Frequency-dependent Behavior Research Articles

MgO nanofiller reinforced biodegradable, flexible, tunable energy gap HPMC polymer composites for eco-friendly electronic applications

This study explores the development and characterization of eco-friendly Magnesium Oxide (MgO) nanofiller reinforced hydroxypropyl methylcellulose (HPMC) polymer composites for eco-friendly electronic applications. The prepared nanocomposites are biodegradable and flexible without any additional plasticizer. MgO nanoparticles were synthesized using the solution combustion method and incorporated into HPMC matrix through solution casting method. The structural, mechanical, optical, AC and DC electrical, and degradation properties of the prepared nanocomposites were systematically investigated. X-ray diffraction (XRD) confirmed the successful integration of MgO nanoparticles into the HPMC matrix, with noticeable interactions affecting the crystallinity. Mechanical testing revealed an optimal MgO concentration of 0.2 g, which provided the best balance of strength and ductility, while higher concentrations led to increased brittleness. UV–Vis spectroscopy results evident that the energy gap of nanocomposites can be tuneable with MgO incorporation. The photoresponsivity study indicated that higher MgO content reduce the photocurrent due to agglomeration and defect states. Dielectric studies showed a typical frequency-dependent behaviour, with enhanced dielectric constants at lower frequencies attributed to interfacial polarization. However, increasing MgO content decreased the dielectric constant and loss due to reduced polymer chain mobility and increased resistive pathways. Current-Voltage (I-V) characteristics demonstrated a non-ohmic conduction behaviour with Poole-Frenkel emission identified as the predominant conduction mechanism. Degradation tests in both tap water and soil, demonstrated that the MgO incorporation significantly slowed the degradation rate of the composites, enhancing their durability. These findings suggest that MgO-HPMC nanocomposites hold promise for sustainable and flexible eco-friendly electronic applications.

Spectro-spatial analysis of van der Pol-type phononic crystals

Abstract The application of phononic chains as metamaterials demonstrates their remarkable capability to manipulate the propagation of waves. These periodic structures yield frequency-dependent behavior of material comprising characteristics with many possible engineering applications. In this paper, we investigate the weak and general nonlinear behaviors of the van der Pol-type damped phononic chains. The analysis of wave propagation is initially conducted for a one-dimensional structure, and subsequently, is extended to consider the wave motion through two-dimensional and three-dimensional lattices. Results are obtained using the method of multiple scales and a Spectro-spatial analysis by employing the numerical method of the 4th-order Runge–Kutta. A new phase-diagram relation within the chain’s unit cell is also introduced aiming to enhance the numerical findings. Our results indicate that in the weakly nonlinear regime, the van der Pol-type damping closely follows the linear dispersion curve, regardless of the initial amplitude. This suggests a symmetry between energy pumping and dissipation modes, where hardening and softening behaviors align with linear characteristics of common damping mechanisms, such as viscous damping. Additionally, the formulation demonstrates the existence of limit-cycle stability in the motion of each mass. For the general damped system, it is observed that a special frequency exists where the system converges, for all wave numbers similar to the synchronization effect. Hence, the motion and the frequency of all masses are synced. Additionally, non-reciprocal wave propagation is observed, resulting in a bandgap structure with a symmetry breaking occurring near the limit cycle. These results are promising in the fields of wave emitters, wave filters, and signal encryption.

Frequency-resolved measurement of two-color air plasma terahertz emission

We investigated the far-field terahertz beam profile generated from an air plasma induced by two-color femtosecond laser pulses. Under our experimental conditions (filament length shorter than the dephasing length between the two-color pulses), using electro-optic sampling in both ZnTe (0.2-2.2 THz) and GaP (0.4-6.8 THz) crystals, and ultra-broadband ABCD technique (1-17.5 THz), we determined that the THz beam exhibits a unimodal beam pattern below 4 THz and a conical one above 6 THz. This experimental finding is consistent with theoretical studies based on the unidirectional pulse propagation equation, which predict the transition of THz emission from a flat-top profile to a conical one due to the destructive interference of THz waves emitted from the plasma filament. Our results also underscore the importance of accounting for experimental artifacts, such as photo-excited losses in silicon resulting in on-axis THz absorption along with the influence of drilled mirrors, in characterizing the complex spatial and frequency-dependent behavior of two-color plasma-induced terahertz emission.

