Wide Power Range Research Articles

Beam-distortion enhanced terahertz radiation generation in air

Here we for the first time report an enhancement of terahertz (THz) radiation generation in air by a partial blocking of bichromatic pump beam consisting of the femtosecond Ti:Sapphire laser fundamental and its second harmonic. Both the experimental results and numerical analysis of the generation process demonstrated an increase of THz radiation yield by 15–20 percent over a wide range of the pump power and other experimental parameters. The dominant mechanism of THz radiation generation enhancement was found to be the pump pulse splitting suppression during its propagation in the plasma channel induced by the distorted beam.

High‐Entropy Alloy‐Induced Metallic Glass Transformation: Challenges Posed by in situ Alloying via Additive Manufacturing

In situ alloying and fabricating glassy structures through a layer‐by‐layer fashion approach are challenging but have high potential to develop novel‐graded materials. For the first time, this cost‐effective approach is applied to additive manufacturing (AM) of a Zr‐based bulk metallic glass (BMG) from high‐entropy alloys (HEAs). A newly developed composition of Zr40Al20Cu20Ti20 is fabricated through laser powder bed fusion (LPBF). Process parameters are optimized within a wide range of laser power (50–200 W) as well as scanning speed (50–800 mm s−1). In all printed samples, microscopic and compositional examinations reveal no glass formation, but very fine grains and CuTi and AlTi nanocrystals. Some glassy transitions at the interfaces may be encouraged to occur with proper melting and mixing. However, the main reason for not obtaining a glassy matrix is the substantial proportion of unmelted Zr raw powder throughout the structure as spherical particles. Consequently, glass formation can be hindered by a considerable amount of compositional deviation. During LPBF, in situ alloying poses significant challenges to developing BMGs. Hence, the various stages of the process, including raw material specifications, laser settings, and process parameters, should be investigated further.

Microstructure homogeneity and strength-toughness balance in submerged arc additive manufactured Mn-Ni-Mo high-strength steel by unique intrinsic heat treatment

The antagonism between ‘internal homogeneity’ and ‘large dimension’ in metallic materials is an intrinsic obstacle to the manufacturing of heavyweight yet reliable structural components used for real commercial production. Economical and scalable manufacturing strategies to this challenge need to be acknowledged. This study elucidated the effectiveness and potential of a novel submerged arc additive manufacturing (SAAM) method to homogenize microstructure in-situ and high-efficiently fabricating large-scale components. By leveraging a ‘full-layer-penetrated’ intrinsic heat treatment inherent to the SAAM process, the thoroughly homogenized microstructure of a Mn-Ni-Mo nuclear power high-strength steel consists of finer equiaxial prior-γ grains (~110 µm) along the build direction, with predominantly fine (~7.2 µm) α-Fe phase (bainite) formed inside. Isotropic mechanical characteristics and superior strength-toughness balance (high tensile strength ~740 MPa and low ductile-brittle transition temperature (DBTT) ~− 34 ℃) were achieved and outperformed a wide range of nuclear power or offshore engineering steels processed by conventional methods. The strengthening behaviors in our SAAMed part mainly attribute to the grain boundary and solid solution strengthening whilst the high impact toughness and low DBTT benefit from finer grains and martensite/austenite islands compared to wrought counterparts. It is envisioned that this novel method shows tremendous promise in the additive manufacturing of heavyweight yet homogeneous components.

Theory of Dronized Laser Source for Next Generation of Optical Wireless Power Transmission

A theory of dronized laser resonator source which can be applied effectively to achieve an efficient remote wireless optical power transmission (WOPT) for the next 6G mobile communications, internet of things (IoT) devices, and continuous flying unmanned aerial vehicles (UAV) is proposed. The proposed laser resonator composes mainly of mirrors and a gain element that can be carried individually by drones to form a relatively long cavity. The airborne components can be assembled according to a specified formation flight of drones to configure a flying laser cavity that exposes its output towards the corresponding target. The stability of the proposed device is theoretically analyzed in terms of main important intracavity parameters, such as length, g-geometrical parameters, and radius of curvature of mirrors. Accordingly, the performance of the confocal symmetric laser resonator is determined in terms of mode size, beam waist size, and beam divergence angle of the fundamental mode in presence of refractive power variation. Simulation results have shown that a stable operation over a wide range of refractive power of confocal long laser resonator can be obtained when the value of curvature of mirror approaches resonator length. In addition, an acceptable fundamental mode size at gain element and mirrors is obtained with an expected efficient gain medium excitation and low diffraction loss.

