High Broadband Research Articles

A High Efficiency Broadband Gallium Nitride Power Amplifier with Harmonic Control technology

ABSTRACT In order to meet the requirements of high efficiency and broadband for the wireless communication system, a high efficiency and broadband gallium nitride power amplifier (PA) is designed and verified. Using the step-matching structure, its bandwidth has been improved. Furthermore, its input matching network is constructed by connecting several microband lines serially to reduce the matching Q value. Meanwhile, the harmonic control network is designed as the output matching network, which is built by a quarter-wave (λ/4) line open circuit and short circuit microwave lines in parallel. Thus, its drain efficiency (DE)can be improved. This design is simulated and tested at 2.2–3 GHz with the gallium nitride (GaN) process. After measuring, it attains an output power (Pout) of 39.5–41.5 dBm, Gain of 10.5–12.5 dB, DE of 65.1%–78.3% with power added efficiency (PAE) of 64.8%–76.2%.

High voltage formation using the amplifiers cascading method

The dividing of high voltage broadband non-inverting cascade amplifiers into separate cascades, each of which has independent power sources, is suggested. These cascades are connected to one another in series, switching on the operational amplifiers and the feedback links. The gain of each cascade is determined by the non-inverting scheme of feedback that assures accurate signal processing. To provide stable and effective functioning, the operational amplifiers are supplied with power from transistor repeaters. That assures the required feeding voltage levels. Due to the thorough selection of the gain factor and feeding source voltage, the amplifier system achieves the expended output voltage range.

High performance self-driven broadband photodetector for polarized imaging based on novel ZrS3/ReSe2 van der Waals heterojunction

The distinctive characteristics of anisotropic two-dimensional (2D) materials, including in-plane anisotropy of optical absorption and carrier mobility, render them exceptionally suitable for application in the field of polarization detection and as a novel platform for the polarization imaging. Meanwhile, the consolidation of diverse functionalities within a single photodetector is highly anticipated to meet the demands of some special scenarios. Herein, a novel ZrS3/ReSe2 van der Waals (vdWs) heterostructure device was successfully constructed to realize polarization-sensitive, self-powered, and broadband photodetection and imaging. Owing to the built-in electric field of the type-II band alignment within the heterojunction, the device achieves a self-powered photoresponse ranging from 300 to 980 nm, an ultralow dark currentt ∼1 pA, and a commendable rise/decay time of 0.35/0.28 ms. Additionally, it has been demonstrated that the self-driven photodetector possesses a polarization-sensitivity with a notable anisotropic ratio about 2.02 (1.98) under 490 nm (980 nm) light illumination with zero bias, coupled with an excellent repeatability and stability. Furthermore, we also demonstrate the polarization imaging capabilities of the device in visible and near-infrared spectrum, realizing a contrast-enhanced degree of linear polarization imaging. This work paves a new platform to develop heterojunction photodetectors for high performance polarization-sensitive photodetection and next-generation polarized imaging.

Turning Trash to Treasure: The Influence of Carbon Waste Source on the Photothermal Behaviour of Plasmonic Titanium Carbide Interfaces.

Pyrolysis of carbonaceous waste materials has emerged as an effective recycling method to generate value-added products. In addition to producing pyrolytic oil and gas, the thermal degradation process yields solid pyrolytic char, which can be further processed. In this study, local waste materials, birch wood residue, Japanese knotweed stems, spent coffee grounds, tire rubber, and lobster shells were assessed for their potential to form pyrolytic char. After a simple acid treatment, many of these chars were successfully incorporated into solid-state synthesis of plasmonic titanium carbide (TiC) nanoparticles (NPs). Each char exhibited unique physical and chemical properties, which were leveraged to synthesize TiC NPs with distinct characteristics. To evaluate the plasmonic behavior of these TiC samples, solar-driven desalination experiments were performed. Notably, TiC derived from tire rubber demonstrated a high broadband absorbance and achieved a solar-to-vapor generation efficiency of 95%, corresponding to an evaporation rate of 1.40 ± 0.01 kg m-2 h-1 under one-sun illumination. This performance is the highest among all chars tested and ranks among the top reported values in the literature. Additionally, the evaporation interface maintained its performance over multiple cycles and under highly hypersaline conditions.

