Search Results (61)

Monitoring nitrogen dioxide (NO₂) in various scenarios is crucial due to its significant environmental impact as a hazardous gas which is emitted by several industrial sectors. This study reports the optimized synthesis of WO₃ flower-like structures using the microwave-assisted hydrothermal method under various experimental conditions, resulting in the optimized sample designated MF-WO₃-K2. Structural, morphological, and chemical characterizations revealed that WO₃ microflowers (MF-WO₃-K2) exhibit a hexagonal crystalline phase, a bandgap of 2.4 eV, and a high specific surface area of 61 m²/g. The gas-sensing performance of WO₃ microflowers was investigated by electrical measurements of six similarly fabricated MF-WO₃-K2 sensors. The MF-WO₃-K2 sensors demonstrated a remarkable sensor signal of 225 for 5 ppm NO₂ at 150 °C and response/recovery times of 14.5/2.4 min, coupled with outstanding selectivity against potential interfering gases such as CO, H₂, C₂H₂, and C₂H₄. Additionally, the sensors achieved a low detection limit of 65 ppb for NO₂ at 150 °C. The exceptional sensing properties of WO₃ microflowers are attributed to the abundance of active sites on the surface, large specific surface area, and the presence of pores in the material that facilitate the diffusion of NO₂ molecules into the structure. Overall, the WO₃ microflowers demonstrate a promising ability to be used as a sensitive layer in high-performance chemiresistive gas sensors due to their high sensor performance and good reproducibility for NO₂ detection. Full article

The steady-state quantum dynamics of a compound sample consisting of a semiconductor double-quantum-dot (DQD) system, non-linearly coupled with a leaking superconducting transmission line resonator, is theoretically investigated. Particularly, the transition frequency of the DQD is taken to be equal to the doubled resonator frequency, whereas the inter-dot Coulomb interaction is considered weak. As a consequence, the steady-state quantum dynamics of this complex non-linear system exhibit sudden changes in its features, occurring at a critical DQD-cavity coupling strength, suggesting perspectives for designing on-chip microwave quantum switches. Furthermore, we show that, above the threshold, the electrical current through the double-quantum dot follows the mean photon number into the microwave mode inside the resonator. This might not be the case any more below that critical coupling strength. Lastly, the photon quantum correlations vary from super-Poissonian to Poissonian photon statistics, i.e., towards single-qubit lasing phenomena at microwave frequencies. Full article

In this study, we have compared different Rydberg atom-based microwave electrometry techniques under the same experimental conditions and using the same Rydberg states ($68S_{1/2}$, $68P_{3/2}$, and $67P_{3/2}$). The comparison was carried out for the following techniques: (i) auxiliary microwave field, (ii) microwave amplitude modulation, and (iii) polarization spectroscopy. Our results indicate that all three techniques have a similar minimum measurable microwave electric field. A slightly better result can be obtained by performing polarization spectroscopy using a Laguerre–Gauss coupling laser beam. Full article

Nonlinear dynamical states generated by self-delayed feedback based on fiber structures have broad applications. However, fiber-based optoelectronic feedback or pure optical feedback systems exhibit long delays, and the coupling mechanisms between these two loops differ significantly from those in short-delay systems. A systematic investigation of feedback coupling mechanisms under long-delay conditions is of great significance for optimizing such systems. In this paper, the nonlinear dynamic state generated by directly modulated distributed feedback semiconductor laser (DM-DFBL) self-delayed feedback with an optoelectronic oscillation loop is studied. Both numerical and experimental results show that the DM-DFBL’s dynamical states vary with changes in optical and electrical feedback intensities. In the self-delayed feedback, the DM-DFBL exhibits an evolutionary path from a chaos (CO) state to a period-one (P1) state and finally becomes a steady state with the decrease of optical feedback intensity. In the optoelectronic oscillation loop, the DM-DFBL generates a microwave frequency comb (MFC), a full-frequency oscillation, and a P1 state. Additionally, the dynamic state of the DM-DFBL can be disturbed, and the stability of the P1 state and the QP state can be enhanced when the optoelectronic oscillation loop is introduced. These conclusions contribute to the precise control of dynamic evolution. Full article

