Search Results (1,476)

ZnO nanostructures have attracted attention as transducer materials in optical biosensing platforms due to their wide bandgap, defect-mediated photoluminescence, high surface-to-volume ratio, and tunable morphology. This review examines how the dimensionality of ZnO nanostructures affects biosensor performance, particularly in terms of charge transport, signal transduction, and biomolecule immobilization. The synthesis approaches are discussed, highlighting how they influence crystallinity, defect density, and surface functionalization potential. The impact of immobilization strategies on sensor stability and sensitivity is also assessed. The role of ZnO in various optical detection schemes, including photoluminescence, surface plasmon resonance (SPR), localized (LSPR), fluorescence, and surface-enhanced Raman scattering (SERS), is reviewed, with emphasis on label-free and real-time detection. Representative case studies demonstrate the detection of clinically and environmentally relevant targets, such as glucose, dopamine, cancer biomarkers, and SARS-CoV-2 antigens, with limits of detection in the pico- to femtomolar range. Recent developments in ZnO-based hybrid systems and their integration into fiber-optic and microfluidic platforms are explored as scalable solutions for portable, multiplexed diagnostics. The review concludes by outlining current challenges related to reproducibility, long-term operational stability, and surface modification standardization. This work provides a framework for understanding structure–function relationships in ZnO-based biosensors and highlights future directions for their development in biomedical and environmental monitoring applications. Full article

This paper presents the design, construction, and tests of a polarization-reconfigurable phased array antenna. The proposed array allows the polarization at the main lobe maximum direction to be electronically reconfigured between right-hand (RHCP) and left-hand circular polarization (LHCP). Single-fed microstrip antennas, each with four tunable varicap diodes, are employed in the phased array to achieve a low axial ratio (AR) at the steering angles. Special attention is given to the microstrip antenna design and varicap modeling, which involves the use of measured data and search algorithms running in an electromagnetic/circuit co-simulation environment. To illustrate the proposed approach, a six-element linear phased array at 2.2 GHz has been built and tested in an anechoic chamber. The experimental results demonstrate an AR below 1 dB in both RHCP and LHCP states over a wide range of steering angles, and even in a multibeam configuration, validating our design method. Full article

This paper presents a design approach for a dual-band substrate-integrated waveguide (SIW) bandpass filter (BPF) featuring passband tunability and wide-stopband characteristics. The proposed circuit is realized using half-mode (HM) SIW cavities loaded with tunable stopband resonators (TSRs). The TSRs are realized using transmission lines and varactor diodes. Passband tunability can be achieved by adjusting the supply voltage on the varactor diode. Wide-stopband characteristics can be achieved by integrating the defected microstrip structure into the proposed circuit. To validate the proposed concept, dual-band HM SIW BPFs with fixed and tunable passbands has been designed and fabricated. Based on the measurement results, the proposed circuits demonstrate high-frequency selectivity, with an attenuation level better than 20 dB and measured up to more than 40 GHz at the highest stopband. Moreover, the proposed tunable dual-band HM SIW BPF provides a passband tuning range of 240 MHz, measured from 4.88 GHz to 5.12 GHz for the first passband, and 310 MHz, measured from 6.19 GHz to 6.5 GHz for the second passband. Within the passband tuning range, the insertion loss varied from 1.7 dB to 2.2 dB for the first passband and 2.1 dB to 2.5 dB for the second passband. Full article

Triboelectric materials can convert irregular mechanical stimuli from human motion or environmental sources into high surface charge densities and instantaneous electrical outputs. Their intrinsic properties, such as flexibility, stretchability, chemical tunability, and compatibility with diverse substrates, play a critical role in determining the efficiency and reliability of triboelectric devices. In the context of active health, triboelectric materials not only serve as the core functional layers for self-powered sensing but also enable real-time physiological monitoring, motion tracking, and human–machine interaction by directly transducing biomechanical signals into electrical information. Soft triboelectric sensors exhibit high sensitivity, wide operational ranges, excellent biocompatibility, and wearability, making them highly promising for active health monitoring applications. Despite these advantages, challenges remain in enhancing surface charge density, achieving effective signal multiplexing, and ensuring long-term stability. This review provides a comprehensive overview of triboelectric mechanisms, working modes, influencing factors, performance enhancement strategies, and wearable health applications. Finally, it systematically summarizes the key improvement approaches and future development directions of triboelectric materials for active health, offering valuable guidance for advancing wearable self-powered biosensors. Full article

