Power Handling Capability Research Articles

Cryogenic optical packaging using photonic wire bonds

The widespread adaptation of systems relying on optically controlled quantum information will require reliable and efficient multi-channel fiber-to-chip connections that function at cryogenic temperatures. Here we demonstrate low loss (2 dB per channel) connections between a single mode fiber array and tapered silicon waveguides down to 5 K using polymer based photonic wire bonds (PWBs). A method is described for assembling the silicon chip and fiber array such that the PWB connections are robust to temperature cycling and cryostat bakeout. The threshold power handling capability of the PWBs is greater than 4 dBm, sufficient to demonstrate optical bistability in silicon microring resonators coupled to the waveguides at 5 K.

Raman suppression in high-power fiber oscillators by femtosecond-written chirped and tilted fiber Bragg gratings

Realizing stimulated Raman scattering (SRS) suppression is a key topic for high-power fiber lasers. Here, we report an effective and simple strategy for SRS suppression using chirped and tilted fiber Bragg gratings (CTFBGs) in high-power fiber oscillators while maintaining the compactness and stability of the system. The CTFBG is inserted on the side of a cavity mirror FBG without cutting the gain fiber. To improve power handling capability, the CTFBG and cavity mirror FBGs are inscribed by femtosecond (fs) lasers. The optimal SRS suppression effect can be realized when the CTFBG is inserted into the resonant cavity and on the side of the output coupler FBG. The SRS threshold is increased by approximately 11% with an SRS suppression ratio of nearly 14 dB. Moreover, the output power of the fiber oscillator is improved to 3.5 kW, which is the maximum power achieved in fiber oscillators with SRS suppression using CTFBGs, to the best of our knowledge. The temperature of the air-cooled CTFBG is 50.2 °C, which has the potential to handle higher power. This work provides new insights for suppressing SRS in fiber oscillators, promoting the application of CTFBGs in high-power lasers.

Development of an accelerator-based neutron source to prototype Mo-99 production, part I: A liquid LBE windowless target

Molybdenum-99 (Mo-99)’s decay product, technetium-99 (Tc-99 m), is one of the most critical isotopes for medical diagnostics. To provide U.S. domestic supply of Mo-99 without using high-enriched uranium (HEU), a subcritical uranium target assembly (UTA) is irradiated by an accelerator-based neutron source to create Mo-99 through fission. This study discusses the development of the accelerator-based neutron source. The high-energy electrons from the accelerator irradiate a liquid lead-bismuth eutectic (LBE) target to produce neutrons. Part I of this work focuses on numerical and experimental analysis towards the development of a liquid LBE windowless target. Unlike the existing windowless targets in literature, the current design creates a vertical free surface for a beam to irradiate. First, a hydrodynamic analysis of the LBE windowless target is performed. Simplified analytical calculations are assisted by 2D computational fluid dynamics (CFD) simulations to design the target, with the focus on eliminating recirculation zones and avoiding cavitation. With the optimized geometry, the experimental study is performed to investigate the flow hydrodynamics using liquid LBE. The experiments (1) compare pressure drop in the system to correlation predictions; (2) visualize the free surface liquid LBE flow from the beam view; (3) validate the LBE flow profile using temperature sensitive paint from the side view; and (4) validate the liquid LBE film thickness using gamma densitometer measurements. Second, the power handling capability of the designed windowless target is investigated. The divider plate in the current design is susceptible to overheating due to the thin LBE film in front. As LBE erosion and corrosion is likely to occur at an LBE velocity of 2.0 m/s and temperature above 500 °C, a power limit of 10 kW of beam power was established to prevent this corrosion from occurring, which is calculated by a Nusselt number correlation. The divider plate surface temperature at 10 kW agrees well with the 3D CFD simulation results. Part I demonstrates the fundamental physics in liquid LBE windowless target design and associated testing. A companion paper, Part II will demonstrate how to couple this windowless target into the Mo-99 production system, including an accelerator system operating under an ultra-high vacuum and the UTA cooled by water at room temperature.

