Search Results (324)

Miniaturized spatial electric field sensors often exhibit insufficient front-end charge coupling because of their limited sensing area. To address this material-level bottleneck, KH550-functionalized graphene composite films were developed as candidate electrode materials for spatial electric-field sensing. Single-layer and multilayer graphene powders were modified with the silane coupling agent KH550 and dispersed in a waterborne polyurethane/PVP matrix to fabricate composite films. The sensing mechanism was analyzed from the Maxwell–Wagner–Sillars interfacial polarization and electrode-equivalent capacitance perspectives. The modified materials were characterized by SEM, EDS, Raman spectroscopy, FTIR spectroscopy, low-frequency dielectric measurements, and broadband high-frequency impedance measurements. KH550 functionalization introduced Si- and N-containing surface species and increased disorder or sp³-related structural features while retaining the layered graphene structure. The film formulation selected through qualitative visual screening contained 0.16 g of graphene, 10 mL of waterborne polyurethane, and 0.05 g of PVP. Under AC excitation, the relative permittivity of the composite film containing KH550-functionalized multilayer graphene was approximately 18% higher than that of its unmodified counterpart. Broadband measurements showed material-dependent changes in the reflection and impedance responses of the electrode–fixture configurations. The modified multilayer-graphene electrode exhibited a different distribution of reflection minima, resistance maxima, and capacitive–inductive transitions from the unmodified and copper electrodes. Because the measured response includes contributions from the coating, substrate, fixture, and parasitic elements, these results are interpreted as comparative system-level responses. These results indicate that interfacial engineering of graphene composite films can enhance electrode-level dielectric response and charge-coupling capability, providing a material basis for non-contact electric field sensing electrodes. Full article

Microwave resonance sensors are promising for dielectric characterization and biochemical detection. However, their sensing performance is constrained by the relatively long wavelength at microwave frequencies and the limited electromagnetic interaction with small-volume samples. In this paper, an exceptional-point (EP)-enhanced chiral spoof localized surface plasmon (SLSP) resonator is proposed for high sensitivity microwave biosensing with sub-microliter sample volumes. By rotating the chiral resonator relative to the microstrip feeding line, two EPs are obtained at α = 49° and α = 210°. The simulated results show that the EP states generate larger frequency splitting than the reference state under both dielectric-constant variation and detection-limit evaluation, confirming the squareroot response to weak perturbations. Experiments further validate the sensing performance using low-loss dielectric materials and high-loss glucose solutions. For dielectric samples with relative permittivities from 2 to 6.15, the frequency splitting increases from 0.287 GHz to 0.359 GHz. For glucose solutions, the frequency splitting decreases from 1.506 GHz to 1.372 GHz as the glucose amount increases from 2.78 nmol to 27.8 nmol. The proposed sensor requires only about 0.5 μL of sample volume and shows higher sensitivity than reported microwave glucose sensors. These results demonstrate that the EP-enhanced chiral SLSP resonator provides a compact and sensitive platform for trace-volume biochemical detection and integrated microwave biosensing. 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

Flexible capacitive sensors for electronic skins and soft robotic systems are expected to provide not only high-pressure sensitivity but also multifunctional sensing capabilities. However, conventional dielectric layer designs often suffer from a trade-off among multiple functionalities. To address this challenge, we developed a flexible sensor featuring a hybrid microstructured functional layer for pressure sensing, distance monitoring, and material identification. The functional layer was a polydimethylsiloxane (PDMS) film embedded with micro-sized sugar particles and patterned with microstructures on its surface. The pressure-sensing performance, such as pressing sensitivity, response time, and hysteresis, was first evaluated. The pressure sensitivity reached 3.55 × 10⁻² kPa⁻¹ at an applied force of 1 N, which is significantly greater than that of the sensor using either a flat PDMS layer or a PDMS film embedded solely with sugar particles. The hybrid microstructured sensor also exhibited superior performance in terms of hysteresis and repeatability. Moreover, the sensor was shown to measure the distance to an object with a sensitivity of 0.023 mm⁻¹. Furthermore, the robust identification of materials with different permittivities was demonstrated using the flexible sensor. Given its multifunctional, non-contact, and high-sensitivity capabilities, this flexible sensor holds significant potential for integration into advanced electronic skins, intelligent soft robotics for tactile object sorting, and human–-machine interfaces. Full article

