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The Microwave Temperature Sounder-3 (MWTS-3) onboard the Chinese FengYun-3E (FY-3E) satellite is the third generation of Chinese microwave temperature sounder. Based on MWTS-2, the number of MWTS-3 channels has been increased from 13 to 17, which can observe the atmospheric temperature and water vapor profiles from the surface to the lower stratosphere. In this study, two generations of MWTSs onboard FY-3D/3E were inter-calibrated by the Double Difference (DD) method to eliminate bias. The results showed that the biases of tropospheric channels were stable (within 1 K) and the biases of stratospheric channels were relatively large (over 2 K). In addition, the weighting functions of all MWTS channels varied with fields of view (FOVs) due to different optical paths, causing the brightness temperature (TB) observations to display strong scan-dependent features, i.e., the limb effect. This work used a limb correction method to remove scan-dependent patterns so that the underlying weather signals could be uncovered. After inter-calibration and limb correction, this work converted the TB observations from MWTS-2/3 onto a global gridded dataset at 0.5° × 0.5° latitudinal and longitudinal resolutions using a method of nested interpolation. Based on this research, more long-term FengYun series satellite climate datasets can be established in the future. [ABSTRACT FROM AUTHOR]

Quantum technologies utilize photons in a wide range of spectra, from microwave to visible light. Interactions between photons at different frequencies can be mediated by the collective excitation of spins in a ferromagnetic material. Here, we present optic-to-microwave conversions using the spin mode. In the conversion system, we observe that the generation of microwaves can be controlled by the polarization of the infrared input. Furthermore, we miniaturize the system and demonstrate conversion in a cryogenic environment, where microwave photons can be manipulated in the quantum regime. We show that the conversion efficiency scales with the intensity of the infrared illumination. [ABSTRACT FROM AUTHOR]

A domain wall based spin torque nano-oscillator is a potential device for microwave generation because of its tunability of frequency, operation at room temperature, and integration with complementary metal–oxide–semiconductors. Here, we proposed and numerically demonstrated a spin nano-oscillator with domain wall steady oscillation in Z-type magnetic nanowires with perpendicular magnetic anisotropy by micromagnetic simulations. We find that the dynamical behavior of domain walls at Z-junctions is highly affected by the dimension of Z-junctions and current density. Three kinds of behaviors are found, i.e., damped oscillation, steady oscillation, and collapse. The observed steady oscillation can be used as spin torque nano-oscillators with a working frequency can approach 20 GHz. Our findings could enrich the investigation of spin torque nano-oscillators at high frequencies for novel microwave emitters. [ABSTRACT FROM AUTHOR]

Extremely high-Q microresonators provide an attractive platform for a plethora of photonic applications including optical frequency combs, high-precision metrology, telecommunication, microwave generation, narrow linewidth lasers, and stable frequency references. Moreover, the desire for compactness and a low power threshold for nonlinear phenomena have spurred investigation into integrated and scalable solutions. Historically, crystalline microresonators with Q 109 were one of the first material platforms providing unprecedented optical performance in a small form factor. A key challenge, though, with these devices is in finding alternatives to fragile, bulky, and free-space couplers, such as tapered fibers, prisms, and cleaved fibers. Here, we present for the first time, the evanescent coupling of a photonic wire bond (PWB) to a MgF2-based microresonator to generate solitons and a pure, low-noise microwave signal based on Kerr-microcombs. These results open a path towards scalable integration of crystalline microresonators with integrated photonics. Moreover, because PWBs possess advantages over traditional coupling elements in terms of ease of fabrication, size, and flexibility, they constitute a more advanced optical interface for linear and nonlinear photonics. [ABSTRACT FROM AUTHOR]

To improve the heating uniformity of ready-to-eat rice during continuous microwave reheating, the microwave power, heating time, and combination arrangement of ready-to-eat rice were selected as influencing factors, and moisture content, average temperature, and temperature uniformity served as evaluation indexes. The single-factor experimental design was employed to investigate the effects of continuous microwave reheating parameters on the temperature and moisture content distribution inside ready-to-eat rice and obtain the optimal processing parameters under continuous microwave reheating. The results demonstrated that microwave power and heating time had significant effects on the uniformity of temperature distribution inside the arrangement of packaged ready-to-eat rice. The temperature distribution inside the combination arrangement of ready-to-eat rice in the cavity of the continuous microwave dryer showed a clear “corner effect” and “rim overheating” due to the intensity decay of incident microwave contacting the arrangement of ready-to-eat rice. The ready-toeat rice arranged in four columns had the highest average temperature and uniform temperature distribution. However, the average temperature of the ready-to-eat rice in two columns was relatively low with the non-uniform distribution. The ready-toeat rice container laid along the width direction of the conveyor belt in the continuous microwave dryer had the obvious uniformity of temperature distribution which is conducive to microwave energy absorption and utilization efficiency. It was appropriate to determine the four-column arrangement of the ready-to-eat rice. The average temperature of ready-to-eat rice increased with microwave power, temperature uniformity initially deteriorated and ultimately dropped with microwave power, and the highest heating uniformity may be achieved at a microwave power of 17.1 kW (19 kW×0.90) with a pulse duty cycle of 0.90. The temperature distribution exhibited a “center focus effect” with an increase of the microwave power, where the conversion point from “corner effect” to “center focus effect” occurred at the microwave power of 16.15 kW (19 kW× 0.85) with a pulse duty cycle of 0.85. During the continuous microwave reheating process of ready-to-eat rice, the top, middle, and bottom layers of ready-to-eat rice showed “hot spots” at the corners and “cold spots” at the center, demonstrating a clear “corner effect” under the total heating time in the range of 120～240 s. The “center focus effect” occurs at a total heating duration of 300～360 s. The average temperature gradually increased with the total heating time, and so does the uniformity of temperature distribution. According to the temperature distribution of the ready-to-eat rice’s overall arrangement during a continuous microwave reheating for 300 s, the average temperature of the top layer is the highest at the initial stage of reheating (60 s), the temperature of the middle layer gradually is higher than the top layer at the middle stage of reheating (120～180 s), and the average temperature of the bottom layer remained the lowest throughout the reheating process (0～300 s). According to the temperature distribution in the top, middle, and bottom layers of ready-to-eat rice during the continuous microwave reheating with a total heating period of 300 s, the temperature distribution trend was similar to the distribution of overall arrangement temperature. The color of the water-containing color-changing silica gel was introduced to determine the changing trend in the moisture content of ready-to-eat rice. It was found that the evaporation trends of the moisture in ready-toeat rice were similar to its temperature distribution under the continuous microwave reheating process. There was a significant phenomenon of high edge temperature and corner thermal focusing in the rectangular rice packaging boxes placed inside the microwave cavity, and a similar distribution also existed in single packaging box. As the increase of pulse duty cycle (microwave power), the depth of microwave transmission into the interior of the rice, and the generation of microwave volumetric heating, the "cold spot" moved towards the center area at gradually falling trend, which improved the uniformity of microwave heating. The arrangement method had little effect on heating uniformity. For boxed rice arranged in 2, 3, and 4 columns in a continuous microwave heating device, the uniformity of rice heating inside the box changed from high to low due to the focusing of microwaves on the edge surface of the boxed rice, attenuation during internal transmission, and the low to high dielectric properties between the boxes and their interior. In order to fully utilize the heating capacity and cavity space size of continuous microwave equipment, the optimal process parameters for ready-to-eat rice under continuous microwave reheating were obtained as microwave power of 17.1 kW (19 kW×0.90) with a pulse duty ratio of 0.90, a heating time of 300 s, and four ready-to-eat rice packaging containers arranged across the width of the conveyor belt of the continuous microwave dryer. The research findings can provide the feasible approaches for reheating cooked-rice food with high quality. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a photonic-assisted approach for generating arbitrary microwave waveforms based on a dual-polarization dual-parallel Mach–Zehnder modulator, offering significant advantages in terms of tunability of repetition rates and anti-dispersion capability. In order to generate diverse microwave waveforms, two sinusoidal radio frequency signals with distinct frequency relationships are applied to the dual-polarization dual-parallel Mach–Zehnder modulator. By adjusting the power of the applied sinusoidal radio frequency signal, the power ratio between these orthogonal polarized optical sidebands can be changed, and thereby desired radio frequency waveforms can be obtained after photoelectric conversion. In our proof-of-concept experiment, we systematically varied the repetition rate of triangular, rectangular and sawtooth waveforms. Meanwhile, we calculated the Root Mean Square Error (RMSE) to assess the approximation error in each waveform. The RMSEs are 0.1089, 0.2182 and 0.1185 for the triangular, rectangular and sawtooth microwave waveforms with repetition rate of 8 GHz, respectively. Furthermore, after passing through 25 km single mode fiber, the optical power decreased by approximately 5.6 dB, which verifies the anti-dispersion transmission capability of our signal generator. [ABSTRACT FROM AUTHOR]