Optimization, dielectric properties, and antibacterial efficacy of copper-grafted MgO nanoparticles synthesized via sol-gel method

This is the first study to optimize magnesium oxide nanoparticles by grafting copper as an effective antibacterial against prevalent pathogenic microorganisms, which were synthesized by sol-gel method with a particle size of 11-17 nm. At a preparation temperature of 70 °C, copper was added at rates of 2.5 wt.%, 5 wt.%, 7.5 wt.% and 10 wt.%. The particles were heated at 600°C. Nanoparticles were analyzed using XRD, FTIR, UV-Vis spectrum, Raman, TGA-DTA, SEM, EDX, zeta potential and TEM. XRD study revealed the crystal structure of the space group of MgO nanoparticles is cubic. Optical measurements yielded optical gap values falling within the range of 2.35 eV, which was reduced to 2.20 eV. The presence of the copper dopants in the MgO host lattice was confirmed by FTIR analysis. It reveals the existence of Mg-O-Cu, Mg-O, and Mg-O-Mg bonds. Additionally, the dielectric and electrical characterization of MgO was conducted using complex impedance spectroscopy over a frequency range of 10 to 106 Hz and conductivity measurements across a temperature range of 60 to 380 °C. The real and imaginary parts of the dielectric constant showed both frequency-dependent and temperature-dependent behaviors. Notably, the variations observed in the imaginary component of the modulus and impedance at the maximum frequency indicates a relaxation process that is not of the Debye type, with calculated activation energies (Ea). Moreover, the samples were evaluated against various bacteria, including, -ve gram (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa), and +ve gram (Staphylococcus aureus, and Streptococcus pneumonia) using two different techniques. Studies have shown that copper-containing samples exhibit resistance to these bacteria. These findings suggest that the samples have potential as useful biomaterials in nanobiotechnology.

The expansion of the GRB 221009A afterglow

We observed γ-ray burst (GRB) 221009A using very long baseline interferomety (VLBI) with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA), over a period spanning from 40 to 262 days after the initial GRB. The high angular resolution (mas) of our observations allowed us, for the second time ever, after GRB 030329, to measure the projected size, s, of the relativistic shock caused by the expansion of the GRB ejecta into the surrounding medium. Our observations support the expansion of the shock with a > 4σ-equivalent significance, and confirm its relativistic nature by revealing an apparently superluminal expansion rate. Fitting a power law expansion model, s ∝ ta, to the observed size evolution, we find a slope a = 0.69−0.14+0.13. Fitting the data at each frequency separately, we find different expansion rates, pointing to a frequency-dependent behaviour. We show that the observed size evolution can be reconciled with a reverse shock plus forward shock, provided that the two shocks dominate the emission at different frequencies and, possibly, at different times.

Tailored proton conductive membranes of PVdF-co-HFP: Investigating the synergistic effects of ammonium tetrafluoroborate and phosphoric acid dopants on dielectric characteristics

This study investigates the structural, thermal, and dielectric properties of pure PVdF-co-HFP matrix and its composite electrolytes, PVdF-co-HFP/NH4BF4[x], both before and after PA doping, using FTIR, SEM, TGA, and dielectric analyses. FTIR spectra reveal characteristic vibrational bands, confirming the presence of various functional groups and phases. SEM images display a smooth and homogeneous surface morphology for pure PVdF-co-HFP, while the composite electrolytes exhibit irregular dispersion of NH4BF4 salt and rougher surfaces upon PA doping. TGA analysis shows that the onset of thermal degradation occurs at approximately 370 ℃ for pure PVdF-co-HFP, while PA-doped samples demonstrate higher decomposition temperatures, exceeding 400 ℃ due to hydrogen bonding and ionic complex formation. The presence of NH4BF4 and PA doping also affects the crystallinity of the PVdF-co-HFP matrix, notably shifting the transition temperatures of the alpha and beta phases. Ionic conductivity measurements indicate that PA doping significantly enhances conductivity by increasing charge carrier concentration and facilitating ion transport. PA-doped PVdF-co-HFP/NH4BF4[10] showed the highest conductivity reaching 1.68 × 10−3 S.cm−1 at 1 MHz and 400 K. Dielectric studies reveal frequency-dependent behavior, with dielectric constant (ε') and loss (ε") showing distinct trends influenced by salt concentration and PA doping. The dielectric tangent loss (tanδ) of PA-doped PVdF-co-HFP/NH4BF4 composite membranes exhibits frequency and temperature dependence. At higher temperatures, tanδ increases with frequency, showing a resonance peak that shifts towards higher frequencies. The study elucidates the impact of PA doping on the structural, thermal, and electrochemical performance of PVdF-co-HFP/NH4BF4 composites, providing insights for their potential applications in advanced electrolyte systems.