Elasticity and modal effects on the optimal performance of micro-perforated multi-layered absorbers

Multi-layered wall-treatments with thin lightweight micro-perforated panels offer a potential solution to achieve broadband noise absorption while complying with mass saving and compactness. This study examines how vibrational effects, often neglected, may impede the wideband acoustical performance of such partitions, made up of a distribution of either periodic or graded micro-perforated membranes or panels. The impedance translation method and a scattering matrix analysis have been implemented. It is found that the elasticity behavior of thin micro-perforated membranes has a beneficial effect on the acoustical efficiency of the partitions. The contributions of the individual acoustical resonances tend to merge if the elasticity effects are accounted for. If the partition is optimized, near-constant high absorption and low transmission values are obtained over a wide frequency range. A more robust design involves partitions made up of micro-perforated panels. It was observed that the first volumetric volumetric mode of the panels modifies the absorption properties of the partition. It cross-couples with the acoustical resonances and redistributes their spectral locations. This structural resonance sets an upper frequency bound, below which the partition achieves a high broadband performance. It should be accounted for when setting the frequency limits of the total dissipation to be optimized.

Research on a broad-band X-band high power relativistic klystron amplifier

This paper introduces a high-power broadband X-band klystron amplifier that achieves an output power of 157 MW and a 3 dB operating bandwidth of 6.7%. The amplifier employs an explosive emission diode with high impedance, which balances the requirements of high power and broadband. The multi-gap input and output cavities are designed to operate at two different longitudinal modes within the operating frequency band, resulting in a flat absorption rate and output efficiency. Moreover, an eight-stage stagger-tuned bunching section is implemented to achieve a uniform fundamental harmonic current modulation depth across the frequency band. Simulation results indicate that when the diode voltage is 550 kV and the beam current is 550 A, the amplifier can achieve a maximum power of 157 MW with an efficiency of 51.9% at the central frequency of 9.8 GHz. Furthermore, within the 3 dB operating bandwidth of 6.7% (670 MHz), the power output remains higher than 80 MW. This novel klystron amplifier structure exhibits exceptional performance in terms of bandwidth, power, and efficiency, thus validating the effectiveness of the design in enhancing bandwidth and providing a solid foundation for the broadband design of high-power microwave sources.

Bright compact ultrabroadband source by orthogonal laser-sustained plasma

Laser-sustained plasma (LSP) source featuring high brightness and broadband spectral coverage is found to be powerful in various fields of scientific and industrial applications. However, the fundamental limit of low conversion efficiency constrains the system compactness and widespread applications of such broadband light sources. In this paper, we propose an innovative orthogonal LSP to break through the conversion efficiency limitation. Driven by the elevated conversion efficiency from absorbed laser power to ultraviolet (UV) emission, a compact broadband source (250–1650 nm) with UV spectral radiance exceeding 210 mW/(mm2⋅sr⋅nm)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${mW}/({{mm}}^{2}\\,\\cdot\\, {sr}\\,\\cdot\\, {nm})$$\\end{document} is achieved with >100 W pump laser. With the plot of a two-dimensional refractive index model, we report an important conceptual advance that the orthogonal design eliminates the influence of the negative lensing effect on laser power density. Experimental results unambiguously demonstrate that we achieve a bright compact UV-VIS-NIR source with negligible thermal loss and the highest conversion efficiency to our knowledge. Significant enhancement of 4 dB contrast-to-noise ratio (CNR) in spectral single-pixel imaging has been demonstrated using the proposed ultrabroadband source. By establishing the quantitative link between pumping optics design and plasma absorption, this work presents a compact broadband source that combines superior conversion efficiency and unprecedented brightness, which is essential to high-speed inspection and spectroscopy applications.

Design, fabrication and vibration characteristics of a novel composite auxetic structure embedded with resonators

With the rapid development of shipbuilding and aerospace industries, the mechanical performance requirements for structures are becoming increasingly demanding. Conventional vibration reduction structures cannot meet the requirements for lightweight, high load capacity, low frequency and broadband vibration reduction. Therefore, it is necessary to consider new structural topologies and material systems. Inspired by the lightweight and high strength characteristics of composite materials, the negative Poisson's ratio characteristics and the locally resonating phononic crystal, the carbon fiber composite auxetic structure embedded with resonators is proposed. Embedded resonators within composite auxetic structures can be strategically positioned to introduce gaps, thereby enhancing the vibration damping performance. The basic auxetic structure is prepared by simpler methods including molding and bonding, and the outer shell of resonator is made by 3D printing technology. The method enables the design of appropriate outer shell based on various cavity types within the structure, ensuring a stable connection between resonators and the structure itself. The range of the band gap can be predicted based on the negative effective mass. Vibration behavior and band gap characteristics of the structure are proved through vibration experiments and numerical simulations. It is revealed that the structure can generate local resonant band gaps at lower frequencies. Meanwhile, the coupling relationship between the auxetic structure and the resonator makes an impact to the band gap range. Therefore, the proposed structure can meet the required multi-functional integrated performance requirements. Furthermore, the parametric analysis is carried out, and the relevant conclusions can provide theoretical guidance for designing porous composite structures with effective low-broadband vibration reduction capabilities.