In a recent publication [J. Appl. Phys. 131, 023301 (2022)], microwave generation by a segmented A6 S-band axial output relativistic magnetron (RM) fed by a split cathode and powered by a small pulsed power generator was demonstrated for the first time. In the present article, we add to the same RM a mode converter and an antenna and drive it by using a modified linear induction accelerator (LIA) (≤450 kV, ≤4 kA, ∼150 ns). It was found that the operation of the RM for a split cathode or a common explosive emission cathode differs significantly. For a split cathode, we optimize for the best microwave output, its geometrical parameters, the external magnetic field, and the LIA's charging voltages. For the optimal choice of these parameters, the RM generates ∼160 ns long microwave pulses of ∼130 MW, 1.78 GHz frequency with an electronic efficiency of ∼40%, without pulse shortening. On the other hand, a common solid cathode fed RM showed microwave pulse shortening. We demonstrated that the segmented anode allows using a μs-timescale magnetic field, making it possible for the RM to operate repetitively. [ABSTRACT FROM AUTHOR]

Cogeneration helps to optimise the energy consumption in modern greenhouse systems. A cogeneration plant produces electrical and thermal energy close to the greenhouse. Thermal energy is used for heating the plants, while electric energy powers the lights. A patent from the University of Genoa proposes to use part of the electricity produced by the cogeneration system to power a low-power microwave heating system that provides additional thermal energy input to the plants. This innovative approach showcases the integration of diverse energy sources for enhanced efficiency. The project aims to create a cost-effective dielectric heating system with feasible installation expenses, underpinned by a comprehensive analysis of power requirements and electric field dynamics that are essential for optimal plant heating. Four microstrip antennas for microwave generation have been designed. Their performance has been compared. A laboratory and an industrial prototype of microwave heaters have been created. The results are discussed. The successful testing of a prototype heater in a small greenhouse environment is a significant step towards the feasibility of this heating solution. The modular heater proposed makes the product suitable for different greenhouse sizes. [ABSTRACT FROM AUTHOR]

A diamond nitrogen-vacancy (NV) ensemble has been developed as a vector magnetometry platform for sensing external time-varying magnetic fields. However, due to the complexity of manipulating electron spins along different directions, a current vector NV magnetometer often needs a large amount of supporting equipment, preventing its applications in a compact circumstance. Here, we develop a hardware-level protocol to realize a multi-axis NV magnetometer using only a single channel of microwave generation and signal detection resources. This mechanism is to monitor each resonance serialized in a sequence and measure the electron-spin frequency shifts concurrently in real time. The functionality is realized by a home-made control system with an on-chip direct digital synthesis generator and signal processor. We finally achieve a vector sensitivity of around 14 n T / Hz on four different axes at the same time. We also analyze the phase delay of the sensing signal between different axes induced by the protocol. This protocol is compatible with other schemes to further improve the performance, such as hyperfine driving, balanced detection, and high-efficiency photon collection methods. [ABSTRACT FROM AUTHOR]

In this study, the on‐chip generation of microwave signals are proposed for controlling nearby quantum bits in a low‐temperature environment, utilizing superconducting logical and RF components. To achieve enhanced amplitude of the microwave, superconducting single flux quantum (SFQ) pulse pairs are employed, which can have either the same or reversal polarity, serving as the basic elements of the generator. The SFQ pulse pairs are then combined and wave‐shaped by using a microwave combining filter, which finally outputs desired microwave signals with narrow line‐width. The amplitude of the microwave signal correlates with the interval between two SFQ pulses in a pair and can be adjusted accordingly. To validate the proposal, test chips are fabricated and performed experiments. The experimental results confirm that the method using a reverse‐polarity pulse can maximize the output microwave amplitude and provide control of the initial phase of the output microwave. This improvement offers a superior alternative for generating microwaves using superconducting circuits to control quantum bits. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive numerical investigation on the generation of a microwave frequency comb (MFC) using a semiconductor laser subjected to periodic-modulated optical injection. To enhance performance, optoelectronic feedback is incorporated through a dual-drive Mach–Zehnder modulator. The results show that the first optoelectronic feedback loop, with a delay time inversely proportional to the modulation frequency, can optimize MFC generation through a mode-locking effect and the second optoelectronic feedback loop with a multiple delay time of the first one can further enhance the performance of the MFC. The comb linewidth appears to decrease with the increase in the second-loop delay time in the power function. These results are consistent with experimental observations reported in the literature. We also explore the impact of the feedback index on comb contrast, the statistical characteristics of the central 128 lines within the MFC, and side peak suppression. The simulation results demonstrate the presence of an optimal feedback index. The study also reveals that linewidth reduction, through increasing the feedback index and delay time, comes at the cost of declining side peak suppression. These findings collectively contribute to a deeper understanding of the factors influencing MFC generation and pave the way for the design and optimization of high-performance MFC systems for various applications. [ABSTRACT FROM AUTHOR]