A comparative study of influence of isovalent and aliovalent A-site substitutions on the structural, magnetic, and dielectric properties of Sr2CrMoO6 double perovskites

We report on a comparative study of the structural, magnetic, and dielectric and properties of isovalent and aliovalent A-site substituted Sr2-xAxCrMoO6 (A = Ca, x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.8, 1.0; A = K, La only x = 0.5) double perovskites, which were synthesized via sol-gel process. X-ray diffraction patterns and Rietveld refinements demonstrated that all the Sr2-xAxCrMoO6 powders crystallized in a cubic crystal structure with space group of Fm3‾m. SEM images revealed that the Sr2-xAxCrMoO6 powders exhibited a spherical morphology. Their chemical compositions were determined by quantitative energy dispersive X-ray spectroscopy, which were close to the nominal values. FTIR spectra analyses verified the presence of (Cr, Mo)O6 octahedra in these powders. XPS spectra validated the existence of Sr2+, K+, Ca2+, La3+, and Cr3+ ions in the powders, and oxygen existed in the forms of lattice oxygen and absorbed oxygen respectively, whereas Mo element had a mixed chemical valence state of Mo4+ and Mo6+. The Sr2CrMoO6 (SCMO) powders had a saturation magnetization (MS) of 0.016 μB/f.u. at 2 K, magnetic Curie temperature (TC) of 337 K, and irreversibility temperature (Tirr) of 329 K where the zero-field cooled (ZFC) and field-cooled (FC) magnetization (MZFC and MFC, respectively) curves became bifurcated. A spin-glass behavior was observed at temperature (TB) of 81 K. Both Tirr and TB shifted towards low temperature with increasing the external magnetic field. In addition, the MZFC and MFC curves became almost overlapped under the external field of 50 kOe, and the spin-glass behavior disappeared. The M-H data demonstrated that both isovalent and aliovalent A-site substitutions could improve the magnetic properties and B-site ordering degree (η) of the SCMO powders. However, isovalent Ca-substitution exhibited more significant enhanced effect on the magnetic properties in comparison with the aliovalent A-site substitutions either by K- or La-substitution. Among the isovalent Ca-substituted Sr2-xCaxCrMoO6 (x = 0.1–1.0) powders, Sr1.2Ca0.8CrMoO6 sample had a maximum MS value of 0.64 μB/f.u. at 2 K, over 30 times enhancement of that of the pristine SCMO powders. The Sr2-xAxCrMoO6 ceramics exhibit a strong frequency dependent dielectric behavior, which can be well interpreted by Maxwell-Wagner relaxation model. The anomalous dielectric relaxor behavior of the SCMO ceramics observed at 260 K was ascribed to the jumping of the electrons trapped in a shallower energy level created by oxygen vacancies. The dielectric constant of the isovalent Ca-substituted Sr1.5Ca0.5CrMoO6 samples was 30 times larger than that of the pristine SCMO samples. Our present results demonstrate that isovalent Ca-substitution at A-site could improve the magnetic and dielectric properties of the sol-gel derived SCMO double perovskite oxides, which have potential applications in the fields of spintronic devices and dielectric devices.

Structural, Morphology and Electromagnetic Interference Shielding Studies of Multifunctional Hybrids of Low-Density Polyethene with Graphene, Carbon Nanotube and Magnetite

ABSTRACT In this study, we investigate the EMI SE (Electromagnetic interference shielding effectiveness) of novel multifunctional polymer hybrids in the X-band and Ku-band frequencies. Magnetite nanoparticles were synthesized via wet chemical reduction and nanographene was synthesized through chemical exfoliation combined with microwave treatment. Nine different composites were prepared with varying weight ratios of graphene and magnetite. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed their structural and morphological properties. SEM analysis revealed magnetite particle sizes ranging from 10.05 nm to 29.8 nm. Vibrating Sample Magnetometer (VSM) analysis indicated that the magnetite nanoparticles exhibit super paramagnetic behavior with a magnetic anisotropy constant (K) of approximately 63.9375 × 106 J/m3. Impedance analysis, permittivity and permeability measurements showed frequency-dependent behaviors, with interfacial polarization effects due to magnetite agglomeration. The highest conductivity, observed in the 50:5:37.5:7.5 hybrid, peaked at 8 S/cm at lower frequencies. The 50:5:37.5:7.5 hybrid demonstrated the highest EMI SE of 50.08 dB (99.999019% suppression) in the X-band, which is suitable for advanced EMI-shielding applications.

