Search Results (1,120)

Diabetes has become a global health challenge, driving the demand for innovative, non-invasive diagnostic technologies to improve glucose monitoring. Urinary glucose concentration, a reliable indicator of metabolic changes, provides a practical alternative for frequent monitoring without the discomfort of invasive methods. In this simulation-based study, we propose a novel asymmetric photonic structure that integrates Tamm plasmon polariton (TPP) modes and a cavity mode for high-precision refractive index sensing, with a conceptual focus on the potential detection of urinary glucose. The structure supports three distinct resonance modes, each with unique field localization. Both the TPP modes, confined at the metallic–dielectric interfaces, serve as stable references whose wavelengths are unaffected by refractive-index variations in human urine, whereas the cavity mode exhibits a redshift with increasing refractive index, enabling high responsiveness to analyte changes. The evaluation of sensing performance employs a sensitivity formulation that leverages either TPP mode as a reference and the cavity mode as a probe, thereby achieving dependable measurement and spectral stability. The optimized design achieves a sensitivity of 693 nm·RIU⁻¹ and a maximum figure of merit of 935 RIU⁻¹, indicating high detection resolution and spectral sharpness. The device allows both reflectance and transmittance measurements to ensure enhanced versatility. Moreover, the coupling between TPP and cavity modes demonstrates hybrid resonance, empowering applications such as polarization-sensitive or angle-dependent filtering. The figure of merit is analyzed further, considering resonance wavelength shifts and spectral sharpness, thus manifesting the structure’s robustness. Although this study does not provide experimental data such as calibration curves, recovery rates, or specificity validation, the proposed structure offers a promising conceptual framework for refractive index-based biosensing in human urine. The findings position the structure as a versatile platform for advanced photonic systems, offering precision, tunability, and multifunctionality beyond the demonstrated optical sensing capabilities. Full article

A ceramic-based wideband capacitive-fed patch-loaded multi-layered rectangular dielectric resonator antenna (CFPL-ML-RDRA) with a compact form factor is proposed in this paper. The proposed antenna is composed of two ceramic substrates and a polymer as an adhesive. A capacitive-fed metallic patch structure is located on the top side of the bottom ceramic substrate. This novel structure generates two distinct resonant modes: the fundamental resonant mode of the RDRA and a hybrid resonant mode, which was confirmed through electric field (E-field) analysis and parametric studies. By merging these two resonant modes, the proposed antenna achieves a wide impedance bandwidth of 5.5 GHz, sufficient to cover the fifth-generation (5G) millimeter-wave (mmWave) frequency bands n257, n258, and n261 (5.25 GHz), while reducing the height of the DRA by 38.5% compared to the conventional probe-fed RDRA (PF-RDRA). Additionally, the 4 dBi realized gain bandwidth of the proposed CFPL-ML-RDRA is 5.4 GHz, which is 28.6% broader than that of the conventional PF-RDRA. To experimentally verify the antenna’s performance, the CFPL-ML-RDRA mounted on a test printed circuit board with a small ground size of 3.2 × 3.2 mm² was fabricated and characterized. The measured data align well with the simulated data. Furthermore, excellent antenna array performance was achieved based on array simulations. Therefore, the proposed antenna structure is well-suited for 5G mmWave mobile applications. Full article

Perfect absorbers operating in the terahertz (THz) band are key enablers for next-generation wireless systems. However, conventional metal–dielectric designs suffer from Ohmic losses and limited reconfigurability. Here, we propose an all-dielectric indium antimonide (InSb) cylindrical pillar metasurface that achieves near-unity absorption at $f_0=1.83$ THz with a high quality factor of $Q=72.3$. Critical coupling between coexisting electric and magnetic dipoles enables perfect impedance matching, while InSb’s low damping minimizes energy loss. The resonance is tunable via temperature and magnetic bias at sensitivities of $S_T\approx 2.8\mathrm{GHz}·{\mathrm{K}}^{-1}$, $S_B^{\mathrm{TE}}\approx -132.7\mathrm{GHz}·{\mathrm{T}}^{-1}$, and $S_B^{\mathrm{TM}}\approx -34.7\mathrm{GHz}·{\mathrm{T}}^{-1}$, respectively, without compromising absorption strength. At zero magnetic bias ($B=0$), the metasurface is polarization-independent under normal incidence; under magnetic bias ($B\ne 0$), it maintains near-unity absorbance for both TE and TM, while the resonance frequency becomes polarization-dependent. Additionally, the 90% absorptance bandwidth ($\Delta f_{A\ge 0.9}$) can be modulated from 8.3 GHz to 3.3 GHz with temperature, or broadened from 8.5 GHz to 14.8 GHz under magnetic bias. This allows gapless suppression of up to 14 consecutive 1 GHz-spaced channels. This standards-agnostic bandwidth metric illustrates dynamic spectral filtering for future THz links and beyond-5G/6G research. Owing to its sharp selectivity, dual-mode tunability, and metal-free construction, the proposed absorber offers a compact and reconfigurable platform for advanced THz filtering applications. Full article