Chemically synthesized graphene oxide nanosheet (GONs) is an efficient electrode material for supercapacitor: Effects of current collectors

Herein, the graphene oxide nanosheets (GONs) with a low degree of agglomeration in the single and multi-layered structure manufactured by the modified Hummer's route. The fundamental, and morphological properties of GONs have been undertaken using X-ray Diffraction (XRD), and scanning electron microscopy (SEM) techniques respectively. The availability of functional groups and stretching-bending vibration in graphite and GONs materials have been investigated using the Fourier transform infrared spectroscopy (FT-IR) and Raman investigation study. Transmissionn electron microscopy (TEM) offers a more in-depth morphological and structural investigation of GONs material. The supercapacitive characteristics such as cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) of GONs-based electrodes were studied in 1 M KOH electrolyte. In addition, the synthetic graphene oxide‑nickel foam (GO-NF) electrode demonstrated excellent capacitance of (302 F/g at 5 mV/s) with power handling capabilities, having specific energy and power up to 33 Wh/kg and 1250 W/kg at 5 mA/cm2 respectively. The cyclic stability of GO-NF electrodes demonstrated long-term electrochemical capacitive retention of 90 % over the 5000 CV cycles. The liquid-state symmetric (GO-NF//GO-NF) device displays a specific capacitance of 224 and 119 F/g with Ed of 32 Wh/kg and Pd of 1100 W/kg at a scan rate of 5 mV/s and a current density of 4 mA/cm2 respectively. These outcomes show the GO-NF's superior electrochemical activity which has a beneficial impact as a potential material for energy-storage technologies.

Influence of growth temperature on the properties of aluminum nitride thin films prepared by magnetron sputter epitaxy

High quality, uni-polar, epitaxial AlN with minimum oxygen content promises excellent surface acoustic wave and bulk acoustic wave resonator characteristics such as high electromechanical coupling coefficient and power handling capabilities, which is particularly useful for RF filter applications. By systematically varying the growth temperature, the study investigates its impact on the oxygen levels, defect states, and crystallographic texture of the AlN thin films using a combination of atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, spectroscopic ellipsometry, scanning transmission electron microscopy, as well as room temperature and temperature dependent I–V measurements. The research demonstrates that the films grown at a temperature of 700°C exhibit the most favorable results. These films exhibit the lowest oxygen levels, possess epitaxial growth, and display the highest crystalline quality (XRD AlN 0002 ω−FWHM=1.3°). Additionally, these films demonstrate a significant reduction in sub-bandgap absorption. By comparing the cathode current measured during deposition, we suggest that the presence of an impurity layer formed during idle time between depositions as a possible source of oxygen in the sputter chamber. In addition, the study presents a possible model to explain the mixed polarity observed in AlN and proposes various ways to achieve uni-polar AlN on silicon substrates.

Evolution, Challenges and Applications of Modern MOSFETs

As technology scales down to the nanoscale regime, MOSFETs are widely used in various applications today, which serve as key components in power supplies, amplifiers, digital circuits, and microprocessors. Their ability to control and switch high currents makes them essential in electronic devices, ranging from smartphones and laptops to industrial machinery and electric vehicles. However, traditional MOSFET designs face significant limitations due to quantum effects, increased variability, and many other issues. They are prone to overheating, which limits their power handling capability, and their switching speeds are relatively slow, leading to inefficiencies in high-frequency circuits. Furthermore, traditional MOSFETs suffer from voltage limitations and require complex driver circuits, restricting their use in certain high-voltage applications. This paper provides a focused exploration of the challenges and opportunities in designing nanoscale MOSFETs, which starts from providing a comprehensive overview of the history, differences, dilemmas, and applications of modern MOSFETs. By examining the evolution of MOSFET technology, discussing the challenges faced by designers, and exploring the wide range of applications, which aims to inspire further research, innovation, and advancements in this critical field of electronics.