Effects of ZnO additive on the electrical and densification properties of A-site deficient barium cerate perovskite

The dual strategies of A-site deficiency and addition of ZnO sintering aid have been employed to optimise stability and densify the high-temperature proton conductor Ba0.95Ce0.8Y0.2O3-δ at 1200 °C (B95CYZn-1200). Structural analysis performed by Rietveld refinement based on X-ray diffraction data indicated perovskite phase with monoclinic symmetry (space group, I2/m). Raman spectroscopy revealed the presence of ZnO for material sintered at 1200 °C, which most likely partially resides in grain-boundary regions, leading to enhanced electrical transport observed by impedance spectroscopy at low temperature. Anomalous and reproducible frequency-dependent impedance behaviour below 500 °C, observed in various atmospheres, is suggested to be attributable to the varistor-type properties of ZnO. The electrical conductivity of B95CYZn-1200 in the range 500–900 °C is typical of perovskite proton conductors but with greater conductivity than both Ba-stoichiometric BaCe0.8Y0.2O3-δ and ZnO-free Ba0.95Ce0.8Y0.2O3-δ in wet O2 and N2, reaching ∼ 1.1 S m−1 at 550 °C in wet O2. Resistance to carbonate formation and mechanical breakdown was demonstrated via prolonged impedance measurements in CO2- and H2-containing atmospheres in the range 600–700 °C.

Towards solving the origin of circular polarisation in FRB 20180301A

Abstract Fast Radio Bursts (FRBs) are short-timescale transients of extragalactic origin. The number of detected FRBs has grown dramatically since their serendipitous discovery from archival data. Some FRBs have also been seen to repeat. The polarimetric properties of repeating FRBs show diverse behaviour and, at times, extreme polarimetric morphology, suggesting a complex magneto-ionic circumburst environment for this class of FRB. The polarimetric properties such as circular polarisation behaviour of FRBs are crucial for understanding their surrounding magnetic-ionic environment. The circular polarisation previously observed in some of the repeating FRB sources has been attributed to propagation effects such as generalised Faraday rotation (GFR), where conversion from linear to circular polarisation occurs due to the non-circular modes of transmission in relativistic plasma. The discovery burst from the repeating FRB 20180301A showed significant frequency-dependent circular polarisation behaviour, which was initially speculated to be instrumental due to a sidelobe detection. Here we revisit the properties given the subsequent interferometric localisation of the burst, which indicates that the burst was detected in the primary beam of the Parkes/Murriyang 20-cm multibeam receiver. We develop a Bayesian Stokes-Q, U, and V fit method to model the GFR effect, which is independent of the total polarised flux parameter. Using the GFR model we show that the rotation measure (RM) estimated is two orders of magnitude smaller and opposite sign (∼28 rad m−2) than the previously reported value. We interpret the implication of the circular polarisation on its local magnetic environment and reinterpret its long-term temporal evolution in RM.

Low Resistivity Pay Zone Detection in Hydrocarbon Formation: The Feasibility of the Spectral Induced Polarization Method

Summary Identifying and characterizing low resistivity pay (LRP) zones within hydrocarbon-rich formations has long been challenging in the petroleum industry due to their complex mineral composition, microporosity, and diminished resistivity contrasts. Traditional methods, such as resistivity measurements, struggle to effectively pinpoint LRP zones, prompting the need for innovative approaches in reservoir evaluation. This paper explores the feasibility of using the spectral induced polarization (SIP) method for detecting LRP zones. The SIP method measures complex conductivity across a frequency range from 1 mHz to 10 kHz. While this technique has been widely used in mining and environmental studies, its potential for petrophysics applications in the oil and gas sector remains largely unexplored. This study acts as a proof of concept, demonstrating the capability of SIP for detecting LRP zones. Laboratory experiments utilized dual-porosity silica gel samples with controlled micro- and macroporosity fractions and added pyrite content. Despite a high crude oil saturation of approximately 60%, the presence of brine in continuous micropores resulted in low resistivity readings (0.7 Ω·m) at low frequencies, as conventionally measured by direct current resistivity tools. However, at higher frequencies (>100 Hz), the study observed high average resistivity values (82 Ω·m), indicating a frequency-dependent behavior in electrical measurements. This behavior is attributed to polarization mechanisms, including the electrical double layer (EDL). This study’s findings propose the SIP method’s potential effectiveness for detecting LRP zones, paving the way for future research to delve deeper into the application of SIP in petrophysics.