Multi‐input battery‐integrated single‐stage DC‐DC converter for reliable operation of solar photovoltaic‐based systems

SummarySolar photovoltaic (PV) systems are emerging progressively due to their wide compatibility range, ease of installation, and environmental friendliness. The module mismatch (MM) losses and module open circuit (MOC) fault can cause the power mismatch between different PV modules. This significantly affects the energy output from the PV module. Also, the intermittent nature of solar PV power makes the solar PV systems unreliable; to compensate for this, conventional PV systems utilize a battery storage system (BSS) with separate bidirectional converter. These bidirectional converters require two‐stage power conversion and massive battery bank connected at the DC link. This leads to the further reduction in overall efficiency. To address these issues, this paper proposed a multi‐input PV battery system (MIPBS) that uses nonisolated buck and boost converter combinations. It requires single‐stage power conversion to extract maximum power from each PV module along with BSS charging and discharging. Its modular design allows it to function across a wide range of voltage, power, and BSS choices. The proposed system is capable of mitigating the MM loss and sustaining the MOC fault. This paper discusses the operation, steady‐state analysis, and dynamic analysis of the proposed MIPBS. The performance of the proposed MIPBS is validated using a state‐of‐the‐art experimental setup with two PV modules, each having a rating of 60.53 W.

A wide-range reconfigurable RF energy harvesting system with integrated storage and load regulation controller

This paper presents an integrated RF energy harvesting system that uses a rectifier with 30 reconfigurable parallel stages to cover a wide input power range extending from -14dBm to 4dBm. The system mitigates the conduction losses associated with the reconfigurable switches via employing gate switching. Additionally, a voltage feedback loop is implemented to regulate the average output voltage level at the main load at 1V, while delivering the excess power to a secondary storage unit (supercapacitor) at 3V. Circuit simulations, using a 130 nm CMOS technology, show that the proposed design is capable of achieving a peak Power Conversion Efficiency (PCE) of 45% at 0dBm using an external matching network, and a maximum of 36% at 0dBm with internal matching. Additionally, the system achieves high PCE (>20%) for an input power range of more than 14dB, along with an excellent load regulation performance of 27mV, eliminating the need for extra voltage regulators at the output.

Research on dual‐frequency modulation strategy of wireless power transfer system

AbstractCompared with traditional wired power transmission, wireless power transfer(WPT) has fully exhibited its key advantages of better safety and convenience, stronger reliability and electrical isolation, and less maintenance. Although the phase‐shift modulation strategy has been widely used in various WPT applications, it has certain limitations in terms of high‐frequency hard‐switching, which increases the power loss of the WPT system during voltage regulation. To achieve efficient operation over a wide range of load power, this paper proposes a dual‐frequency modulation strategy for the WPT system. The advantages of the dual‐frequency modulation strategy are the simple modulation logic and the lower switching loss. It maintains the optimal load impedance during constant voltage output and improves the overall efficiency of the system. For validation, we designed the control circuit and wrote the control program and built the experimental prototype of the WPT system to carry out the phase‐shift modulation experiment and the dual‐frequency modulation experiment, respectively. The experimental results show that the soft switching range and efficiency of the WPT system under the dual‐frequency modulation strategy are better. At the rated output power, the efficiency of the WPT system under dual‐frequency modulation strategy is 89.75%. The feasibility of the dual‐frequency modulation strategy has been confirmed.

Ultrawideband Rectifier With Extended Dynamic-Power-Range Based on Wideband Impedance Compression Network

This article proposes an ultrawideband rectifier with high efficiency at wide input power range. It consists of a wideband impedance compression network (WICN) and two subrectifiers. The proposed impedance compression network (ICN) offers a more universal design method and higher design flexibility. Thus, the impedance variation of subrectifiers at wide input power range can be reduced at several frequencies. With proper setting of these frequencies, the rectifier can maintain stable, high efficiency at wideband, and wide input power range simultaneously. Besides, the proposed network can also realize impedance matching, hence saving extra matching components. The mechanism of the proposed rectifier is analyzed. For verification, a prototype is implemented and measured. The optimal efficiency of 72.2% is found at 6.5 dBm and 1.2 GHz. The prototype can maintain an efficiency beyond 70% of the peak value at frequencies ranging from 1.0 to 2.7 GHz. The relative bandwidth (91.9%) is so far the widest among the rectifiers with resistance compression networks (RCNs)/ICNs. At the operating band, the rectifier can maintain an efficiency beyond 70% of the peak at input power ranging from −6.2 to 13 dBm. The total size is as compact as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.19\lambda \times 0.16\lambda $ </tex-math></inline-formula> at the central frequency.

