crystal-based high speed logical encoder for optical computing application. The encoder consists of a ring resonator, four waveguides and two reflectors arranged in a hexagonal lattice platform. The optical encoder works on the interference effect which guides the propagation of light in the desired path. The light behavior is simulated with four different logic states. The Plane Wave Expansion (PWE) method is used to analyze the band gap and Finite Difference Time Domain (FDTD) analyzes the performance characteristics of the encoder, such as bit rate, delay time, and contrast ratio. The proposed structure has a footprint area of 143.84 µm2. The small compact size structure with simple defect paths reduces the encoder delay time, which in turn increase the data bit rate. The response time of the proposed encoder is 0.119 ps and bit rate is 8.403 Tbps. The encoder is designed with very low output power in “0” logic state and high output power in “1” logic state leading to high contrast ratio of 22.57 dB. Therefore, highly efficient 4 × 2 optical encoder is suitable to build in optical integrated circuits.

Triboelectric nanogenerator based on multi-component crosslinked network hydrogel for intelligent human motion sensing

With the continuous development of intelligent wearable devices, new requirements are put forward for the collection of human motion information. In this paper, a self-powered motion sensor with high precision, high stability and high output power was prepared by utilizing the flexibility and stretchability of the conductive hydrogel and combining with the nanogenerator. Even at a contact frequency of 3.0 Hz, the sensor can produce an open circuit voltage of 225 V and a power density of 187 mW m−2. It can not only be used as a power source to drive electronic devices, but also to achieve accurate acquisition of human movement steps and walking speed. When applying different forces, the sensor shows a more obvious difference, and its theoretical resolution can reach 0.1 N. Because the hinge hydrogel has good flexibility, resilience and stability, it can still maintain its original shape after 4000 times of pressure testing, and can be directly attached to the human skin surface, providing a new idea for the field of self-powered pressure sensors.

Improving Sustainability in Urban and Road Transportation: Dual Battery Block and Fuel Cell Hybrid Power System for Electric Vehicles

Improving Sustainability in Urban and Road Transportation: Dual Battery Block and Fuel Cell Hybrid Power System for Electric Vehicles

High-performance PCW-DFB laser diodes using offset quantum well epitaxial structures.

We demonstrated a high-performance partially corrugated waveguide distributed feedback (PCW-DFB) laser with high output power, low relative intensity noise (RIN) and narrow linewidth. By introducing offset quantum-well structure that provides enough threshold gain difference for single transverse mode operation, the laser can achieve single mode behavior with an 8-µm-wide ridge waveguide. The laser has been designed by the simulation model based on the coupled wave equations, and the fabricated PCW-DFB laser with the cavity length of 1.3 mm exhibited an output power higher than 190 mW. Stable single mode characteristics have been achieved with a side-mode suppression-ratio (SMSR) over 55 dB. The RIN was less than -160.5 dB/Hz at an injection current of 470 mA, and the linewidth reached 45 kHz.

A novel nanocomposite of MXene/cadmium azide with high detonation performance

A novel MXene/cadmium azide nanocomposite with a low input energy and high output power is designed by self-assembly of Cd ions on the MXene layers and subsequent in situ azidation in a solution reaction. The research result shows that cadmium azide nanoparticles with a uniform size of ∼50 nm are well dispersed on the MXene nanosheet’s surface, which is benefited from the rich functional groups on the MXene surface that can effectively immobilize and prevent the aggregation of the nanoparticles through electrostatic interaction. The thermal decomposition temperature (378.42 °C) and crystal structure of cadmium azide show no noticeable change after hybridizing with the MXene; more positively, the required input energy of the MXene/cadmium azide nanocomposite is significantly reduced, which is verified by its electric initiation input voltage of just 4.65 V. In addition, detonation can be realized by loading a less amount of the MXene/cadmium azide nanocomposite. These results demonstrate that the MXene/cadmium azide nanocomposite has the potential to be used as detonators in high-temperature environments.

975 nm multimode semiconductor lasers with high-order Bragg diffraction gratings

The 975 nm multimode diode lasers with high-order surface Bragg diffraction gratings have been simulated and calculated using the 2D finite difference time domain (FDTD) algorithm and the scattering matrix method (SMM). The periods and etch depth of the grating parameters have been optimized. A board area laser diode (BA-LD) with high-order diffraction gratings has been designed and fabricated. At output powers up to 10.5 W, the measured spectral width of full width at half maximum (FWHM) is less than 0.5 nm. The results demonstrate that the designed high-order surface gratings can effectively narrow the spectral width of multimode semiconductor lasers at high output power.