A high-power single-frequency continuous-wave wideband continuously tunable dual-wavelength laser at 1064/532 nm is presented in this paper. Firstly, a thermally insensitive cavity containing a type-I phase-matching LiB₃O₅ crystal and an uncoated quartz etalon was specially designed, which provided the fundamental condition for the generation of a high-power single-frequency 1064 nm and 532 nm laser. By carefully optimizing the mode matching, the maximal output powers of 13.3 W at 1064 nm and 12.5 W at 532 nm were achieved when the pump power was 63.7 W, and the total optical–optical efficiency of 40.5% was achieved. After the transmission peak of etalon was locked to the oscillating frequency of the resonator, the continuous frequency tuning ranges of the achieved laser were as wide as 26.75 GHz at 1064 nm and 53.5 GHz at 532 nm. Full article

MXenes are relatively new 2D materials made up of carbides and/or nitrides of transition metals with a chemical formula M_n+1X_nT_x. They are usually fabricated by chemically etching a ceramic phase. MXenes possess tunable catalytic, optical, and electronic properties, which have attracted significant research interest, primarily in energy storage and biosensing applications. Since their first fabrication in 2011, there has been a rapid increase in studies investigating the use of MXenes in a wide range of applications. In this review, the synthesis methods of MXenes are discussed. Then, the potential application of MXenes in cancer treatment is highlighted based on current research. The ability of MXene to convert light, usually NIR (I and II), to heat with improved conversion efficiencies makes it a competitive candidate for photothermal cancer therapy. Moreover, the surface of MXenes can be modified with drugs or nanoparticles, thereby achieving synergistic photo/chemo/, and sonodynamic therapy. This review also examines the available research on the biocompatibility and cytotoxicity of MXenes. Full article

Based on first-principles calculations and linear-response time-dependent density functional theory within the random phase approximation (LR-TDDFT-RPA), this work systematically investigates the modulation of Dirac plasmons in germanene via carrier doping, biaxial strain, and substrate effects. The results demonstrate that carrier doping induces highly tunable Dirac plasmons whose excitation energy follows the ω ∝ n^1/4 scaling relation, leading to a sublinear increase with doping concentration. Furthermore, biaxial strain effectively modulates the Fermi velocity, and the established ω ∝ √V_F relationship directly explains the observed linear tuning of plasmon energy with strain. More importantly, the combined modulation of carrier density and strain enables a significantly broader plasmon energy range (0.16–0.61 eV) than achievable through individual parameter control. When supported on hBN substrates, germanene maintains the characteristic √q plasmon dispersion despite band hybridization and a redshift in energy, a behavior well explained by the 2D free electron gas model. This study provides important theoretical insights into the multi-parameter control of Dirac plasmons and supports the design of germanene-based tunable nanophotonic devices. Full article

A broad-temperature-range wavelength tracking system employing a thermistor monitoring circuit and a tunable optical filter is proposed and experimentally demonstrated. In this scheme, a thermistor monitoring circuit is utilized to acquire the real-time resistance values of a distributed feedback laser diode (DFB-LD). When the mapping relationship curve among thermistor resistance, temperature, and center wavelength of the DFB-LD is established, the drive voltage of the narrowband tunable optical filter is dynamically adjusted to regulate its filter window. Therefore, wavelength tracking is achieved by matching the filter window and the center wavelength of the DFB-LD. The experimental results show that the proposed system can achieve adaptive wavelength tracking within the operation band of 1539.4 nm to 1548.6 nm across a temperature range from −40 °C to 60 °C. The wavelength detection resolution and the minimum step of wavelength control are better than 0.79 pm and 0.1 nm, respectively. By exploiting the conversion characteristics between the thermistor and the center wavelength of the DFB-LD, this approach transforms laser wavelength detection into a low-cost, real-time electrical measurement, significantly enhancing transmission stability and reliability of laser sources in complex thermal environments. Full article