A Harmonic Suppression Energy Collection Metasurface Insensitive to Load and Input Power for Microwave Power Transmission

This article describes a high-efficiency harmonic suppression metasurface (HSMS) energy collector, which is insensitive to frequency, input power, and load. A method of integrating harmonic suppression function into energy collection metasurface (MS) to improve system conversion efficiency is proposed. Integrated RF synthesis channels in HSMS improve diode power availability and turn-on time. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> finite element MS array was designed and fabricated, achieving a conversion efficiency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {RF}-\mathrm {ac}}$ </tex-math></inline-formula> of 96%. The measurement results show that the integrated harmonic suppression can improve the efficiency of ac–dc conversion by 2%–4%. In addition, we propose an impedance compression rectifier to reduce the input power and load requirements of the system. Since HSMS eliminates harmonic suppression networks, the rectifier structure is simple and compact. Finally, the system achieved an efficiency of 74.5% at 5.8 GHz with an input power of 18 dBm. Importantly, it shows that HSMS energy collectors can remain efficient over a wide range of power 6–25 dBm and loads of 500– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2000~\Omega $ </tex-math></inline-formula> . The proposed concept is suitable for high-efficiency microwave power transmission (MPT) systems with different input power and load conditions.

Wideband Photonic Microwave Frequency Divider With Large Harmonic Suppression Capability

An all-optical photonic microwave frequency divider (PMFD) is presented. It is based on injecting an RF phase modulated optical signal into a semiconductor laser oscillating in the period-two state. New optical frequency components with frequency separation of half of the input RF signal frequency are generated at the laser output. A frequency divided signal can be obtained by the beating of these optical frequency components at a photodetector. Large harmonic suppression can be achieved by using an optical filter to select only two optical frequency components to be detected by the photodetector. The proposed PMFD is free of electrical components and does not suffer from the modulator bias drift problem. It has the potential to operate over a 100 GHz frequency range. System parameters required to realise divide-by-two frequency division operation for different input RF signal frequencies are investigated. Experimental results are presented for the novel PMFD, which demonstrate the generation of a 1/2 frequency component for different input RF signal frequencies by controlling the forward bias current of an off-the-shelf semiconductor laser, and which also show the important advantages of large harmonic suppression and high signal-to-noise ratio performance. Wide input RF signal power range and high output stability performance are also demonstrated experimentally.

Energy Efficiency Enhancement of Inductively Coupled Plasma Torch: Computational Study.

In this research, we studied the performance analysis of inductively coupled radiofrequency plasma “RF-ICP” torch used in multi-material processing. A 2D numerical model built with COMSOL Multiphysics was used to study the discharge behavior and evaluate the overall efficiency transmitted into the plasma system. The temperature and velocity flow of the plasma were investigated. The numerical results are consistent with previous experimental studies. The temperature and velocity profiles are represented under a wide range of RF power and for different sheath gas flow rates. With increasing power, the radial peak temperature typically shifts towards the wall. The resistance of the torch rises whereas the inductance diminishes with increasing RF power. The overall dependency of the coupling efficiency to the RF power is also estimated. The stabilization of the plasma flow dependency to the sheath swirl flow was investigated. The incorporation of Helium (0.02%) into an Argon gas was established to minimize the energy lost in the sidewall. The number and spacing of induction coil numbers affects the temperature and flow field distribution. A valuable approach to designing and optimizing the induction plasma system is presented in the proposed study. The obtained results are fundamental to specify ICP torch design criteria needed for multi-material processing.

