Search Results (933)

Climate change and increasing water scarcity are intensifying pressure on irrigated agriculture, which currently represents 70% of global freshwater withdrawals. Remote sensing technologies have become essential tools for monitoring soil moisture, evapotranspiration, crop growth, and irrigation performance across multiple spatial and temporal levels. This review synthesizes 83 peer-reviewed studies published between 2002 and 2025, focusing on the use of optical, thermal, and microwave sensors to support irrigation water management under climate variability. The analysis highlights progress in multi-sensor integration, UAV-based monitoring, crop and agro-hydrological modeling, and emerging machine learning approaches that enhance irrigation scheduling, soil moisture estimation, and crop water stress detection. Despite these advancements, several methodological challenges persist, including data integration constraints, sensor-specific limitations, model transferability issues, insufficient ground validation, and difficulties in translating remote sensing outputs into operational decision support systems. In addition, structural gaps at the policy level restrict the evaluation of irrigation efficiency and climate resilience. This review aims to clarify current limitations and outline priority research directions to enhance the climate resilience and sustainability of irrigated agricultural systems. Full article

Addressing the challenges of electromagnetic compatibility testing and non-destructive inspection of internal structures in miniaturized electronic devices. This paper reports a non-destructive testing method based on wide-field imaging using diamond nitrogen-vacancy (NV) centers, and systematically demonstrates its application on a black-epoxy-encapsulated Universal Serial Bus (USB) flash drive. In the experiment, a swept microwave signal from 2.82 GHz to 2.97 GHz was sequentially injected into the four external interface pins of the USB drive. A bulk diamond served as the quantum sensing layer, and optically detected magnetic resonance (ODMR) was employed to perform wide-field imaging of the microwave field distribution on the surface of the signal lines within a 1 × 1 mm² region of interest. The experimental results show that the microwave field distributions corresponding to different interface channels are significantly different. Based on these differences, the connection relationship between each signal line and its corresponding interface pin can be clearly identified, and the differences in field distribution as well as crosstalk characteristics among channels can be revealed. The method established in this work provides an effective technical pathway for non-destructive electromagnetic testing and functional verification of electronic products. Full article

A two-step growth process was developed to fabricate a 3-inch homogeneously {100}-textured free-standing diamond wafer by microwave plasma enhanced chemical vapor deposition (MPCVD). The sequential growth process is based on a change in the growth parameter α, which is given by the growth rates on {100} and {111} facets, α = $\sqrt{3}$·(V₁₀₀/V₁₁₁). Initial growth was executed with nitrogen addition, yielding an α value close to 3 for evolutionary selection of the (100) face, followed by cessation of nitrogen addition to yield a lower α value. A homogeneously grown {100}-textured diamond over an area of ca. 175 cm² with a thickness ≥ 0.8 mm was obtained after 196 h growth. The diamond growth rate was 4.0–5.5 µm/h, which is four times higher than the conventional growth of oriented diamond. This was substantiated by optical microscopy, Raman spectroscopy, and XRD analysis. The large crystal size of 210 ± 60 µm has been assigned to the second growth step, where growth is preferentially in the <111> direction. The homogeneous {100} texture and the large crystal size are conducive to achieving high thermal conductivity, as the in-plane thermal conductivity of the polycrystalline diamond wafer was increased from ca. 850 W/(mK) to 1125 W/(mK). Full article

We demonstrate a reconfigurable microwave frequency measurement (MFM) scheme based on the period-one (P1) dynamics of an optically injected semiconductor laser. Unlike conventional architectures relying on electrical frequency-sweeping, our approach utilizes the P1 oscillation to generate a wideband linear optical chirp. A spectral gating mechanism is introduced, where an optical bandpass filter creates a negative temporal marker by rejecting free-running component of distributed feedback laser (DFB), thereby eliminating the need for external synchronization or pilot tones. The measurement range is flexibly tunable by adjusting the injection parameters, enabling a measurement range from 10 to 48 GHz. Experimental results demonstrate a frequency resolution of 50 MHz with chirp rate of 1 GHz/μs and a root-mean-square (RMS) error below 15 MHz, confirming the validity of this all-optical, self-referenced frequency-to-time mapping technique. Full article