Mid-infrared (MIR) spectroscopy enables non-invasive identification of chemical species by probing absorption spectra associated with molecular vibrational modes, where spectral filters play a central role. Conventional plasmonic metasurfaces have been explored for MIR filtering in reflection and transmission modes but typically suffer from broad spectral profiles and low efficiencies. All-dielectric metasurfaces, although characterized by low intrinsic losses, are largely limited to reflection mode operation. To overcome these limitations, we propose a hybrid metal-dielectric metasurface that combines the advantages of both platforms while simplifying fabrication compared to conventional Fabry–Pérot filters. The proposed filter consists of silicon (Si) crosses atop gold (Au) square patches and demonstrates a transmission efficiency of 87% at the operating wavelength of 4.28 µm, with a full width half maximum (FWHM) as narrow as 43 nm and a quality factor of approximately 99.5 at λ = 4.28 μm. Numerical simulations attribute this performance to hybridization of Mie lattice resonances in both the gold patches and silicon crosses. By providing narrowband, high-transmission filtering in the MIR, the hybrid metasurface offers a compact and versatile platform for selective gas detection and imaging. This work establishes hybrid metal–dielectric metasurfaces as a promising direction for next-generation MIR spectroscopy. Full article

We propose a dual-groove few-mode fiber surface plasmon resonance sensor that exploits the LP₁₁ mode for enhanced plasmonic sensing. The device incorporates two physically separated grooves with distinct metallic coatings, enabling dual-channel operation via wavelength-division multiplexing. Finite element method simulations show that the optimized design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40. The introduction of a TiO₂–Au bilayer enhances mode coupling and ensures complete spectral separation, thereby improving stability and reducing environmental interference. Biosensing simulations at 37 °C further confirm the practicality of the proposed architecture. Channel 1, filled with ethanol as a temperature-sensitive medium, provides temperature monitoring, while Channel 2 successfully distinguishes between normal and tumor cells, reaching a sensitivity of up to 9428.57 nm/RIU for Jurkat cells. Overall, the TiO₂-enhanced dual-channel FMF-SPR sensor combines ultra-high sensitivity, spectral independence, and biosensing capability, demonstrating strong potential for next-generation fiber-optic sensing and biomedical applications. Full article

This paper introduces a dual-band planar microwave sensor system for measuring the complex dielectric constant of solid material. The sensor system comprises three constituent parts: the sensing probe, the circuit module and the broadband coupler. The sensing probe is composed of a host part and a sensing area. The host part is composed of a microstrip line, which facilitates system integration with other planar microwave components. The sensing area comprises two pairs of E-interdigital structures, which were originally developed from the interdigital capacitor. This configuration manifests two resonant frequency points, specifically 3 GHz and 3.92 GHz. Consequently, any environmental effects exhibit equivalent variation at both resonant frequency points, thereby substantiating the efficacy of the proposed sensor system for differential operation, which has the capacity to mitigate the impact of environmental conditions. The circuit module comprises a controller, two detectors and a signal generator, which facilitate the generation and processing of radio frequency signals within the system. The function of the broadband coupler is to differentiate between the incident signal and the reflected signal. The operating principle is predicated on the variation in the resonant frequency and peak attenuation with respect to the complex dielectric constant of the material under test (MUT). In order to validate the effectiveness of the proposed sensor system, a prototype is fabricated and tested. The proposed sensor system is distinguished by its high sensitivity and low cost. The apparatus is capable of performing measurements independently and without the necessity for auxiliary equipment. Full article

