Limited Output Power Research Articles

3 × 1 all-fiber signal combiner with high beam quality for high-power lasers

An all-fiber signal combiner is an essential component to break through the incoherent beam output power limitation of fiber laser power. So far, the high-power signal combiners reported before usually had output core diameters of higher than 100 µm with NAs of 0.22, leading to serious beam quality degradation. In order to improve the beam quality, a 50 µm core diameter output fiber with a smaller NA of 0.12 is utilized in this work. We have theoretically made a detailed simulation of the combiner. Combiners with three 20/400 µm input fibers are fabricated, and three ~1064 nm fiber lasers with a maximum output power of over 2 kW have been used as the input light source. A maximum output power of up to 6.06 kW was achieved by incoherent beam combining, and the final output power was 6.06 kW with a beam quality factor (M2) of 3.69. To our best knowledge, it is the first report on a multi-kW class laser based on a beam combiner with an M2 of less than 4.

High power, single-frequency, monolithic fiber amplifier for the next generation of gravitational wave detectors.

Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.

Power-Angular Spectra Correlation Based Two Step Angle of Arrival Estimation for Future Indoor Terahertz Communications

The future terahertz (THz) communication is a promising solution to the high data rate and short-range communication due to its broad available bandwidth. However, the high propagation path loss and the limited output power of the amplifier require highly directive antennas with high antenna gain in order to realize a reasonable signal-to-noise ratio (SNR). An angle-of-arrival (AoA) estimation is necessary to adjust the main lobe direction of the antenna. A major challenge of the AoA estimation is the compromise between accuracy and time consumption due to the big number of main lobe directions. This paper proposes a novel efficient AoA algorithm, which utilizes the fact that the power-angular spectrums (PASs) of different frequencies are highly correlated and the THz communication devices are equipped with radio frequency (RF) frontends of lower frequency. By means of a rough and quick estimation at the lower frequency, the range of the true AoA can be significantly confined and the precise estimation can be efficiently carried out. To begin with, an antenna model with discrete main lobe directions is proposed and the relationship between antenna gain, half power beamwidth (HPBW), and number of main lobe directions is analyzed. The PAS correlation is then validated with channel sounding measurement. The two-step AoA estimation algorithm is derived, formulated, and finally validated with hardware demonstration.

Optimization of LCL Filter With Integrated Intercell Transformer for Two-Interleaved High-Power Grid-Tied Converters

Paralleling of voltage source converters (VSCs) with a limited maximum output power is essential when the power rating of a system must be increased. Interleaving (ILV) of the switching signals for parallel-connected VSCs provides a better harmonic spectrum than hard paralleling (HP), i.e., applying identical signals to all VSCs. This can be particularly beneficial for grid-tied converters, since a smaller LCL filter can be realized. To investigate the performance limitations and the impact of ILV operation on the LCL filter hardware, a comprehensive optimization procedure for LCL filters and intercell transformers (ICTs) for two paralleled VSCs is presented in this paper. In addition, a comparative evaluation of HP and ILV operation of VSCs is carried out. The developed optimization procedure and the hardware benefits of ILV operation were verified through testing on a 260-kW full-scale system. Compared with the commercial state-of-the-art weight-optimized LCL filter for HP, the developed LCL filter for ILV utilizing an integrated ICT reduces the total filter weight by 30% while guaranteeing harmonic standard compliance and meeting thermal requirements.

Optimisation of Pedal Power Output and Pedalling Rate Based on the Physiological Response of Male Agricultural Worker

Human power can be better utilised in rotary mode either by cranking or by pedalling. In occupational workload, pedalling is preferred over cranking as the former results less physiological cost. The present study aimed to determine the most economical pedalling rates at various power outputs as well as to arrive at the optimum power output and pedalling rate combination. Ten male subjects participated as replications with two independent parameters viz. power output (4 levels) and pedalling rate (5 levels). Three physiological parameters viz HR, OCR and ∆HR were studied. It was observed that all physiological parameters initially decreased, and then increased following a curvilinear relationship with respect to pedalling rate for all power outputs. The limiting power output for male agricultural workers was about 60 W in pedalling mode with pedalling rate 60 rpm. The HR, ∆HR and OCR at this power–pedalling rate combination were 116 beats.min-1, 33 beat.min-1 and 0.8 l.min-1, respectively.