High-efficiency hard X-ray blazed diffraction via refraction by nanometer-scale prism arrays

X-ray transmission gratings are widely utilized as wavelength dispersion elements in inertial confinement fusion and X-ray astronomy fields due to their high tolerance for alignment errors, light weight and compact size. However, the high transmittance of the grating bars in the hard X-ray range can lead to reduced efficiency of all other diffraction orders except for straight through zeroth order. We propose a novel blazed refraction grating design for the hard X-ray range that combines the advantages of transmission gratings and compound refraction lenses for the first time, demonstrating its superior performance in high broadband efficiency through compound refraction and diffraction from nanometer-scale periodic arrays of silicon prisms using beam propagation method and Fraunhofer diffraction simulation. This research develops blaze methods in gratings design and provides a new solution for compact and sensitive spectrum measurement in hard X-ray range.

Elevating electron energy gain and betatron x-ray emission in proton-driven wakefield acceleration

The long proton beams present at CERN have the potential to evolve into a train of microbunches through the self-modulation instability process. The resonant wakefield generated by a periodic train of proton microbunches can establish a high acceleration field within the plasma, facilitating electron acceleration. This paper investigates the impact of plasma density on resonant wakefield excitation, thus influencing the acceleration of a witness electron bunch and its corresponding betatron radiation within the wakefield. Various scenarios involving different plasma densities are explored through particle-in-cell simulations. The peak wakefield in each scenario is calculated by considering a long pre-modulated proton driver with a fixed peak current. Subsequently, the study delves into the witness beam acceleration in the peak wakefield and its radiation emission. Elevated plasma density increases both the number of microbunches and the accelerating gradient of each microbunch, consequently resulting in heightened resonant wakefield. Nevertheless, the scaling is disrupted by the saturation of the resonant wakefield due to the nonlinearities. The simulation results reveal that at high plasma densities, an intense and broadband radiation spectrum extending into the domain of the hard x-rays and gamma rays is generated. Furthermore, in such instances, the energy gain of the witness beam is significantly enhanced. The impact of wakefield on the witness energy gain and the corresponding radiation spectrum is clearly evident at elevated densities.

A comparative study of broadband PbS quantum dots/graphene photodetectors with monolayer and bilayer graphene

Colloidal quantum dots (QDs)/graphene nanohybrids provide a unique platform to design photodetectors of high performance. These photodetectors are quantum sensors due to the strong quantum confinement in QDs for spectral tunability, and in graphene for high charge mobility. Quantitatively, the high carrier mobility of graphene plays a critical role to enable high photoconductive gain and understanding its impact on the photodetector performance is imperative. Herein, we report a comparative study of PbS QDs/graphene nanohybrids with monolayer and bilayer graphene for broadband photodetection ranging from ultraviolet, visible, near-infrared to short-wave infrared spectra (wavelength: 400 nm–1750 nm) to determine if a specific advantage exists for one over the other. This study has revealed that both the monolayer and bilayer graphene grown in chemical vapor deposition can provide a highly efficient charge transfer channel for photo-generated carriers for high broadband photoresponse.

Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

High-Efficiency Photothermal Water Evaporation under Low-Intensity Sunlight Using Wood Biochar Monolith.