When measuring the size or relative permittivity of a dielectric particle, usually one of the parameters needs to be known for determining the other one. Scattering measurement methods offer an alternative that allows for extracting both the size and the permittivity of the particle under test at the same time. In this paper, bi-static scattering measurements at millimeter-wave frequencies are applied to characterize sub-resonant dielectric spheres of sub-wavelength size. The size and relative permittivity are extracted simultaneously from measurements at Ka-band (26.5–40 GHz). The experimental setup and the data processing procedure are detailed in depth, and the sources of the systematic errors are discussed. Alumina ceramic spheres (with relative permittivity of approximately 10) of diameter as small as 0.8 mm (less than 1/10 of free-space wavelength) were investigated. The extracted diameters and permittivities agree well with the expected values. Full article

This paper presents a fully passive and wireless glucose concentration sensor that integrates a capacitively coupled complementary split-ring resonator (CSRR) with an H-slot UHF RFID antenna. The CSRR serves as the primary sensing element, where changes in glucose concentration alter the effective permittivity of the surrounding solution, thereby modifying the resonator capacitance and shifting its resonance behavior. Through near-field capacitive coupling, these dielectric variations affect the antenna input impedance and backscatter response, enabling wireless sensing by modulating the maximum read range. The proposed sensor operates within the 902–928 MHz UHF RFID band and is interrogated using commercial RFID readers, eliminating the need for specialized laboratory equipment such as vector network analyzers. Full-wave electromagnetic simulations and experimental measurements validate the sensor performance, demonstrating a variation in the read range from 6.23 m to 4.67 m as glucose concentration increases from 50 to 200 mg/dL. Moreover, the sensor exhibits excellent linearity, with a high coefficient of determination ($R^2=0.986$) based on the curve-fitted data. These results underscore the feasibility of the proposed sensor as a low-cost and fully portable platform for concentration monitoring, with potential applications in liquid characterization and chemical sensing. Full article

This paper presents a novel compact 4 × 4 Butler matrix (BM) employing a quasi-twisted branch line coupler (QBLC) as the unit cell to achieve enhanced bandwidth performance. The proposed BM integrates four QBLCs, a uniquely designed 0 dB crossover, and a 45° phase shifter, all fabricated on a double-layer Rogers RO4003C substrate with a thickness of 0.8 mm, dielectric constant (εr) of 3.3, and a loss tangent of 0.0027. A common ground plane is used to separate the layers. Both simulation and experimental results indicate a reflection coefficient of approximately −6.5 dB at the resonant frequency of 6.5 GHz and isolation levels better than −20 dB at all ports. The system achieves output phase differences of ±13°, ±41°, ±61°, ±89°, and ±120° (±10°) at the designated frequencies. The BM occupies a compact area of 13.8 mm × 38.8 mm, achieving a 92.5% size reduction compared to conventional T-shaped BM structures. The design was modeled and simulated using CST Microwave Studio, with a strong correlation observed between simulated and measured results, validating the design’s reliability and effectiveness. Furthermore, the BM’s beamforming performance is evaluated by integrating it with a 1 × 4 microstrip antenna array. The measured return loss at all ports is below −10 dB at 6.5 GHz, and the system successfully achieves switched beam steering toward four distinct angles: −5°, +6°, +26°, −24°, +43, and −43 with antenna gains ranging from 7 to 10 dBi. Full article

High sugar intake from commercial beverages is a public health concern, motivating rapid, user-friendly tools for sugar quantification. We present a compact planar microwave metamaterial sensor that estimates sugar concentration by monitoring resonant frequency shifts induced by dielectric loading. Tests with aqueous glucose solutions demonstrated a wide dynamic range (0 to 12,000 mg/dL), perfect linearity (R² = 1), and high repeatability. Validation on two commercial beverages showed sensor-predicted sugar contents consistent with their nutrition labels. The method is reagent-free, tolerates opaque samples, and operates under ambient conditions, making it suitable for on-site consumer use as well as regulatory inspection and quality-control applications. Full article

This study presents a reconfigurable planar photonic device capable of dynamically switching between optical filter and absorber functionalities by exploiting the phase transition properties of GeTe, a chalcogenide phase-change material. The device adopts a Metal–Dielectric–PCM architecture composed of silver (Ag), silicon dioxide (SiO₂), and GeTe layers, each playing a distinct role: the silver layer governs the transmission and absorption efficiency, the SiO₂ layer controls the resonance conditions, and the GeTe layer determines the device’s scattering behavior via its tunable optical losses. Numerical simulations revealed that the structure enables high RGB transmission in the amorphous state and broadband absorption in the crystalline state. By adjusting geometric parameters—especially the metallic thickness—the device exhibits finely tunable spectral responses under varying polarizations and incidence angles. These findings highlight the synergistic interplay between material functionality and layer configuration, positioning this platform as a compact and energy-efficient solution for applications in tunable photonics, optical sensing, and programmable metasurfaces. Full article