An Ultra-Wideband, High Power and High Isolation Single-Pole-Double-Throw Switch Using Capacitive Loading Approach

This paper presents an ultra-wideband, series-shunt type single-pole-double-throw (SPDT) switch with high isolation and good power handling capability from DC to 40 GHz. A new topology using capacitive loading on the shunt arms was proposed to improve the isolation across the entire band. The effect of the capacitive loading has been theoretically analyzed. Using the simple SPDT topology with one shunt arm as comparison, the capacitive loading approach exhibited an improvement of 5.9 dB in isolation at 40 GHz. To enhance the power handling capability, the stacked-FET configuration was adopted at the shunt arms. The optimum design has been implemented in the commercially available 0.15-lm GaAs pseudomorphic high-electron-mobility transistor (pHEMT) process and demonstrated an insertion loss of less than 3 dB, an isolation of greater than 39 dB, and an input 1-dB compression point (P1dB) of better than 32 dBm from DC to 40 GHz. To our knowledge, the proposed SPDT switch demonstrates the highest isolation over the widest bandwidth among other reported works to date.

Electro-Absorption Modulator Thermo-Optical Self-Heating Analysis

In this work a novel methodology is presented for coupled thermo-optical modelling of an electro-absorption modulator (EAM). First, an optical FDTD simulation results in the light absorption map in the EAM waveguide. This absorption is used as a heat source boundary condition in a thermal finite element (FE) simulation in order to calculate the waveguide temperature. The FE model is validated with experimental data. The temperature is averaged over the device length and used as input in a compact, fully coupled thermo-optical model. The model reveals a thermal instability of the device characteristic, which limits the maximum amount of optical power the device can handle. Finally, using the thermal FE model, a self-heating mitigation strategy is proposed. Using process compatible design changes, self-heating can be reduced by up to 40%, greatly increasing the EAM optical power handling capabilities.

RF design of helical long-wire traveling wave antenna for helicon current drive in KSTAR

This paper presents the development, fabrication, and implementation of a state-of-the-art helical long-wire traveling wave antenna (LW-TWA) for the Korea Superconducting Tokamak Advanced Research (KSTAR) helicon wave current drive (HCD). A multi-stage design approach has been employed incorporating schematic and simplified radio frequency (RF) modeling, to fulfill critical antenna performance criteria, such as parallel refractive index, while maintaining low electric field properties and load resilience. The advanced design includes a Faraday shield and a structurally rigid support for mechanical stability and minimal RF performance distortion. The sophisticated design and megawatt (MW)-class RF power handling capability of the LW-TWA hold the potential to improve HCD performance in KSTAR plasma.

A New 3D Frequency-Selective Structure for 5G Communication

Background: In this paper, a new frequency-selective structure (FSS) for 3 to 4 GHz frequency band of fifth generation (5G) is proposed as a result of an analytical mode-matching method. Methods: A new periodic structure with stepped rods is designed using a closed-form equation derived by the analytical mode-matching method. Performance of the structure is simulated by different numerical packages. Results: The analytical and simulation results demonstrate that the designed structure transmits incident waves in 3.4 to 3.9 GHz frequency range with return loss lower than 10 dB and insertion loss of about 0.5 dB. The structure reflects the frequencies out of this range, especially wireless local area network (WLAN) 5 GHz, which is adjacent to this band. Furthermore, the performance of the proposed structure is independent of the TE and TM polarization of the incident wave and relative to the angle of the incident wave up to 60 degrees from perpendicular to the FSS surface, it has minor variations of about 8% in the transmitted frequency bandwidth. In addition, the average value of maximum field enhancement factor (MFEF) as the ratio of maximum field magnitude on the FSS surface to the magnitude of the incident field, used for assessing power handling capability of the structure, is about 4.5. Conclusion: Therefore, these features make the proposed structure suitable for 5G communication and high power systems.

