Search Results (265)

This study fabricated SrTiO₃ grain boundary layer ceramics using hot isostatic pressing (HIP), achieving a remarkably high dielectric constant of 60,350 and a superior breakdown strength of 1722 kV/m. Microstructural characterization via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that HIP treatment significantly refined grain size uniformity and homogenized bismuth distribution at grain boundaries, thus enhancing the interfacial barrier effect. Probe-based impedance spectroscopy elucidated the dielectric behavior and conduction mechanisms of individual grain boundaries. HIP promotes the formation of interfacial barrier layers (IBLs), significantly improving electrical performance. Compared to untreated samples (average breakdown strength: 555 kV/m), HIP-processed ceramics exhibited a threefold enhancement in breakdown strength (1722 kV/m). The treated ceramic exhibited excellent temperature stability, with TCC ≤8% over −55 to 125 °C. The optimized dielectric properties stem from HIP-induced structural modifications, including reduced oxygen vacancy concentrations and homogenized electronic distribution at grain boundaries. These findings establish a quantitative correlation between HIP parameters, grain boundary restructuring, and macroscopic performance, providing critical insights for designing high-energy-density dielectric materials. Full article

Polymer composites with high dielectric permittivity (>10) and low dielectric loss are critical for energy storage and microelectronic applications. This study reports on a semi-transparent composite of a PVDF copolymer filled with Cu₇S₄ nanoparticles synthesized via a wet chemical route. Only a small content (6%) of copper sulfide increases the dielectric permittivity of the material from 10.4 to 15.9 (1 kHz), maintaining a low dielectric loss coefficient (less than 0.1). The incorporated nanoparticles affect the morphology of the composite film surface and crystalline phases in the whole volume, which was studied with FTIR spectroscopy, differential scanning calorimetry and scanning probe microscopy. Full article

This work presents the validation of a low-cost measurement system based on an open-ended coaxial SMA (SubMiniature version A) probe for the characterization of complex permittivity in the microwave frequency range. The system combines a custom-fabricated probe, a vector network analyzer, and a dedicated software application that implements three analytical models: capacitive, radiation, and virtual transmission line models. A comprehensive experimental campaign was carried out involving pure polar liquids, saline solutions, and biological tissues, with the measurements compared against those obtained using a high-precision commercial probe. The results confirm that the proposed system is capable of delivering accurate and reproducible permittivity values up to at least 6 GHz. Among the implemented models, the radiation model demonstrated the best overall performance, particularly in biological samples. Additionally, reproducibility tests with three independently assembled SMA probes showed normalized deviations below 3%, confirming the robustness of the design. These results demonstrate that the proposed system constitutes a viable alternative for cost-sensitive applications requiring portable or scalable microwave dielectric characterization. Full article

SPR biosensors operate on the principle of evanescent wave propagation at metal–dielectric interfaces in total internal reflection conditions, with consequent photonic energy attenuation. This plasmonic excitation occurs in specific conditions of incident light wavelength, angle, and the dielectric refractive index. This principle has been the basis for SPR-based biosensor setups wherein mass/concentration-induced changes in the refractive indices of dielectric media reflect as plasmonic resonance condition changes quantitatively reported as arbitrary response units. SPR biosensors operating on this conceptual framework have been designed to study biomolecular interactions with real-time readout and in label-free setups, providing key kinetic characterization that has been valuable in various applications. SPR biosensors often feature antibodies as target affinity probes. Notably, the operational challenges encountered with antibodies have led to the development of aptamers—oligonucleotide biomolecules rationally designed to adopt tertiary structures, enabling high affinity and specific binding to a wide range of targets. Aptamers have been extensively adopted in SPR biosensor setups with promising clinical and industrial prospects. In this paper, we explore the growing literature on SPR setups featuring aptamers, specifically providing expert commentary on the current state and future implications of these SPR aptasensors for drug discovery as well as disease diagnosis and monitoring. Full article

Gastroesophageal reflux disease (GERD) is a widespread condition that requires reliable and non-invasive diagnostic methods to minimize patient discomfort. This study presents a radiofrequency spectrophotometry sensor specifically designed to detect esophageal liquid flow and ionicity in real time without disrupting the patient’s daily life. The sensor operates by measuring dielectric properties and ionic conductivity through the thoracic plexus, eliminating the need for invasive probes or prolonged monitoring. A study conducted on 49 participants demonstrated the sensor’s ability to differentiate between various liquid media and identify beta dispersion relaxation as a biomarker for esophageal tissue damage, a key indicator of GERD progression. Additionally, alpha dispersion conductivity effectively distinguished reflux episodes, proving the sensor’s high sensitivity. Unlike traditional diagnostic techniques such as endoscopy or pH monitoring, this radiofrequency spectrophotometry sensor enables continuous, real-time reflux detection, allowing patients to maintain a normal lifestyle during assessment. The results validate its potential as an innovative alternative for GERD diagnosis and monitoring, with future research focused on clinical validation, optimization, and integration into long-term patient monitoring systems. Full article