The growing demand for high-performance electromagnetic interference (EMI) shielding materials in modern communication and integrated electronics has stimulated interest in materials with tunable dielectric responses. In this study, a series of A-site-doped perovskite oxides—LaCoO₃, (La_0.5Sr_0.5)CoO₃, and (La₁/₃Sr₁/₃Ba₁/₃)CoO₃—were synthesized via a sol–gel method to investigate their dielectric behavior in the radio-frequency (RF) range. Dielectric spectroscopy reveals that LaCoO₃ exhibits a positive permittivity characteristic of semiconductors, whereas Sr substitution induces a metallic state in (La_0.5Sr_0.5)CoO₃, whose dielectric response exhibits a Drude-like dispersion behavior within the measured RF frequency range. Further incorporation of Ba into the A-site results in ternary co-doping, suggesting a reduction in effective carrier transport and a shift in the characteristic dispersion frequency toward the low-frequency region. Consequently, (La₁/₃Sr₁/₃Ba₁/₃)CoO₃ displays a near-zero permittivity at approximately 2.5 kHz, indicating a transition in the dominant reactive response from inductive-like to capacitive-like behavior, which is consistent with the impedance spectroscopy results. This work demonstrates that cation engineering at the A-site enables precise control over the RF dielectric response in perovskite oxides, offering a potential pathway for the design of tunable electromagnetic functional materials relevant to EMI shielding applications with tailored permittivity characteristics. Full article

The rapid expansion of microwave and millimeter-wave telecommunication systems has intensified the need for precise dielectric material characterization at high frequencies. As operating frequencies increase, small uncertainties in permittivity and loss tangent significantly degrade resonance stability, bandwidth control, and quality factor, directly affecting RF system reliability and performance. However, the growing diversity of resonator architectures and extraction methodologies has led to fragmentation in the literature, making it difficult to identify optimal solutions for telecommunication-oriented applications. This review provides a structured and application-driven assessment of high-frequency resonator-based dielectric characterization techniques relevant to modern telecommunication systems. Resonator topologies—including cavity, planar, substrate-integrated, metamaterial-inspireds—are systematically classified and critically compared. Their sensing mechanisms and parameter-extraction approaches are analyzed in terms of frequency-shift sensitivity, Q-factor performance, scalability toward millimeter-wave bands, integration capability, and measurement robustness. By synthesizing performance trade-offs, practical limitations, and emerging research directions, this review establishes clear design guidelines and a forward-looking framework for advancing dielectric metrology in next-generation high-frequency telecommunication technologies. Full article

Gel-based materials are emerging as lightweight, mechanically compliant, and electromagnetically tunable platforms for next-generation antennas, electromagnetic interference (EMI) shields, microwave absorbers, and radomes. This review summarizes recent progress in hydrogel-, aerogel-, ionogel-, organohydrogel-, and xerogel-based electromagnetic materials, with emphasis on how network structure, pore architecture, solvent phase, and functional fillers regulate permittivity, conductivity, impedance matching, and attenuation. The device-level roles of gels are discussed in miniaturized and reconfigurable antennas, absorption-dominated shielding systems, broadband microwave absorbers, high-temperature wave-transparent radomes, and metamaterial, energy-harvesting, and bioelectronic systems. Particular attention is paid to the mechanisms of dipolar relaxation, ionic conduction, interfacial polarization, conduction loss, magnetic loss, and multiple scattering. Finally, key challenges are identified, including hydrogel dehydration and freezing, aerogel fragility, ionogel cost and leakage, limited long-term reliability, and the lack of standardized performance metrics. Future directions toward durable, scalable, multifunctional, and device-integrated gel-based electromagnetic materials are proposed. Full article

Oxide systems with the nominal composition LaCaCuVMnO_7.5 and composites modified with the YBa₂Cu₃O_x phase were synthesized by the solid-state reaction method. The phase composition and structural features were systematically investigated by X-ray diffraction (XRD), Rietveld refinement, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX). The parent oxide was found to form a two-phase system, consisting of an orthorhombic perovskite-like phase and a cubic manganite–vanadate phase, whereas the introduction of 10 wt.% YBa₂Cu₃O_x resulted in the formation of a three-phase composite containing an additional cuprate phase. Thermophysical investigations in the 298–673 K range revealed λ-type-like anomalies in the heat capacity, which may be associated with possible structural or interphase transformations in the investigated oxide systems. The incorporation of YBa₂Cu₃O_x significantly modified the temperature dependence of heat capacity and increased its values over both low- and high-temperature regions. Electrophysical measurements in the 293–483 K range confirmed the semiconducting nature of conductivity, while the addition of YBa₂Cu₃O_x reduced electrical resistance and enhanced dielectric permittivity. These findings demonstrate that YBa₂Cu₃O_x modification provides an effective route for tuning the thermophysical and electrophysical properties of LaCaCuVMnO_7.5-based oxide systems, suggesting their potential as promising candidates for multifunctional oxide materials with possible electronic and sensor-related applications. Full article

