High Output Power Research Articles

An enhanced electromagnetic energy harvester based on dual ratchet structure with secondary energy recovery

Abstract With the continuous advancement of ultra-low-power electronic devices, capturing energy from the surrounding environment to power these smart devices has emerged as a new direction. However, most of the mechanical energy available for harvesting in the environment exhibits ultra-low frequencies. Therefore, the feasibility of self-powering low-power devices largely depends on the effective utilization of this ultra-low-frequency mechanical energy. Consequently, this work proposes an enhanced electromagnetic energy harvester based on a dual ratchet structure with secondary energy recovery. It converts ultra-low frequency vibrations into fast rotational movements by means of a rack and pinion mechanism, thus achieving high power output while maintaining a simple structure. Experimental tests demonstrate that the proposed harvester exhibits excellent power output under ultra-low-frequency external excitation. Under external excitation with a frequency of 1.5 Hz and an amplitude of 22 mm, with the optimal load matched at 20 Ω, the maximum power output reaches 598 mW, with a power density of 1572.65 μW/cm³. The secondary energy recovery power accounts for 34.4 %, resulting in a 52.56 % enhancement in the energy harvester's output performance. Additionally, hand-cranking tests indicate that the fabricated prototype of the electromagnetic energy harvester can power some common electronic devices, including smartphones, showcasing significant application potential.

Performance Analysis and Rapid Optimization of Vehicle ORC Systems Based on Numerical Simulation and Machine Learning

The organic Rankine cycle (ORC) system is an important technology for recovering energy from the waste heat of internal combustion engines, which is of significant importance for the improvement of fuel utilization. This study analyses the performance of vehicle ORC systems and proposes a rapid optimization method for enhancing vehicle ORC performance. This study constructed a numerical simulation model of an internal combustion engine-ORC waste heat recovery system based on GT-Suite software v2016. The impact of key operating parameters on the performance of two organic Rankine cycles: the simple organic Rankine cycle (SORC) and the recuperative organic Rankine cycle (RORC) was investigated. In order to facilitate real-time prediction and optimization of system performance, a data-driven rapid prediction model of the performance of the waste heat recovery system was constructed based on an artificial neural network. Meanwhile, the NSGA-II multi-objective algorithm was used to investigate the competitive relationship between different performance objective functions. Furthermore, the optimal operating parameters of the system were determined by utilizing the TOPSIS method. The results demonstrate that the highest thermal efficiencies of the SORC and RORC are 6.21% and 8.61%, respectively, the highest power outputs per unit heat transfer area (POPAs) are 6.98 kW/m2 and 8.99 kW/m2, respectively, the lowest unit electricity production costs (EPC) are 7.22 × 10−2 USD/kWh and 3.15 × 10−2 USD/kWh, respectively, and the lowest CO2 emissions are 2.85 ton CO2,eq and 3.11 ton CO2,eq, respectively. The optimization results show that the RORC exhibits superior thermodynamic and economic performance in comparison to the SORC, yet inferior environmental performance.

Improvement of DC Performance and RF Characteristics in GaN-Based HEMTs Using SiNx Stress-Engineering Technique.

In this work, the DC performance and RF characteristics of GaN-based high-electron-mobility transistors (HEMTs) using the SiNx stress-engineered technique were systematically investigated. It was observed that a significant reduction in the peak electric field and an increase in the effective barrier thickness in the devices with compressive SiNx passivation contributed to the suppression of Fowler-Nordheim (FN) tunneling. As a result, the gate leakage decreased by more than an order of magnitude, and the breakdown voltage (BV) increased from 44 V to 84 V. Moreover, benefiting from enhanced gate control capability, the devices with compressive stress SiNx passivation showed improved peak transconductance from 315 mS/mm to 366 mS/mm, along with a higher cutoff frequency (ft) and maximum oscillation frequency (fmax) of 21.15 GHz and 35.66 GHz, respectively. Due to its enhanced frequency performance and improved pinch-off characteristics, the power performance of the devices with compressive stress SiNx passivation was markedly superior to that of the devices with stress-free SiNx passivation. These results confirm the substantial potential of the SiNx stress-engineered technique for high-frequency and high-output power applications, which are crucial for future communication systems.

