Search Results (154)

Epoxy resin (EP) has been extensively used in electrical insulation systems because of its favorable adhesion, chemical resistance, thermal stability, and dielectric reliability. Nevertheless, the dense three-dimensional network formed during curing generally gives EP a brittle nature, which restricts its use in insulating components that require both mechanical robustness and long-term reliability. In this work, a hydroxyl-terminated hyperbranched polymer (HBP-OH) was synthesized from itaconic acid (IA) and dipentaerythritol (DPE) through an Ax + By polycondensation route and then incorporated into an anhydride-cured epoxy system as a reactive toughening component. The influence of HBP-OH on the structure, mechanical behavior, dielectric response, and DC breakdown strength of the resulting HBP-OH/EP composites was systematically evaluated. The results demonstrate that HBP-OH effectively improves the mechanical performance of EP. At an HBP-OH loading of 9 wt%, the tensile strength increased from 15.00 MPa for pure EP to 33.27 MPa, while the elongation at break and flexural strength reached 6.5% and 88 MPa, respectively. Meanwhile, only a slight reduction in DC breakdown strength was observed at the optimal HBP-OH content. These results indicate that the proposed hyperbranched-polymer modification strategy can improve the toughness and strength of epoxy resin while retaining its dielectric and insulation performance, providing a feasible approach for developing epoxy insulating materials for high-voltage electrical equipment. Full article

This study presents an initial effort to develop Low-Temperature Cofired Ceramics (LTCC) using local bio-sourced materials: Saint Jacques shells and slate tiles. Chemical analysis confirms that the Saint Jacques shells provide CaO and CaCO₃, while slate supplies the needed SiO₂ and Al₂O₃. The constituents, processed from a formulation targeting 70 wt% slate and 20 wt% shell fragments are crushed and ball-milled, mixed with 10 wt% boron trioxide (B₂O₃), and calcinated at 700 °C for two hours to remove organics, followed by a second milling. An aqueous slurry is then prepared and manually tape-cast to form tapes that are processed through standard LTCC process steps. Initial green-state mechanical tests showed elongation values up to ~7.8% and tensile break forces in the range of ~0.5–1.0 N, with lamination performed successfully using standard isostatic conditions. Cofiring yielded limited lateral shrinkage (~6%) but substantial vertical shrinkage (27%). Two-line method measurements indicate a relative permittivity of approximately 4.3 with a comparatively high loss tangent of 0.03, suggesting a vitreous phase and/or porous, inhomogeneous microstructure. A final resonator prototype is fabricated, yielding somewhat encouraging results for the feasibility of this bio-sourced LTCC route while highlighting the need to reduce dielectric losses in future work. Full article

Conventional snapshot-type polarization devices often suffer from inherent ohmic losses caused by the metal structure, resulting in low utilization of system light energy. This research proposes a dual-layer sandwich architecture metasurface that integrates polarization control and high light transmittance for the mid-wave infrared 3~5 μm band. The top metal polarization-selective structures and the bottom dielectric hemispherical anti-reflection (AR) array are integrated monolithically on the same substrate. Specifically, the numerical simulations predict a peak transmittance of 95% at 4.4 and 4.8 μm, while maintaining extinction ratios ranging from 81.8 dB to 84.3 dB. This enables high extinction ratio polarization splitting while significantly broadening the transmittance flux of the device. It breaks the inherent trade-off between “high extinction ratio” and “high transmittance” in polarization devices, providing a high signal-to-noise ratio hardware foundation for high temporal resolution detection. Full article