Carbon dots (CDs), including carbon quantum dots (CQDs), are ultra-small carbon-based nanomaterials, typically below 10 nm, with tunable photoluminescence, high aqueous dispersibility, favorable biocompatibility, low toxicity, and abundant surface functional groups. These properties make CDs promising multifunctional platforms for nanomedicine, particularly in bioimaging, biosensing, targeted drug/gene delivery, photodynamic therapy (PDT), photothermal therapy (PTT), antimicrobial treatment, and theranostic applications. This review critically examines recent advances in CD fabrication, including top-down, bottom-up, green biomass-derived, microwave-assisted, hydrothermal, and emerging hybrid strategies, with emphasis on how precursor selection, heteroatom doping, surface passivation, and polymer/ligand functionalization regulate optical performance, biological interaction, and therapeutic efficiency. The review discusses structural classification, including CQDs, graphene quantum dots (GQDs), carbon nanodots, and carbonized polymer dots (CPDs), together with major characterization approaches such as ultraviolet–visible (UV–Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). Particular attention is given to red/near-infrared (NIR) emission, renal clearance, drug-loading behavior, reactive oxygen species (ROS) generation, toxicity mechanisms, biodistribution, and long-term biosafety. This review also highlights key translational barriers, including batch-to-batch variability, limited standardization, scalable manufacturing, regulatory uncertainty, and incomplete pharmacokinetic evaluation. It considers artificial intelligence (AI) and machine learning (ML) as emerging tools for reproducible CD design. CDs represent versatile and clinically promising nanoplatforms, but their translation requires standardized synthesis, rigorous safety assessment, and application-specific regulatory validation. Full article

Laser sources emitting light at 1064 nm enable key applications in lidar, quantum photonics, and remote sensing, where high-extinction-ratio intensity modulation is desired to suppress the leakage light at the “off” states during modulation. Here we demonstrate a 1064 nm thin-film lithium niobate (TFLN) Mach–Zehnder electro-optic modulator featuring a half-wave voltage–length product of 2.1 V·cm and a measured electro-optic 3 dB bandwidth exceeding 10 GHz. By optimizing the waveguide and MMI-based interferometer design to improve device balance, we achieve an extinction ratio exceeding 30 dB without thermal tuning. This high extinction ratio enables high-contrast optical modulation at 1064 nm, which is essential for optical switching and other photonic applications requiring high on–off contrast. Full article

The systematic influence of signal electrode width on electro-optic bandwidth and insertion loss in L-type traveling-wave lithium niobate modulators has not yet been comprehensively quantified, limiting the parametric engineering design of this device configuration. This study presents a full-band systematic simulation sweep of signal electrode width and three auxiliary geometric parameters in an L-type traveling-wave lithium niobate Mach–Zehnder modulator, combined with optical mode simulation to establish joint microwave–optical optimization constraints. The study reveals the coupled modulating effect of signal electrode width on characteristic impedance, velocity mismatch, and transmission loss; it elucidates the competition mechanism underlying non-monotonic high-frequency loss behavior; and it identifies the complete impedance-neutral characteristic of the electrode–waveguide contact width as an independent loss-tuning degree of freedom decoupled from the impedance constraint. Full-system validation confirms that the final design simultaneously satisfies broadband impedance matching, low insertion loss, and high electro-optic bandwidth. The results are distilled into four quantitative design rules that provide simulation-driven guidance directly applicable to the engineering design of L-type thin-film lithium niobate modulators, advancing the systematic establishment of a parametric design methodology for this device configuration. Full article

Multi-target radar speed measuring instruments play a crucial role in monitoring speeding violations of multiple targets in multiple lanes, ensuring the safety, order, and efficient operation of traffic. In order to verify the stability of these instruments under long-term and complex working conditions, accelerated life testing was conducted, and the failure mechanisms of the radar were studied using optical and scanning electron microscopic analysis methods. The results indicated that at a test temperature of 85 °C and humidity of 79% RH, all five speed measuring specimens failed after testing for 55 days. The primary cause of failure was the malfunction of the microwave signal receiving chip in the radar speed module under the combination of temperature and humidity. The failure modes of the chip were mainly related to its structure, design, selection of soldering materials, and soldering process. This study provides references and insights for the reliability research of other metrological instrument products. Full article

To accelerate the transition to sustainable energy, efficient methods for CO₂-free hydrogen production and carbon utilization are needed. This study presents a new, sustainable approach for the simultaneous production of hydrogen, valuable hydrocarbons, and functional carbon materials by converting methane in low-pressure microwave plasma. Compared to traditional methane reforming methods (such as steam reforming), our plasma-based process operates at low temperatures, eliminates direct CO₂ emissions, and enables the conversion of methane into three valuable products: (1) environmentally friendly hydrogen for fuel cells and energy storage systems, (2) a range of valuable organic products (C₂H₂, C₂H₄, C₂H₆), and (3) functional carbon films with self-improving catalytic properties. Optical emission spectroscopy (OES) and the Langmuir double probe method were used for plasma diagnostics, revealing an increase in the concentration of active species (CH, Hα, C₂) and electron temperature upon argon addition. The structure, morphology, and impurity composition of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Gas-phase byproducts were analyzed using gas chromatography–mass spectrometry (GC-MS). Argon addition at an Ar/CH₄ ratio of 1 leads to the formation of carbon films with a more ordered structure, as confirmed by XRD data, and improved surface morphology. It was established that argon, by effectively participating in the excitation and dissociation processes of methane molecules through energy transfer from metastable states and increased electron temperature, optimizes plasma–chemical reactions, promoting the deposition of higher-quality carbon coatings. Full article