Nonlinear photonics has unveiled new avenues for applications in metrology, spectroscopy, and optical communications. Recently, there has been a surge of interest in integrated platforms, attributed to their fundamental benefits, including compatibility with complementary metal-oxide semiconductor (CMOS) processes, reduced power consumption, compactness, and cost-effectiveness. This paper provides a comprehensive review of the key nonlinear effects and material properties utilized in integrated platforms. It discusses the applications and significant achievements in supercontinuum generation, a key nonlinear phenomenon. Additionally, the evolution of chip-based optical frequency combs is reviewed, highlighting recent pivotal works across four main categories. The paper also examines the recent advances in on-chip switching, computing, signal processing, microwave generation, and quantum applications. Finally, it provides perspectives on the development and challenges of nonlinear photonics in integrated platforms, offering insights into future directions for this rapidly evolving field. [ABSTRACT FROM AUTHOR]

BACKGROUND: Asiatic hard clam (Meretrix meretrix) is an underutilized bivalve resource. This study discusses dried clam powders prepared from this resource to enhance its utilization and improve nutritional security in protein‐deficient populations. Dried clam powder was prepared from Asiatic hard clam and the effects of different pre‐cooking methods (boil‐dried clam powder, BDCP; steam‐dried clam powder, SDCP; and microwave‐dried clam powder, MDCP) on nutritional (proximate composition, amino acid profiling, mineral profiling, fatty acid profiling) and physicochemical qualities were investigated. RESULTS: Different pre‐cooking methods significantly influenced the characteristics of the clam powder. The MDCP sample showed the highest concentration of amino acids, polyunsaturated fatty acids, Na, K, Ca and Mg content compared to BDCP and SDCP. The boiling process led to a loss of nutritional quality in terms of amino acids and macrominerals. The MDCP displayed the highest solubility in water (30.10%) but its oil and water absorption characteristics were the lowest among all the samples. Boil‐cooked clam powder displayed the highest oil binding (2.03 mL g−1 protein) capacity. Boiling and steaming processes resulted in malondialdehyde generation compared to microwaving. Different pre‐cooking processes did not influence the colour attributes significantly, but the control sample prepared without pre‐cooking (CCP) had a significantly lower L* value (32.34), resulting in a darker product. In vitro digestibility of the clam powder varied in the order MDCP > SDCP > BDCP > CCP. CONCLUSION: The study demonstrated that nutritionally rich protein powder can be prepared from Asiatic hard clam. Based on the results, microwave pre‐cooking is considered the best pre‐cooking method to preserve the nutritional qualities of clam powder. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

In recent times, photonic synthesis and processing of arbitrary microwave waveforms have gained interest due to their high frequency and huge time–bandwidth product. This study reviews methods for producing dual‐chirp microwave waveforms, focusing mostly on system topologies based on external modulation techniques, such as cascaded Mach–Zehnder modulator (MZM), dual parallel MZM, and dual polarized MZM. Other photonic approaches, like using semiconductor laser and optical heterodyne detection methods, are also discussed. These techniques are preferable because of high frequency, enhanced time–bandwidth product, greater chirp rate, and many more advantages. Additionally, the difficulties associated with integrating the systems into real‐world applications are also addressed. [ABSTRACT FROM AUTHOR]

Optoelectronic oscillators (OEOs), which have attracted extensive studies in the past decades, are high quality-factor optoelectronic feedback loops for generating various ultra-pure microwave signals. In essence, OEOs are also dissipative nonlinear systems with multiple timescale characteristics and abundant nonlinearities, which open the possibilities for exploring localized dissipative solitary waves. In this paper, we demonstrate a new-class temporal dissipative soliton, i.e., dissipative microwave photonic soliton molecule (DMPSM), in a dual-bandpass OEO. Both the numerical simulation and experiment are conducted to reveal the physical mechanism of DMPSM generation and to evaluate the characteristics of the generated DMPSM sequences. Unlike optical soliton molecules in mode-locked lasers, the formation of DMPSMs arises from the combined action of multiple timescale coupling, nonlinear bistability, and time-delayed feedback in the OEO cavity, where the soliton interval and number in a DMPSM can be well-controlled through varying the multiple timescale variables in the OEO cavity, and the repetition frequency of the DMPSMs can be tuned through changing that of the initially injected perturbation signal. Meanwhile, the generated DMPSM sequence performs with high stability and excellent coherence, which shows enormous application potentials in pulse radar detection, dense microwave comb generation, and neuromorphology. [ABSTRACT FROM AUTHOR]

C-band high-power microwave devices have important application prospects in communication, radar and other fields, and the demand for compact and lightweight devices is becoming more and more urgent in the industrial sector. A C-band high-efficiency coaxial transit-time oscillator (CTTO) with three-cavity buncher and dual-cavity extractor is proposed and investigated in theory and 2.5-dimensional particle-in-cell simulations, which is good for high power microwave generation devices at low frequency towards miniaturization and compactness. In order to avoid the transverse electromagnetic mode (TEM) leaking to the diode region, the reflector is designed and adopted in front of the buncher, which also can pre-modulate the beams and lead to the higher conversion efficiency. In this simulation, the typical performance of the CTTO reveals that microwaves with a power of 1.83 GW are generated at a frequency of 6.37 GHz when the beam voltage and current are 458 kV and 9.6 kA respectively, under a guiding magnetic field of 1.05 T. The corresponding power conversion efficiency is as high as 41.6%. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) cathodes have attracted much attention in recent years due to the advantages of large field enhancement factor and low emission threshold. However, the severe ablation under intense emission makes the lifetime short and therefore limits the application in the field such as high power microwave generation. To resolve this problem, this paper proposes to mix CNTs with metals, and a novel CNT/Cu composite cathode is manufactured. The lifetime experiments under voltage of 940 kV and repetition frequency of 20 Hz demonstrate that the lifetime of the CNT/Cu composite cathode is over 3 × 105 pulses, which is much longer than that of the normal copper cathode by at least one order of magnitude. The microscopic morphology analysis reveals that the CNT micro-protrusions and whiskers should be vital for the good emission property of the new cathode. [ABSTRACT FROM AUTHOR]

To understand the plasma evolution mechanism of microwave ion source (MIS), a hybrid discharge heating (HDH) mode is proposed. That mode contains two parts: ignition discharge by surface wave plasma (SWP) and ionization by electron cyclotron resonance. Compared with the traditional electron cyclotron heating (ECH) mode, the HDH mode has a wider scope of application for MIS with a chamber diameter smaller than the cutoff size. The spatio-temporal evolution of electric field, power deposition, electron temperature, and electron density of a miniaturized microwave ion source (MMIS) at Peking University is investigated based on the HDH mode. In addition, the MMIS is optimized based on the theoretical results of the HDH mechanism. Preliminary experiments show that a mixed hydrogen continuous wave beam of up to 25 mA at 30 keV can be extracted with a power efficiency of 25 mA/100 W. [ABSTRACT FROM AUTHOR]