Utilizing energy directly from the sun, solar water evaporation drives the global hydrological cycle and produces freshwater from saline water in the oceans and on land. As water is a poor solar absorber, a photothermal material is needed to facilitate the conversion of photons to thermal energy and increase the efficiency of solar desalination. However, the current photothermal materials are less efficient and expensive to be manufactured. Inspired by nature, we created a new photothermal material called a wood biochar monolith (WBM) by carbonizing wood using the pyrolysis process at 1000 °C and subsequently steaming at high pressure. Under low light intensity (193 W/m2), the light to vapor efficiency of maple WBM is more than 100%. The outstanding performance of WBM is attributed to (1) the facilitated water transport in the hierarchical, open-pore network preserved from the wood precursor in WBM and (2) the reduced evaporation enthalpy of confined water in WBM and the high broadband sunlight absorptivity of WBM. Moreover, the high evaporation rate causes the temperature of WBM to be lower than that of the surrounding water, enabling thermal energy harvesting by WBM from water and making a light-to-vapor efficiency of >100% feasible. This discovery offers opportunities for developing low-cost, high-performance water desalination or humidification devices deployable in remote areas with nonconcentrated natural sunlight.

A flow through coaxial cell to investigate high frequency broadband complex permittivity: Design, calibration and validation

This paper presents a new apparatus: a large flow through coaxial cell designed for broadband dielectric characterization of material under controlled hydraulic and chemical boundaries. The cell is calibrated with a single measurement made on a perfectly known dielectric liquid (deionized water) together with an optimization procedure. Then, two methods are proposed to compute the dielectric characteristics: an iterative solver and an optimization method. These two methods are systematically investigated for two reference liquids: a low loss dielectric material (ethylene glycol) and high loss dielectric liquid (saline solutions with different concentration). Tabulated data were used to perform a quantitative error analysis in terms of estimated complex permittivity. The results have shown high performance in terms of real part and good performance in terms of real part. The measurements on saline solution also highlight the impact of electrode polarization with dramatic effect in the lower part of the frequency range.

Graphene Thermal Infrared Emitters Integrated into Silicon Photonic Waveguides.

Cost-efficient and easily integrable broadband mid-infrared (mid-IR) sources would significantly enhance the application space of photonic integrated circuits (PICs). Thermal incandescent sources are superior to other common mid-IR emitters based on semiconductor materials in terms of PIC compatibility, manufacturing costs, and bandwidth. Ideal thermal emitters would radiate directly into the desired modes of the PIC waveguides via near-field coupling and would be stable at very high temperatures. Graphene is a semimetallic two-dimensional material with comparable emissivity to thin metallic thermal emitters. It allows maximum coupling into waveguides by placing it directly into their evanescent fields. Here, we demonstrate graphene mid-IR emitters integrated with photonic waveguides that couple directly into the fundamental mode of silicon waveguides designed to work in the so-called "fingerprint region" relevant for gas sensing. High broadband emission intensity is observed at the waveguide-integrated graphene emitter. The emission at the output grating couplers confirms successful coupling into the waveguide mode. Thermal simulations predict emitter temperatures up to 1000 °C, where the blackbody radiation covers the mid-IR region. A coupling efficiency η, defined as the light emitted into the waveguide divided by the total emission, of up to 68% is estimated, superior to data published for other waveguide-integrated emitters.

Examining the types and purpose of cloud computing used for library services delivery in academic libraries in Kwara State, Nigeria

Background of the study: The implementation and integration of information and communication technology in library services and operations has revolutionized traditional practices, enabling libraries to adapt to the evolving needs of users in the digital era. Purpose: The main purpose of this study is to examine the types and purposes of cloud computing used for library service delivery in academic libraries in Kwara State, Nigeria. Methods: The study used a descriptive survey approach. The population was all the 108 librarians in the eight universities in Kwara State, Nigeria. A total enumeration sampling technique was employed, and a questionnaire was used to collect data from the librarians. The study answered three research questions. Findings: The study revealed that OCLC, Word cat, Google Docs, and other types of cloud computing are being utilized by the librarians. The study also revealed that poor internet connectivity, among other challenges, militates against the use of cloud computing for academic library service delivery. Conclusion: The study concluded that the librarians make use of cloud computing for library services. The study recommends that the library should provide reliable internet facilities with fast speeds, high broadband, and reliable power supplies, among others.

Feasibility of Stereo EEG Based Brain Computer Interfacing in An Adult and Pediatric Cohort.

Stereoelectroencephalography (sEEG) is a mesoscale intracranial monitoring method which records from the brain volumetrically with depth electrodes. Implementation of sEEG in BCI has not been well-described across a diverse patient cohort. Across eighteen subjects, channels with high frequency broadband (HFB, 65-115Hz) power increases during hand, tongue, or foot movements during a motor screening task were provided real-time feedback based on these HFB power changes to control a cursor on a screen. Seventeen subjects established successful control of the overt motor BCI, but only nine were able to control imagery BCI with ≥ 80% accuracy. In successful imagery BCI, HFB power in the two target conditions separated into distinct subpopulations, which appear to engage unique subnetworks of the motor cortex compared to cued movement or imagery alone. sEEG-based motor BCI utilizing overt movement and kinesthetic imagery is robust across patient ages and cortical regions with substantial differences in learning proficiency between real or imagined movement.