Fully nonlinear three-dimensional modeling of parametric interactions in the field of a dual-frequency acoustic array.

An algorithm is developed for fully nonlinear three-dimensional (3D) simulation of a difference-frequency acoustic beam resulting from the interaction of two high-intensity pump waves. Simulations are performed in the frequency domain based on the Khokhlov-Zabolotskaya-Kuznetsov equation. A spectrum filtering method is used to enable accurate solutions for the difference-frequency fields in strongly nonlinear beams and with a high downshift frequency ratio using only dozens of spectral components retained in the algorithm. As an example, the dual-frequency operation of an underwater multi-element ellipsoidal array is considered, and numerical solutions describing parametric interactions in the array field are analyzed. It is shown that difference-frequency beams are more symmetric in transverse directions compared with the pump beams. The most efficient parametric generation of difference-frequency beams corresponded to close and beyond shock-forming conditions. Axial pressure amplitude of the difference frequency was shown to grow first quadratically with the source pressure following the quasi-linear solution and then linearly once shocks start to develop. The percentage of the total power converted to the difference frequency from pump waves increased at high power outputs without saturation. Up to twofold increase in directivity angles of difference-frequency beams under shock-forming conditions was observed compared with quasi-linear conditions.

Pulsed Optical Vortex Array Generation in a Self-Q-Switched Tm:YALO3 Laser.

Optical vortex arrays are characterized by specific orbital angular momentums, and they have important applications in optical trapping and manipulation, optical communications, secure communications, and high-security information processing. Despite widespread research on optical vortex arrays, the 2 μm wavelength range remains underexplored. Pulsed lasers at 2 μm are vital in laser medicine, sensing, communications, and nonlinear optic applications. The need for 2 μm-pulsed structured optical vortices, combining the advantages of this wavelength range and optical vortex arrays, is evident. Therefore, using just three elements in the cavity, we demonstrate a compact self-Q-switched Tm:YALO3 vortex laser by utilizing the self-modulation effect of a laser crystal and a defect spot mirror. By tuning the position of the defect spot and the output coupler, the resonator delivers optical vortex arrays with phase singularities ranging from 1 to 4. The narrowest pulse widths of the TEM00 LG0,-1, two-, three-, and four-vortex arrays are 543, 1266, 1281, 2379, and 1615 ns, respectively. All the vortex arrays in our study have relatively high-power outputs, slope efficiencies, and single-pulse energies. This work paves the way for a 2 μm-pulsed structured light source that has potential applications in optical trapping and manipulation, free-space optical communications, and laser medicine.

Superior specific capacity and energy density simultaneously achieved by Sr/In co-deposition behavior of Mg-Sr-In ternary alloys as anodes for Mg-Air cells

In this work, the combined addition of strontium/indium (Sr/In) to the magnesium anode for Mg-Air Cells is investigated to improve discharge performance by modifying the anode/electrolyte interface. Indium exists as solid solution atoms in the α-Mg matrix without its second-phase generation, and at the same time facilitates grain refinement, dendritic segregation and Mg17Sr2-phases precipitation. During discharge operation, Sr modifies the film composition via its compounds and promoted the redeposition of In at the substrate/film interface; their co-deposition behavior on the anodic reaction surface enhances anode reaction kinetics, suppresses the negative difference effect (NDE) and mitigates the “chunk effect” (CE), which is contributed to uniform dissolution and low self-corrosion hydrogen evolution rate (HER). Therefore, Mg-Sr-xIn alloy anodes show excellent discharge performance, e.g., 0.5Sr-1.0In shows an average discharge voltage of 1.4234 V and a specific energy density of 1990.71 Wh kg−1 at 10 mA cm−2. Furthermore, the decisive factor (CE and self-discharge HE) for anodic efficiency are quantitively analyzed, the self-discharge is the main factor of cell efficiency loss. Surprisingly, all Mg-Sr-xIn anodes show anodic efficiency greater than 60% at high current density (≥10 mA cm−2), making them excellent candidate anodes for Mg-Air cells at high-power output.