Graphene nanoplatelets (GnPs) exhibit exceptional properties for advanced functional applications; nevertheless, their effective utilization is critically limited by agglomeration and poor dispersion. The incorporation of polycarboxylate-based superplasticizers (SPs) enables improved dispersion yet simultaneously introduces insulating effects that hinder conductive network formation. In the present article, we systematically investigate the interplay between GnPs and an SP under varying ultrasonic energy inputs to optimize dispersion and electrical performance through low-cost suspension processing. Dielectric measurements identify the key parameters governing conductive network formation and reveal the dual role of the SP as both dispersant and electrical barrier. Electrochemical impedance spectroscopy, combined with optical microscopy, provides further insights into the state of dispersion and charge-transport behaviour of the suspensions. For the first time, a wide range of SP and GnP concentrations were systematically analysed in terms of electrical properties. The proposed methodology provides a robust and facile approach for on-site characterization of aqueous suspensions with varying GnPs and SP concentrations. Furthermore, an equivalent circuit model is developed to quantitatively validate the experimental results, offering deeper insights into the underlying conduction mechanisms. GnP concentrations of 0.15, 0.50 and 1.00 wt.% were investigated at varying ratios of SP to GnP (0, 1, 2, 4, and 8). Dispersions without SP addition require ultrasonication up to 80 kJ for the GnP agglomerates to break. SP addition at a quantity equal to GnPs (SP1) reduces the amount of appropriate ultrasonic energy for creating a conductive network up to 65 kJ and even more (SP2) at 45 kJ. The fourfold (SP4) and eightfold (SP8) ratio of SP to GnP require higher ultrasonic energy, up to 82 kJ and 70 kJ, accordingly. Full article

To address the challenge of simultaneously achieving broadband absorption, multi-mechanism tunability, and angular stability in terahertz multifunctional devices, this paper proposes a MoS₂/VO₂ composite terahertz metamaterial absorber based on an asymmetric multi-nested C-shaped structure. The device adopts a three-layer configuration consisting of a MoS₂/VO₂ composite plane–SiO₂ dielectric–Au reflector layer. Unlike conventional symmetric structures, which are limited by selection rules and symmetry-protected dark modes that hinder the excitation of higher-order resonances, this design effectively breaks structural symmetry protection through geometric asymmetry. This induces strong mode hybridization between originally orthogonal dark and bright modes, enabling broadband high absorption exceeding 96.7% across the 1.88–3.52 THz frequency range (61% RBW). Notably, the device demonstrates synergistic tuning advantages: the macroscopic on/off switching of broadband absorption characteristics via the phase transition of VO₂, combined with fine blind-spot compensation and enhancement in absorption peaks using the electrical tunability of MoS₂. Furthermore, thanks to its sub-wavelength unit cell design, the structure maintains excellent performance stability over a wide incident angle range from 0° to 60°. This study reveals a synergistic enhancement mechanism combining the asymmetric unit cell and hybrid materials, providing a systematic physical solution for resolving the trade-off between bandwidth extension and dynamic reconfigurability. Full article

The development of sustainable polymer composites reinforced with renewable resources and advanced nanomaterials has attracted considerable attention for multifunctional engineering applications. In this study, an environmentally friendly epoxy-based biocomposite (EBC) reinforced with coconut shell powder (CSP) and graphene nanopowder (GNP) was successfully produced through a casting process. CSP was employed as a bio-based filler, while GNP was incorporated at concentrations ranging from 0 to 0.75 wt.% to improve the overall performance of the composites. The effects of GNP loading on bulk density, tensile strength, elongation at break, Shore D hardness, thermal conductivity, dielectric properties, thermal stability, mechanical and microstructural characteristics were systematically investigated. The results demonstrated that the incorporation of GNP significantly enhanced the multifunctional properties of the improved EBCs. Bulk density increased from 1137.5 to 1143.1 kg m⁻³ with increasing GNP content. The optimum tensile strength of 28.6 MPa and Shore D hardness of 77.4 were achieved at 0.45 wt.% GNP, indicating effective stress transfer and strong interfacial interactions between the epoxy matrix, CSP, and GNP. Thermal conductivity increased from 0.110 to 0.149 W m⁻¹ K⁻¹, while the dielectric constant increased from 3.06 to 4.25 with increasing GNP concentration. Thermogravimetric analysis revealed improved thermal stability and enhanced char formation in graphene-containing composites. FTIR analysis confirmed that graphene acted primarily as a physical reinforcement without altering the fundamental chemical structure of the epoxy network. SEM and EDX investigations demonstrated improved structural compactness, homogeneous filler dispersion, and successful graphene incorporation. The findings indicate that GNP and CSP reinforced EBCs possess significant potential for lightweight structural materials, thermal management systems, dielectric components, and sustainable multifunctional engineering applications. Full article