High-efficiency 2.3 µm Tm:YLF laser based on 0.79 µm and 1.05 µm dual-wavelength pumping scheme.

A high-efficiency Tm:YLF laser at 2.3 µm is demonstrated based on a dual-wavelength pumping scheme with 790 nm LD and a tunable Yb:CALGO laser at around 1.05 µm. When employing single-wavelength pumping at 790 nm, a maximum output power of 3.1 W is obtained, while the maximum output powers of 0.35 W and 0.25 W are achieved for single-wavelength up-conversion pumping at 1055 nm and 1041 nm, respectively. By using 790 nm and 1055 nm dual-wavelength pumping regime, the maximum output power is enhanced to be 3.52 W, which is the highest output power ever achieved from the 2.3 µm Tm:YLF lasers, to the best of our knowledge. The output power of 3.52 W achieved by dual-wavelength pumping exceeds the sum of output powers obtained with the separate single-wavelength pumping at 790 nm and 1055 nm, which well shows that the ground state absorption process 3H6→3H4 under intense 790 nm pumping would induce a significant accumulation of Tm3+ ions on metastable level 3F4 via cross-relaxation process, greatly promoting the excited-state absorption process 3F4→3F2,3 and enhancing the 2.3 µm radiation.

High power lateral coupled InAs/GaAs quantum dot distributed feedback lasers grown on Si(001) substrates

High-quality single-frequency semiconductor lasers play a key role in silicon optical integrated systems. Combining high density 8-stacked quantum dot (QD) material and low–loss laterally coupled gratings, we here demonstrate a high output power, low noise, and insensitivity to light feedback 1.3 µm InAs/GaAs QD distributed feedback (DFB) laser grown on Si(001) substrates. For a QD DFB laser of a 3 × 1500 µm2 cavity, it exhibits a high single-mode output light power of up to 25 mW at 20 °C and 1.8 mW at 70 °C, respectively and maintains a stable single–mode operation in the entirely measured temperature range with a maximum side mode suppression ratio (SMSR) of 56.5 dB. Furthermore, the laser has an average relative intensity noise value low to –155.9 dB/Hz and a Lorentzian linewidth narrow to 243 kHz. In addition, the laser shows an insensitivity to optical feedback with a feedback level of –24.9 dB. Lastly, a 7-channel QD DFB laser array emitting at wavelengths from 1274.5 nm to 1290.0 nm are also exhibited with all SMSRs of higher than 45 dB. The results achieved here enable a practical single-frequency Si-based light source for the development of high-performance silicon photonic chips.

A Novel CEM-Based 2-DOF PID Controller for Low-Pressure Turbine Speed Control of Marine Gas Turbine Engines

Gas turbine engines have several advantages over piston reciprocating engines, such as higher output per unit volume, reduced vibration, rapid acceleration and deceleration, high power output, and clean exhaust gases. As a result, their use for propulsion in ships has been steadily increasing. However, gas turbine engines exhibit significant parameter variations depending on the rotational speed, making the design of controllers to ensure system stability while achieving satisfactory control performance, a very challenging task. In this paper, a novel CEM-based 2-DOF PID controller design technique is proposed to ensure the stability of a gas turbine engine while improving tracking and disturbance rejection performance. The proposed controller consists of a PID controller focused on enhancing disturbance rejection performance and a set-point filter to improve tracking performance. The set-point filter is composed of gains from the controller and a single weighting factor. When tuning the gains of the controller, the maximum sensitivity is considered to maintain an appropriate balance between system stability and response performance. The key novelty of this study can be summarized in two main points. One is that the controller is designed by matching characteristic equations, and by setting the roots of the desired characteristic equation as multipoles, the gains of the PID controller can be tuned with only one adjusting variable, making the tuning of the 2-DOF controller easier. The other is that the controller parameters are tuned based on maximum sensitivity, thus taking into account the robust stability of the control system. To demonstrate the feasibility of the proposed method, simulations are conducted for four scenarios using various performance indices.