Part II: State-of-the-Art Technologies of Solar-Powered DC Microgrid with Hybrid Energy Storage Systems: Converter Topologies

Over the past few years, there have been significant advancements in Microgrid (MG) systems, particularly in the field of power electronics. These advancements aim to address the needs of the grid and loads, while integrating low-voltage, non-linear, and highly sensitive power sources, such as solar PV modules, batteries, and supercapacitors. It is crucial to select the appropriate converter configuration and power converters in MG systems, as they greatly impact their optimal performance. To achieve the best results, numerous architectures and converter configurations have been suggested for integrating different energy sources. As a result, a considerable number of research articles have been published, necessitating a thorough review. This article continues studies of Part I and presents a comprehensive overview of various architectures based on the arrangement of different sources and provides a detailed analysis and discussion of these architectures. This article covers thirty-three different categories of DC-DC converters, both isolated and non-isolated. These converters are divided into subcategories, such as conventional type, switched-capacitor type, soft-switching type, multi-phase type, and multilevel type. The article also evaluates the suitability of these topologies based on factors such as high conversion gain, power decoupling, efficiency, isolation, power handling capabilities, and compact design. The critical examination and comparative study presented in this work can be valuable for industry professionals and academics in selecting the most suitable architectural and power converter topologies for optimal performance.

Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER

Numerical simulations explore a possible tightly baffled, long-legged divertor (TBLLD) concept in a future upgrade of the tokamak à configuration variable (TCV). The SOLPS-ITER code package is used to compare the exhaust performance of several TBLLD configurations with results from unbaffled and baffled TCV configurations. The investigated TBLLDs feature a range of radial gaps between the separatrix and the divertor baffles, with a smaller gap resulting in tighter baffling. All modeled TBLLDs are predicted to lead to a denser and colder plasma in front of the targets and increase the power handling by factors of 2–3 compared to the present, baffled, divertor and by up to a factor of 12 compared to the original, unbaffled, configuration. This improved TBLLD performance is attributed to an increased neutral confinement with more plasma–neutral interactions in the divertor region. Both power handling capability and neutral confinement increase with tighter baffling. The core compatibility of TBLLDs with nitrogen seeding is also evaluated and the detachment window, with acceptable core pollution, for these TBLLDs is explored, showing a reduction of the required upstream impurity concentration to achieve detachment by up to 18% with tighter baffling.

Double-Side Cooled SiC MOSFET Power Modules With Sintered-Silver Interposers for a 100-kW/L Traction Inverter

Low-profile double-side cooled power modules are emerging in electric-drive inverters to achieve higher power density and efficiency. However, the rigid interconnection between the devices and two substrates raises the thermo-mechanical reliability issue of double-side cooled modules. In the prior work, we proposed the use of porous sintered-silver (Ag) interposers in the double-side cooled modules, resulting in reduced thermo-mechanical stresses, better heat extraction, and lower package parasitic inductance. To further improve the power density and demonstrate the benefits of using the sintered-Ag interposers, we proposed a revised half-bridge module layout that further reduced the power-loop parasitic inductance by 23%, improved the power handling capability by 44%, and retained a similar thermo-mechanical stress reduction. After carefully selecting high-temperature packaging materials, we fabricated the improved module layout with a reasonably high yield due to the deformable feature of sintered-Ag interposers. The thermal testing showed that the module had excellent power handling capability with a junction-to-fluid thermal resistance of 0.76°C/W due to the double-sided cooling. The electrical characterization at elevated temperatures up to 250°C and the switching characterization validated the functionalities of the power modules with SiC devices aimed for high-temperature and fast switching. Six of the double-side cooled power modules with sintered-Ag interposers were assembled into a segmented traction inverter, demonstrating a high power density of over 100 kW/L.

A Novel Four-Port Configuration With Improved Efficiency and Power-Handling Capability for Diode-Based Doublers in Submillimeter Waves

We present a novel four-port balanced configuration for Schottky diode-based doublers featuring improved power-handling capability and conversion efficiency. The circuit design includes two frequency doubler cells associated with compact functional networks, which provides unique phase differences for those generated harmonic currents. So, this circuit could achieve the inherent suppressions on odd-order harmonics as well as the fourth harmonic without any filter, which guarantees the efficient frequency multiplying and overcomes the efficiency degradations exists in conventional power-combined multipliers. Example of the diode-based frequency doubler, operating up to 115 GHz, has been demonstrated based on this prototype. At room temperature, the fabricated doubler exhibits a 13.6% 3-dB bandwidth and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 46.1% peak conversion efficiency (at 105 GHz) for a nominal input power of 240–360 mW. At the same time, this module could deliver maximum power over 230 mW with the maximum achievable input power level.