Investigating the hybrid potential of PVA-chitosan-loaded TiO2@NiO films for advanced conductivity and dielectric performance

The synthesis and characterization of PVA-chitosan-NiO, PVA-chitosan-TiO2, and PVA-chitosan-TiO2@NiO films have opened avenues for tailoring materials with specific electrical, dielectric, and optical properties. The synergistic effects arising from the combination of polymers and metal oxides offer a platform for further optimization and application-specific tuning. The synthesis process successfully incorporated NiO and TiO2 nanoparticles into the PVA-chitosan matrix, creating three distinct films: PVA-chitosan-NiO, PVA-chitosan-TiO2, and PVA-chitosan-TiO2@NiO. Structural analyses, including X-ray diffraction (XRD) and scanning electron microscopy (SEM), revealed well-defined nanostructures with crystalline metal oxide dispersions. Dielectric characterization demonstrated frequency-dependent behavior, elucidating the influence of metal oxides on dielectric constants and loss tangents. Cole–Cole plots provide insights into relaxation processes and can guide applications in capacitors and energy storage devices. Conductivity measurements highlight the enhanced electrical performance of NiO and TiO2. This study provides a foundation for future research on the development of advanced functional materials for a wide range of technological applications. The insights gained from this work contribute to the growing body of knowledge on polymer-metal oxide composites and pave the way for innovations in electronic, optoelectronic, and energy-related technologies.

Sol-gel auto-combustion synthesis of Co0.5Cu0.5Cr0.5GdxFe1.5-xO4 spinel ferrites and their magneto-dielectric properties

In this work, Gadolinium (Gd3+) substituted Co–Cu–Cr (CCC) SFs with the chemical formula Co0.5Cu0.5Cr0.5GdxFe1.5-xO4 (x = 0.00, 0.05, 0.10, 0.15, and 0.20) were synthesized via the self-combustion process. The single-phase matrix of the Gd3+ substituted CCC SFs was verified using X-ray diffraction (XRD). The crystallite size (D) of Gd3+ doped CCC SFs was reduced from 51.20 nm to 36.27 nm with increasing Gd3+ doping. The addition of Gd3+ in the CCC SFs lattice enhanced specific surface area (S) from 22.11 cm2/g to 28.57 cm2/g. The energy bandgap (Eg) was increased from 4.83 eV to 5.40 eV and revealed an inverse relation with crystallite size. The tangent loss (tan δ), dielectric loss (ε″), dielectric constant (ε′), and ac conductivity (σac) of Gd3+ doped CCC SFs exhibit frequency-dependent behaviour. The behaviour of these dielectric properties has been analyzed using both Koop's theory and the Maxwell-Wagner model. Moreover, it was found that the ε′ was enhanced, while σac and tan δ was reduced with the doping of Gd3+ in CCC SFs. The saturation magnetization and microwave operating frequency were increased with the doping of Gd3+ in CCC SFs. Because of their diverse dielectric and magnetic properties, the Gd3+ doped CCC SFs have considerable potential for different applications, including microwave absorption materials, switching high-frequency devices, and microwave frequency-operating devices.

Investigating the dielectric characteristics, electrical conduction mechanisms, morphology, and structural features of mullite via sol-gel synthesis at low temperatures

