Large Output Power Research Articles

Survey of terahertz photonics and biophotonics

We review the advances of terahertz (THz) science and technology in biophotonics, including related challenges and solutions. The main impediment to THz spectroscopy and imaging in this field is the high absorption of the THz beam in water. Hence, transmission imaging and spectroscopy of thick wet tissue using THz radiation has generally been quite difficult. However, the absorption of THz waves by water molecules is so strong that increasing the power of the THz source can lead to structural and functional changes in tissues, so solutions must go beyond a larger power output. In terms of resolution, THz imaging is superior to ultrasound but inferior to visible light microscopy. Owing to its unique material analysis capabilities, promising diagnosis applications have been demonstrated through THz imaging and spectroscopy. Unfortunately, many applications are limited by beam penetration depth and resolution. Hence, researchers from a wide variety of scientific and technical fields have been actively improving these features through the development of electronic devices and materials. In addition, groundbreaking optical architecture and materials to reduce beam absorption in the optics of a system and generate focused beams with smaller diameters have been proposed. On the software side, image processing techniques to computationally enhance the resolution and quality of THz imaging have been proposed. Data science and machine learning to automate the diagnosis of defects and diseases through processing THz images and spectroscopy data have been proposed. We have reviewed the applications of THz radiation in biophotonics and research achievements toward advancing these applications. A conclusion with a roadmap toward increasing the footprint of the THz technology in biophotonics is also proposed.

Study on thermal effect of mid-infrared single-ended bonded Tm LuAG laser crystals

This paper has established thermal models for mid-infrared single-ended bonded Tm: LuAG laser crystal based on different crystal topographies and has analyzed the temperature distribution in the crystal under different crystal topographies used COMSOL software. The thermal stress distribution in the crystal under different morphology, the thermal stress distribution at different locations, the volumetric strain of the crystals under the thermal stress and the temperature distribution have been analyzed. Experimental verification has been carried out. With the increase of the pumping power, the bonded slab crystal had larger output power, but the lower pump power it can withstand. The threshold power, output power, and slope efficiency of bonded rod-shape crystals were similar to those of bonded block crystals. This article has been provided an effective theoretical support for choosing the cutting morphology of single-ended bonded Tm: LuAG crystal, which can provide better output performance.

A Review of Technology Development of Thermionic Energy Conversion for Space Application

Space nuclear reactor power can supply the large output and long life power required by future space missions. The technology of thermionic energy conversion is one of the major key points of space thermionic nuclear reactor power. The whole construction and operating principle of space thermionic nuclear reactor power are summarized. And the development state, exsiting issues, and trend are reviewed for the technology of thermionic energy conversion, including the principle of thermionic energy conversion, varieties and characteristic of thermionic cell, electrode material, and experimental apparatus.

Compensation Parameters Optimization of Wireless Power Transfer for Electric Vehicles

For wireless charging of electric vehicles (EVs), increasing the output power level is particularly important. In this paper, the purpose of improving the output power while maintaining optimal transmission efficiency is achieved by optimizing the parameters of the compensation topology under the premise that the coupled coils of the system does not need to be redesigned. The series-series (SS) and hybrid-series-parallel (LCC, composed by an inductor and two capacitors) compensation topology are studied. The influence factors of load resistance to achieve optimal efficiency, the influence of LCC compensation parameters on the power output level, and the influence of parameter changes on system safety are analyzed. Theorical results show that by rationally designing the LCC compensation parameters, larger output power and optimal transfer efficiency can be achieved under different load resistance by adjusting the inductances of the primary and secondary compensation circuits. The output power of the optimized system with adjusted LCC compensation topology is increased by 64.2% with 89.8% transfer efficiency under 50 ohms load in experiments. The correctness and feasibility of this parameter design method are verified by both theorical and experimental results.