Iron and carbon granules added to anode enhanced the sludge decrement and electrical performance of sludge microbial fuel cell

Sludge microbial fuel cell (SMFC) can utilize the organics in sludge to generate power, and has attracted widespread attention. However, the low efficiency of organics utilization and limited power-output are the main challenges that need to be addressed. This study proposed an in situ method without additional energy to enhance the performance of SMFC by adding the package of iron and carbon granules (FeC). In the reactors including FeC-SMFC (the FeC package placed under the carbon felt anode and separated from the closed-circuit), FeC-OSMFC (FeC-SMFC in open-circuit), and FeCSMFC (the FeC package attached to the anodic bottom and closed-circuit), the degradation of refractory organics especially humic acid-like substances was significantly promoted, due to the FeC micro-electrolysis at neutral pH. More organics were beneficial for the enrichment of typical exoelectrogens belonging to Proteobacteria and Firmicutes, thereby improving the electrical performance of FeC-SMFC and FeCSMFC, compared with normal SMFC without FeC package (NSMFC). In FeCSMFC, the soluble and total chemical oxygen demand removal efficiencies were 65.60% and 52.64%. The removal efficiency of volatile suspended solids in FeCSMFC was 69.26%, which was 30.05%, 14.97%, 9.87% and 6.62% higher than that in open-circuit SMFC, NSMFC, FeC-OSMFC and FeC-SMFC, respectively. The power output of FeCSMFC was 37.28 W m−3, 6.06 and 1.76 times higher than that of NSMFC and FeC-SMFC, respectively. The addition of FeC package to anode is a cost-saving and effective method to enhance electricity generation and sludge decrement of SMFC.

Output Power Limit in Energy Harvesting Systems Based on Magnetic Induction Incorporating High-Frequency Effects

Wireless power transfer systems based on magnetic induction are usually modeled using the magneto-quasi-static approximation, and by neglecting skin effects and radiation losses. These assumptions imply that the extracted power can grow unlimitedly by increasing frequency or coil size. To bridge this gap, this work proposes general expression for the actual received power of magnetic induction-based energy harvesting transducer, extracting power from a given ambient magnetic field, while accounting for the high-frequency effects. A primary result is that the receiver’s output power is inherently limited by radiation losses at high frequencies and impaired by skin and proximity effects at medium frequencies. The approach provides a design tool for estimating the maximal power that can be delivered through a given transducer, and the optimal operating frequency.

Efficiency optimization of rotary ultrasonic motors using extremum seeking control with current feedback

Despite their great features, ultrasonic motors’ (USM) driving schemes still suffer from suboptimum driving efficiencies and limited operating range. The driving efficiency and operation range are mainly functions of the vibration amplitude and the preload. Vibration amplitude is generally controlled by means of adjusting the driving frequency. Unfortunately, there exists a narrow frequency band where efficiency is maximized resulting in a limited output power range. Due to temperature rise, this frequency is continuously shifting which necessitates dynamic tracking of the optimum state. Fortunately, maximum driving efficiency was experimentally confirmed to have good correspondence with minimum current. Current feedback was thus utilized within an Extremum Seeking Control (ESC) loop to track maximum efficiency. Besides driving frequency control, voltage amplitude and preload can be controlled to realize the desired output power while maintaining maximum efficiency. Using ESC technique, the maximum efficiency was successfully located and tracked under different voltage amplitudes and preloads. The output power under optimum condition was found to have a wider control range with preload control than with voltage amplitude control.

Study of Fiber-Based Wearable Energy Systems.

Fiber-based electronic and photonic devices have the most desired human-friendly features, such as being soft, ubiquitous, flexible, stretchable, light, and permeable, and thus are ideal to be employed as the interface platform between humans, the environment, and machines. Today, these smart wearable devices are normally powered by rechargeable batteries. It is extremely desirable to have an undisrupted power supply for us to go anywhere at any time. Harvesting energy from the ambient environment or our body can potentially fulfill such a goal. Explorations of high performance, flexible functional materials and energy conversion devices have led many exiting discoveries. In order to realize their applications, equally important are fundamental studies of the physical phenomena and mechanisms that will provide scientific guidance for the direction of exploration and development of devices and systems. Hence, this Account provides a brief review of our recent progress in this topic area. Based upon materials science, mechanics and device physics, we have succeeded in establishment of several new theoretical models for fiber-based piezoelectric, triboelectric, and hybrid generators. These models have been verified experimentally. Excellent results were obtained for fiber-based triboelectric generators without any adjustable parameters. Reasonable agreement was demonstrated for the piezoelectric generators because of some uncertainty in the material properties and deformation modes. From both simulated and experimental results, we did not detect any synergic effect in the hybrid generator consisting of cascaded piezoelectric and triboelectric units. The verified models can be used to predict the output voltage, current, and power of the devices in terms of material properties, parameters of device structure, harvesting circuits, and operating conditions. Furthermore, by considering the electric breakdown due to field-induced-emission and gas-ionization, we have identified the theoretical upper limits of charge density and output power from contact-mode fiber-based triboelectric nanogenerators. The analysis sheds new light on the scope and focus for further exploration and provides guidance on engineering design of such devices. In addition, we have setup an experimental platform for reliable triboelectric charge measurement of highly deformable and porous materials like fabrics. An extended triboelectric series has been reported by us including 21 types of commercial and new fibers. Based upon the findings, we have made significant improvements of the performance of these energy harvesting devices. Finally, we have explored a class of new flexible thermoelectric materials exhibiting high performance for fiber-based thermoelectric generators, which can be fabricated by low-temperature and cost-effective processes, such as in situ reduction coating and three-dimensional printing. The resultant large-area, flexible, and wearable fiber-base thermoelectric generators are key devices for great potential applications such as powering wearable microelectronic systems, active microclimate regulating systems, and waste thermal energy harvesting.