This research explores the fabrication of mullite precursor powder utilizing the sol-gel process at low temperatures. Silicon tetraethoxide (Si(C2H5O)4) and aluminum nitrate nonahydrate (Al(NO3)3.9H2O) were employed as the sources of SiO2 and Al2O3 oxides, respectively. Various analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), dilatometry, differential thermal analysis (DTA), and X-ray powder diffractometer (XRD), were utilized to investigate the formation and crystallization of the amorphous powder. The microstructure of specimens sintered at 1600 °C for 1 h was examined utilizing scanning electron microscopy (SEM). Measurements of hardness (HV) and coefficient of thermal expansion (CTE) were conducted on mullite samples heated to 1600 °C and then cooled, revealing an increase in HV from 888 to 1000 HV as the sintering temperature rose from 1500 to 1600 °C. The CTE of mullite within the temperature range of 50–1300 °C was determined as 5.23 × 10−6/°C. Additionally, the dielectric and electrical characterization of mullite was analyzed utilizing complex impedance spectroscopy at a frequency of 0.1–106 Hz and conductivity measurements over a temperature range of 40–400 °C. The real and imaginary parts of the dielectric permittivity exhibited frequency-dependent and temperature-dependent behaviors. Significantly, the observed variations in the imaginary component of the modulus and impedance maximum frequency point to a relaxation process that is not Debye-type, with calculated activation energies (Ea) consistent across different methods.

Structural, optical, and electrical characteristics of HPMC/PVA-I2O5 composites: Fabrication and performance analysis for energy storage applications

Polymer composites (PCs) are increasingly utilized in energy storage applications, notably in dielectric capacitors, due to their distinct properties and advantages over conventional liquid electrolytes. In this study, we investigate the structural, optical, electrical, and dielectric properties of hydroxypropyl methylcellulose (HPMC)/polyvinyl alcohol (PVA) composite films filled with varying concentrations of iodine pentoxide (I2O5), prepared via a solution casting method. Incorporating I2O5 into the polymer matrix significantly impacted the composite's properties. FTIR and XRD analyses revealed disturbances in molecular structure, crystallization order, and the presence of I2O5 crystal phases in the composite films. Calculations of crystallinity percentage indicated a reduction with I2O5 addition, leading to increased amorphous phase content suitable for enhancing electrical conductivity (σ). UV/vis spectroscopy studies demonstrated decreased optical energy gaps, suggesting improved charge storage capability. The σ analysis revealed enhanced values with I2O5 addition, indicative of improved charge mobility within the composite films. Frequency-dependent behaviors in complex permittivity (ε′ and ε″) highlighted the potential of these composites for efficient charge storage across different frequency ranges. Impedance analysis provided insights into space charges and conductive paths within the composites, influencing their electrical characteristics. Capacitors fabricated from the HPMC/PVA-I2O5 composites exhibited enhanced energy storage capacity and controlled conductance characteristics, demonstrating promising performance for energy storage applications. Our findings demonstrate that the HPMC/PVA-I2O5 composites are potential dielectric materials for capacitor technology.

Frequency-Dependent Dielectric Permittivity and Water Permeability in Ordered Mesoporous Silica-Grafted Fluorinated Polyimides.

Polymers with a low dielectric constant (Dk) are promising materials for high-speed communication networks, which demand exceptional thermal stability, ultralow Dk and dissipation factor, and minimum moisture absorption. In this paper, we prepared a series of novel low-Dk polyimide films containing an MCM-41-type amino-functionalized mesoporous silica (AMS) via in situ polymerization and subsequent thermal imidization and investigated their morphologies, thermal properties, frequency-dependent dielectric behaviors, and water permeabilities. Incorporating 6 wt.% AMS reduced the Dk at 1 MHz from 2.91 of the pristine fluorinated polyimide (FPI) to 2.67 of the AMS-grafted FPI (FPI-g-AMS), attributed to the free volume and low polarizability of fluorine moieties in the backbone and the incorporation of air voids within the mesoporous AMS particles. The FPI-g-AMS films presented a stable dissipation factor across a wide frequency range. Introducing a silane coupling agent increased the hydrophobicity of AMS surfaces, which inhibited the approaching of the water molecules, avoiding the hydrolysis of Si-O-Si bonds of the AMS pore walls. The increased tortuosity caused by the AMS particles also reduced water permeability. All the FPI-g-AMS films displayed excellent thermooxidative/thermomechanical stability, including a high 5% weight loss temperature (>531 °C), char residue at 800 °C (>51%), and glass transition temperature (>300 °C).