Optical resonators are indispensable tools in optical metrology that usually benefit from an evacuated and highly-isolated environment to achieve peak performance. Even in the more sophisticated design of Fabry-Perot (FP) cavities, the material choice limits the achievable quality factors. For this reason, monolithic resonators are emerging as promising alternative to traditional designs, but their design is still at preliminary stage and far from being optimized. Here, we demonstrate a monolithic FP resonator with 4.5 cm3 volume and 2 × 105 finesse. In the ambient environment, we achieve 18 Hz integrated laser linewidth and 7 × 10−14 frequency stability measured from 0.08 s to 0.3 s averaging time, the highest spectral purity and stability demonstrated to date in the context of monolithic reference resonators. By locking two separate lasers to distinct modes of the same resonator, a 96 GHz microwave signals is generated with phase noise -100 dBc/Hz at 10 kHz frequency offset, achieving orders of magnitude improvement in the approach of photonic heterodyne synthesis. The compact monolithic FP resonator is promising for applications in spectrally-pure, high-frequency microwave photonic references as well as optical clocks and other metrological devices. ©2024. All rights reserved. Optical resonators are essential tools for high precision metrology and applications where the spectral purity is highly demanded. Here, the authors demonstrate a monolithic resonator made of fused silica to support 18 Hz integrated laser linewidth in the ambient environment, and W-band microwave generation with low phase noise of -100 dBc/Hz at 10 kHz frequency offset. [ABSTRACT FROM AUTHOR]

In work, a new method of optical microwave signal generation with frequency 18-tupling using three parallel polarization modulators (PolMs) was proposed, in which the PolM is integrated through a polarization beam splitter, two phase modulators, an electrical phase shifter, and a polarization beam coupler. To generate a frequency 18-tupling millimeter-wave (mm-wave) signal, the polarization controller must first be employed to bring out linearly polarized light. Next, the linearly polarized light is faded into three PolMs to be modulated by a radio frequency signal, which can achieve multi-frequency optical sidebands. Last, controlling a polarizer to cancel unwanted optical sidebands to obtain ±9th optical sidebands is used to generate an 18-tupling mmwave signal. We have conducted detailed mathematical formula derivation and computer simulation for the scheme. The results show that the scheme can be experimentally realized and accurate enough with the performance of the signal: the optical sideband suppression ratio can reach 48.02 dB, and the radio frequency spurious suppression ratio can reach 42.25 dB, almost equal to the theoretical model. [ABSTRACT FROM AUTHOR]

Ultralow-noise microwaves are essential in a wide variety of scientific and technological applications, such as metrology, radars, and communications. Here, we propose and demonstrate a scheme for generating an ultralow-noise microwave signal using a Brillouin optical frequency comb (OFC), which is based on the stimulated Brillouin scattering in combination with a frequency-shifted optical injection locking mechanism. The generated two intra-cavity Brillouin lasers are used as the intra-cavity pump for the eventual formation of the OFC and thus the microwave signal via the cascaded four-wave mixing process. Exploiting the cascaded narrowing effect in the Brillouin cavity assisted by the frequency-shifted optical injection locking, the proposed microwave signal source exhibits ultralow phase noise. Experimental results show that the phase noise of the microwave signal is equivalent to below −115 dBc / Hz for a 200-GHz carrier at 10 kHz offset. The system can work in stable operation without the need for any active feedback loop. [ABSTRACT FROM AUTHOR]

Pulsed power generators utilizing magnetic switch technology within the 100 ns scale have become widespread for surface treatment, high power microwave generation, and food processing, in which the dynamic characteristics of the magnetic switch perform an important function. The saturation process, electric field between layers, and energy loss are closely associated with the applied time scale of the magnetic core, which affects the dynamic characteristics of the switch. However, compared with the study within the microsecond scale, the dynamic characteristics of magnetic switches within the 100 ns scale have not been studied in depth. In this paper, the dynamic characteristics of a coaxial magnetic switch modulating pulse forming networks (PFNs) are studied via both field-loop co-simulation and scaled experimental test. It is found that increasing PFN section number (Ns) leads to an acceleration in the saturation process of the core, which helps understand the switch performance of the magnetic core more clearly. With respect to a specific magnetic switch based on a ferromagnetic core, it is quantitatively analyzed that increasing Ns from 1 to 10 leads to a 16.1% reduction in core saturation time (tsat), a 13.4% increase in eddy loss (EET), and a 5.7% rise in maximum interlamination field strength (Emax) under the 100 ns scale; however, tsat is reduced by 19.3%, EET increases by 5.2%, and Emax rises by 2.3% under the microsecond scale. The results could provide a design reference for magnetic switches in pulsed power generators. [ABSTRACT FROM AUTHOR]

A photonic method for flexible multi-band dual-chirped microwave waveform generation is proposed using a recirculating frequency shifting loop (RFSL). The RFSL can be used as an optical frequency comb (OFC) generator with adjustable frequency spacing and line numbers. By heterodyning the OFC with a lightwave modulated by a baseband linearly chirped waveform in a balanced photodetector, a flexible multi-band dual-chirped microwave waveform can be generated. The frequency spacing and the number of the sub-bands can be easily adjusted by tuning the frequency shift and the bandwidth of the optical filter in the RFSL. The bandwidth and duration of each sub-band signal can also be tuned by adjusting the baseband linearly chirped waveform. A numerical simulation is conducted to verify the proposed generator. A flat four-band dual-chirped waveform with frequency spacing of 3 GHz and six-band dual-chirped waveform with frequency spacing of 4 GHz are generated successfully. Due to the flexible reconfigurability and high performance, the proposal may have great potential in multi-band radar systems. [ABSTRACT FROM AUTHOR]

This paper addresses the challenge of extending the pulse duration of high-power microwave (HPM) sources, a critical focus in HPM technology. Transit-time oscillators (TTOs) typically modulate electron beams by forming standing waves through the cutoff of the TM01 mode in the modulation cavity. This study proposes enhancing the power capacity of TTOs by widening the drift channel. To enhance modulation capability without compromising power capacity, front and rear reflectors are strategically introduced. In particle-in-cell simulations, the device exhibits an output power of 1.65 GW at a frequency of 12.6 GHz, with an efficiency of 33.6%. The saturation time for the output microwave is 30 ns, and the maximum internal electric field strength is 860 kV/cm. The presented TTO, with design improvements, offers a promising solution for applications requiring prolonged pulse durations in high-power microwave sources. [ABSTRACT FROM AUTHOR]