VS2 as saturable absorber for Q-switched pulse generation

Abstract Transition metal dichalcogenides have been widely utilized as nonlinear optical materials for laser pulse generation applications. Herein, we study the nonlinear optical properties of a VS2-based optical device and its application as a new saturable absorber (SA) for high-power pulse generation. Few-layer VS2 nanosheets are deposited on the tapered region of a microfiber to form an SA device, which shows a modulation depth of 40.52%. After incorporating the microfiber-VS2 SA into an Er-doped fiber laser cavity, passively Q-switched pulse trains could be obtained with repetition rates varying from 95 to 233 kHz. Under the pump power of 890 mW, the largest output power and shortest pulse duration are measured to be 43 mW and 854 ns, respectively. The high signal-to-noise ratio of 60 dB confirms the excellent stability of the Q-switching state. To the best of our knolowdge, this is the first illustration of using VS2 as an SA. Our experimental results demonstrate that VS2 nanomaterials have a large potential for nonlinear optics applications.

Experimental and Theoretical Analysis of a Mono PV Cell with Five Parameters, Simulation Model Compatible with Iraqi Climate

The present work included study of the effects of weather conditions such as solar radiation and ambient temperature on solar panels (monocrystalline 30 Watts) via proposed mathematical model, MATLAB_Simulation was used by scripts file to create a special code to solve the mathematical model , The latter is single –diode model (Five parameter) ,Where the effect of ambient temperature and solar radiation on the output of the solar panel was studied, the Newton Raphson method was used to find the output current of the solar panel and plot P-V ,I-V curves, the performance of the PV was determined at Standard Test Condition (STC) (1000W/m2)and a comparison between theoretical and experimental results were done .The best efficiency ranging from 0.15 to 0.16. With a particularly, error about (-0.333) for experimental power (30 Watt) comparing with theoretical power (30.1), through these results it is concluded the validity of the proposed model. This model can be used for all types of photovoltaic panels and also with larger output power.

High power edge-cum-surface emitting terahertz laser arrays phased locked by vacuum guided plasmon waves

Terahertz semiconductor quantum-cascade lasers (QCLs) are widely implemented with metallic cavities that support low-loss plasmonic optical modes at long wavelengths. However, resonant optical modes in such cavities suffer from poor radiative characteristics due to their subwavelength transverse dimensions. Consequently, single-mode terahertz QCLs with metallic cavities and large (>100 mW) output power have only been realized in the surface-emitting configuration that affords a large radiating surface. Here, we demonstrate a method to enhance radiative outcoupling from such plasmonic lasers for high-power emission in the edge-emitting (end-fire or longitudinal) direction. Single-sided plasmon waves propagating in vacuum are resonantly excited in surrounding medium of metallic cavities with the QCL semiconductor medium. The vacuum guided plasmon waves with a large wavefront phase-lock multiple metallic cavities longitudinally, which leads to intense radiation in multiple directions, including that in the longitudinal direction in a narrow single-lobed beam. The multicavity array radiates predominantly in a single spectral mode. A peak-power output of 260 mW and a slope efficiency of 303 mW/A are measured for the end-fire beam from a 3.3 THz QCL operating at 54 K in a Stirling cooler. Single-mode operation and lithographic tuning across a bandwidth of ∼150 GHz are demonstrated.

Flexible piezoelectric nanogenerators using metal-doped ZnO-PVDF films

Piezoelectric nanomaterial-polymer composites represent a unique paradigm for making flexible energy harvesting and sensing devices with enhanced devices’ performance. In this work, we studied various metal doped ZnO nanostructures, fabricated and characterized ZnO nanoparticle-PVDF composite thin film, and demonstrated both enhanced energy generation and motion sensing capabilities. Specifically, a series of flexible piezoelectric nanogenerators (PENGs) were designed based on these piezoelectric composite thin films. The voltage output from cobalt (Co), sodium (Na), silver (Ag), and lithium (Li) doped ZnO-PVDF composite as well as pure ZnO-PVDF samples were individually studied and compared. Under the same experimental conditions, the Li-ZnO based device produces the largest peak-to-peak voltage (3.43 Vpp) which is about 9 times of that of the pure ZnO based device, where Co-ZnO, Na-ZnO and Ag-ZnO are 1.2, 4.9 and 5.4 times, respectively. In addition, the effect of doping ratio of Li-ZnO is studied, and we found that 5 % is the best doping ratio in terms of output voltage. Finally, we demonstrated that the energy harvested by the device from finger tapping at ∼2 Hz can charge a capacitor with a large output power density of 0.45 W/cm3 and light up an ultraviolet (UV) light-emitting diode (LED). We also showed the device as a flexible wearable motion sensor, where different hand gestures were detected by the device with distinctive output voltage amplitudes and patterns.