Impedance-Based Method for Predictive Stability Assessment

Impedance-based analysis methods enable a more specific and earlier foundation for assessing harmonic stability in decentralized converter-based power plants compared to the conventional compliance testing in the grid connection process. Essentially, they can be implemented as black-box model approaches without the necessity to disclose internal control models. Initially, only knowledge of the input impedances of the planned grid connection point and the planned PV system is required for application. For this purpose, the method of impedance spectroscopy for inverters has already been developed as a means to determine the effective impedance profile and the internal harmonic sources of inverters, allowing for the description of the frequency-dependent behavior of individual units. The time- and frequency-dependent grid impedance at the grid connection point (GCP) has also been successfully measured in several campaigns on medium and low-voltage grids. Through the coordinated application of both measurement methods, a predictive harmonic assessment is intended in the future, ensuring high planning reliability and grid quality even in grids with a high penetration of power electronics-coupled systems. This paper provides an overview of the current state of research on impedance-based stability criteria and presents measurement methods for practical implementation. Furthermore, it outlines remaining open questions until application in the field.

The Study of Mode-switching Behavior of PSR J0614+2229 Using the Parkes Ultra–wide-bandwidth Receiver Observations

In this paper we present a detailed single-pulse and polarization study of PSR J0614+2229 based on the archived data observed on 2019 August 15 (MJD 58710) and 2019 September 12 (MJD 58738) using the ultra−wide-bandwidth low-frequency receiver on the Parkes radio telescope. The single-pulse sequences show that this pulsar switches between two emission states, in which the emission of state A occurs earlier than that of state B in pulse longitude. We found that the variation in relative brightness between the two states varies temporally and both states follow a simple power law very well. Based on the phase-aligned multifrequency profiles, we found that there is a significant difference in the distributions of spectral index across the emission regions of the two states. Furthermore, we obtained the emission height evolution for the two emission states and found that, at a fixed frequency, the emission height of state A is higher than that of state B. What is even more interesting is that the emission heights of both states A and B do not change with frequency. Our results suggest that the mode switching of this pulsar is possibly caused by changes in the emission heights that alter the distributions of spectral index across the emission regions of states A and B, resulting in frequency-dependent behaviors, i.e., intensity and pulse width.

A Theoretical Approach to Study the Frequency Dependent Dielectric behavior of Breast Cancer Cells using AlN buffer-based AlGaN/GaN HEMT

Abstract This article investigates the applicability of open gated high electron mobility transistor (HEMT) as a biosensing platform for Breast cancer detection. The present study reports the detection of healthy (MDA-10) and malignant cells (MDA-MB-231) associated with breast cancer using high-quality AlN buffer AlGaN/GaN HEMT with dual cavity structure formed by etching out the gate metal from source and drain sides under the gate region. The AlN buffer AlGaN/GaN HEMT provides better 2DEG confinement and large conduction band offset than GaN buffer. The proposed design is analyzed at frequencies of 900 MHz and 10 GHz, as breast cells have distinct dielectric properties at different microwave frequencies. The variation in dielectric constant of the cavity region corresponding to biomolecular species will change the device’s electrical characteristics and hence can be used to detect breast cancer cells. In this work, the device sensing parameters considered for analysis are shift in threshold voltage and drain current sensitivity. The device performance has also been analyzed by optimizing cavity thickness and length to select the best design for the sensing. The effect of non-ideal conditions such as steric hindrance and probing is also studied by emulating these real time effects in simulation. The device shows a maximum drain current sensitivity of 29.94% for 20 nm of cavity thickness and 1µm of the cavity length. The results depict that the proposed device design exhibits a highly sensitive response and can be promising alternate for future biosensing applications.

Temperature and frequency dependent conductive behavior study on polymer-derived SiBCN ceramics

Conductive behavior research is vital for in-depth understanding the conductive capabilities of materials as well as promoting the development of their applications in fields such as electronics, energy and sensing. In the article, the AC conductive behavior was systematically evaluated for polymer-derived SiBCN ceramics by complex impedance spectroscopy and electrical modulus methods. The results suggest that SiBCN ceramics have a frequency-independent conductivity at low frequencies, whereas it exhibits a relaxation process with increasing frequency at high frequencies. In addition, the SiBCN ceramics follow the electron hopping conductive mechanism in both low and high-frequency bands over the testing temperature range. By considering the relationship between the prefactor σ0 and T0, the conductive mechanism is revealed to be the band-tailed state hopping instead of the variable range hopping. It is worth noting that although the material has the same conductive mechanism at various testing temperatures, hopping is mainly controlled by the matrix phase at low frequencies; while at high frequencies, hopping is dominated by free carbon phase. Our results provide the underlying insights needed to guide the design of amorphous SiBCN ceramics for applications in electrically relevant fields.