Development of a Tree-Shaped Hybrid Nanogenerator Using Flexible Sheets of Photovoltaic and Piezoelectric Films

This paper reports on the feasibility of a tree-shaped hybrid nanogenerator (TSHG) made of flexible sheets of photovoltaic (PV) and piezoelectric (piezo) films for harnessing both wind and solar energy. The proposed system has been designed to produce electricity if there is any light, wind or strong rainfall. It shows how the power developed by each piezo film sheet was integrated in conjunction with its limited power output which is produced by the sporadic movement of the sheets. Regardless of its magnitude, the AC power output of each piezo film sheet was converted with a full wave bridge rectifier and then passed to a capacitor. The TSHG has an excellent performance with an open circuit voltage of 5.071 V, a short-circuit current of 1.282 mA, and a maximum power output of 3.42 mW at a loading resistance of 5 kΩ. Moreover, a wind driven TSHG was capable of charging a 1000 µF capacitor, which was subsequently discharged through LED lighting.

Optimisation of Pedal Power Output and Pedalling Rate Based on the Physiological Response of Male Agricultural Worker

Human power can be better utilised in rotary mode either by cranking or by pedalling. In occupational workload, pedalling is preferred over cranking as the former results less physiological cost. The present study aimed to determine the most economical pedalling rates at various power outputs as well as to arrive at the optimum power output and pedalling rate combination. Ten male subjects participated as replications with two independent parameters viz. power output (4 levels) and pedalling rate (5 levels). Three physiological parameters viz HR, OCR and ∆HR were studied. It was observed that all physiological parameters initially decreased, and then increased following a curvilinear relationship with respect to pedalling rate for all power outputs. The limiting power output for male agricultural workers was about 60 W in pedalling mode with pedalling rate 60 rpm. The HR, ∆HR and OCR at this power–pedalling rate combination were 116 beats.min-1, 33 beat.min-1 and 0.8 l.min-1, respectively.

A Time-Interleave-Based Power Management System with Maximum Power Extraction and Health Protection Algorithm for Multiple Microbial Fuel Cells for Internet of Things Smart Nodes

Microbial Fuel Cell (MFC) technology is a novel Energy Harvesting (EH) source that can transform organic substrates in wastewater into electricity through a bioelectrochemical process. However, its limited output power available per liter is in the range of a few milliwatts, which results very limited to be used by an Internet of Things (IoT) smart node that could require power in the order of hundreds of milliwatts when in full operation. One way to reach a usable power output is to connect several MFCs in series or parallel; nevertheless, the high output characteristic resistance of MFCs and differences in output voltage from multiple MFCs, dramatically worsens its power efficiency for both series and parallel arrangements. In this paper, a Power Management System (PMS) is proposed to allow maximum power harvesting from multiple MFCs while providing a regulated output voltage. To enable a more efficient and reliable power-harvesting process from multiple MFCs that considers the biochemical limitations of the bacteria to extend its lifetime, a power ranking and MFC health-protection algorithm using an interleaved EH operation was implemented in a PIC24F16KA102 microcontroller. A power extraction sub-block of the system includes an ultra-low-power BQ25505 step-up DC-DC converter, which integrates Maximum Power Point Tracking (MPPT) capabilities. The maximum efficiency measured of the PMS was ~50.7%. The energy harvesting technique presented in this work was tested to power an internet-enabled temperature-sensing smart node.