Effect of RF sputtering parameters on the nanoscratch properties of quinary Ti-Zr-Cu-Ni-Al thin film metallic glass

Recently, thin film metallic glasses (TFMGs) gained renewed attention as they can circumvent the brittleness problem of bulk metallic glasses. When sputtered from a multicomponent cast target, the composition control of TFMG is always challenging. Here, we demonstrate the tight composition control of sputtered Ti-Zr-Cu-Ni-Al TFMG by a spark plasma sintered multicomponent target and investigate their structural and nanoscratch properties. The radio frequency (RF) power and Ar pressure were tuned to optimize nanoscratch properties. The highest hardness (~16.2 GPa) and thus best nanoscratch resistance was obtained at an RF power of 160 W and Ar pressure of 7 Pa. The best nanoscratch properties originated from the dense, fine column morphology of the TFMG. Moreover, it was found that the scratch mechanism changed from plowing to a combination of plowing and stick-slip under a ramping scratching load of 10 mN. The transition happened progressively at lower loads when the hardness of the TFMG decreased. This study provides a useful guideline for developing TFMG as a scratch-resistant protective coating. • Multicomponent target fabricated through low-temperature spark plasma sintering allowed precise composition control of TFMG. • A wide range of RF power and Ar pressure (160-240 W and 4–7 Pa) can produce glassy phase in the Ti-Zr-Cu-Ni-Al system. • Optimum nano-scratch resistance and hardness achieved for TFMG deposited at lower power and higher pressure (160 W and 7 Pa).

A 1 V -21 dBm threshold voltage compensated rectifier for radio frequency energy harvesting

Due to the limitations of battery life and capacity, power supply has been the bottleneck for scaling of a wireless sensor network in thousands or millions of nodes. RF energy harvester (RFEH) is a promising solution to power up sensors and wireless devices due to increasing accessibility of RF energy sources, better silicon integration of the harvester circuit and compatibility with wireless networks. One of the significant limitations of RF energy harvester is low power efficiency rectifier where the main function of the micropower rectifier is to convert RF energy into DC energy. To achieve higher power conversion energy (PCE), this paper presents a five-stage charge pump rectifier, with implementation of diode-connected MOS transistors and an auxiliary circuit to produce compensation voltage to the charge pump to achieve higher efficiency over a wide input range. This work is designed and implemented using 130nm CMOS technology and achieved a wide input power range of 15 dBm with efficiency higher than 20%; and at -21 dBm sensitivity for 1V output is achieved while driving 1 MΩ load at 920MHz.

Effects of unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio

The large height-radius ratio design of the Hall thruster increases the difference of radial distributions of magnetic field and plasma parameters in the channel, so that the optimal discharge effect of the thruster cannot be guaranteed under the symmetrical magnetic field configuration relative to the channel centerline. In this work, the effects of the unsymmetrical magnetic field on discharge characteristics of Hall thruster with large height-radius ratio were studied through experiments and PIC simulations. The results show that the thruster can realize stable discharge in a wide power range under unsymmetrical magnetic fields. Also, the unsymmetrical magnetic field plays a positive role in improving the discharge performance and prolonging the service life of the thruster. The inward-inclined magnetic field can effectively improve the discharge performance of the thruster, and the discharge efficiency can be increased by 1.5% under the rated working condition compared with the symmetrical magnetic field. The advantage in performance is mainly attributed to the improvement of ionization efficiency of propellant. The outward-inclined magnetic field is more conducive to prolong the service life of the thruster, and the peak value of ion power deposition on the inner wall can be reduced by 40% under the rated working condition due to the outward inclination of the ionization zone and the reduction of the radial electric field. However, under unsymmetrical magnetic field, the ionization zone deviates from the channel center, and the high ionization rate zone is more dispersed in distribution, thus leading to the increase in plume divergence angle. This study verifies that the unsymmetrical magnetic field has certain advantages under the structure of large height-radius ratio, which could be used as a guidance for the optimal design of Hall thruster with large height-radius ratio.

6.85 kW Ytterbium-Raman Fiber Amplifier Based on Adjustable Raman Threshold Method

To achieve a high spectral purity Raman laser in a wide range of pump power, we propose the adjustable Raman threshold method and experimentally demonstrate a 6.85 kW ytterbium-Raman (Yb-Raman) fiber amplifier in this paper. The Raman threshold is adjusted to coordinate with pump power level via manipulating the Raman proportion from the master oscillator. The spectral purity of Raman laser at 1120 nm reaches 86.0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> at the highest output power and keeps over 65 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> throughout. And the 3 dB bandwidth is maintained within 2.5 nm. The system shows potential in further power scaling-up because the four-wave-mixing-induced high-order Raman noise is circumvented by designing wavelengths of the seeders. This work not only reports the highest output power of the Yb-Raman fiber lasers (to the best of our knowledge), but also provides an approach to achieve an agile lasing threshold in the Yb-Raman fiber amplifiers without any structural adjustments. The Yb-Raman fiber amplifiers with high spectral purity over a broad range of power will have promising applications in communications, industry and scientific researches.