In this paper, we propose and demonstrate a sensitivity-enhanced sensing interrogation scheme based on an Optoelectronic oscillator (OEO), in which a switchable dual-passband microwave photonic filter (MPF) is introduced into the loop. The switchable dual-passband MPF is a combination of a modified fiber Mach–Zehnder interferometer (FMZI), an electro-optical modulator (EOM), a roll of dispersion compensating fiber (DCF), and a photodetector (PD). The dual-passband switching of the MPF can be achieved by simply adjusting the polarization state via rotating a polarization controller (PC) in the FMZI. The sensitivity can be improved by a factor of two by tracking the frequency corresponding to the central frequency of the high-frequency passband relative to the low-frequency passband. Temperature-sensing experiments were conducted to verify the concept of enhanced sensitivity. Experimental results on temperature sensing show that tracking low- and high-frequency OEO signals yields sensitivities of 5.23 MHz/°C and 10.84 MHz/°C, respectively, and temperature resolutions of 0.009 °C and 0.004 °C, thereby increasing sensitivity and resolution. Full article

Quantum secret sharing (QSS) has been previously demonstrated with conceivability in optical-fiber channels. However, extending this framework to the microwave frequency band presents challenges in achieving secure quantum communications over turbulent channels, as intricate turbulence can induce amplitude and phase jitter in quantum signals, leading to decoherence or even interruptions in the communication link. In this work, we propose a microwave-enabled continuous-variable quantum secret sharing (CVQSS) scheme operating over turbulent free-space channels. The protocol explicitly addresses the extreme sensitivity of microwave quantum states to environmental turbulence, which manifests as severe amplitude and phase fluctuations. It incorporates the Shamir threshold scheme to facilitate multi-user secret sharing. We suggest a flexible approach to solving problems of adaptive phase compensation and multi-aperture reception techniques when characterizing an equivalent noise channel based on the Kolmogorov turbulence model. The proposed measurement-device-independent (MDI) architecture renders the protocol immune to all detector-side attacks, provided that the state preparation at the users’ side is trusted. Numerical simulations ascertain the performance of the microwave continuous-variable measurement-device-independent quantum secret sharing (CV-MDI-QSS) system and demonstrate the feasibility of practical deployment in complicated turbulent channels. This approach offers a turbulence-resistant solution for dynamic quantum networks through harsh free-space channels implemented in microwave-propagated environments. Full article

Electro-optic frequency combs (EOFCs), generated through the microwave-driven modulation of continuous-wave lasers, have emerged as a highly reconfigurable and system-compatible class of optical frequency combs with growing importance in microwave photonics, coherent communications, spectroscopy, and precision metrology. In contrast to mode-locked lasers and Kerr microresonator combs, EOFCs offer electrically programmable repetition rates, deterministic phase coherence, and intrinsic compatibility with radiofrequency electronic systems, making them particularly attractive for integrated and application-oriented implementations. As EOFCs evolve toward broader bandwidths, lower power consumption, and full on-chip integration, their achievable performance is increasingly constrained by the interplay between electro-optic physical mechanisms, modulator architectures, and material platform properties. This review establishes a unified analytical framework that systematically connects EOFC generation mechanisms, device configurations, key performance metrics, and platform-level limitations. We first summarize the fundamental electro-optic effects underpinning EOFC generation and analytically examine representative modulator architectures, including phase modulators, Mach–Zehnder modulators, and microresonator-based schemes, to clarify their respective comb-generation characteristics. Key performance determinants, such as modulation depth, bandwidth, electro-optic efficiency, and optical loss, are then discussed to elucidate their coupled influence on comb-line count, spectral flatness, output power, and phase noise. Subsequently, the performance of EOFCs implemented on major integrated platforms, including Silicon on Insulator (SOI), Indium Phosphide on Insulator (InPOI), Lithium Niobate on Insulator (LNOI), and Lithium Tantalate on Insulator (LTOI), is comparatively reviewed to highlight the material-dependent advantages and constraints. Finally, emerging directions based on heterogeneous integration and ferroelectric materials with ultrahigh electro-optic coefficients are discussed as promising pathways to overcome the current performance bottlenecks. This review provides clear physical insights and engineering guidance for the future development of high-performance, integrated EOFC systems. Full article