Viologens are promising candidates for next-generation electrochromic devices due to their reversible color changes, low operating voltages, and structural tunability. However, their practical performance is often constrained by limited color range, stability issues, and poor charge delocalization. In this study, we present a detailed density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation of asymmetric viologens based on the Benzyl-4,4′-dipyridyl-R (BnV-R) framework. A series of electron-donating and electron-withdrawing substituents (CN, COOH, PO₃H₂, CH₃, OH, NH₂) were introduced via either benzyl or phenyl linkers. Geometry optimizations for neutral, radical cationic, and dicationic states were performed at the CAM-B3LYP/6-31+G(d,p) level with C-PCM solvent modeling. Electronic structure, frontier orbital distributions, and redox potentials were correlated with substituent type and linkage mode. Natural Bond Orbital analysis showed that electron-withdrawing groups stabilize reduced states, while electron-donating groups enhance intramolecular charge transfer and switching kinetics. TD-DFT calculations revealed significant bathochromic and hyperchromic shifts dependent on substitution patterns, with phenyl linkers promoting extended conjugation and benzyl spacers minimizing aggregation. Radical cation stability, quantified via ΔE_red and comproportionation constants, highlighted cyano- and amine-substituted systems as particularly promising. These insights provide predictive design guidelines for tuning optical contrast, coloration efficiency, and electrochemical durability in advanced electrochromic applications. Full article

MXenes, an emerging class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have demonstrated exceptional potential in tribology: the study of friction, wear, and lubrication. Their remarkable mechanical strength, thermal stability, and tunable surface chemistry make them ideal candidates for solid lubricants, lubricant additives, and protective coatings in mechanical systems. This review comprehensively examines the tribological performance of MXenes under diverse environmental conditions, including high temperatures, vacuum, humid atmospheres, and liquid lubricants. A particular emphasis is placed on the influence of surface terminations (-OH, -O, -F) on friction reduction and wear resistance. Additionally, we discuss strategies for enhancing MXene performance through hybridization with polymers, nanoparticles, and ionic liquids, enabling superior durability in applications ranging from micro/nano-electromechanical systems (MEMS/NEMS) to aerospace and biomedical devices. We also highlight recent advances in experimental characterization techniques and computational modeling, which provide deeper insights into MXene tribomechanics. Despite their promise, key challenges such as oxidation susceptibility, high synthesis costs, and performance variability hinder large-scale commercialization. Emerging solutions, including eco-friendly synthesis methods and optimized composite designs, are explored as pathways to overcome these limitations. Overall, MXenes represent a transformative avenue for developing next-generation tribological materials that combine high efficiency, sustainability, and multifunctionality. Continued research and innovation in this field could unlock groundbreaking advancements across industrial and engineering applications. Full article

A series of PTT-b-PTMG copolyesters was synthesized via direct esterification followed by melt polycondensation using purified terephthalic acid (PTA), bio-based 1,3-propanediol (PDO), and poly(tetramethylene glycol) (PTMG) of varying molecular weights (650–3000 g/mol). The resulting materials were comprehensively characterized in terms of chemical structure, molecular weight, thermal behavior, phase morphology, crystalline architecture, and mechanical performance using a range of analytical techniques: Fourier-transform infrared spectroscopy (FTIR), ¹H-NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), dynamic mechanical thermal analysis (DMA), tensile testing, and other standard physical methods. FTIR, ¹H-NMR, and GPC data confirmed the successful incorporation of both PTT-hard and PTMG-soft segments into the copolymer backbone. As the PTMG molecular weight increased, the average sequence length of the PTT-hard segments (L_n,T) also increased, leading to higher melting (T_m) and crystallization (T_c) temperatures, albeit with a slight reduction in overall crystallinity. DMA results indicated enhanced microphase separation between hard and soft domains with increasing PTMG molecular weight. WAXS and SAXS analyses further revealed that the crystalline structure and long-range ordering were strongly dependent on the copolymer composition and block architecture. Mechanical testing showed that tensile strength at break remained relatively constant across the series, while Young’s modulus increased significantly with higher PTMG molecular weight—concurrently accompanied by a decrease in elongation at break. Furthermore, the elastic deformability and recovery behavior of PTT-b-PTMG block copolymers were evaluated through cyclic tensile testing. TGA confirmed that all copolyesters exhibited excellent thermal stability. This study demonstrates that the physical and mechanical properties of bio-based PTT-b-PTMG elastomers can be effectively tailored by adjusting the molecular weight of the PTMG-soft segment, offering valuable insights for the rational design of sustainable thermoplastic elastomers with tunable performance. Full article