Composites of ferromagnetic and ferroelectric phases are of interest for studies on mechanical strain-mediated coupling between the two phases and for a variety of applications in sensors, energy harvesting, and high-frequency devices. Nanocomposites are of particular importance since their surface area-to-volume ratio, a key factor that determines the strength of magneto-electric (ME) coupling, is much higher than for bulk or thin-film composites. Core–shell nano- and microcomposites of the ferroic phases are the preferred structures, since they are free of any clamping due to substrates that are present in nanobilayers or nanopillars on a substrate. This review concerns recent efforts on ME coupling in coaxial fibers of spinel or hexagonal ferrites for the magnetic phase and PZT or barium titanate for the ferroelectric phase. Several recent studies on the synthesis and ME measurements of fibers with nickel ferrite, nickel zinc ferrite, or cobalt ferrite for the spinel ferrite and M-, Y-, and W-types for the hexagonal ferrites were considered. Fibers synthesized by electrospinning were found to be free of impurity phases and had uniform core and shell structures. Piezo force microscopy (PFM) and scanning microwave microscopy (SMM) measurements of strengths of direct and converse ME effects on individual fibers showed evidence for strong coupling. Results of low-frequency ME voltage coefficient and magneto-dielectric effects on 2D and 3D films of the fibers assembled in a magnetic field, however, were indicative of ME couplings that were weaker than in bulk or thick-film composites. A strong ME interaction was only evident from data on magnetic field-induced variations in the remnant ferroelectric polarization in the discs of the fibers. Follow-up efforts aimed at further enhancement in the strengths of ME coupling in core–shell composites are also discussed in this review. Full article

Rotational spectra for hexafluoroacetone imine, the singly substituted ¹³C isotopologues, and the ¹⁵N isotopologue, have been recorded using both cavity and chirped pulse Fourier transform microwave spectrometers. The spectra observed present as being doubled with separations between each pair of transitions being on the order of a few tens of kilohertz which is consistent with a large amplitude motion producing two torsional substates. The observed splitting is most likely due to the combined motions of the CF3 groups, for which the calculated barrier is small. However, no transitions between states could be observed and, similarly, no Coriolis coupling parameters were required to achieve a satisfactory fit for the transition frequencies. Hence, and somewhat curiously, the two states have been fit independently of each other such that the two states may simply be considered near-equivalent conformers. The structural properties of hexafluoroacetone imine are compared with two isoelectronic molecules hexafluoroisobutene and hexafluoroacetone. Rotational constants, quartic centrifugal distortion constants, and the ¹⁴N nuclear electric quadrupole coupling tensor have been determined and are presented together with supporting quantum chemical calculations. Full article

Introduction: The use of electrical appliances using extremely low frequency (ELF) electromagnetic fields (EMF) has increased in the past few years. These ELF MF are reported to be linked to several adverse health effects. However, only a couple of studies have been conducted on the association between risk of tumours and use of electronic devices using low frequency (LF) EMF. Methods: We studied the use of common household electrical appliances and suspected risk of tumours in a multi-hospital-based case-control study. In total, 316 patients were included in the final analysis. Results: The study results showed a below unity risk for most of the devices. A slight increased risk of tumour was observed for computer screen use OR: 1.13 (95% CI: 0.43–3.02) and use of microwave oven OR: 1.21 (95% CI: 0.36–4.04). We also had chance to investigate ELF MFs exposure association with tumour. Where we observed elevated odd ratios in individuals living near electricity transformer stations, with a statistically significant risk OR: 2.16 (95% CI: 1.30–3.59). However, the risk was below unity (OR: 0.98) in individuals residing close to powerlines. Conclusion: The current study serves as a pilot study of primary data and will be helpful in future epidemiological research studies on the topic in the region. Full article

This paper examines the random nature of interharmonics generated by power converters connected to sustainable energy sources and loads, such as wind turbines, photovoltaic (PV) panels, and electric vehicles (EVs). Current research often overlooks the stochastic behavior of interharmonics and their impact on power system reliability and resilience, leading to gaps in effective modeling and mitigation strategies. Thus, this study examines a low-voltage installation with a PV panel, an EV and a microwave operating simultaneously, providing practical insights into real-world scenarios of interharmonic related disruptions and solutions for enhancing the reliability and resilience of sustainable energy grids. By leveraging real-time measurements of interharmonics, suitable probability distribution functions (PDFs) are initialized to develop a probabilistic model using Monte Carlo simulation. This enables the derivation of a time-domain aggregation model of interharmonics from multiple sources operating together at the point of common coupling (PCC). The findings reveal that the peak values of voltage or current fluctuations at the PCC are influenced by the randomness in the number of devices connected and the frequency components originating from different sources. Through multiple case studies, the dependency of these fluctuations on stochastic parameters is systematically established. Empirical relationships are formulated to predict aggregated interharmonic values under varying scenarios, enhancing the accuracy and applicability of the model. The results demonstrate that higher interharmonic frequencies and fewer randomly connected devices significantly increase the probability of elevated aggregated peak values. These insights can serve as benchmarks for grid operators and policymakers in mitigating interharmonic related issues in modern power systems. Full article