An analytical study of charged particle dynamics in the presence of an elliptically polarized electromagnetic wave and a uniform axial magnetic field is presented. It is found that a charged particle resonantly gains energy for g ω 0 / ω ′ = ± 1 , ω0, and ω ′ , respectively, being the cyclotron frequency of the charged particle in the external magnetic field and Doppler-shifted frequency of the wave seen by the particle, and g = ± 1 , respectively, correspond to right and left-handedness of polarization. An explicit solution of the governing equation is also presented in terms of particle position or laboratory time, for the specific case of resonant energy gain in a circularly polarized electromagnetic wave. These explicit position- or time-dependent expressions are useful for better insight into various phenomena, viz., cosmic ray generation, microwave generation, plasma heating, and particle acceleration. [ABSTRACT FROM AUTHOR]

The generation modes of high-voltage microwave oscillations of nonlinear coaxial transmission lines filled with NiZn ferrite rings with an ordinary (smoothed) hysteresis loop and MgMn ferrite rings with a rectangular hysteresis loop are presented for comparison. Results across a wide frequency range (∼5.5–12.7 GHz) demonstrated that the anisotropic magnetic properties of ferrite with a rectangular loop provide a much more stable and effective generation of powerful microwave oscillations with peak amplitudes up to −350 kV and deep modulation in a wide biasing field (∼4–85 kA/m), as well as the possibility of a generation mode without an external biasing field. New experimental data enable the observed processes in nonlinear ferrite lines to be related to the theoretical positions of the ferrite anisotropic properties and the spin waves of magnetization precession under high-power microwave radiation. Results were also considered in relation to the theory of ferrite. The possibility of achieving an effective frequency of oscillations of 18.5 (up to 20) GHz using solid-state nonlinear transmission lines was also shown. [ABSTRACT FROM AUTHOR]

This review covers the recent achievements in high-power rare earth (RE)-doped fiber lasers, Raman fiber lasers, and Brillouin fiber lasers. RE-doped fiber lasers have many applications such as laser cutting, laser welding, laser cleaning, and laser precision processing. They operate in several wavelength ranges including 1050–1120 nm (ytterbium-doped fiber lasers), 1530–1590 nm (erbium- and erbium–ytterbium-doped fiber lasers), and 1900–2100 nm (thulium- and holmium-doped fiber lasers). White spaces in the wavelength spectrum, where no RE-doped fiber lasers are available, can be covered by Raman lasers. The heat power generated inside the laser active medium due to the quantum defect degrades the performance of the laser causing, for example, transverse-mode instability and thermal lensing. It can even cause catastrophic fiber damage. Different approaches permitting the mitigation of the heat generation process are considered in this review. Brillouin fiber lasers, especially multiwavelength Brillouin fiber lasers, have several important applications including optical communication, microwave generation, and temperature sensing. Recent progress in Brillouin fiber lasers is considered in this review. [ABSTRACT FROM AUTHOR]

We propose a photonics scheme to generate rectified cosinusoidal shaped (RCS) and rectified sinusoidal shaped (RSS) microwave waveforms and the duty cycle of the generated waveforms can be freely tunable. In this proposed method, two cascaded Mach-Zehnder modulators (MZMs) with polarization sensitive characteristics are employed. By setting the rotation angle of polarization controller, phase shift of the phase shifters and modulation index of the front MZM's (modulation index of the rear MZM is unfixed) properly, the obtained RCS and RSS microwave waveforms with arbitrary duty cycle by the superposition of beating signals, can be seen as an approximation of the first three terms of the Fourier series expansion of the ideal waveforms. The detailed theoretical analysis and simulations are given. In the simulations, the duty cycle of 100%, 80% and 50% of the RCS and RSS microwave waveforms are successfully obtained. Also, fitting errors are introduced to measure the similarity between the generated waveforms and the ideal waveforms. Different from previous works, the RCS and RSS microwave waveforms can be both generated by our scheme and the duty cycle is freely tunable. Moreover, the modulation index of the rear MZM is unfixed, thus increasing the flexibility of the scheme. [ABSTRACT FROM AUTHOR]

Optical frequency combs have emerged as a new generation of metrological tools, driving advancements in various fields such as free-space two-way time–frequency transfer, low-noise microwave source generation, and gas molecule detection. Among them, fiber combs based on erbium-doped fiber mode-locked lasers have garnered significant attention due to their numerous advantages, including low noise, high system integration, and cost-effectiveness. In this review, we discuss recent developments in erbium-doped fiber combs and analyze the advantages and disadvantages of constructing fiber combs utilizing different erbium-doped mode-locked fiber lasers. First, we provide a brief introduction to the basic principles of optical frequency combs. Then, we explore erbium-doped fiber combs implemented utilizing various mode-locking techniques, such as nonlinear polarization rotation (NPR), real saturable absorber (SA), and nonlinear amplifying loop mirror (NALM). Finally, we present an outlook on the future perspectives of erbium-doped fiber combs. [ABSTRACT FROM AUTHOR]

The development of a flexible and robust metamaterial absorber is a great motivation for the new generation of microwave absorbers covering any conformal shape. Ceramic–polymer composites with variable dielectric constant within the microwave frequencies are proposed as a flexible middle dielectric spacer (MDS) layer to provide an additional degree of design freedom for metamaterial absorber applications. By varying the dielectric constant of the MDS layer, the resonance band of the metamaterial absorber can be tuned while retaining a low profile in addition to enhancing its electromagnetic performance for transverse magnetic (TM) polarized waves. To formulate these composites, tetragonal structured barium titanate (BaTiO3) powder is selected as an excellent candidate when mixed with elastomer polydimethylsiloxane (PDMS), resulting in high mechanical strength substrates. Experimentally, samples with a range of dielectric permittivity from 2.81 to 5.67 were obtained for a 0%–20% volume fill fraction of BaTiO3 in PDMS. The obtained dielectric permittivities are consistent with the Bruggeman effective medium theory. Utilizing an optimized composition (10% BaTiO3), resulting in ϵ r = 4 substrate, an X-band flexible absorber is designed and fabricated to absorb more than 90% of incident electromagnetic waves within a frequency band of 8.16–12.12 GHz. [ABSTRACT FROM AUTHOR]

In this paper, photonic generation of arbitrary shape radio-frequency (RF) waveforms like triangular, square and fullwave rectifier types are demonstrated based on a dual-parallel Mach–Zehnder modulator (DP-MZM) driven by a single sinusoidal RF signal. In the proposed technique, one of the sub-MZM (MZM-2) has no driven signal, while other the sub-MZMs (MZM-1) of the DP-MZM is driven by the sinusoidal RF signal. The powers of even and odd-order sidebands are separately controlled by proper adjustment of modulation index through modulating the bias of the MZM-1. An RF signal with controllable harmonics are generated, after detecting the modulated signal by a photodetector. Thus, by separately modulating its harmonics a desired RF waveform is generated. The proposed method is theoretically analysed followed by experimental validation. [ABSTRACT FROM AUTHOR]