Topology Selection and Parametric Design of Electromagnetic Vibration Energy Harvesters by Combining FEA-in-the-Loop and Analytical Approaches

Electromagnetic energy harvesters have been used to capture low-frequency vibration energy of large machines such as diesel generators. The structure of an electromagnetic energy harvester is either planar or tubular. Past research efforts focus on optimally designing each structure separately. An objective comparison between the two structures is necessary in order to decide which structure is advantageous. When comparing the structures, the design variations such as magnetization patterns and the use of yokes must also be considered. In this study, extensive comparisons are made covering all possible topologies of an electromagnetic energy harvester. A bench mark harvester is defined and the parameters that produce maximum output power are identified for each topology. It is found that the tubular harvesters generally produce larger output power than the planar counterparts. The largest output power is generated by the tubular harvester with a Halbach magnetization pattern (94.7 mW). The second best is the tubular harvester with axial magnetization pattern (79.1 mW) when moving yokes are inserted between permanent magnets for flux concentration. When cost is of primary concern, the tubular harvester with axial pattern may become a best option.

Design and testing of a new dual-axial underfloor piezoelectric energy harvester

This paper presents the design, fabrication, and testing of a dual-axial underfloor piezoelectric energy harvester based on piezoelectric stack. Usually, an underfloor energy harvester can only scavenge the energy from vertical force excitation. In addition to vertical pressure, the floor also suffers from lateral friction force during human walking. One uniqueness of the designed underfloor energy harvester lies in that it can collect energy from both vertical and horizontal excitation forces. To amplify the input force to get a larger output power, a flexure-based two-stage force amplifier is introduced and optimally designed. In order to transmit the two-directional (2-D) input force into the single direction that can be received by the force amplifier, the conical transmission mechanisms and slider mechanisms are introduced. Position limiters are adopted to protect the proposed mechanism. A prototype has been fabricated and tested. Experimental results indicate that the fabricated dual-axial piezoelectric energy harvester can provide an average output power up to 1.25 mW with a load resistance of 12 kΩ from 5 Hz force excitation of 100 N in two directions. With a load resistance of 26 kΩ, the harvested energy per walking footstep is derived as 7.00 mJ for the underfloor energy harvester.

A 68.5~90 GHz High-Gain Power Amplifier With Capacitive Stability Enhancement Technique in 0.13 μm SiGe BiCMOS

This article presents a wideband millimeter-wave power amplifier (PA) with a capacitive stability enhancement technique. It is composed of three differential cascode stages to attain high-power gain and large output power. To ensure the stabilization of the amplifier, a robust technique based on a series base capacitor is proposed and applied in each stage. Each capacitor creates a low-frequency zero to adjust the phase and amplitude responses of the differential cascode structure. As a result, the phase margin of the loop gain is increased remarkably. By adjusting the series base capacitors, the low-frequency zeros and gains of the three stages can be optimized. Therefore, the operating bandwidth is also extended. Meanwhile, a transformer-based four-path power combination network with a large current capacity is developed to further enlarge the output power. The circuit is demonstrated in a commercial $0.13~\mu \text{m}$ SiGe BiCMOS process. According to the measurement results, the PA obtains a saturated output power ( ${P}_{\text {Sat}}$ ) of 18.5 dBm and output referred 1-dB compression point ( ${\mathrm{ OP}}_{1\,\text {dB}}$ ) of 16.32 dBm at 77 GHz. The tested small-signal gain is 26.7 dB at 77 GHz. Its 3 dB gain bandwidth is beyond 21.5 GHz, which ranges from 68.5 to 90 GHz. The ${P}_{\text {Sat}}$ variation is less than 0.57 dB at the frequency range from 70 to 85 GHz. The measurement also shows the PA with the proposed technique is unconditionally stable over the entire frequency band. The chip area is only 0.684 $\text {mm}^{2}$ .