High-voltage cable joints are critical components where electric stress concentration often leads to insulation failure. This study evaluated three materials to find optimal configurations for controlling stress in 33 kV applications: PVC tape, stress-grading mastic, and semiconductive rubber tape, with initial relative permittivities of 2.96, 2.66, and 5.07, respectively. Dielectric measurements using a Schering Bridge at voltages of up to 3700 V determined material properties and breakdown characteristics. Semiconductive rubber withstood the highest voltage of 3700 V, while mastic failed at 1350 V. Finite element simulations showed that baseline configurations without proper insulation had a peak stress of 4.3 kV/mm. Simulations of individual materials identified non-linear resistive compounds, such as ZnO-based materials and carbon-black-filled polymers, as the most effective for stress control at conductor interfaces. A three-layer graded design, arranging materials by decreasing permittivity from the conductor outward, reduced the peak stress by 33% to 2.9 kV/mm. These results demonstrate that strategic permittivity grading combined with appropriate material selection ensures uniform field distribution and improved reliability in HV cable joints. Full article

Reconstructing high-resolution images of anisotropic targets in microwave imaging remains a challenging problem due to the strong directionality of electromagnetic responses and the inherent nonlinearity of the inverse scattering process. To address these issues, we propose a novel Perceptual Generative Adversarial Network (PGAN) enhanced with a Self-Attention mechanism for anisotropic electromagnetic imaging. The perceptual loss encourages the preservation of high-level structural features, while the Self-Attention module enables the model to capture long-range dependencies and directional correlations that are critical in representing anisotropic material distributions. This joint architecture is trained to refine coarse permittivity estimates obtained from conventional Back-Propagation Schemes (BPSs). Numerical simulations and validation using measured experimental data demonstrate that the proposed method achieves improved reconstruction accuracy and structural similarity compared with the PGAN without SA and U-Net. In particular, PGAN with SA reduces the Root Mean Square Error (RMSE) by 15.1% and improves the Structural Similarity Index Measure (SSIM) by 3.8%, confirming its effectiveness in recovering fine-scale details and enhancing reconstruction quality. These results suggest that the proposed framework offers a promising solution for robust and high-resolution electromagnetic imaging in geophysical and remote sensing applications. Full article

This paper presents a practical implementation of a 3D-printed spherical Luneburg lens for gain enhancement of a WR-28 open-ended waveguide antenna operating in the Ka-band. The lens is designed based on Luneburg theory and realized using a six-zone discretized gradient-index structure, providing a balance between theoretical performance and fabrication feasibility. The proposed design enables the realization of the required permittivity distribution using a single dielectric material, where the effective permittivity of each zone is controlled through infill variation in a fused deposition modeling (FDM) process. To facilitate fabrication, the lens is divided into two hemispherical parts, enabling reliable manufacturing and assembly while maintaining the intended dielectric profile. The antenna performance is experimentally evaluated through reflection coefficient (S₁₁) measurements and radiation pattern characterization in both the XZ and YZ planes over the frequency range of 26.5–40 GHz, including co-polarized and cross-polarized responses. The proposed antenna achieves a simulated realized gain ranging from 17.6 dBi to 19.83 dBi, while the measured realized gain ranges from 16.42 dBi to 18.43 dBi, with a maximum deviation of 1.47 dB. In comparison, the standalone WR-28 open-ended waveguide exhibits a measured realized gain of 7.22–8.01 dBi. The integration of the six-zone Luneburg lens results in a realized gain enhancement of 9.20–10.97 dB across the operating band. These results confirm that the proposed approach provides a simple, low-cost, and experimentally validated solution for high-gain millimeter-wave antenna applications, while maintaining good agreement between simulation and measurement. Full article

High-temperature vulcanized (HTV) silicone rubber serves as the core material for composite insulators, and its high-frequency dielectric properties directly dictate its macroscopic insulation performance. However, traditional electrical detection methods encounter a “high-frequency blind zone” above the gigahertz (GHz) range due to limited precision and ambiguous physical mechanisms. In this study, terahertz time-domain spectroscopy (THz-TDS) was employed to characterize the complex permittivity spectra of silicone rubber specimens, incorporated with varying ratios of alumina trihydrate (ATH) and silica (SiO₂) fillers, across the 0.1–3.0 THz frequency range. Experimental results reveal that the terahertz dielectric characteristics of silicone rubber exhibit a pronounced filler dependency: as the ATH content increases from 95 phr to 185 phr, the real part of the permittivity at 1 THz increases by 32%. Notably, all specimens manifest a sharp dielectric transition near 1.2 THz, characterized by distinct dual absorption peaks in the imaginary permittivity spectra. To characterize this non-linear transition, a hybrid Debye–Lorentz model is innovatively introduced. This approach overcomes the inherent limitations of traditional double Debye models, which are restricted to relaxation processes and fail to account for high-frequency resonance. Fitting results and physical analysis demonstrate that the response at 1.2 THz is primarily attributed to the bending vibrations of Si-O-Si bonds in the polymer backbone, alongside the collective vibration modes of Al-O bonds and the hydrogen-bonded network within the fillers. The hybrid model successfully decouples three distinct polarization mechanisms: conduction loss (<0.5 THz), dipole relaxation (0.5–1.0 THz), and lattice resonance (>1.0 THz). This work provides a robust characterization framework for the quantitative evaluation of the high-frequency dielectric response and microstructural integrity of composite insulators. Full article