A Sub-GHz CMOS SPDT Antenna Switch Employing Linearity-Enhanced Biasing Strategy for Second-Order Harmonic Reduction

A CMOS single-pole double-throw (SPDT) antenna switch employing linearity-enhanced biasing strategy is proposed for the second-order harmonic (H2) reduction. It was implemented and demonstrated using a 0.28-lm thick-oxide MOSFET in 65-nm CMOS process. The NMOS transistor of the conventional antenna switch is replaced with the CMOS transistor composed of an NMOS and PMOS transistor in parallel to improve second-order harmonic distortion (HD2). The optimum channel width of an NMOS and PMOS transistor is chosen to achieve odd symmetry characteristic of I-V curve with respect to the drain-to-source voltage swing (VDS), and, as a result, enhance HD2 of the antenna switch. In addition, the linearity-enhanced biasing scheme is adopted to the PMOS transistor as a conventional negative biasing method of the NMOS transistor. This prevents the degradation of the power handling capability in adopting the PMOS transistor to the antenna switch. In the measurement, the proposed single-stack SPDT antenna switch shows an insertion loss of less than 0.6 dB and an isolation of greater than 38 dB from 100 MHz to 1 GHz with an input and output return loss of greater than 25 dB. Concerning for H2 and third-order harmonic (H3), it shows H2 of -65 dBm and H3 of -90 dBm at 150 MHz when a single-tone RF signal with a power of +5 dBm is applied. Compared to the conventional NMOS-based antenna switch, the proposed CMOS-based antenna switch improves HD2 by approximately 8 dB, 7 dB, and 1 dB at 150 MHz, 400 MHz, and 1 GHz, respectively, while maintaining the comparable insertion loss, isolation, and third-order harmonic distortion (HD3).

Mechanically Controlled, Wide-Angle Scanning, Series-Fed Antenna Array With Low Profile for High-Power Radar Systems

This paper presents the design and implementation of a mechanically-controlled, series-fed antenna array featuring wide-angle beamsteering at the X-band. A theoretical model of a series-fed array, including phase shifters inserted between consecutive elements, is initially developed to derive design rules and gain insight into crucial performance trade-offs. Subsequently, a mechanically-controlled, reflection-type phase shifter consisting of a branch line coupler and two Pi-network reflective loads is presented. A movable metallic overlay tunes the impedance of the reflective loads, thus effectively modifying the output phase. While requiring a minimal linear displacement of only 0.06λ0, this topology provides a maximum phase shift of 300° with an average insertion loss of 1 dB and is exploited for synthesizing a series-fed patch array. Based on simulations and measurements, the proposed antenna offers an almost constant realized gain of about 15 dBi within a wide scanning range of ±50°, and the side lobe level is better than -12 dB. The average total efficiency is 50%, and the cross-polarization levels are at least 11 dB below the maximum realized gain. The main weaknesses are the narrow bandwidth of 2.5% and the slight beam squint as the frequency varies. The proposed design is ideal for radars due to its excellent performance and high power-handling capability.

Mechanically Driven Solidly Mounted Resonator‐Based Nanoelectromechanical Systems Magnetoelectric Antennas