Terahertz waves have great potential for applications in security imaging, wireless communication, and other fields, but efficient and tunable terahertz-absorbing devices are the key to their technological development. In this paper, a tunable terahertz metamaterial based on graphene and vanadium dioxide materials is proposed. When the vanadium dioxide conductivity is 1.6 × 10⁵ S/m and the Fermi energy level of graphene is 0.75 eV, the metamaterial exhibits high absorptivity exceeding 90% in ultra-broadband of 2.05–14.03 THz; when the Fermi energy level of graphene is adjusted to 0 eV, the high absorption wavelength range narrowed to 4.07–13.80 THz; when the vanadium dioxide conductivity is adjusted to 200 S/m, the metamaterial exhibits high transmissivity exceeding 80% in the wavelength range up to 15 THz. Additionally, the metamaterial is insensitive to polarization angles and incident angles, allowing it to adapt to changes in the angle of incidence and polarization in practical applications. The metamaterial has potential applications in optical switches, electromagnetic wave stealth devices, and filtering devices. Full article

Electromagnetic interference (EMI) represents a growing challenge in the modern era, as electronic systems and wireless technologies become increasingly integrated into daily life. This review provides a comprehensive overview of EMI, beginning with its historical evolution over centuries, from early power transmission systems and industrial machinery to today’s complex environment shaped by IoT, 5G, smart devices, and autonomous technologies. The diverse sources of EMI and their wide-ranging effects are examined, including disruptions in electrical and medical devices, ecological impacts on wildlife, and potential risks to human health. Beyond its technical and societal implications, the economic dimension of EMI is explored, highlighting the rapid expansion of the global shielding materials market and its forecasted growth driven by telecommunications, automotive, aerospace, and healthcare sectors. Preventative strategies against EMI are discussed, with particular emphasis on the role of advanced materials. Carbon-based nanomaterials—such as graphene, carbon nanotubes, and carbon foams—are presented as promising solutions owing to their exceptional conductivity, mechanical strength, tunable structure, and environmental sustainability. By uniting perspectives on EMI’s origins, consequences, market dynamics, and mitigation strategies, this work underscores the urgent need for scalable, high-performance, and eco-friendly shielding approaches. Special attention is given to recent advances in carbon-based nanomaterials, which are poised to play a transformative role in ensuring the safety, reliability, and sustainability of future electronic technologies. Full article

We present the design of an optically transparent, flexible, and tunable microwave absorber covering the X and Ku frequency bands. The absorber is based on a metasurface composed of a periodic array of graphene spiral resonators (GSRs) attached to an ultrathin PET film placed over an ITO-backed dielectric spacer. An equivalent circuit model (ECM), described by closed-form equations, is proposed to optimize the structure for maximum absorption within the target frequency range. The optimized absorber achieves a peak absorbance of 99.7% for normally incident waves while maintaining over 90% absorption at various incident angles in the frequency range from 8.5 GHz to 17.4 GHz. In addition, a double-layer graphene spiral resonator (DGSR) metasurface is proposed to extend the absorber’s operational bandwidth, demonstrating a bandwidth enhancement of approximately 3 GHz and a relative bandwidth of 90% without compromising miniaturization or incident angle stability. Given their remarkable attributes, both GSR and DGSR configurations show great potential for applications in radar stealth technology and transparent electromagnetic compatibility. Full article

Multispectral LiDAR (MSL) systems offer a significant advantage by actively capturing both spatial and spectral information. These systems offer significant promise in supporting the comprehensive analysis and precise classification of underwater targets. In this study, we build an MSL system based on an acousto-optic tunable filter (AOTF) to investigate the feasibility of underwater sphere classification. The MSL prototype features a spectral resolution of 20 nm and 13 spectral channels, covering a range from 560 to 800 nm. Laboratory-based experiments were conducted to evaluate the accuracy of range measurements and the classification performance of the system. The spectral curves of nine distinct spheres acquired by the MSL were utilized for classification using a support vector machine (SVM). The experimental results indicate that classification using multispectral data yields a higher accuracy and Kappa coefficient. Finally, the point cloud acquired from scanning experiments further validated the MSL system’s performance. This finding preliminarily validates the feasibility of multispectral LiDAR for classifying submerged spherical targets. Full article