Improvement and Experimental Study of Scroll Expander for Organic Rankine Cycle

The scroll expander used in organic Rankine cycle (ORC) system is improved, and its performance is analyzed experimentally. The modified profile and inlet hole of the scroll expander are enhanced, and the performance of the scroll expander before and after the improvement is analyzed. The results show that when the inlet pressure exceeds 0.7 MPa, the waist-shaped hole with a larger area is preferable. The scroll expander with a waist-shaped hole has a larger output power and wider optimal pressure range, and when the inlet pressure is 1.6 MPa, the maximum output power increases by 230 W. The output power and isentropic efficiency of the scroll expander can be improved by modifying the profile. When the inlet pressure is 1.6 MPa and the rotational speed is 1750 r/min, the maximum output power of the scroll expander is 1235 W, which is 120 W higher than that before the improvement.

A 26.4-dB Gain 15.82-dBm 77-GHz CMOS Power Amplifier With 15.9% PAE Using Transformer-Based Quadrature Coupler Network

This letter presents a novel compact power amplifier (PA) using the transformer-based quadrature coupler as the power splitter and combiner to achieve a large output power and high gain for automotive radar application. Compared with conventional transmission-line-based power splitter and combiner, the transformer-based quadrature coupler offers a low loss, wide bandwidth, and compact footprint. As a proof of concept, a 77-GHz PA is designed and implemented in a 65-nm CMOS technology. The measured small-signal power gain is 26.4 dB with a 8.5-GHz 3-dB bandwidth from 74 to 82.5 GHz. The measured $P_{\text {sat}}$ , OP1 dB, and peak power added efficiency (PAE) are 15.82, 11.5 dBm, and 15.9%, respectively. In addition, the saturated output power at 77 GHz is 16.5 dBm at −40 °C and still remains as high as 13.5 dBm at 130 °C, which enables the automotive application. The proposed PA occupies a core area of $270\,\,\mu \text{m}\,\,\times 530\,\,\mu \text{m}$ and the total dc power consumption is 240 mW.

A 230-GHz High-Power and Wideband Coupled Standing Wave VCO in 65-nm CMOS

This article presents a 230-GHz wideband harmonic voltage-controlled oscillator (VCO) with large output power based on a compact and low-loss structure of coupled standing wave oscillators. In order to boost the output power, oscillators are coupled together without adding extra passive loss to the circuit. Transistors with inductive drain impedances provide the necessary negative resistance to the oscillators while simultaneously acting as active variable capacitors for frequency tuning and generate the desired second-harmonic power through their nonlinearities. Transmission lines at the drains are responsible for creating the inductive impedance as well as coupling adjacent oscillators and routing and combining the output power. Therefore, the circuit has a compact structure that minimizes passive losses. A varactor-less frequency tuning scheme is used and allows for wideband operation without sacrificing the output power. In addition to oscillator coupling and minimizing the losses, the output power has been boosted by engineering the harmonic impedance that is seen by the transistors in the circuit. The prototype chip was implemented in a 65-nm CMOS process. The output power of the VCO covers 219-238 GHz frequency band (8.35% tuning range) and delivers 3.4-dBm maximum output power. The minimum measured phase noise is -105.8 dBc/Hz (at 10-MHz offset) while consuming 195 mW from a 1.5-V supply.