Unlocking superior safety, rate capability, and low-temperature performances in LiFePO4 power batteries

The safety concerns associated with lithium-ion batteries (LIBs) have sparked renewed interest in lithium iron phosphate (LiFePO4) batteries. It is noteworthy that commercially used ester-based electrolytes, although widely adopted, are flammable and fail to fully exploit the high safety potential of LiFePO4. Additionally, the slow Li+ ion diffusion and low electronic conductivity of LiFePO4 batteries limit their utility in high-power applications. Despite the crucial role played by liquid electrolytes in LIBs, achieving simultaneous improvements in safety, rate capability, and low-temperature performance remains a formidable challenge. In this study, we addressed these challenges by innovatively applying a single solvent ethyl vinyl sulfone (EVS) electrolyte to graphite/LiFePO4 batteries. While renowned for its broad electrochemical window, low freezing point and superior safety performance, the EVS electrolyte exhibited compatibility issues with the graphite anode. To overcome this hurdle effectively, we utilized vinylene carbonate as an additive with lower reductive reactivity than EVS to modify the interphase formed by EVS successfully. Simultaneously, the EVS-based electrolyte was found to create a sulfone-rich interphase on the LiFePO4 cathode surface, significantly enhancing Li+ ion diffusion both across the interphase and within the material. These modifications culminated in a conspicuous improvement in the performance of graphite/LiFePO4 batteries. Our study illuminates the potential of EVS-based electrolytes in boosting the rate capability, low-temperature performance, and safety of LiFePO4 power lithium-ion batteries. It yields valuable insights for the design of safer, high-output, and durable LiFePO4 power batteries, marking an important stride in battery technology research.

A C-Core Connected Two-Phase Switched Reluctance Motor With Embedded Permanent Magnets for Developed Torque Enhancement

Conventional switched reluctance motors (SRMs) face challenges like low torque density and high noise. To overcome these challenges, the structure of SRMs can be modified. This paper introduces a new hybrid-excited 16/18 two-phase SRM with a C-core structure. Each pole of the C-core has two teeth, which develop a positive torque during the rotor rotation; this enhances the torque and torque density of the motor. To show the merits of the proposed SRM with PMs, its static and dynamic characteristics, including flux density, flux-linkage, and torque, are obtained and compared with the SRM with no PMs, the 8/12 two-phase conventional SRM, and other motors with the same volume; a significant match was achieved. Finally, both proposed SRMs were prototyped and tested. Comparing the simulation and test results elucidates that the proposed SRM with PMs has unique high output power, torque, and efficiency.

All-Automated Fabrication of Freestanding and Scalable Photo-Thermoelectric Devices with High Performance.

Flexible photo-thermoelectric (PTE) devices have great application prospects in the fields of solar energy conversion, ultrabroadband light detection, etc. A suitable manufacturing process to avoid the substrate effects as well as to create a narrow transition area between p-n modules for high-performance freestanding flexible PTE devices is highly desired. Herein, an automated laser fabrication (ALF) method is reported to construct the PTE devices with rylene-diimide-doped n-type single-walled carbon nanotube (SWCNT) films. Thewet-compressing approach is developed to improve the thermoelectric power factors and figure of merit (ZT) of the SWCNT hybrid films. Then, the films are cut and patterned automatically to make PTE devices with various structures by the proposed ALF method. The freestanding PTE device with a narrow transition area of ≈2-3 µm between the p and n modules exhibits a high-power density of 0.32 µW cm-2 under the light of 200 mW cm-2, which is among the highest level for freestanding-film-based PTE devices. The results pave the way for the automatic production process of PTE devices for green power generation and ultrabroadband light detection.

Design of enlarged-asymmetric-power single-mode silicon evanescent lasers with asymmetric distributed feedback gratings

Great achievements in the bonded III–V lasers have pushed the productization process of silicon photonic chips. In this work, we report the design of silicon evanescent lasers with asymmetric gratings, which can provide high output power and stable single-longitudinal-mode operation. The high coupling efficiency and low threshold current density are achieved by linearly expanding the width of rib waveguide from 0.4 µm to 2 µm through 150 µm taper coupler. By optimizing the λ/4 phase-shift position ratio from conventional 0.50 to 0.64, the ratio of output power at both sides of the bonded lasers (P2/P1) is improved from1.0 to 5.0, and the normalized grating coupling coefficient (κL) remains at 2.78. By optimizing the duty cycle at one side of λ/4 phase-shift from 0.5 to 0.8 and another side remains at 0.5, P2/P1 is 3.3, and κL lowers from 2.78 to 2.21. Besides, keeping the phase-shift position ratio at 0.64 while changing the duty cycle to 0.7, P2/P1 increases significantly to 7.5 with κL of 2.59. This work provides a step forward towards the development of high-power silicon-based light sources.

Improving temperature characteristics of GaN-based ultraviolet laser diodes by using InGaN/AlGaN quantum wells.

Temperature characteristics of GaN-based laser diodes are investigated. It is noted that the characteristic temperature of the threshold current (T0) decreases with decreasing lasing wavelength for GaN-based LDs. The performance deteriorates seriously for UV LDs at high temperature. It is ascribed to the increase of carriers escaping from quantum wells due to the lower potential barrier height. In this Letter, AlGaN is used as the barrier layer in UV LDs instead of GaN to improve the temperature characteristic of the threshold current and slope efficiency by increasing the potential barrier height of quantum wells. Based on this structure, a high output power of 4.6 W is obtained at the injection current of 3.8 A; its lasing wavelength is 386.8 nm.