Methylene blue (MB), a widely used industrial dye, is a persistent pollutant with documented toxicity to aquatic organisms and potential health risks to humans, even at ultra-trace levels. Conventional monitoring techniques such as UV–Vis spectroscopy and fluorescence emission suffer from limited sensitivity, typically failing to detect MB below ~10⁻⁷ M. In this study, we introduce a surface-enhanced Raman spectroscopy (SERS) platform based on silver nanowire (AgNW) substrates that enables MB detection over an unprecedented dynamic range—from 1.5 × 10⁻⁴ M down to 1.5 × 10⁻¹⁶ M. Raman mapping confirmed the presence of individual signal hot spots at the lowest concentration, consistent with the theoretical number of analyte molecules in the probed area, thereby demonstrating near-single-molecule detection capability. The calculated enhancement factors reached up to 1.90 × 10¹², among the highest reported for SERS-based detection platforms. A semi-quantitative calibration curve was established spanning twelve orders of magnitude, and this platform was successfully applied to monitor MB degradation during two advanced oxidation processes (AOPs): TiO₂ nanotube-mediated photocatalysis under UV irradiation and atmospheric-pressure dielectric barrier discharge (DBD) plasma treatment. While UV–Vis and fluorescence techniques rapidly lost sensitivity during the degradation process, the SERS platform continued to detect the characteristic MB Raman peak at ~1626 cm⁻¹ throughout the entire treatment duration. These persistent SERS signals revealed the presence of residual MB or partially degraded aromatic intermediates that remained undetectable by conventional optical methods. The results underscore the ability of AgNW-based SERS to provide ultra-sensitive, molecular-level insights into pollutant transformation pathways, enabling time-resolved tracking of degradation kinetics and validating treatment efficiency. This work highlights the importance of integrating SERS with AOPs as a powerful complementary strategy for advanced environmental monitoring and water purification technologies. By delivering an ultra-sensitive, low-cost sensor (<USD 0.16 per test) and promoting reagent-free treatment methods, this study directly advances SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production). Full article

Spaceborne radar is a powerful tool for probing planetary subsurface structures. Earlier radar studies of the Moon have primarily examined large-scale horizontal structures. However, recent discoveries of vertical holes suggesting the existence of lava tubes and theoretically predicted subsurface gas voids formed by volatiles in magma have highlighted the importance of small-scale subsurface structures. We developed a method using SELENE Lunar Radar Sounder (LRS) data to detect small-scale subsurface echoes (hundreds of meters). Surface scattering simulations incorporating incoherent scattering from sub-resolution roughness were performed using a high-resolution digital elevation model generated by a generative adversarial network. Detection thresholds for subsurface echo candidates (SECs) were determined from the histograms of difference intensities between LRS and simulation B-scans. Results show that some SECs exist in the extension area of the analyzed graben. SECs were also detected continuously across multiple LRS ground tracks in areas unrelated to grabens. Using the radar equation analysis, the echo intensities of SECs could be explained for subsurface structures with 50–600 m widths and dielectric constants of 1–4. This suggests the existence of either subsurface voids or materials with a high porosity of more than 35%. Among the SECs detected continuously across multiple LRS ground tracks, those that are more or less aligned in the downward elevation direction are likely indicative of lava tubes. On the other hand, the SECs distributed along the extension of the graben are aligned parallel to the contour lines. These SECs likely suggest gas voids at the tip of the intrusive magma that formed the graben. Full article