Design optimization under uncertainty of hybrid fuel cell energy systems for power generation and cooling purposes

Reliance on point estimates when developing hybrid energy systems can over/underestimate system performance. Analyzing the sensitivity and uncertainty of large-scale hybrid systems can be a challenging task due to the large number of design parameters to be explored. In this work, a comprehensive and efficient sensitivity/uncertainty methodology is applied on two fuel cell hybrid systems to help analysts to investigate hybrid systems more efficiently. This methodology also includes a step-by-step approach to perform design optimization under uncertainty of energy systems. The two hybrid systems are: molten carbonate fuel cell with thermoelectric generator (MCFC-TEG) and phosphoric acid fuel cell with refrigerator (PAFC-REF). Various sensitivity and uncertainty methods are utilized to analyze the design parameters and their effect on the performance of these two systems. These methods perform local and regression-based sensitivity analysis, Monte Carlo uncertainty propagation, parameter screening, and variance decomposition. Detailed approach is adopted to identify and rank the influential design parameters for each system. Results demonstrate that the optimum power output of the MCFC-TEG has 10% uncertainty, driven mainly by the operating temperature, cahtode activation energy, TEG figure of merit, and TEG thermal conductivity. However, PAFC-REF is more reliable with larger power output and 1.4% uncertainty, driven by the charge transfer coefficient, heat transfer in the refrigeration cycle, cold reservoir temperature, and operating temperature. Based on this identification, design optimization under uncertainty is performed using these sensitive parameters to improve the system performance through increasing the power output and reducing its uncertainty.

Current Evidence and Practical Applications of Flywheel Eccentric Overload Exercises as Postactivation Potentiation Protocols: A Brief Review.

To summarize the evidence on postactivation potentiation (PAP) protocols using flywheel eccentric overload (EOL) exercises. Studies were searched using the electronic databases PubMed, Scopus, and Institute for Scientific Information Web of Knowledge. In total, 7 eligible studies were identified based on the following results: First, practitioners can use different inertia intensities (eg,0.03-0.88kg·m2), based on the exercise selected, to enhance sport-specific performance. Second, the PAP time window following EOL exercise seems to be consistent with traditional PAP literature, where acute fatigue is dominant in the early part of the recovery period (eg,30s), and PAP is dominant in the second part (eg,3 and 6min). Third, as EOL exercises require large force and power outputs, a volume of 3 sets with the conditioning activity (eg,half-squat or lunge) seems to be a sensible approach. This could reduce the transitory muscle fatigue and thereby allow for a stronger potentiation effect compared with larger exercise volumes. Fourth, athletes should gain experience by performing EOL exercises before using the tool as part of a PAP protocol (3 or 4 sessions of familiarization). Finally, the dimensions of common flywheel devices offer useful and practical solutions to induce PAP effects outside of normal training environments and prior to competitions. EOL exercise can be used to stimulate PAP responses to obtain performance advantages in various sports. However, future research is needed to determine which EOL exercise modalities among intensity, volume, and rest intervals optimally induce the PAP phenomenon and facilitate transfer effects on athletic performances.

Expanding the portfolio of tribo-positive materials: Aniline formaldehyde condensates for high charge density triboelectric nanogenerators

The rapid uptake of energy harvesting triboelectric nanogenerators (TENGs) for self-powered electronics requires the development of high-performance tribo-materials capable of providing large power outputs. This work reports on the synthesis and use of aniline formaldehyde resin (AFR) for energy-harvesting applications. The facile, acidic-medium reaction between aniline and formaldehyde produces the aniline-formaldehyde condensate, which upon an in-vacuo high temperature curing step provides smooth AFR films with abundant nitrogen and oxygen surface functional groups which can acquire a tribo-positive charge and thus endow AFR with a significantly higher positive tribo-polarity than the existing state-of-art polyamide-6 (PA6). A TENG comprising of optimized thin-layered AFR against a polytetrafluoroethylene (PTFE) film produced a peak-to-peak voltage of up to ~1000 V, a current density of ~65 mA m−2, a transferred charge density of ~200 μC m−2 and an instantaneous power output (energy pulse) of ~11 W m−2 (28.1 μJ cycle−1), respectively. The suitability of AFR was further supported through the Kelvin probe force microscopy (KPFM) measurements, which reveal a significantly higher average surface potential value of 1.147 V for AFR as compared to 0.87 V for PA6 and a step-by-step increase of the surface potential with the increase of energy generation cycles. The work not only proposes a novel and scalable mouldable AFR synthesis process but also expands with excellent prospects, the current portfolio of tribo-positive materials for triboelectric energy harvesting applications.