A miniaturized electromagnetic energy harvester with volt-level output based on stacked flexible coils

The bottleneck of the miniaturized electromagnetic vibration energy harvester (EVEH) device is the limited output voltage and power. Commonly reported mV-level AC output of the EVEHs cannot be rectified and used. In this work, we report a cost-effective EVEH device based on batch-fabricated flexible springs and coils. At an acceleration of ±1 g peak-to-peak amplitude (±9.8 m s−2), a maximum output peak-to-peak voltage of 1.57 V and an output power of 91.8 μW are measured, at a frequency of 66 Hz. The output voltage of the EVEH is successfully rectified, amplified (passively) and used to charge a supercapacitor.

Investigation of load modulated inverse Class-F power amplifier with extended conduction angle

A novel design space of load modulated (LM) inverse Class-F power amplifiers (PAs) with extended conduction angle is proposed. The effects of the driven level factor β and the biasing operation factor ρ on the third-harmonic generation are discussed. The harmonic generation mechanism shows that the knee voltage effects are the source of third-harmonics for LM inverse Class-F PAs. The definition of the inverse Class-F mode is consistently valid under the circumstance of load modulation in a limited output power back-off (OPBO) range. Meanwhile, the conduction angle θ0 can be extended from π/2 to a limited value (<110°) to keep the standard waveforms of inverse Class-F mode and maintain high efficiency. After introducing the “continuous concept” and the second harmonic manipulation method, the mathematical design space of inverse Class-F PAs with extended conduction angle is derived. Calculation shows that the purely conductive load modulation can enable high back-off efficiency operation for LM inverse Class-F PAs. As proof of concept, a demonstrator amplifier is fabricated and measured. The experimental results show that the power added efficiency (PAE) with optimum Vctrl is improved by 5% over an OPBO range of 6 dB compared with the same PA with fixed Vctrl.

Polymer-Based Ultrasonic Motors Utilizing High-Order Vibration Modes

Our previous studies showed that traveling-wave rotary ultrasonic motors with polymer-based vibrators yielded limited output power when operating in the commonly used low-order bending vibration modes. In this study, we employ a high-order bending mode in the polymer-based cylindrical ultrasonic motor, because this mode yields a relatively high electromechanical coupling factor, which may lead to high output power of the motor. Additionally, in contrast with the low-order modes with only vertical nodal lines, the high-order mode has both horizontal and vertical nodal lines on the circumferential outer surface of the polymer-based vibrator. With these attractive advantages, it is worth investigating basic vibration characteristics of polymer-based vibrators operating in high-order modes and their applications to ultrasonic motors. The vibrating body is made of poly phenylene sulfide, a functional polymer exhibiting low mechanical loss even under high-amplitude ultrasonic vibration and is activated by a piezoelectric ceramic element bonded on the back surface. The high-order modes are optimal for polymer-based vibrators with practical thicknesses, because their equivalent stiffnesses and masses are relatively low when operating in this mode. Polymer-based motors with the high-order modes exhibit relatively high output torques and powers, compared with not only polymer-based motors with low-order bending modes, but also metal-based motors operating in high-order vibration modes.

Determination of Generator Steady State Stability Limit for Multimachine System based on Network Losses Concept

In the multimachine circumstances, it is difficult to analyze the steady state stability of each generator. In previous research, analysis of the steady state stability limit has been carried out but only look at the stability of the overall system. Therefore, to analyze the stability of each generator, the multimachine system must be changed into a Single Machine to Infinite Bus (SMIB) system by collecting all the loads into one central load in the infinite bus. The method to change from the multimachine system to SMIB system is presented in this paper. The multimachine system is converted into an equivalent impedance (req and xeq) and an equivalent load based on losses concept. After req and xeq is calculated, then by using steady state stability limit concept, the value of the maximum generation of each generator units can be determined. By means of maximum generation is the maximum output power limit that can be generated without causing unstability. ETAP simulation is used to validate the calculation results of the proposed method. The method was applied to units generator in Java Bali system 500 kV.

Watt-level 10-gigahertz solid-state laser enabled by self-defocusing nonlinearities in an aperiodically poled crystal

Femtosecond modelocked lasers with multi-gigahertz pulse repetition rates are attractive sources for all applications that require individually resolvable frequency comb lines or high sampling rates. However, the modelocked laser architectures demonstrated so far have several issues, including the need for single-mode pump lasers, limited output power, Q-switching instabilities and challenging cavity geometries. Here, we introduce a technique that solves these issues. In a two-dimensionally patterned quasi-phase-matching (QPM) device, we create a large, low-loss self-defocusing nonlinearity, which simultaneously provides SESAM-assisted soliton modelocking in the normal dispersion regime and suppresses Q-switching induced damage. We demonstrate femtosecond passive modelocking at 10-GHz pulse repetition rates from a simple straight laser cavity, directly pumped by a low-cost highly spatially multimode pump diode. The 10.6-GHz Yb:CaGdAlO4 (Yb:CALGO) laser delivers 166-fs pulses at 1.2 W of average output power. This enables a new class of femtosecond modelocked diode-pumped solid-state lasers with repetition rates at 10 GHz and beyond.