Liver fluke infections, especially those induced by Opisthorchis viverrini, pose considerable health and economic difficulties in aquaculture, particularly in Southeast Asia. Traditional approaches for parasite elimination, including chemical treatments and freezing, exhibit constraints regarding efficacy, environmental sustainability, and practicality. This research investigates an improved dielectric heating system utilizing a 2.45 GHz horn antenna for the selective thermal targeting of parasite-associated regions in Cirrhinus microlepis (small-scale mud carp). The dielectric characteristics of fish tissues, encompassing scales, skin, and muscle, were analyzed utilizing an open-ended coaxial probe technique. Simulation and experimental evaluations were performed to improve energy absorption, heating uniformity, and a particular absorption rate to enable precise thermal localization while preserving the integrity of fish tissue. The findings demonstrate that dielectric heating can specifically elevate the temperature of fish scales, where parasites predominantly inhabit, to levels beyond 70 degrees Celsius, while reducing thermal impact on the underlying muscle tissue. The application of a salt coating on fish scales markedly increased their dielectric loss, exceeding that of muscle tissue, thus enhancing selective heating efficiency and supporting targeted thermal treatment. The ideal distance from the antenna to the sample was established as ranging from 6 to 9 cm, ensuring a balance between energy efficiency and homogeneous heating. This work illustrates the efficacy of dielectric heating as a novel and non-chemical approach for thermal management of parasite-prone tissues in aquaculture, providing a sustainable and viable substitute for traditional treatments. Full article

Objective: The air content within the lungs directly influences the dielectric properties of lung tissue; however, previous studies were conducted under ex vivo conditions and without quantitatively controlling air volume. This study aims to develop an improved model using in vivo measurements to accurately characterize the dielectric properties of rabbit lung tissue across various tidal volumes. Methods: In this study, six sets of different tidal volumes (30, 40, 50, 60, 70, 80 mL) were set in the frequency band of 100 MHz~1 GHz to analyze the trend of the dielectric properties, and the dielectric parameters were systematically constructed under the conditions of different tidal volumes. Results: It was found that the conductivity and permittivity of rabbit lung tissue showed a decreasing trend with increasing tidal volume in the measuring frequency band. The traditional Cole–Cole model has limitations in simulating the dielectric properties of in vivo lung tissues. Therefore, by refining and optimizing the model, this study successfully reduced the average error between the measured data and the model fitting to less than 5%. Conclusions: This study lays the groundwork for investigating the relationship between total air volume within the lungs and their dielectric properties in vivo. Full article

Near-field microwave microscopy (NSMM) is a promising technique for the non-destructive, high-resolution imaging of electrical and dielectric properties at the microscale. However, its performance is highly sensitive to the probe-to-sample distance, often requiring extremely close proximity, which limits its practical application in device manufacturing, especially in scenarios involving coatings and packaging. In this study, we propose a distance inversion method based on a dual-port symmetrical microwave probe to improve imaging performance at larger, safer scanning distances. This method utilizes the correlation between probe height and resonant frequency to compensate for distance-induced signal distortions. The experimental results demonstrate that even at a probe–sample distance of 80 µm, clear and distinguishable NSMM images of printed circuit boards (PCBs) can be obtained. The imaging resolution reached 13 µm. The defect structure with dimensions of 130 × 130 µm² on the PCB was successfully identified. The signal-to-noise ratio was significantly enhanced after applying the correction method. This approach not only improves the robustness and flexibility of NSMM in industrial scenarios but also extends its applicability to packaged or coated electronic devices, offering a valuable tool for advanced non-destructive testing. Full article

We investigate the resonant characteristics of planar surfaces and distinct edges of structures with the excitation of phonon-polaritons. We analyze two materials supporting phonon-polariton excitations in the mid-infrared spectrum: silicon carbide, characterized by an almost isotropic dielectric constant, and hexagonal boron nitride, notable for its pronounced anisotropy in a spectral region exhibiting hyperbolic dispersion. We formulate a theoretical framework that accurately captures the excitations of the structure involving phonon-polaritons, predicts the response in scattering-type near-field optical microscopy, and is effective for complex resonant geometries where the locations of hot spots are uncertain. We account for the tapping motion of the probe, perform analysis for different heights of the probe, and demodulate the signal using a fast Fourier transform. Using this Fourier demodulation analysis, we show that light enhancement across the entire apex is the most accurate characteristic for describing the response of all resonant excitations and hot spots. We demonstrate that computing the demodulation orders of light enhancement in the microscope probe accurately predicts its imaging. Full article

The emergence of GaN-based micro-LEDs has revolutionized display technologies due to their superior brightness, energy efficiency, and thermal stability compared to traditional counterparts. However, the development of red-emitting micro-LEDs on silicon substrates (GaN-on-Si) faces significant challenges, among them including hydrogen-induced deactivation of p-GaN caused by hydrogen species generated from SiH₄ decomposition during SiO₂ passivation layer growth, which degrades device performance. This study systematically investigates the use of high-density metal-oxide dielectric passivation layers deposited by atomic layer deposition (ALD), specifically Al₂O₃ and HfO₂, to mitigate these effects and enhance device reliability. The passivation layers effectively suppress hydrogen diffusion and preserve p-GaN activation, ensuring improved ohmic contact formation and reduced forward voltage, which is measured by the probe station. The properties of the epitaxial layer and the cross-section morphology of the dielectric layer were characterized by photoluminescence (PL) and scanning electron microscopy (SEM), respectively. Experimental results reveal that Al₂O₃ exhibits superior thermal stability and lower current leakage under high-temperature annealing, while HfO₂ achieves higher light-output power (LOP) and efficiency under increased current densities. Electroluminescence (EL) measurements confirm that the passivation strategy maintains the intrinsic optical properties of the epitaxial wafer with minimal impact on Wp and FWHM across varying process conditions. The findings demonstrate the efficacy of metal-oxide dielectric passivation in addressing critical challenges in InGaN red micro-LED on silicon substrate fabrication, contributing to accelerating scalable and efficient next-generation display technologies. Full article