This research presents the development and analysis of a microwave sensor designed with a microstrip band-stop filter, aimed at applications in electrical engineering and food quality assessment. The sensor employs parallel-coupled lines within the microstrip, integrating a band-stop filter at 2.45 GHz on an FR4 substrate. The primary objective is to evaluate preserved fish samples to demonstrate the sensor’s efficacy and applicability. Measurements were conducted using a KEYSIGHT model E5063A network analyzer, covering a frequency range from 0.1 GHz to 3 GHz. The analysis focuses on the frequency response of the insertion loss (S₂₁) across specified frequencies. The results indicate a significant correlation between the percentage shift in the transmission coefficient and the frequency, even when the sample range was meticulously adjusted. These findings underscore the potential of microwave sensors in monitoring the physical properties of preserved food, particularly within food production and quality control processes. The sensor facilitates rapid and precise assessments of food properties, highlighting its broad applicability in various sectors of the food industry. Furthermore, this research contributes to the advancement of microwave technology, suggesting new pathways for future studies and applications in engineering and industrial contexts. The integration of microstrip technology with band-stop filters in sensor design presents a novel approach that enhances the accuracy and efficiency of food quality monitoring systems. This study not only establishes a foundation for further technological developments but also emphasizes the interdisciplinary nature of modern engineering solutions, combining principles of electrical engineering with practical applications in the food industry. This innovative approach could lead to more sophisticated and reliable methods for ensuring food safety and quality. Full article

We propose extended one-way waveguide states of large-area propagation in a photonic crystal waveguide consisting of two honeycomb gyromagnetic photonic crystals with opposite external magnetic fields. When the width of the waveguide is small enough, the edge states along both boundaries of the waveguide couple with each other strongly and thus create the so-called extended one-way waveguide states. Of note, this structure supports both even and odd extended states, which can be excited under different excitation conditions. For the odd mode, electromagnetic waves have opposite phase distributions along the centerline of the waveguide on both sides, while for the even mode, they have in-phase distributions on both sides. In addition, the odd and the even modes both have the large-area propagating property. Moreover, we have carried out a microwave experiment to verify the simulation results. The measured transmission spectrum shows that the structure has strong non-reciprocity, and the measured electric field distributions of the even and odd modes prove that it supports excellent large-area transmission behaviors. These results provide feasible ideas for achieving topological high-throughput transmission. Full article

The process of microwave heating involves the coupling of multiple physical phenomena, specifically including the distribution of the electromagnetic field in the resonant cavity. The electromagnetic effect generates heat and encourages the transfer of heat inside the material. In this numerical study, a 3D computer model of microwave heating of Al₂O₃/SiC composites using a multimode microwave heating chamber was established based on the simulation software COMSOL Multiphysics 5.6, and the symmetry treatment of the model was carried out, which effectively reduced the amount of model calculations and accurately analyzed the microwave heating characteristics of the samples. The analysis of the microwave heating characteristics of the sample was mainly preformed from the perspective of the electric field distribution in the resonant cavity, the sample heating rate and the sample heating uniformity, and then it was determined how the microwave source power and sample mold selection affect the temperature and electric field parameters of the sample. After experimental verification, the error between the simulation results and the temperature parameters obtained from the actual experiments is less than 2%. This study contributes to further understanding the heating behavior of Al₂O₃/SiC composites in complex multimode microwave heating environments and can be used to control the dynamic parameters during microwave heating in order to improve the heating rate and heating uniformity of samples. Full article

Board milling is one of the most widespread methods for manufacturing printed circuit boards from low frequencies to the microwave and millimeter wave range. In this contribution, the detrimental effect of defects typical of printed circuit board plotters has been investigated. In detail, a systematic frequency shift in the circuit performance has been observed both in terms of S21 and S11 parameters. The performance degradation has been analyzed and attributed to the inaccurate milling depth, which is typical of many plotters, particularly for less recent models. After the conductor removal step, the unwanted milling of dielectric material changes the electrical properties of the microstrip structure, in turn affecting the circuit performance. This circumstance has been investigated by means of electromagnetic simulations performed on the real case study of a parallel coupled lines filter. Therefore, a filter prototype has been realized and measured to confirm the simulated results. This study can be beneficial to those professionals involved in the design and realization of microwave and millimeter waves circuits with board milling machines. Full article