Microwave sensors possess the capacity to effectively penetrate through clouds and fog and are widely used in obtaining soil moisture, atmospheric water vapor, and surface temperature measurements. Long time-series datasets play a pivotal role in climate change studies. Unfortunately, the lifespan of operational satellites often falls short of the needs of these extensive datasets. Hence, comparing and cross-calibrating sensors with similar configurations is paramount. The Microwave Radiation Imager (MWRI) onboard Fengyun-3D (FY-3D) is the latest generation of satellite-based microwave remote sensing instruments in China, and its data quality and application prospects have attracted widespread attention. To comprehensively assess the data quality of MWRI, a comparison of the orbital brightness temperature (TB) data between FY-3D/MWRI and Global Change Observation Mission 1st-Water (GCOM-W1)/Advanced Microwave Scanning Radiometer 2 (AMSR2) is conducted, and then a calibration model is established. The results indicate a strong correlation between the two sensors, with a correlation coefficient exceeding 0.9 across all channels. The mean bias ranges from −1.5 K to 0.15 K. Notably, the bias of vertical polarization is more pronounced than that of horizontal polarization. The TB distribution patterns and temporal evolutions are highly consistent for both sensors, particularly under snow and ice. The small intercepts and close-to-1 slopes obtained during calibration further demonstrate the minor data differences between the two sensors. However, the calibration process effectively reduces the existing errors, and the calibrated FY-3D/MWRI TB data are closer to GCOM-W1/AMSR2, with a mean bias approximately equal to 0 K and a correlation coefficient exceeding 0.99. The excellent consistency of the TB data between the two sensors provides a vital data basis for retrieving surface parameters and establishing long time-series datasets. [ABSTRACT FROM AUTHOR]

We find and study the generation regime of microwave waves in a model resonator cavity based on an array of ordered semiconductor carbon nanotubes. Within the framework of the phenomenological approach, the Gunn effect was discovered for aligned carbon nanotubes with a length of 25–150 μm, the influence of the main parameters (changes in the electric field, the distance between the electrodes, the voltage at the contacts, etc.) was studied and it was shown that the electronic efficiency during lasing can reach 13%. The results obtained can be used to design new resonator structures such as compact microwave amplifiers and emitters based on ordered arrays of nanotubes. [ABSTRACT FROM AUTHOR]

We demonstrate a high finesse, microfabricated mirror-based, air-gap cavity with volume less than 1 ml, constructed in an array, that can support low-noise microwave generation through optical frequency division. We use the air-gap cavity in conjunction with a 10 nm bandwidth mode-locked laser to generate low phase noise 10 GHz microwaves, exhibiting a phase noise of −95 and −142 dBc/Hz at 100 Hz and 10 kHz offset frequencies, respectively. This is accomplished using the 2-point lock optical frequency division method, where we exploit 40 dB common-mode rejection of two lasers separated by 1.29 THz and locked to the same air-gap cavity. If used with an octave spanning comb, the air-gap cavity is capable of supporting 10 GHz phase noise below −160 dBc/Hz at 10 kHz offset, a level significantly lower than electronic synthesizers. These results show how extremely small optical reference cavities, operated without the benefit of vacuum enclosures or thermal insulation, can, nonetheless, support state-of-the-art microwave phase noise in compact and portable systems. [ABSTRACT FROM AUTHOR]

We study the generation and control of the microwave (MW)-induced reverse saturable absorption (RSA) and optical limiting (OL) in a three-level pump-probe V-type quantum system. It is shown that the saturable absorption switches to the RSA by applying the MW field to the transition between two upper levels. Moreover, it is demonstrated that the RSA and the induced OL threshold are controlled by either the intensity or detuning of the MW field. In addition, the effect of the coupling field on the induced optical limiting is studied, and it is obtained that the cross-Kerr nonlinearity has a major role in establishing efficient optical power limiting. In addition, we demonstrate that an increase in the atomic density and length of the medium makes the optical limiter more powerful. Finally, the theoretical Z-scan technique is presented to confirm the obtained results of the microwave-induced OL. The proposed scheme can be used to prepare a controllable optical limiter with various thresholds, which can protect the optical devices with different sensitivities. [ABSTRACT FROM AUTHOR]

The Maxwell–Lindblad transmission line (MLT) equations are introduced as a model for hybrid photonic and microwave‐electronic quantum devices. The hybrid concept has long enabled high‐bandwidth photodetectors and modulators by using waveguide structures supporting microwave–optical co‐propagation. Extending this technique to quantum‐engineered lasers provides a route for greatly improved short‐pulse and frequency comb operation, as impressively demonstrated for quantum cascade lasers. Even more, the self‐organized formation of coupled microwave and optical oscillation patterns has recently enabled photonics‐based ultralow‐noise microwave generation. The MLT model provides a suitable theoretical description for hybrid quantum devices by combining optical and microwave propagation equations with a Lindblad‐type approach for the quantum active region dynamics. A stable numerical scheme is presented, enabling realistic device simulations in excellent agreement with experimental data. Based on numerical results and analytical considerations, it is demonstrated that the functionality of the investigated hybrid quantum devices does not only rely on local coupling effects, but rather benefits from microwave‐optical co‐propagation, settling an ongoing debate. The MLT equations provide the basis for systematic device development and extension of the concept to other quantum‐engineered hybrid devices based on, for example, quantum dot or interband cascade structures, as well as for simplified analytical models providing additional intuitive insight. [ABSTRACT FROM AUTHOR]

Electrical signals derived from optical sources have achieved record‐low levels of phase noise, and have demonstrated the highest frequency stability yet achieved in the microwave domain. Attaining such ultrastable phase and frequency performance requires high‐fidelity optical‐to‐electrical conversion, typically performed via a high‐speed photodiode. This paper reviews characteristics of the direct photodetection of optical pulses for the intent of generating high power, low phase noise microwave signals from optical sources. The two most popular types of photodiode detectors used for low noise microwave generation are discussed in terms of electrical pulse characteristics, achievable microwave power, and photodetector nonlinearities. Noise sources inherent to photodetection, such as shot noise, flicker noise, and photocarrier scattering are reviewed, and their impact on microwave phase fidelity is discussed. General guidelines for attaining the lowest noise possible from photodetection that balances power saturation, optical amplification, and amplitude‐to‐phase conversion are also presented. [ABSTRACT FROM AUTHOR]

Compact and robust frequency-stabilized laser sources are critical for a variety of fields that require stable frequency standards, including field spectroscopy, radio astronomy, microwave generation, and geophysical monitoring. In this work, we applied a simple and compact fiber ring-resonator configuration that can stabilize both a continuous-wave laser and a self-referenced optical frequency comb to a vibration-insensitive optical fiber delay-line. We could achieve a thermal-noise-limited frequency noise level in the 10 Hz–1 kHz offset frequency range for both the continuous-wave laser and the optical frequency comb with the minimal frequency instability of 2.7 × 10−14 at 0.03-s and 2.6 × 10−14 at 0.01-s averaging time, respectively, under non-vacuum conditions. The optical fiber spool, working as a delay reference, is designed to be insensitive to external vibrations, with a vibration sensitivity of sub-10−10 (1/g) and a volume of 32 ml. Finally, the ring-resonator setup is packaged in a palm-sized aluminum case with 171-ml volume with a vibration-insensitive spool, as well as an even smaller 97-ml-volume case with an ultracompact 9-ml miniaturized fiber spool. [ABSTRACT FROM AUTHOR]