The long-term effects of water immersion on the physicochemical and functional properties of ethylene-propylene-diene monomer (EPDM) elastomer, widely used as insulation in medium-voltage electrical cables, were investigated over a period of 140 days at room temperature. A multi-scale experimental approach combining complementary characterization techniques was employed to establish quantitative correlations between moisture-induced physicochemical changes and the resulting evolution of functional performance. Water uptake, governed by Fickian diffusion kinetics, remained limited to 0.30 wt%. At the surface, progressive roughening was observed alongside the formation of microcavities and microcracks. Leaching of mineral fillers and an increase in surface polarity were found to enhance wettability. These combined physicochemical alterations translated into measurable degradation of functional properties, with two distinct kinetic regimes identified. Shore hardness, volume resistivity, and dielectric strength underwent rapid deterioration within the first few days of immersion, whereas tensile strength, elongation at break, dielectric permittivity, and dielectric loss factor evolved more gradually over timescales of several tens of days. Temporal profiles for each property were fitted to appropriate models, and characteristic degradation timescales were estimated. These findings provide a structured, physically grounded picture of EPDM degradation under water exposure and offer quantitative data to support the development of service-life prediction models for cable insulation systems. Full article

Strong chiral responses in planar dielectric metasurfaces are important for polarization-selective nanophotonic devices, but achieving large and reversible circular dichroism (CD) in simple dielectric structures remains challenging. This work proposes a symmetry-broken silicon metasurface that realizes near-infrared chiral response based on bound states in the continuum (BICs). The unit cell consists of a silicon nanoblock with two through-air grooves. The in-plane displacement of the air grooves breaks the C₂ rotational symmetry and splits the BIC-related polarization singularity into two circularly polarized points (C points) with opposite handedness. By further introducing out-of-plane tilting, one of the C points is shifted to the Г point, enabling spin-selective coupling between normally incident circularly polarized light and the quasi-BIC mode. Reversing the out-of-plane tilt switches the sign of CD, with values reaching −0.98 and 0.98, approaching the theoretical limits of ±1. Under oblique incidence, the structure can also exhibit near-limit CD responses. Finally, by introducing graphene, the structure achieves tunable circular-polarization-selective absorption, with the absorption of CD approaching the theoretical limits of ±0.5 for the coupled system. This work provides a new design idea for compact chiral nanophotonic materials by using symmetry breaking to control spin-selective quasi-BIC coupling and tunable chiral absorption. Full article

The incorporation of ground tire rubber (GTR) into elastomeric compounds offers a sustainable route for recycling end-of-life tires; however, its effect on the structure–property relationships governing mechanical and dielectric performance remains insufficiently understood. In this study, NR/SBR composites containing 0–50 phr of devulcanized GTR were prepared and characterized through Fourier-transform infrared spectroscopy (FTIR), swelling analysis, thermogravimetric analysis (TGA), mechanical testing, and broadband dielectric spectroscopy. FTIR and swelling results revealed enhanced matrix–GTR interaction at intermediate GTR loadings (10–20 phr), evidenced by an increased intensity of sulfur-related bands and reduced swelling degree, indicating partial chemical integration of the recycled phase into the elastomer network. Mechanical testing showed that increasing GTR content increased stiffness at high loadings, while tensile strength, elongation at break, and toughness progressively decreased due to interfacial debonding mechanisms. TGA demonstrated that the main degradation temperature of the NR/SBR matrix remained essentially unchanged (418–425 °C) across all formulations, confirming preservation of thermal stability despite increasing structural heterogeneity. Dielectric spectroscopy (10⁻²–3 × 10⁶ Hz, 40–120 °C) revealed pronounced Maxwell–Wagner–Sillars interfacial polarization and thermally activated charge transport, with conductivity increasing with GTR content without evidence of electrical percolation, even at 50 phr. The results demonstrate that the performance of NR/SBR/GTR/SiO₂ composites is primarily controlled by the interfacial structure generated by the recycled phase. Intermediate GTR contents (10–20 phr) provide the most effective matrix–GTR interaction, while higher loadings mainly affect mechanical integrity and dielectric response through increased structural heterogeneity. These findings provide practical guidelines for designing sustainable elastomeric compounds with high recycled content while maintaining thermal stability and controlled electrical insulation properties. Full article