Dental implants are widely used to replace missing teeth, but peri-implantitis remains a major biological complication associated with bacterial biofilm formation on implant surfaces. The increasing incidence of peri-implant infections underscores the need for alternative antimicrobial strategies that effectively decontaminate complex titanium implant surfaces. This study evaluated the inhibitory effect of low-temperature microwave argon plasma on bacteria in an experimental model simulating peri-implant conditions and compared the responses of microorganisms with different biological characteristics. A 3D-printed mandibular bone segment model with an inserted Straumann BLX Roxolid^® dental implant was used to reproduce the peri-implant environment. Bacterial suspensions of Streptococcus mutans NBIMCC 1786 and the extremophilic bacterium Chromohalobacter canadensis NBIMCC 9077 have been exposed to a microwave non-equilibrium argon plasma jet (2.45 GHz, atmospheric pressure) for 1–7 min. Optical density measurements and colony growth analysis were used to assess antimicrobial effects. Plasma treatment induced a pronounced reduction in bacterial growth during the early post-treatment period. In C. canadensis, growth inhibition reached a plateau (~47–55% at 24 h) regardless of exposure time. In contrast, S. mutans showed a nonlinear response, with stable inhibition after short exposures (1–3 min) and partial recovery after longer treatments (5–7 min). These findings indicate that microwave argon plasma exhibits significant antimicrobial activity under controlled in vitro conditions, although its effectiveness depends on microorganism-specific biological characteristics. Because the present model was based on simplified single-species systems, direct clinical extrapolation remains limited and should be addressed in future studies using polymicrobial peri-implant biofilm models. Full article

Graphene oxide (GO) was employed as an additive to improve the electrochemical activity of zinc oxide (ZnO) used as both a photoelectrocatalyst for water splitting and an electrochemical sensor for detection of diclofenac. To comprehend the influence of a small amount of GO on the electrochemical activity of ZnO, a series of ZnO/xGO (x = 0, 0.1, and 0.5) particles was synthesized by microwave processing of Zn(OH)₂ precipitate in the presence of 0.1 and 0.5 wt.% of previously prepared GO. The phase composition and crystal structure ordering of ZnO/xGO particles were investigated by XRD and Raman spectroscopy. The optical properties were studied by UV–Vis DRS and PL spectroscopy. The particle morphology was inspected by FE–SEM while the textural properties were analyzed by the low-temperature nitrogen adsorption–desorption method. The (photo)electrocatalytic and electrochemical sensing activities were examined on the ZnO/rxGO modified glassy carbon electrodes (GCEs) prepared by in situ reduction of the ZnO/xGO modified GCEs for 120 s. The electro- and photoelectrocatalytic activity of ZnO/rxGO modified GCEs for water splitting was tested in dark conditions and after 60 min under illumination, respectively, employing linear sweep voltammetry in 0.1 M NaOH and 0.1 M H₂SO₄ as electrolytes. The electrochemical sensing activity of ZnO/rxGO modified GCEs was tested for detection of diclofenac in aqueous solution. The improvement in the electrochemical activity of ZnO was correlated with the added amount of GO, structural defects, and particle morphology. Full article

Since their initial discovery in 2003, carbon quantum dots (CDs) have attracted significant attention due to their unique optical properties and potential biomedical applications. This review critically examines the past 20 years of research on CDs, with a particular focus on cytotoxicity studies from the last decade. CDs, typically less than 10 nm in size, have been synthesized from various organic and inorganic precursors using multiple methods, including hydrothermal, microwave, and chemical reduction techniques. Their properties can be finely tuned by modifying synthesis parameters and incorporating dopants. The preliminary studies on the biological effects of CDs were published in 2013, highlighting their antibacterial properties and low toxicity in certain contexts. Subsequent research has explored their bioactivity, including their application in drug delivery, bioimaging, and photothermal therapy. However, the cytotoxicity of CDs remains a critical area of investigation. Further studies have demonstrated that surface functional groups, charge, concentration, and size significantly influence their interaction with biological systems. For instance, CDs with positive surface charges exhibit higher cellular uptake and greater cytotoxicity compared to their negatively charged counterparts. In vivo studies utilizing animal models such as zebrafish, mice, and planarians have provided valuable insights into the potential toxicological impacts of CDs. The results indicate that while CDs generally exhibit low toxicity at certain concentrations, high doses can lead to adverse effects, including oxidative stress, organ damage, and disrupted cellular functions. Notably, the route of administration (oral, intravenous, or intraperitoneal) also affects the observed toxicity profiles. The goal of this review is to integrate the results of various studies to provide a balanced perspective on the potential risks and benefits of CDs, guiding future research and applications in nanomedicine. This review underscores the necessity for standardized and comprehensive toxicological evaluations of CDs to fully understand their safety and efficacy for biomedical applications. Full article