Efficiency of dry versus wet Er,Cr:YSGG laser debonding of lithium disilicate veneers using different power outputs

Since water is the chromophore for the erbium, chromium-yttrium scandium gallium garnet (Er,Cr:YSGG) laser, the laser energy reaching the restoration decreases as part of it is absorbed by water. Theoretically, reducing the water or implementing dry debonding could reduce the energy consumed by water, increasing laser efficiency. Studies on whether it is suitable for removing veneers without using coolant are lacking. The purpose of this in vitro study was to evaluate the debonding time, intrapulpal temperature, and translucency of veneers during wet versus dry debonding with an Er,Cr:YSGG laser using different power outputs. Sixty-three maxillary central incisors were flattened labially to receive ceramic specimens. After cementation, ceramic specimens were irradiated with an Er,Cr:YSGG laser for debonding with different power outputs and water percentages (N=70): subgroup A1, 4W and 1% water; A20, 4W and 20% water; A40, 4W and 40% water; B1, 5W and 1% water; B20, 5W and 20% water; B40, 5W and 40% water; C1, 6W and 1% water; C20, 6W and 20% water; C40, 6W and 40% water, and a control group of unbonded ceramic specimens. During debonding, the temperature rise and debonding time were evaluated, followed by the evaluation of the translucency and surface topography of the debonded specimens. Two-way analysis of variance (ANOVA) and the Dunnett test were used to analyze the data (α=.05). The mean intrapulpal temperature rise varied significantly among groups B and C (P<.001), with the highest mean temperature rise found in subgroup B1 (4.00 ±0.00 ºC) and the lowest mean temperature rise in subgroup C20 (1.20 ±0.45 ºC). For the debonding time, the mean values of time required for debonding varied significantly among different groups (P<.001), with the longest time recorded in subgroup A1 (333.4 ±74.8s) and the shortest time recorded in subgroup C20 (17.0 ±6.0s). Only subgroups C1 (18.89 ±0.2) and C40 (18.60 ±0.2) showed a significantly lower translucency than the control group (19.44 ±0.06) (P<.001). Dry Er,Cr:YSGG laser debonding resulted in increased intrapulpal temperature when using high power outputs, but without exceeding the critical threshold of dental pulp temperature. Dry debonding also limited the transmission of laser energy, affecting the debonding efficiency. A power output of 5W and 20% water can be considered efficient and safe laser parameters for debonding lithium disilicate veneers if their reuse is intended.

High-power diode laser spectrally narrowed with prism-etalon feedback.

A simple method for reducing the linewidth of a diode laser while maintaining high output power is described. It is based on a dispersive prism and a thin etalon for retroreflective feedback. The etalon creates two weak external cavities that provide spectral selectivity that is periodic with a period equal to the etalon's free spectral range. The method was applied to a multimode blue laser diode, which in the absence of feedback features a linewidth of several nanometers. The spectral properties of the laser were investigated for different etalon thicknesses and operating currents and tested in the presence of temperature fluctuations. With a SF11 equilateral uncoated prism near Brewster's angle and a 0.3 mm-thick uncoated fused silica etalon, the linewidth was reduced 20-fold to 70pm (3.6 cm-1) with an output power of 3W at a current of 2.15A. The largest diode current probed was 2.75A, which resulted in a linewidth of 100pm (5.1 cm-1) and an output power of 4W. In contrast to the use of, for example, a volume Bragg grating, a high degree of flexibility is afforded as the same prism-etalon pair can be used across the visible and near infrared.

High power spectral beam combining based on four long-wave infrared quantum cascade laser emitters

In this study, we experimentally investigate spectral beam combining based on four long-wave infrared quantum cascade lasers (QCLs) with three dichroic mirrors. The coating curves of the dichroic mirrors were finely designed according to the output spectrum of the four adopted QCLs, whose central wavelength locates in 7.5 μm, 8.3 μm, 9.0 μm and 10.2 μm, respectively. At room temperature the highest combined power reaches as high as 2.39 W, corresponding to a combining efficiency of 83.0 %, and meanwhile, the combined beam keeps a high beam quality with average M2 of 1.78. To the best of our knowledge, this is the highest output power among spectral beam combining for QCLs. Due to the advantage of wide spectral range, high power, high beam quality and compact size, this demonstration may meet the demands of medical diagnosis, remote sensing, free-space optical communication and military application.