Suspended microchannel resonators (SMRs) are powerful tools for mass, density, and viscosity sensing. Among various transduction methods, full piezoelectric transduction offers key advantages, including on-chip integration, low energy dissipation, and linear response. This work explores sub-200 nm Al_0.6Sc_0.4N thin films for SMR transduction, benchmarking them against their well-established AlN predecessor. By integrating the piezoelectric stack into low-stress silicon nitride (ls-SiN_x) beam resonators, we investigate the impact of bottom electrode design, photoresist removal prior to deposition, and deposition bias on film quality. Characterization includes X-ray diffraction (XRD), scanning electron microscopy (SEM), d₃₁ piezoelectric coefficient, relative dielectric permittivity, and breakdown field measurements. Results illustrate the impacts of the studied parameters and demonstrate a fourfold increase in d₃₁, compared to AlN, confirming the strong potential of Al_0.6Sc_0.4N for high-performance SMR transduction. Full article

Alzheimer’s disease (AD) has emerged as a global health threat that demands early detection to seize the optimal intervention opportunity. Central nervous system (CNS)-derived extracellular vesicles (EVs), lipid-bilayer nanoparticles released by CNS cells, carry key biomolecules involved in AD pathology, positioning them as a promising source of biomarkers for early detection. Current breakthroughs in EV-based isolation and detection technologies have opened up the possibility of early, accurate AD diagnosis. This review summarizes their multifaceted roles in AD pathogenesis, including amyloid-β (Aβ) aggregation, tau propagation, neuroinflammation, and synaptic dysfunction, and highlights neuron- and glia-derived EV biomarkers with translational potential. We further outline recent advances in EV isolation techniques—including density-, size-, charge/dielectric-, immunoaffinity-, and acoustics-based approaches—and emerging detection platforms such as fluorescence, surface plasmon resonance (SPR), surface-enhanced Raman spectroscopy (SERS), electrochemical, and nanomechanical sensors for sensitive, multiplex AD diagnostics. Finally, we discuss key challenges, including standardization, sensitivity, and high-throughput adaptation, and explore future directions such as automated microfluidics and single-vesicle analysis. CNS-derived EVs hold significant promise as minimally invasive, next-generation tools for early AD detection and precision medicine. Full article

Most electromagnetic invisibility devices are designed while relying on rigid structures, which have limitations in adapting to complex curved surfaces and dynamic deployment. In contrast, flexible invisibility structures have great application value due to their bendable and easy-to-fit characteristics. In this paper, we propose a flexible metasurface suitable for broadband SAR (Synthetic Aperture Radar) imaging invisibility, which realizes multi-domain joint regulation of electromagnetic waves by designing two subwavelength unit structures with differentiated reflection characteristics and combining array inverse optimization methods. The metasurface employs a sponge-like dielectric substrate and integrates resistive ink to construct a resonant structure, which can suppress electromagnetic scattering through joint phase and amplitude modulation, achieving low detectability of targets in UAV (Unmanned Aerial Vehicle) detection scenarios. Indoor microwave anechoic chamber tests and outdoor UAV-borne SAR experiments verify its stable invisibility performance in a wide frequency band, providing theoretical and experimental support for the application of flexible metasurfaces in dynamic electromagnetic detection countermeasures. Full article

This article introduces a substrate-integrated, low-cost, and low-profile E-band high-gain Fabry–Perot (FP)/leaky-wave (LW) antenna. This design enables the full integration of a high-gain antenna within a single-layer substrate for millimeter-wave (mm-wave) applications. The antenna design layout comprises a partially reflective surface (PRS) mounted on a thin, metal-coated, low-cost I-Tera MT40 dielectric substrate. The proposed antenna differs from conventional air-cavity-based FP/LW antennas, as it is fabricated on a low-cost dielectric substrate, eliminating the need for an air cavity, which restricts integration with printed circuit boards (PCBs) and planar circuits. The antenna is excited using a rectangular WR12 waveguide located beneath the ground plane. Impedance matching is achieved by employing a rectangular iris. The formulation for analyzing leaky waves within a cavity is thoroughly discussed using the Transverse Resonance Method (TRM). The proposed FP antenna achieves a maximum realized gain of 14.6 dBi with good impedance matching ($|S_{11}|$ = –14 dB). Finally, the proposed antenna is fabricated, and its performance is validated through experimental measurements. Full article