Millefeuille-inspired biomass alternate multilayer composite, for excellent absorption-dominated, broadband EMI shielding and joule heating

The development of biomass electromagnetic interference (EMI) shielding materials with low cost, low reflection(R-value), and high shielding efficiency is promising but also challenging. Inspired by the alternate structure of a millefeuille, we propose an alternating assembly approach for conductive and magnetic layers. Employing sustainable bamboo fibers (BF) and biodegradable polylactic acid (PLA) as raw matrix, the magnetic and conductive layers were fabricated by compositing copper-plated BF (Cu@BF) and iron-plated BF (Fe@BF) with PLA, respectively. By alternately stacking magnetic and conductive layers and followed by hot pressing, the high EMI SE and low R-value biomass multilayer composite with “multi-(absorption-reflection-reabsorption)” structures were obtained. The performance of different alternating layers (3/5/7/9 layers) was studied, and a linear correlation between layer number, SE, and R-value was established. The results demonstrate that increasing the alternate layer number could readily tune the SE in the X-band from 45.02 dB (3-layer) to 80.2 dB (9-layer) and reduce Rmin from 0.40 to 0.25. Furthermore, the 9-layer composite exhibits approximately 75 dB SE in 1–18 GHz, simultaneously realizing high efficiency, low reflectivity, and broadband shielding. Notably, its excellent conductivity also provides reliable Joule heating performance. The shielding and thermal features of the composite highlight its potential in construction and smart housing heating applications.

The Arctic marine soundscape of the Amundsen Gulf, Western Canadian Arctic

The underwater soundscape, a habitat component for Arctic marine mammals, is shifting. We examined the drivers of the underwater soundscape at three sites in the Amundsen Gulf, Northwest Territories, Canada from 2018 to 2019 and estimated the contribution of abiotic and biotic sources between 20 Hz and 24 kHz. Higher wind speeds and the presence of bearded seal (Erignathus barbatus) vocalizations led to increased SPL (0.41 dB/km/h and 3.87 dB, respectively), while higher ice concentration and air temperature led to decreased SPL (−0.39 dB/% and − 0.096 dB/°C, respectively). Other marine mammals did not significantly impact the ambient soundscape. The presence of vessel traffic led to increased SPLs (12.37 dB) but was quieter at distances farther from the recorder (−2.57 dB/log m). The presence of high frequency and broadband signals produced by ice led to increased SPLs (7.60 dB and 10.16 dB, respectively).

2D–3D heterostructure of PtS2−x /Ga2O3 and their band alignment studies for high performance and broadband photodetector

For deep ultraviolet (UV-C) photodetectors, gallium oxide (Ga2O3) is a suitable candidate owing to its intrinsic ultra-wide band gap and high stability. However, its detection is limited within the UV-C region, which restricts it to cover a broad range, especially in visible and near-infrared (NIR) region. Therefore, constructing a heterostructure of Ga2O3 with an appropriate material having a narrow band gap is a worthwhile approach to compensate for it. In this category, PtS2 group-10 transitional metal dichalcogenide stands at the top owing to its narrow band gap (0.25–1.65 eV), high mobility, and stability for heterostructure synthesis. Moreover, heterostructure with Ga2O3 sensing in UV and PtS2 broad response in visible and IR range can broaden the spectrum from UV to NIR and to build broadband photodetector. In this work, we fabricated a 2D–3D PtS2−x /Ga2O3 heterostructure based broadband photodetector with detection from UV-C to NIR region. In addition, the PtS2−x /Ga2O3 device shows a high responsivity of 38.7 AW−1 and detectivity of 4.8 × 1013 Jones under 1100 nm light illumination at 5 V bias. A fast response of 90 ms/86 ms illustrates the device’s fast speed. An interface study between the PtS2−x and Ga2O3 was conducted using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy (UPS) which confirmed type-I band alignment. Finally, based on their band alignment study, a carrier transport mechanism was proposed at the interface. This work offers a new opportunity to fabricate large-area high-performance 2D–3D heterostructures based photodetectors for future optoelectronics devices.