The miniaturization of antennas has been a significant challenge in the field of electronics and telecommunications. In recent years, mechanically driven thin‐film bulk acoustic resonator (FBAR) magnetoelectric (ME) antennas have emerged as a promising solution, demonstrating superior miniaturization capabilities compared to conventional state‐of‐the‐art compact antennas. While nanoelectromechanical systems (NEMS) FBAR ME antennas exhibit high miniaturization potential, their suspended thin‐film heterostructures render them fragile and exhibit low power handling capabilities. The findings demonstrate that solidly mounted resonator (SMR) NEMS ME antennas on a Bragg acoustic resonant reflector offer a compelling solution. With a circular resonating disk of 200 μm diameter operating at 1.75 GHz, these SMR‐based antennas display a high antenna gain of −18.8 dBi and a 1 dB compression point (P1dB) of 30.4 dBm. Compared to same‐size FBAR ME antennas with a free‐standing membrane, SMR‐based antennas exhibit significantly higher structural stability and 23.3 dB stronger power handling capability, in addition to easier fabrication processes. The compatibility of the simple fabrication processes with complementary metal–oxide–semiconductor technology, along with the dramatic miniaturization, high power handling, robust mechanical properties, and much higher antenna radiation gain, make these SMR‐based ME antennas a promising candidate for future antenna systems.

Robust femtosecond-written chirped and tilted fiber Bragg gratings for Raman filtering in multi-kW fiber lasers.

We present a robust chirped and tilted fiber Bragg grating (CTFBG) in a large-mode-area double-cladding fiber (LMA-DCF) written by a femtosecond (fs) laser. By implementing the fs-CTFBG into the output end of a high-power fiber laser for Raman filtering, a power handling capability of 4 kW is achieved with a Raman filtering ratio of ∼13 dB. To the best of our knowledge, this is the maximum handling power of a CTFBG for Raman filtering. The signal loss of the fs-CTFBG is 0.03 dB, which has little effect on the output laser beam quality. The air-cooled fs-CTFBG has a minimum temperature slope of 7.8°C/kW due to a self-annealing effect. This work proves the excellent performance of the fs-CTFBG, promoting the development of high-power CTFBGs.

A Wideband, 1-bit, Electronically Reconfigurable Phase Shifter for High-Power Microwave Phased-Array Applications

We present the design and high-power experimental characterization of a wideband, high-power-capable, electronically reconfigurable phase shifter for high-power phased-array applications. The device studied in this work offers an electronically switchable, 1-bit phase shift using the concept of polarization rotation (PR). The PR-based phase shifter is designed to work in a custom-designed, double-ridge (DR) waveguide environment. Two p-i-n diodes are used to control the transmission phase of the signal by rotating the polarization of the incident wave by either <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+90^\circ$</tex-math> </inline-formula> or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-90^\circ$</tex-math> </inline-formula> with respect to that of the incident wave, thereby creating a wideband, 1-bit phase shift between the two states. Simulation results demonstrated that this element can work over one octave bandwidth ranging from 6 to 12 GHz. A prototype of the device was fabricated and experimentally characterized at low and high power levels. The measurement results confirmed the simulations and demonstrated the wideband, high-power-density capability of the device. High-power continuous-wave (CW) experiments were conducted across the entire 6–12 GHz band and demonstrated that the unit-cell-averaged, CW power handling capability of the device exceeds 23.6 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> . High-power pulsed power experiments conducted at 9.382 GHz demonstrated that the unit-cell-averaged, peak power handling capability of the device exceeds 347 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^2$</tex-math> </inline-formula> for short-duration pulses.

Closed corner divertor with B × ∇B away from the divertor: a promising divertor scenario for tokamak power exhaust

A major challenge facing the steady-state operation of tokamak fusion reactors is to develop a viable divertor solution with order-of-magnitude increase in power handling capability as compared with present experience. A recently developed divertor concept for this end has been tested recently on EAST tokamak through combining the effects of a closed divertor corner and E × B drifts. The E × B drifts in the divertor move particles towards the outer divertor corner area in the scrape-off layer for B × ∇B directed away from the divertor, which can significantly enhance the particle concentration there, facilitating divertor detachment. In recent EAST experiments, the effects have been demonstrated where the lowest electron temperature at the divertor plate is obtained with strike point located close to the corner in the horizontal target and with B × ∇B away from the divertor. These experimental results are in reasonable agreement with SOLPS-ITER simulations including drift effects, suggesting that the new divertor concept potentially provides a promising divertor solution for long-pulse operations of future tokamak fusion reactors with much higher power fluxes.