Objectives: This study highlighted the key role played by high-pressure (HP) dielectric spectroscopic measurements of amorphous CBD to probe the molecular dynamics in order to examine the physical stability of the drug. The pharmacological properties of CBD assure that this can be a promising drug for the pharmaceutical industry. Hence, it is important to check the physical stability under elevated temperature and pressure conditions to understand the behavior of the drug under manufacturing conditions. Methods: This research investigated the molecular dynamics at various temperatures and pressures. We utilized the HP dielectric studies which are considered as an advanced and sensitive tool to determine both the molecular dynamics and the phase transformations. Results: This paper discusses the physical stability by analyzing the behavior of structural relaxation and crystallization tendencies of the amorphous drug under ambient and elevated pressure conditions. This study verified that amorphous CBD is highly physically stable at storage and elevated temperature conditions under ambient pressure. Conclusions: Accordingly, we examined the physical stability under elevated pressures at storage temperature, and we observed that the compression induced the crystallization of amorphous CBD. The breaking of weak hydrogen bonds present in the CBD might be the reason for this destabilization at elevated pressures. The least physical stability at high-pressure conditions was also confirmed by the broadening of the α-relaxation peak at high pressures. Full article

Dimer and trimer acids are interesting viscous liquids produced from fatty acids derived from renewable sources. The chemical structures of dimer and trimer acids are known and quite complex and are presented here, discussed and further elucidated through electronic absorption spectroscopy, FT-IR and Raman spectroscopy. Dimer and trimer acids have a number of applications in their original form or in the form of derivatives. In the present study, a series of esters of dimer and trimer acids with alcohols from renewable sources were synthesized for use as plasticizers for rubber and plastics. The polarity of the dimer and trimer acids as well as their esters with alcohols from renewable sources (dimerates and trimerates) were systematically studied using a Nile red solvatochromic probe. The resulting E(NR) values were compared with the E(NR) values of the most common types of rubber and plastics. Compatibility and other physical properties expected from the E(NR) scale were studied and successfully confirmed in tire tread rubber compound formulations and in nitrile rubber and PVC matrices, confirming once again the sensitivity and the validity of the Nile red solvatochromic polarity scale for the development of new plasticizers. The validity of the liquids polarity measured with the Nile Red dye is supported by the correlation found between the E(NR) scale and the dielectric constants (ε) of carboxylic acids (including dimer and trimer acids, hydrogenated dimer acids and isostearic acid) and alcohols. A correlation was even found linking the E(NR) values the with the ε values of thin solid films of rubbers and plastics. In the case of the esters the correlation of their E(NR) values was found with the length of the aliphatic chains of the alcohols used in the esterification. Full article

Measuring surface soil moisture is vital for understanding water availability, agricultural productivity, and climate change impacts, as well as for drought prediction and water resource management. However, obtaining accurate data is challenging due to the lack of reliable probes that work across diverse soil types and conditions. This study evaluated a prototype dielectric probe developed by Daiki Rika Kogyo Co., Ltd., Saitama, Japan, through controlled laboratory experiments. The probe measures the real and imaginary parts of dielectric permittivity over 10–150 MHz in a 5.6 cm diameter, with a 2 cm length volume, achieving a ±2% accuracy for the real part of oil–ethanol and ethanol–water mixtures (3.26–79). The imaginary part of the dielectric permittivity of aqueous solutions is convertible into electrical conductivity (EC) with reasonable accuracy. For variably saturated sand, the real part is convertible to a volumetric soil-moisture content (≥0.10 m³m⁻³) using a custom equation. The probe’s variable-frequency measurements reduce the limitations of fixed-frequency approaches, accounting for the EC, clay, porosity, and organic matter effects. With its VNA principle and simultaneous measurement of dielectric properties, it offers innovative capabilities for addressing water management, agriculture, and climate prediction challenges. Full article