Quantum dot fourth-harmonic colliding pulse mode-locked laser for high-power optical comb generation

Quantum-dot mode-locked lasers have advantages such as high temperature stability, large optical bandwidth, and low power consumption, which make them ideal optical comb sources, especially for wavelength-division multiplexing (WDM) telecommunications, and optical I/O applications. In this work, we demonstrate an O-band quantum dot colliding pulse mode-locked laser (QD-CPML) to generate optical frequency combs with 200 GHz spacing with maximum channels of 12 within 3 dB optical bandwidth. To achieve the high output power of individual comb lines, four channel conditions are implemented at central wavelength of 1310 nm for WDM transmission experiments. Each channel exhibits more than 10 dBm output power with 200 Gb/s PAM-4 and 270 Gb/s PAM-8 modulation capability via thin-film LiNbO3 Mach–Zehnder interferometer modulator without the requirement of any optical amplifications. This high-order QD-CPML is an ideal comb source for power-efficient optical interconnects and large bandwidth optical data transmission.

Facile and binder free nano-architecturing of anode with biocompatible g-C3N4-PPy for bacterial community enrichment and green energy generation in microbial fuel cells

The adoption of microbial fuel cells (MFCs) as waste-to-power solution for green energy generation while treating wastewater has attracted considerable attention. However, their wide-scale expansion requires further improvements, particularly by anode modifications which necessitates the development of anodes with large surface area, high electrical conductivity, and biocompatibility. Thus, herein, we present a novel and facile approach for the modification of carbon felt (CF) with graphitic carbon nitride (g-C3N4) and polypyrrole (PPy) to create a highly biocompatible anode following a binder-free route. Increased surface area with microporous rough surface of modified electrodes was confirmed through scanning electron microscopy (SEM) and atomic force microscopy (AFM). The g-C3N4@PPy-CF anode exhibited minimal water contact angle of 0.9°, in contrast to g-C3N4-CF (53.5°) and pristine CF (123.8°), indicating enhanced hydrophilicity essential for biofilm formation. The synergy between g-C3N4 and polypyrrole results in remarkable 80.7% higher power output (205.8 ± 7.36 mW/m2) and 47% higher current response (8.24 mA) as compared to pristine-CF. Efficient extracellular electron transport (EET) was enacted through better interfacial contact between electrode and electroactive bacteria (EAB), as evidenced by the minimal charge transfer resistance in g-C3N4@PPy-CF (4.21 Ω) and g-C3N4-CF (6.47 Ω), while 68% higher resistance (7.06 Ω) with pristine-CF. Microbial characterization of biofilms showed enrichment of electroactive bacteria, mainly the Proteobacteria phylum comprised 79–82% of total microbial community in modified electrodes while it was 74% in pristine CF. Acinetobacter (25.9%) and Desulfuromonas (17.9%) emerges as major electroactive genera on g-C3N4@PPy-CF contributing to its excellent bio-electrogenic performance. Thus, the low-cost, binder-free and facilely fabricated novel anode with stable electrogenic efficiency provides solution to longstanding challenge of suboptimal anode performance and opens new avenues for scale-up of sustainable energy generation from wastewater using MFCs.

Research on high beam quality 3 × 1 double-cone fiber signal combiner at 9 kW level.

The fiber signal combiner with high output power and high beam quality is an urgent problem to be solved. In this paper, the structure of the double-cone (both the input fibers and the output fiber are tapered) is proposed to improve the beam quality of the fiber signal combiner, and it is verified by simulation and experiment, with the output fiber of 50 µm core tapered to 35 µm as an example. The prepared 3 × 1 double-cone fiber signal combiner reaches the output power of 8.64 kW, and the beam quality is measured as M2 = 2.91. Compared with the M2 = 3.41 of the fiber signal combiner with non-tapered output fiber, the M2 of the double-cone fiber signal combiner is reduced by 14.7%.