Piezoelectric energy harvesting from human walking using a two-stage amplification mechanism

This paper presents the design, modeling and experimental tests of a novel piezoelectric energy harvester with a two-stage force-amplification compliant mechanism for scavenging energy from human walking. The harvester consists of four units of two-stage force amplification piezoelectric transducers sandwiched between two heel-shaped plates. The dynamic reaction force at a heel is amplified twice by the two-stage force amplification frames before applied to the 33-mode piezoelectric stacks and therefore a large power output is achieved. Experiments were performed on the prototype of the two-stage piezoelectric energy harvester over different load levels and frequencies. Numerical simulation results based on a simplified single degree-of-freedom model agreed well with the experiment results. An average power of 34.3 mW and a peak power of 110.2 mW were obtained from the simulation under the dynamic force with the amplitude of 500 N and frequency of 3 Hz. At 2 Hz and 1.0 Hz, the average power outputs of 23.9 mW and 11.0 mW, peak power outputs of 65.8 mW and 31.7 mW were experimentally achieved. Numerical simulations show that the average power output of 12.8 mW and peak power output of 204.7 mW could be obtained at the walking speed of 3.5 mph (5.6 km/h) from a male subject with the body weight of 84 kg and height of 172 cm. Comparison study demonstrated that the proposed two-stage piezoelectric harvester has a larger power output than the reported results in literature.

Broadband energy harvesting by nonlinear magnetic rolling pendulum with subharmonic resonance

Nonlinear systems may exhibit secondary resonances, which can provide an additional and thus broadened bandwidth for energy harvesting. However, the secondary resonances of nonlinear energy harvesters reported in the literature suffer from low-power output and limited bandwidth. This work proposes a novel magnetic rolling pendulum (MRP) with a large bandwidth and high power output in both primary and secondary resonances for energy harvesting. The MRP employs the rolling motion of a magnetically levitated permanent magnet with minimal mechanical damping. A prototype was fabricated and characterised. An analytical model combined with finite element analysis was developed and validated by experiment. Both experiment and simulation show that the MRP has a linear resonance frequency of 4.6 Hz and peak power of 3.7 mW. It exhibits strong nonlinear behaviours and broadband characteristics with excitation amplitude as low as 2 m/s2 in the primary resonance. As the excitation amplitude is larger than 5 m/s2, the secondary resonance (1/2 order subharmonics) is excited. The responses of the MRP at the subharmonic resonance take the same form as the primary resonance in terms of displacement and power outputs. This helps the subharmonic resonance to produce the same power level as the primary resonance but with a larger bandwidth. When excited at 14 m/s2, the MRP shows 1-mW-bandwidth of 9.7 Hz, 2/3 of which is attributed to the subharmonic resonance.

Pd-doped lanthanum ferrites for symmetric solid oxide fuel cells (SSOFCs)

Pd-doped lanthanum strontium ferrite powders La0.6Sr0.4Fe1-xPdxO3-δ with x = 0.05, 0.1 (LSFPd05 and LSFPd10) are synthesized by combustion synthesis method and investigated as electrocatalysts for fuel and air electrodes of symmetric solid oxide fuel cells (SSOFCs). X-ray diffraction (XRD), Rietveld refinement, surface area (BET), temperature programmed reaction (TPR) and temperature programmed oxidation (TPO) analyses are performed on LSFPd powders. Electrical measurements both in oxidizing and reducing conditions are carried out on sintered pellets. Electrolyte (La0.8Sr0.2Ga0.8Mg0.2O3-δ) supported cells are prepared using LSFPd powders as electrodes. The electrochemical performances are evaluated in hydrogen and methane mixtures and promising performance are revealed in terms of large power output density and low polarization resistance.