High Thermoelectric Performance and Flexibility in Rationally Treated PEDOT:PSS Fiber Bundles

Organic thermoelectric fibers have great potential as wearable thermoelectric textiles because of their one-dimensional structure and high flexibility. However, the insufficient thermoelectric performance, high fabrication cost, and mechanical fragility of most organic thermoelectric fibers significantly limit their practical applications. Here, we employ a rapid and cost-effective wet-spinning method to prepare dimethyl sulfoxide-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) fiber bundles, followed by rational post-treatment with concentrated sulfuric acid (98% H2SO4) to enhance their thermoelectric performance. The wearable fiber bundles composed of multiple individual PEDOT:PSS fibers have effectively reduced resistance and overall high tensile strength and stability. Rational treatment with H2SO4 partially removes excessive PSS, thereby increasing the electrical conductivity to 4464 S cm‒1, while the parallel bundle is also a major factor in improving the power factor of up to 80.8 μW m‒1 K‒2, which is super-competitive compared with those of currently published studies. Besides, the thermoelectric device based on these fiber bundles exhibits high flexibility and promising output power of 2.25 nW at a temperature difference of 25 K. Our work provides insights into the fabrication of all-organic flexible high-conductivity textiles with high thermoelectric properties.Graphical

Thermoelectric and magneto-transport characteristics of interconnected networks of ferromagnetic nanowires and nanotubes

Macroscopic-scale nanostructures, situated at the interface of nanostructures and bulk materials, hold significant promise in the realm of thermoelectric materials. Nanostructuring presents a compelling avenue for enhancing material thermoelectric performance as well as unlocking intriguing nanoscale phenomena, including spin-dependent thermoelectric effects. This is achieved while preserving high power output capabilities and ease of measurements related to the overall macroscopic dimensions. Within this framework, the recently developed three-dimensional interconnected nanowire and nanotube networks, integrated into a flexible polymer membrane, emerge as promising candidates for macroscopic nanostructures. The flexibility of these composites also paves the way for advances in the burgeoning field of flexible thermoelectrics. In this study, we demonstrate that the three-dimensional nanowire networks made of ferromagnetic metals maintain the intrinsic bulk thermoelectric power of their bulk constituent even for a diameter reduced to approximately 23 nm. Furthermore, we showcase the pioneering magneto-thermoelectric measurements of three-dimensional interconnected nickel nanotube networks. These macroscopic materials, comprising interconnected nanotubes, enable the development of large-area devices that exhibit efficient thermoelectric performance, while their nanoscale tubular structures provide distinctive magneto-transport properties. This research represents a significant step toward harnessing the potential of macroscopic nanostructured materials in the field of thermoelectrics.

Electrochemical performance of symmetric solid oxide cells employing a Sc-doped SrFeO3-δ-based electrode

Symmetrical solid oxide cells (SSOCs) integrate the capabilities of solid oxide fuel cells and solid oxide electrolysis cells within a symmetric device, which have the advantage of simple fabrication and lower cost compared to conventional devices. Herein, to develop more advanced electrode materials to meet the catalytic activity for different electrode reactions, this study explores Sc-doped Sr0.9Fe0.8Sc0.1Co0.1O3−δ (SFSC) as an SSOC electrode material. Experiments show that Sc doping enhances the crystal stability of Sr0.9Fe0.9Co0.1O3−δ (SFC) in H2 and provides more oxygen vacancies for CO2 adsorption. Electrochemical tests reveal that the SFSC-Gd0.1Ce0.9O1.95 (GDC) electrode offers high power output, high CO2 electrolysis rates, and stability. Specifically, when operated as a fuel cell, the thus fabricated SSOC exhibits a peak power density of 781 mW·cm−2 and a polarization resistance of 0.117 Ω·cm2 at 850 °C, with operational stability over 300 h. Additionally, it reaches a peak current density of 1.96 A·cm−2 at 850 °C for CO2 electrolysis and is stable for 200 h at 0.45 A·cm−2 and 800 °C. Ab initio simulations further reveal a higher probability for oxygen vacancies in SFSC and an improved catalytic dissociation ability relative to Sr0.9Fe0.9Co0.1O3−δ for hydrogen and CO2. The stable and multi-functional SFSC-GDC electrode thus represents a compelling choice for SSOCs, advancing the prospects for efficient and cost-effective energy solutions.