(Invited) The Impact ofin-Situ Activation of a C-Coated Catalyst on the Performance and Durability in Proton-Exchange Membrane Fuel Cells

Zero-emission electricity production for stationary or mobile applications can be realized by PEM fuel cells (PEMFCs), making it an important constituent for a renewable energy transition. Especially relevant in heavy-duty applications, a high power output at low current densities (related to a high mass activity, MA) under dry conditions is necessary to meet the efficiency targets.[1] In general, mass activity of a Pt/C catalyst can be negatively affected by ionomer poisoning, which describes the adsorption of ionomer endgroups onto the active Pt surface. This effect is especially pronounced for platinum supported on so-called solid carbon supports (e.g., Vulcan – Pt/V)[2] and by operating a fuel cell at low relative humidity (RH).[3] In order to minimize performance losses due to ionomer poisoning, concepts exist to shield the Pt particle from the ionomer, e.g., by alkanethiol masking[4] or by Pt-overlayers of porous SiO2 [5] and carbon derived from dopamine coatings.[6] In the latter case, the authors observed that it was possible to decrease ionomer poisoning and increase MEA performance under dry conditions. However, the transport of reactants to the Pt active sites is hindered by the carbon-overlayer, resulting in inferior high current density (HCD) performance.In this work, we developed multiple in-situ activation strategies for a carbon-coated Pt/V cathode catalyst, synthesized following an adapted protocol from Yamada et al.[6] Our results show that apart from a significantly improved MA, high current density performance is retained for an activated carbon-coated Pt/V (C-Pt/Vactivated, solid orange symbols in Figure 1). Compared to the Pt/V baseline catalyst (blue symbols), the MA can be increased by a factor of ~2 (C-Pt/Vactivated with im 0.9V = 248±9 A gPt -1 and Pt/V with im 0.9V = 110±13 A gPt -1) while simultaneously maintaining comparable high current density performance at 90% RH. However, as we will show, the beneficial effect of the activated carbon-coated Pt/V is particularly pronounced at operation under dry conditions, where C-Pt/Vactivated outperformed the Pt/V baseline over the entire current density range (e.g., by 80 mV at 1.7 A cm-2).Furthermore, possible limitations in terms of durability of the C-overlayer used in this work will be discussed. Figure 1: Differential-flow H2/Air performance at 80 °C/90% RH and 145 kPaabs for different cathode catalysts: baseline catalyst (Pt/V), C-coated Pt/V catalyst before activation (C-Pt/Vb efore activation), and activated C-coated Pt/V catalyst (C-Pt/Va ctivated). In the 5 cm2 active area single-cell, the catalyst loadings were 0.25 mgPt cm-2 and 0.05 mgPt cm-2 on cathode and anode, respectively; a 15 µm reinforced low-EW PFSA membrane was used.

High-power 940 nm DFB laser diode with large optical cavity.

High-power laser diodes with a stable wavelength and narrow linewidth are crucial for many applications. In this study, we introduce a first-order distributed feedback (DFB) grating into an asymmetric large-cavity laser diode operating around 940 nm. This design maintains high output power and offers a wide temperature locking range. The nearly sinusoidal shape first-order grating is fabricated by ultraviolet (UV) nanoimprint lithography, inductively coupled plasma (ICP) dry etching, and wet polishing. At a heat sink temperature of 25°C, the DFB laser diode, with a 200 µm stripe width and 4 mm cavity length, achieves a maximum output power of 24.8 W and a full width at half maximum (FWHM) of 0.4 nm under continuous-wave (CW) conditions. The maximum slope efficiency is calculated to be 1.04 W/A. At an output power of 10.7 W, the device reaches a peak wall-plug efficiency of 56%. Under quasi-continuous operation at 20 A, the laser output spectrum remains locked to the DFB grating over a temperature range from -10°C to 110°C, with a temperature coefficient of 0.062 nm/°C.