Frequency combs from continuous-wave-driven Kerr-nonlinear microresonators have evolved into a key photonic technology with applications from optical communication to precision spectroscopy. Essential to many of these applications is the control of the comb's defining parameters, i.e., carrier-envelope offset frequency and repetition rate. An elegant and all-optical approach to controlling both degrees of freedom is the suitable injection of a secondary continuous-wave laser into the resonator onto which one of the comb lines locks. Here, we experimentally study such sideband injection locking in microresonator soliton combs across a wide optical bandwidth and derive analytic scaling laws for the locking range and repetition rate control. As an application example, we demonstrate optical frequency division and repetition rate phase-noise reduction to three orders of magnitude below the noise of a free-running system. The presented results can guide the design of sideband injection-locked, parametrically generated frequency combs with opportunities for low-noise microwave generation, compact optical clocks with simplified locking schemes, and, more generally, all-optically stabilized frequency combs from Kerr-nonlinear resonators. [ABSTRACT FROM AUTHOR]

Low-noise microwave signals can be efficiently generated with microresonator-based dissipative Kerr solitons (microcombs). However, the phase noise level in integrated microcombs is presently several orders of magnitude above the limit imposed by fundamental thermorefractive noise, resulting from residual pump laser frequency noise transduction to the soliton repetition rate. This effect can be substantially reduced by accessing a quiet point (QP) in the parameter space, where the transduction is compensated by the dispersive wave (DW) recoil, which conventionally relies on accidental mode crossings. Here we present a method to deterministically engineer the QP, both in terms of spectral width and position, and we discover a continuum of possible QPs within the soliton existence region. Using two controlled mode crossings, we obtain regions where the QPs interact with each other, extending the noise suppression range. Our work demonstrates a promising way to reach the fundamental limit of low-noise microwave generation in integrated microcombs. Quiet points (QPs) in chip-integrated microcomb platforms allow the cancellation of transduction noise arising due to the presence of Raman self-frequency shifts, but the conditions to exploit them are fortuitous and system-dependent. The authors propose a strategy to deterministically engineer QPs both in terms of spectral width and position. [ABSTRACT FROM AUTHOR]

This study examined the effectiveness of a 915 MHz atmospheric pressure microwave torch for bulk syngas or hydrogen generation via noncatalytic greenhouse gas (GHG) reforming and its flexibility regarding the amount of soot formed by the process. The investigation shows that plasma-GHG reforming for mass hydrogen generation is feasible without a catalyst at high gas flow rate and microwave power. The best hydrogen production rate and energy yield were 1672 g (H 2)/h and 41.8 g (H 2)/kWh, respectively, at 160 lpm gas flow rate and 40 kW microwave power at a CH 4 /CO 2 ratio of 1. The conversion rates of CH 4 and CO 2 under the same conditions were 95.59% and 95.59%, respectively. The plasma reforming method employed in this study shows its excellent potential for industrial application. [Display omitted] • Greenhouse gases (GHG) reforming for mass hydrogen generation. • Investigated a 915 MHz atmospheric pressure microwave plasma torch for GHG reforming. • Attained hydrogen production rate and energy yield of 1672 g (H 2)/h and 41.8 g (H 2)/kWh. • CH 4 and CO 2 conversion of 95.6% and 95.4%, respectively, were realized. [ABSTRACT FROM AUTHOR]

Frequency combs with mode spacing of 10–20 GHz are critical for increasingly important applications such as astronomical spectrograph calibration, high-speed dual-comb spectroscopy, and low-noise microwave generation. While electro-optic modulators and microresonators can provide narrowband comb sources at this repetition rate, a significant remaining challenge is a means to produce pulses with sufficient peak power to initiate nonlinear supercontinuum generation spanning hundreds of terahertz (THz) as required for self-referencing. Here, we provide a simple, robust, and universal solution to this problem using off-the-shelf polarization-maintaining amplification and nonlinear fiber components. This fiber-integrated approach for nonlinear temporal compression and supercontinuum generation is demonstrated with a resonant electro-optic frequency comb at 1550 nm. We show how to readily achieve pulses shorter than 60 fs at a repetition rate of 20 GHz. The same technique can be applied to picosecond pulses at 10 GHz to demonstrate temporal compression by 9× and achieve 50 fs pulses with a peak power of 5.5 kW. These compressed pulses enable flat supercontinuum generation spanning more than 600 nm after propagation through multi-segment dispersion-tailored anomalous-dispersion highly nonlinear fibers or tantala waveguides. The same 10 GHz source can readily achieve an octave-spanning spectrum for self-referencing in dispersion-engineered silicon nitride waveguides. This simple all-fiber approach to nonlinear spectral broadening fills a critical gap for transforming any narrowband 10–20 GHz frequency comb into a broadband spectrum for a wide range of applications that benefit from the high pulse rate and require access to the individual comb modes. [ABSTRACT FROM AUTHOR]

This research aimed to purify the environment of undesired substances by converting oily sludge (OS) micro-char fuel generation by microwave. The North Refineries Company (NRC) Baiji was the source of the OS sample utilized in this study. Micro-char manufacture, which has improved solid carbon characteristics, uses various microwave power and irradiation times. The parameters conditions at a range of power: feed of 5 g, 10 min of irradiation time, and microwave power ranges of 200, 400, and 600 W, respectively, under a nitrogen pressure of 3 L/min. While at the range of irradiation time: the feed was 5 g, microwave power was fixed at 600 W (the best microwave power discovered), and the range of irradiation duration was 5, 10, and 15 min. The ideal circumstances were (5 g, 600 W, and 15 min, under N2 pressure). The fuel ratio was increased from 0.70 to 0.97 OS with a 38.57% rise in the percentage of micro-char at 600 W and 15 min of irradiation time, while the HHV was increased from 9.40 to 17.22 MJ/kg at a rate of 83.20% as finding micro-char had improved as a solid carbon fuel. In general, micro-char has a fuel ratio and a higher HHV, making it suitable for solid carbon fuel in the oil industry. [ABSTRACT FROM AUTHOR]