Due to its potential harm to space payload, microwave corona breakdown of microstrip circuits has attracted much attention. This work describes an efficient way to suppress corona breakdown. Since the corona breakdown threshold is determined by the highest electric field intensity at the surface of microstrip circuits, lacquer coating with a thickness of tens of microns is sprayed on top of microstrip circuits. The applied dielectric coating is used to move the discharge location away from the circuit’s surface, which is equivalent to reducing the highest electric field intensity on the interface of solid/air of the circuit and thus results in a higher breakdown threshold. Two designs of a classic coupled-line bandpass filter were used for verification. Corona experimental results at 2.5 GHz show that in the low-pressure range of interest (100 to 4500 Pa), a 5.3 dB improvement of the microwave corona breakdown threshold can be achieved for a filter with a narrowest gap of 0.2 mm, while its electrical performances like insertion loss and Q-factor are still acceptable. A threshold improvement prediction method is also presented and validated. Full article

Nitrides are the leading semiconductor material used for the fabrication of high electron mobility transistors (HEMTs). They exhibit piezoelectric properties, which, coupled with their high mechanical stiffness, expand their versatile applications into the fabrication of piezoelectric devices. Today, due to advances in device technology that result in a reduction in the size of individual transistor elements and due to increased structural complexity (e.g., multi-gate transistors), the integration of piezoelectric materials into HEMTs leads to an interesting occurrence, namely acoustic emission from the transistor gate due to piezoelectric effects. This could affect the device’s performance, reliability, and durability. However, this phenomenon has not yet been comprehensively described. This paper aims to examine this overlooked aspect of AlGaN/GaN HEMT operation, that is, the acoustic emission from the gate region of the device induced by piezoelectric effects. For this purpose, dedicated test structures were designed, consisting of two narrow 1.7 μm-wide metallization strips placed at distances ranging from 5 μm to 200 μm fabricated in AlGaN/GaN heterostructures to simulate and examine the gate behavior of the HEMT transistor. For comparison, the test device structures were also fabricated on sapphire, which is not a piezoelectric material. Measurements of acoustic and electrical interactions in the microwave range were carried out using the “on wafer” method with Picoprobe’s signal–ground–signal (SGS)-type microwave probes. The dependence of reflectance |S11| and transmittance |S21| vs. frequency was investigated, and the coupling capacitance was determined. An equivalent circuit model of the test structure was developed, and finite element method simulation was performed to study the distribution of the acoustic wave in the nitride layers and substrate for different frequencies using Comsol Multiphysics software. At frequencies up to 2–3 GHz, the formation of volume waves and a surface wave, capable of propagating over long distances (in the order of tens of micrometers) was observed. At higher frequencies, the resulting distribution of displacements as a result of numerous reflections and interferences was more complicated. However, there was always the possibility of a surface wave occurrence, even at large distances from the excitation source. At small gate distances, electrical interactions dominate. Above 100 µm, electrical interactions are comparable to acoustic ones. With further increases in distance, weakly attenuated surface waves will dominate. Full article

Nitrogen-rich wastewater is a major environmental issue that requires proper treatment before disposal. This comprehensive overview covers biological, physical, and chemical nitrogen removal methods. Simultaneous nitrification–denitrification (SND) is most effective in saline water when utilizing both aerobic and anoxic conditions with diverse microbial populations for nitrogen removal. Coupling anammox with denitrification could increase removal rates and reduce energy demand. Suspended growth bioreactors effectively treated diverse COD/N ratios and demonstrated resilience to low C/N ratios. Moving biofilm bioreactors exhibit reduced mortality rates, enhanced sludge–liquid separation, increased treatment efficiency, and stronger biological structures. SND studies show ≥90% total nitrogen removal efficiency (%RE_TN) in diverse setups, with Defluviicoccus, Nitrosomonas, and Nitrospira as the main microbial communities, while anammox–denitrification achieved a %RE_TN of 77%. Systems using polyvinyl alcohol/sodium alginate as a growth medium showed a %RE_TN ≥ 75%. Air-lift reflux configurations exhibited high %RE_TN and %RE_NH4, reducing costs and minimizing sludge formation. Microwave pretreatment and high-frequency electric fields could be used to improve the %RE_NH4. Adsorption/ion exchange, membrane distillation, ultrafiltration, and nanofiltration exhibit promise in industrial wastewater treatment. AOPs and sulfate-based oxidants effectively eliminate nitrogen compounds from industrial wastewater. Tailoring proposed treatments for cost-effective nitrogen removal, optimizing microbial interactions, and analyzing the techno-economics of emerging technologies are crucial. Full article