The Effect of Inspiratory Resistance on Exercise Performance and Perception in Moderate Normobaric Hypoxia.

Respirators are simple and efficient in protecting workers against toxic airborne substances; however, their use may limit the physical performance of workers. The purpose of this study was to determine the effect of inspiratory resistance on physical performance and breathing perception in normobaric hypoxia. Nine healthy men wore a tight-fitting respiratory mask outfitted with one of four different inspiratory resistors (R) (0, 1.5, 4.5, 7.5 cm H2O/L/Sec) while exercising at normobaric hypoxia (17% O2) at submaximal exercise workloads of 50, 100, and 150 W on a cycle ergometer for 10 minutes each, followed by a maximal oxygen uptake (VO2max) test to exhaustion. Maximal power output at R7.5 was significantly lower than R0 (p = 0.016) and R1.5 (p = 0.035). Respiration rate was significantly reduced at R4.5 (p = 0.011) and R7.5 (p ≤ 0.001) compared with R0. Minute ventilation was significantly decreased in R7.5 compared with R0 (p = 0.003), R1.5 (p = 0.010), and R4.5 (p = 0.016), whereas VO2 was not significantly changed. Breathing comfort (BC) and breathing effort (BE) were significantly impaired in R7.5 (BC: p = 0.025, BE: p = 0.001) and R4.5 (BC: p = 0.007, BE: p = 0.001) compared with R0, but rating of perceived exertion (RPE) remained unchanged. Added inspiratory resistance limited maximal power output and increased perceptions of BC and BE in normobaric hypoxia. However, low-to-moderate inspiratory resistance did not have a deleterious effect on VO2 or RPE at submaximal or maximal exercise. Perceptual and physiological characteristics of respirators of varying inspiratory resistances should be considered by manufacturers and end users during design and respirator selection processes.

Dynamics characteristics analysis and control of FWID EV

Compared with internal combustion engine (ICE) vehicles, four-wheel-independently-drive electric vehicles (FWID EV) have significant advantages, such as more controlled degree of freedom (DOF), higher energy efficiency and faster torque response of an electric motor. The influence of these advantages and other characteristics on vehicle dynamics control need to be evaluated in detail. This paper firstly analyzed the dynamics characteristics of FWID EV, including the feasible region of vehicle global force, the improvement of powertrain energy efficiency and the time-delays of electric motor torque in the direct yaw moment feedback control system. In this way, the influence of electric motor output power limit, road friction coefficient and the wheel torque response on the stability control, as well as the impact of motor idle loss on the torque distribution method were illustrated clearly. Then a vehicle dynamics control method based on the vehicle stability state was proposed. In normal driving condition, the powertrain energy efficiency can be improved by torque distribution between front and rear wheels. In extreme driving condition, the electric motors combined with the electro-hydraulic braking system were employed as actuators for direct yaw moment control. Simulation results show that dynamics control which take full advantages of the more controlled freedom and the motor torque response characteristics improve the vehicle stability better than the control based on the hydraulic braking system of conventional vehicle. Furthermore, some road tests in a real vehicle were conducted to evaluate the performance of proposed control method.

Rotating-Sleeve Triboelectric-Electromagnetic Hybrid Nanogenerator for High Efficiency of Harvesting Mechanical Energy.

Currently, a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) have been hybridized to effectively scavenge mechanical energy. However, one critical issue of the hybrid device is the limited output power due to the mismatched output impedance between the two generators. In this work, impedance matching between the TENG and EMG is achieved facilely through commercial transformers, and we put forward a highly integrated hybrid device. The rotating-sleeve triboelectric-electromagnetic hybrid nanogenerator (RSHG) is designed by simulating the structure of a common EMG, which ensures a high efficiency in transferring ambient mechanical energy into electric power. The RSHG presents an excellent performance with a short-circuit current of 1 mA and open-circuit voltage of 48 V at a rotation speed of 250 rpm. Systematic measurements demonstrate that the hybrid nanogenerator can deliver the largest output power of 13 mW at a loading resistance of 8 kΩ. Moreover, it is demonstrated that a wind-driven RSHG can light dozens of light-emitting diodes and power an electric watch. The distinctive structure and high output performance promise the practical application of this rotating-sleeve structured hybrid nanogenerator for large-scale energy conversion.