A CMOS RF energy harvester with high PCE over a wide range of input power

A CMOS RF energy harvester with high PCE over a wide range of input power

Broad Dual-Band Rectifier With Wide Input Power Ranges for Wireless Power Transfer and Energy Harvesting

This letter presents a broad dual-band rectifier with a wide input power range that employs a dual-band matched voltage doubler (DMVD). The DMVD is composed of a voltage doubler and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -type matching networks connected with each diode; it transforms the input reactance of each diode independently over wide input power and broad dual-band ranges, thereby widening the dynamic input power range. The proposed rectifier was implemented with the dimensions of 40 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times15$ </tex-math></inline-formula> mm. Measurements reveal that the power conversion efficiency (PCE) was maintained at over 50% in the wide input power ranges of 10.3–32 dBm and 13.5–31.5 dBm at 0.915 and 2.45 GHz, respectively. PCEs exceeding 50% were measured over frequency ranges of 0.3–1.1 GHz and 1.5–2.6 GHz.

Experimental and Numerical Study of the Flammability Limits in a CH4/O2 Torch Ignition System

The current work is devoted to studying combustion initiation inside the methane-oxygen torch igniter for a hybrid rocket motor. The ignition system can generate a wide range of power and oxidizer-to-fuel ratios. It has a self-cooled vortex combustion chamber with one fuel jet injector and one circumferential vortex oxidizer injector. The system adjusts the mass flow rates of the propellants through the control valves and organizes cooling of the wall and flame stabilization. Experimental analysis of the ignition limits was investigated on the laboratory test bench. The propellants’ pressure and mass-flow rates, combustion temperature, ignition delay, and spark frequency were controlled during the tests. The authors executed a series of tests with different propellants’ mass flow rates. As a result, the region of stable ignition was found as well as the regions of ignition failure or unreliable ignition. A previously validated numerical model was used to analyze the flow in the reliable ignition region and the ignition failures region. Several numerical simulations of the transient three-dimensional chemically reacting flow were implemented. Consequently, the ignition delay and the thermal impact on the combustion chamber wall were determined numerically. Results of the simulations were compared with theoretical and experimental data showing good correspondence.

Controllable multiple-pulse dynamic patterns in the mode-locking ultrafast laser with a GIMF-YDF-based saturable absorber

An Yb-doped mode-locked fiber laser with controllable multiple-pulse dynamic patterns is experimentally demonstrated by use of an all-fiber saturable absorber (SA) based on graded index multimode fiber (GIMF)-Yb-doped fiber (YDF) structure. In addition to stable fundamentally mode locked pulses with 11 MHz, multi-pulse patterns operated in bunched pulses could be obtained with different pump powers. Besides, harmonically mode-locked pulses with pulse width of 105 ps and bandwidth of 0.093 nm are realized. The harmonically mode-locking operation exhibited a high stability and worked at a wide range of pump power. To our knowledge, this is also the first report of both harmonically mode-locked pulses and bunched pulses in a fiber laser with a GIMF-YDF based SA. The results reveal the versatility and flexibility of the GIMF-YDF structured device in controlling the pulse dynamics for different experimental requirements.

A Current-Sharing Compensation Method for High-Power-Medium-Frequency Coils Composed of Multiple Branches Connected in Parallel

In inductive power transfer (IPT) systems, the coils with paralleled multiple branches are commonly used in high power applications where the frequency range is between 20 and 90 kHz. The traditional compensation method takes multiple branches as a whole and the compensation capacitors are connected outside the coils, which suffers from current unbalance among multiple branches, but currently few researchers analyze it. Therefore, this article illustrates the current-unbalance mechanism and proposes a current-sharing compensation method for IPT coils. The current-unbalance characteristics of coils with paralleled multiple branches are illustrated to prove the current-sharing necessity. Then, based on the relation between the impedance of branch and current unbalance, a compensation capacitor with a specially designed value is connected in each branch, so that the current unbalance can be suppressed by the increased branch impedance. Besides, the cost, volume, and weight of IPT systems remain unchanged approximately. Finally, a 30-kW IPT prototype is built up to verify the availability of the proposed method, and the currents and temperatures of multiple branches are equally distributed within wide power range with this method.