Theoretical Models for Performance Analysis of Spintronic THz Emitters

The terahertz (THz) region of the electromagnetic spectrum, spanning from 0.1 to 10 THz, offers unique opportunities for imaging, spectroscopy, and communication applications. However, the potential of THz technologies has been limited by the availability of efficient and versatile THz emitters. Spintronic THz emitters (STEs), leveraging the ultrafast dynamics of electron spins in magnetic materials, have emerged as a promising solution to this challenge. STEs offer significant advantages, including broad bandwidth, high power output, and room-temperature operation, positioning them at the forefront of THz technology development. Despite these advances, understanding the operational principles and improving the performance of STEs remain areas of active research. This review focuses on the theoretical models that describe the behavior of STEs, aiming to provide a comprehensive overview of the underlying physics and suggest directions for future enhancements. Through a detailed examination of these models, the review seeks to clarify the basics of the physics driving STE performance and highlight innovative strategies for their optimization and application expansion.

A review of single stage and multistage power converters for doubly fed induction generator integrated with power grid

The doubly fed induction generator (DFIG) is the most popular induction generator for onshore wind energy conversion system (WECS). Therefore, the purpose of research is to optimize power transfer from DFIG to power grid which requires frequency and voltage stability in power converters. Hence, the single-stage and multistage power converter topologies associated with grid-integrated DFIG are thoroughly examined in this work. In the single stage, a matrix converter and cycloconverter are used. Whereas, the multistage topologies include two-level back-to-back (2L-B2B) converter, Z-source converter, and multilevel converters. Furthermore, three-level neutral point clamped (3L-NPC) voltage source converters with battery energy storage systems (BESS) and modified superconducting fractional order terminal sliding mode controllers (MSTFOTSMC) have been used with multilevel converter both at rotor side converter (RSC) and grid side converter (GSC) for stabilized generated voltage and higher power output. The MATLAB simulation results demonstrate that the system effectively controls fluctuations in voltage and current thereby improving the power quality in unbalanced situations.

Conjointly active and passive modelings with deep neural networks as fully automated optimizations for upper-mid band 6G communications

Today wireless systems include the fifth and sixth generations (5G and 6G) technologies and are growing day by day that result in exponentially increasing data traffic. For providing a reliable and high performance radio frequency (RF) designs especially for 6G networks, amplifiers and antenna as active and passive components play important roles. In the 5G/6G communication systems, the propagation loss is considerably large and its compensation requires high output power generated from the amplifiers for guaranteeing the satisfied quality of transmitted signal. From another point of view, the installed antennas must be able to optimally manage the radiated signals and handle/compensate nonlinear performances of the RF circuitry. Hence, advanced modeling and multi-objective optimization algorithms are required for designing and optimizing high performance amplifiers and antennas in terms of output power, gain, efficiency, linearity, and bandwidth. Concurrently optimizing active and passive components is not straightforward and typically it requires additional efforts by the RF designers. To tackle this drawback, a two-step methodology is proposed: (1) configuring the initial structure of active and passive devices, and (2) sizing the configured devices. In this work, various methods are introduced for structuring the topology of circuits and then artificial intelligence, including machine learning and neural networks, is preferred among other surrogate modelling for sizing the designs. These neural networks are satisfied due to the accurate modeling responses and are able to provide an automated optimization process leads to employ multi-objective optimization methods. In this work, an automated optimization process for comprehensive design of high-performance amplifiers with antennas through bottom-up optimization (BUO) method and long short-term memory (LSTM)-based deep neural networks (DNNs) is proposed. At the output layer of DNNs, the multi-objective multi-verse optimizer (MOMVO) method is employed for optimizing various specifications of active device (i.e., amplifier), and passive device (i.e., antenna), concurrently. In the presented method, all the electromagnetic (EM) design rules are implemented which results in reducing simulation time in the harmonic balance simulation environment that also provides ready to fabricate layouts. The novelty consists of the all-inclusive style that (1) reduces the manual breaks, aka time-to-market, and (2) delivers ready-to-fabricate layouts of the device that exhibits global optimum performances, automatically. The validation of the proposed method is verified by designing and optimizing high power amplifier (HPA) with antenna in the frequency band from 9.0 GHz to 9.6 GHz, suitable for upper-mid band 6G communications.