Quantum bianisotropy and chirality are fundamental concepts in light–matter interaction that describe how materials with broken symmetries respond to electromagnetic fields at the level of macroscopic quantum electrodynamics. In quantum bianisotropy, magnetoelectric (ME) energy plays a critical role in mediating and enhancing light–matter interactions. This concept is essential for bridging the gap between classical electromagnetics (where bianisotropy often involves field non-locality) and quantum mechanics in metamaterials. The precise manipulation of a quantum emitter’s properties at a subwavelength scale is due to near fields, which effectively function as a tunable environment. In this paper, it is shown that the ME near field, interpreted as a structure combining the effect of bianisotropy/chirality with a quantum atmosphere, is a non-Maxwellian field with space–time symmetry breaking. Quantum ME fields arise from the dynamic modulation and topological coupling of magnetization and electric polarization within ME meta-atoms—specific subwavelength structural elements with magnetic and dielectric subsystems in magnetic insulators, which are assumed to have quantum properties. Full article

Extrinsic chiral metasurfaces offer a promising route for controlling chiroptical responses through incident angle variation, yet the simultaneous realization of strong circular dichroism and full-space polarization beam splitting remains challenging. In this work, we propose an all-dielectric extrinsic chiral metasurface that leverages obliquely incident terahertz waves to break in-plane symmetry, thereby activating out-of-plane multipoles and inducing strong spin-selective scattering. At an incident angle of 30°, the metasurface achieves efficient full-space separation of left- and right-handed circularly polarized waves, with a circular dichroism peak exceeding 0.7 near 0.48 THz. Moreover, by varying the incident angle or operating frequency, the polarization state of the reflected wave can be continuously tuned from linear to elliptical to nearly circular, as visualized on the Poincaré sphere. This angle-dependent, full-space polarization manipulation capability highlights the potential of the proposed metasurface for applications in advanced terahertz imaging, LiDAR, and integrated photonic systems. Full article

Accurate determination of the optical absorption coefficient, ${\mu }_a$, in turbid media is fundamental to biomedical optics and material characterization. Integrating sphere techniques, which measure total transmittance and reflectance, are a standard method for this purpose. However, the inverse models typically employed rely on the assumption of isotropic light propagation. In fiber-structured materials—a common geometry in biological tissue–this assumption often breaks down, leading to significant quantification errors. In this study, we investigated this effect using Monte Carlo simulations and proof-of-concept experiments on mechanically stretched PTFE tape. The medium was modeled as a slab of aligned dielectric cylinders embedded in an isotropic matrix, and the performance of an isotropic inverse model was compared with that of an anisotropic inverse model. The isotropic model showed substantial systematic errors in ${\mu }_a$, with a mean absolute error (MAE) of 19.3%, typical errors between approximately $-40\%$ and 50%, and outliers reaching up to 300%. In contrast, the matched anisotropic model achieved a MAE of 1.2%. Even when the structural parameters of the anisotropic model were perturbed, the MAE remained low at 1.8% for moderate perturbations and 3.9% for severe perturbations. The simulation results therefore indicate that, for the integrating sphere framework considered here, incorporating anisotropic light propagation can improve absorption retrieval more strongly than precise knowledge of all geometric details. Measurements on stretched PTFE tape showed the same qualitative trend and provide proof-of-concept experimental support for the simulation-based findings. Full article