Isotope fractionation of metals/metalloids in biological systems is an emerging research area that demands the application of state-of-the-art analytical chemistry tools and provides data of relevance to life sciences. In this work, Se uptake and Se isotope fractionation were measured during the biofortification of baker's yeast (Saccharomyces cerevisiae)—a product widely used in dietary Se supplementation and in cancer prevention. On the other hand, metabolic labeling with 15N is a valuable tool in mass spectrometry-based comparative proteomics. For Se-yeast, such labeling would facilitate the assessment of Se impact on yeast proteome; however, the question arises whether the presence of 15N in the microorganisms affects Se uptake and its isotope fractionation. To address the above-mentioned aspects, extracellularly reduced and cell-incorporated Se fractions were analyzed by hydride generation–multi-collector inductively coupled plasma–mass spectrometry (HG MC ICP–MS). It was found that extracellularly reduced Se was enriched in light isotopes; for cell-incorporated Se, the change was even more pronounced, which provides new evidence of mass fractionation during biological selenite reduction. In the presence of 15N, a weaker preference for light isotopes was observed in both, extracellular and cell-incorporated Se. Furthermore, a significant increase in Se uptake for 15N compared to 14N biomass was found, with good agreement between hydride generation microwave plasma–atomic emission spectrometry (HG MP–AES) and quadrupole ICP–MS results. Biological effects observed for heavy nitrogen suggest 15N-driven alteration at the proteome level, which facilitated Se access to cells with decreased preference for light isotopes. [ABSTRACT FROM AUTHOR]

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Bottle beams have drawn considerable research interest due to their attractive features and applications in beam trapping. Herein, the flexible generation and modulation of bottle beams utilizing a reconfigurable metamirror over a non‐negligible frequency band ranging from 8.5 to 9.5 GHz is investigated. A varactor diode is embedded into each meta‐atom on the metamirror enabling the achievement of a nearly 2π phase coverage by varying the external bias voltage. Based on the caustic theory, several configurations of bottle beam with distinct radius a are realized as proof‐of‐concept validation. Besides, the flexible modulation of the operating frequency is analyzed by judiciously controlling the bias voltages applied to the metasurface. The experimental results are in good agreement with those obtained from numerical simulations. Such a flexible bottle beam generator shows good potential in the microwave regime for near‐field applications, such as imaging and power transmission. [ABSTRACT FROM AUTHOR]

The knowledge of physical mechanism of microwave generation in coaxial gyromagnetic nonlinear transmission lines (GNLTLs) is not complete up until now, especially the action of spinwave excitation during this process. In this paper, control experiments on different groups of GNLTLs with a single variable of NiZn ferrite material spinwave linewidth ΔHk are proposed as an indirect way to demonstrate this microscopic process. Comparative analyses of different groups of GNLTL experimental results are conducted to clarify the existence and effect of spinwave excitation. Theoretical treatment of conditions of spinwave excitation in GNLTLs is derived to explain the experimental results. It is illustrated that spinwave can be excited when the synchronism condition between the working frequency of GNLTL and the spinwave frequency spectrum is satisfied. The unstable spinwave excitation will consume the RF energy of GNLTLs heavily and cause a rapid decrease in RF oscillation. [ABSTRACT FROM AUTHOR]

Based on the coupling of hydride generation (HG) and microwave plasma torch (MPT), a rapid and sensitive method of hydride generation-microwave plasma torch-mass spectrometry (HG-MPT-MS) for arsenic under atmospheric condition was developed. The mass spectral behavior of arsenic under different ionization conditions was investigated. In both positive and negative ion modes, arsenic displayed characteristic mass spectrum peaks, which was significantly different from electrospray ionization (ESI), inductively coupled plasma (ICP) and other common ionization techniques. HG-MPT-MS enabled ionization of analytes at molecular level, and it formed adduct ions with NO3-, and even dimers of arsenate ions. Due to the combination of hydride generation and microwave plasma torch, the background noise and the signal intensity of analytes were greatly improved. Therefore, this method was suitable for direct mass spectrometry analysis of trace arsenic in complex samples. In addition, the influence of HCl concentration on the signal intensity, and the regulation of arsine generation behavior by microwave power were studied. Compared with ICP, microwave plasma torch showed more obvious advantages on the analysis of arsenic, such as extremely low power and argon consumption, soft ionization and continuous energy regulation. The total ion chromatography (TIC) and the extracted ion chromatography (EIC) of all analytes displayed good signal stability and peak shape. In addition, arsenic concentration and its signal intensity showed a good linear relationship (R2>0.998) in the concentration range of 1-500 μg/L, and the detection limit was 0.02 μg/L. This method was applied to analysis of a reference water standard and two real water samples of lake water and river water. The results showed that the determined value was in agreement with the certified value for the reference standard. Spiked recoveries of the river water and lake water samples ranged from 95.0% to 105.0% with the relative standard deviation (RSD) of 8.0%-11.0%. On the other hand, the commonly used hydride generation-atomic fluorescence spectrometry (HG-AFS） was also compared with MPT and ICP, which was more economic on power and argon consumption, and had even lower detection limit. However, MPT might have more advantages on simultaneous analysis of multi-elements, such as As, Sb, Bi, Se, Te, Hg and so on. This method was expected to provide a useful tool for sensitive analysis of As and other metalloids from complex matrices. [ABSTRACT FROM AUTHOR]

This paper presents new experimental data that enable the observed processes in nonlinear ferrite lines to be related with the theoretical positions of the spin waves of the magnetization precession under the conditions of a high-power microwave. Such an approach has not been considered in earlier discussions on the subject and can contribute to the theory of the generation of oscillations in a gyromagnetic ferrite medium. These new aspects were used to design a new type of generator. The specific feature is the presence of regularity in the ferrite lines in the generation mode of microwave oscillations. The repeating regularity enabled the implementation of multistage pulse shape converters capable of operating in two modes and providing extreme parameters of the output pulses. Two variants of multistage converters of nanosecond high-voltage pulse shapes with a duration of ∼4 ns at a half-height and with an amplitude of −500 kV were designed and tested. The assembly of the converters and the driving generator are described in the stationary setup. In the first case, the rise time shortened to ∼45 ps, and the amplitude increased to −850 kV due to the sharpening of a pulse and the formation of a shock wave by the cascade of three nonlinear transmission lines. A record rate for the increase of the leading peak voltage of ∼15.5 MV/ns was reached. In the second case, the new approach for the generation of a sequence of subnanosecond pulses was presented and tested, and each pulse of the previous stage was modulated by the next stage doubling the number of pulses while conserving a deeper modulation. As a result, at the top of the incident pulse, a sequence of subnanosecond peaks with a large modulation depth (∼70%) was formed when the maximum voltage amplitude reached −700 kV. The results of the emission of such pulses are also presented. [ABSTRACT FROM AUTHOR]

In this paper, transparent metasurfaces generating microwave beams with both orbital angular momentum (OAM) and spin angular momentum (SAM) are proposed. A multilayered metasurface unit cell was designed for simultaneously manipulating the transmission phase and polarization state of a linearly polarized incident wave around 4.6 GHz. Using such unit cell design, the proposed metasurfaces can introduce additional SAM and OAM to the transmitted wave by linear-to-circular polarization conversion and vortex transmission phase distributions. The simulation and measurement results are in good agreement with each other and demonstrate the generation of microwave beams with both OAM and SAM. [ABSTRACT FROM AUTHOR]