Performance evaluation of photovoltaic-phase change material-thermoelectric system through parametric study

The dual-directional photovoltaic-thermoelectric generator (PV-TEG) system offers higher performance. However, there may be scenarios where the PV and TEG devices receive different levels of irradiation, leading to variations in performance. Under these conditions, the impact of using a PCM heat sink on the system's thermal management effectiveness has not yet been clearly established. Given these considerations, this study builds a coupled heat transfer-laminar flow-electromagnetic numerical model to explore the variations in system performance when subjected to different radiation intensities. The investigation also explores the implications of integrating PCM with varying thicknesses and melting points. Based on the obtained data, it can be concluded that when the PV and TEG devices are exposed to different radiation intensities, the system exhibits distinctly different performance. The highest power output and conversion efficiency are more than 0.16 W and 16 % for the PV device, and 0.08 W and 1 % for the TEG device. Furthermore, using thicker PCM allows the PV and TEG devices to maintain higher output power and efficiency for a longer period, surpassing the performance of systems with thinner PCM. Moreover, the PCM with a melting point of 301.15K has demonstrated the best potential for thermal management in the PV-TEG system.

Effects of acute simulated altitude on the maximal lactate steady state in humans.

We sought to determine the effects of acute simulated altitude on the maximal lactate steady state (MLSS) and physiological responses to cycling at and 10 W above the MLSS-associated power output (PO) (MLSSp and MLSSp+10, respectively). Eleven (4 females) participants (means [SD]; 28 [4] yr; V̇o2max: 54.3 [6.9] mL·kg-1·min-1) acclimatized to ∼1,100 m performed 30-min constant PO trials in simulated altitudes of 0 m sea level (SL), 1,111 m mild altitude (MILD), and 2,222 m moderate altitude (MOD). MLSSp, defined as the highest PO with stable (<1 mM change) blood lactate concentration ([BLa]) between 10 and 30 min, was significantly lower in MOD (209 [54] W) compared with SL (230 [56] W; P < 0.001) and MILD (225 [58] W; P = 0.001), but MILD and SL were not different (P = 0.12). V̇o2 and V̇co2 decreased at higher simulated altitudes due to lower POs (P < 0.05), but other end-exercise physiological responses (e.g., [BLa], ventilation [V̇e], heart rate [HR]) were not different between conditions at MLSSp or MLSSp + 10 (P > 0.05). At the same absolute intensity (MLSSp for MILD), [BLa], HR, and V̇E and all perceptual variables were exacerbated in MOD compared with SL and MILD (P < 0.05). Maximum voluntary contraction, voluntary activation, and potentiated twitch forces were exacerbated at MLSSp + 10 relative to MLSSp within conditions (P < 0.05); however, condition did not affect performance fatiguability at the same relative or absolute intensity (P > 0.05). As MLSSp decreased in hypoxia, adjustments in PO are needed to ensure the same relative intensity across altitudes, but common indices of exercise intensity may facilitate exercise prescription and monitoring in hypoxia.NEW & NOTEWORTHY This study demonstrates the power output and metabolic rate associated with the maximal lactate steady-state (MLSS) decline in response to simulated altitude; however, common indices of exercise intensity remained unchanged when cycling was performed at the work rate associated with MLSS at each simulated altitude. These results support previous studies that investigated the effects of hypoxia on alternative measures of the critical intensity of exercise and will inform exercise prescription/monitoring across altitudes.

High-power and efficiency W-band InAlGaN/AlN/GaN high-electron-mobility transistors for future high-capacity wireless communications

This study describes high-power and high-efficiency W-band InAlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) for future sub-terahertz wireless communications. A low-thermal-budget selective-area growth (SAG) process was developed to obtain low contact resistance with low trap states. Transmission lines and substrate structures were optimized to obtain high-thermal conductivity and low substrate resonance. Consequently, a high output power of 28.7 dBm (742 mW), output power density of 4.6 W mm−1, and power-added efficiency (PAE) of 28.0% were achieved with pre-matched InAlGaN/AlN/GaN HEMTs at 90 GHz, which were superior combination of output power and PAE compared to the conventional high-temperature SAG process.