In optical sensing, electromagnetically induced transparency (EIT) and bound states in the continuum (BIC) substantially enhance light–matter interactions by leveraging high-Q resonances. This study theoretically demonstrates dual-resonance phenomena—namely, a quasi-symmetry-protected BIC (SP-BIC) and a quasi-BIC-induced EIT-like (QBIC-EIT) resonance—using a dielectric metasurface composed of pyramid-shaped lithium niobate nanoarrays operating in the near-infrared. The QBIC-EIT transmission window originates from the interference between surface lattice modes and toroidal dipole modes, triggered by symmetry breaking of the BIC state. Due to the absence of C_4v rotational symmetry in the pyramidal unit cells, the metasurface exhibits pronounced polarization-dependent responses: Under x-polarized incidence, a single quasi-SP-BIC resonance appears; under y-polarization, dual quasi-SP-BIC resonances along with a distinct QBIC-EIT resonance are observed. Both the high-Q quasi-SP-BIC resonance and the EIT-like window show strong sensitivity to changes in the ambient refractive index (RI). Specifically, the EIT-like window achieves a sensitivity of 404.9 nm/RIU, while the quasi-SP-BIC resonance delivers an exceptional sensitivity of 887.7 nm/RIU, confirming the metasurface’s performance as a high-sensitivity RI sensor. These findings establish a multi-band detection platform for advanced RI sensing and contribute to the development of high-performance metasurface-based optical sensors. Full article

Poly(vinyl alcohol)/chitosan (PVA/CS) biodegradable films reinforced with acid-functionalized multi-walled carbon nanotubes (f-MWCNTs) were fabricated via solution casting to investigate the effects of nanotube incorporation on structural, mechanical, thermal, dielectric, and physicochemical properties. Unlike conventional CNT-reinforced systems, this study focuses on the role of acid functionalization in improving nanotube dispersion and interfacial interactions, enabling simultaneous enhancement of multiple performance characteristics. Fourier transform infrared spectroscopy (FTIR) analysis confirmed strong intermolecular interactions between PVA/CS functional groups and carboxyl groups on f-MWCNTs, while scanning electron microscopy (SEM) revealed homogeneous nanotube dispersion at low loadings and partial aggregation at higher contents. X-ray diffraction (XRD) indicated that crystallinity was modified in a non-monotonic manner with increasing nanotube concentration due to competing nucleation and chain-restriction effects, while dielectric measurements showed an increase in dielectric constant from 3.78 to 4.27 as a result of enhanced interfacial polarization. The thermal conductivity improved from 0.195 to 0.247 W·m⁻¹·K⁻¹, and tensile strength increased from 19.8 to 24.5 MPa at 0.2 wt.% f-MWCNT, with elongation at break decreasing from 37.9% to 25.1%, reflecting increased stiffness. The degree of swelling and water solubility decreased with higher nanotube content, indicating reduced hydrophilicity and enhanced structural compactness. The results provide new insights into how surface-functionalized nanofillers can be used to tailor the multifunctional performance of biodegradable polymer nanocomposite films, highlighting their potential in advanced applications such as sustainable packaging, flexible electronics, sensors, and membrane technologies. Full article

High quality factor (Q factor) resonant metasurfaces enable efficient mid-infrared (MIR) upconversion, yet their narrow operating bandwidths severely limit practical broadband detection and imaging applications. Although high Q magnetic toroidal dipole (MTD) modes exhibit outstanding momentum space ($k$-space) stability in linear optics, their application in nonlinear processes has primarily been confined to degenerate second-harmonic generation (SHG), leaving complex non-degenerate processes such as sum-frequency generation (SFG) largely unexplored. Here, we propose a tunable MIR upconversion platform based on an all-dielectric gallium phosphide (GaP) dimer metasurface. Breaking the in-plane symmetry to trigger Brillouin zone folding excites robust MTD quasi-guided modes (MTD-QGM), tightly confining the locally enhanced optical fields within the highly nonlinear GaP nanostructure. Synchronizing this high Q resonance with a spatially overlapping pump mode yields an exceptional SFG conversion efficiency of $7.9\times {10}^{-4}$, successfully translating a 3101.8 nm MIR signal to the 903 nm near-infrared band. Crucially, the intrinsic $k$-space stability of the MTD-QGM enables continuous, broadband upconversion through simple angle tuning. This mechanism effectively overcomes the narrow-band limitations characteristic of typical symmetry-protected resonators, establishing a robust paradigm for room-temperature MIR detection. Full article