Polymer–ceramic piezoelectric composites are widely investigated to combine the high piezoelectric performance of ferroelectric ceramics with the flexibility and processability of electroactive polymers. However, achieving enhanced dielectric properties while preserving the intrinsic piezoelectric response of the polymer matrix remains challenging, particularly due to dielectric mismatch between the constituent phases and interfacial effects. In this work, barium titanate (BaTiO₃) loaded poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) nanocomposites were fabricated by solvent casting using polyvinylpyrrolidone (PVP) and polysorbate 80 (PS80) as dispersing agents, aiming to obtain polarizable materials capable of retaining high piezoelectric strain coefficient (d₃₃) values and potentially exploiting the opposite polarity of matrix and filler through tailored poling strategies. Morphological, crystallographic, structural, thermal, thermomechanical, dielectric, and piezoelectric characterizations were performed by SEM/EDXS, XRD, FTIR, DSC, TGA, DMTA, dielectric spectroscopy, and d₃₃ measurements. Both dispersants improved filler dispersion and film densification, increasing the crystalline fraction of the matrix, without altering the relative fraction of β-phase (up to 93%). PVP enabled moderate and stable permittivity enhancement with weak frequency dependence, whereas PS80 introduced an electrically active interfacial contribution that amplified low-frequency permittivity at high filler loadings but made the permittivity more frequency-dependent. The piezoelectric response (between −20 pC/N and −25 pC/N) remained predominantly governed by the polymer phase, suggesting limited polarization played by BaTiO₃. These results underlined the critical role of interfacial electrical properties in designing stable high-performance flexible PVDF-TrFE/BaTiO₃ composites. Full article

This study addresses the impact of temperature gradient-induced non-uniform aging on the accuracy of space charge measurements in cross-linked polyethylene (XLPE) insulation for high-voltage direct-current cables. Existing pulse-echo acoustic (PEA) recovery algorithms neglect the evolution of material acoustic and dielectric properties during aging. To overcome this limitation, the systematic degradation of sound velocity, attenuation dispersion, and dielectric constant subjected to temperature gradient aging was experimentally investigated. Specimens were aged at temperatures ranging from 40 to 100 °C for durations up to 49 days. Then, quantitative models describing the dependence of acoustic and dielectric properties on aging severity were established. A space charge signal correction algorithm was then developed, incorporating nonlinear adjustments for sound velocity, attenuation, and permittivity according to the through-thickness aging profile. The algorithm’s accuracy was validated by comparing recovered charge waveforms and electric field distributions under 5 kV/mm for samples aged under different temperature gradients. The application of the method under high-voltage DC conditions revealed that aging induces non-monotonic changes in sound velocity, increased attenuation coefficients, and elevated low-frequency dielectric constants. Temperature gradient aging promotes heteropolar charge accumulation. This work provides a theoretical and methodological basis for improving the accuracy of the insulation condition assessment in long-term service HVDC cables. Full article

Detecting changes in the permittivities of materials has important applications in electronic information, materials science, biomedicine, and many other fields. However, existing detection methods are limited by factors such as sample thickness and resonance intensity, making it difficult to achieve sensitive dielectric constant detection at desired frequency bands. This paper proposes a method for detecting the dielectric constant changes in samples based on destructive interference of spoof surface plasmon polaritons (SSPPs) in a dual-path transmission structure, which forms a characteristic absorption peak at the SSPPs’ cutoff frequency. Specifically, by utilizing the dependence of the SSPPs’ phase on the periodic unit, a constant π phase difference is formed at the cutoff frequency through the periodic unit number difference between the two paths, resulting in a cutoff frequency absorption peak. When the sample is coated on the SSPPs’ dual-path structure, the boundary conditions are altered, leading to a cutoff frequency shift, thereby enabling dielectric constant detection at the specified frequency. Simulation results show that, with proper structural design, the normalized characteristic frequency shift reaches 10.8%/${\epsilon }_S$ and further demonstrates dramatic robustness against initial phase difference, sample thickness and sample loss. In summary, this work provides a novel high-precision and high-robustness method for detecting dielectric constant changes in samples at specified frequencies. Full article