Imaginary Part Of Permittivity Research Articles

A first-principle study on the pressure-dependent structural, electronic, and optical properties of 4-Hydrazine Benzene Sulfonamide

This study utilizes first-principle density functional theory (DFT) to explore the high-pressure behavior of 4-hydrazine benzene sulfonamide. Our investigation, spanning pressures from 0 to 300[Formula: see text]GPa, delves into diverse properties of the crystal (C6H9N3O2S), encompassing the crystal structure, band gap, density of states, permittivity, and conductivity. Under increasing pressure, intriguing observations emerge. Distortions in the molecular structure manifest notably at 70, 130, and 270[Formula: see text]GPa, accompanied by distinctive anisotropic behavior in lattice constants. Notably, our scrutiny of the band gap and density of states exposes a transition from a semiconductor to a metallic state and back to a semiconductor state, illuminating the profound influence of pressure on the material’s electronic structure. At 0[Formula: see text]GPa, the real part of permittivity registers negative values within the 15.6–20.2[Formula: see text]eV energy range, suggesting the crystal’s inability to propagate light and its manifestation of metallic reflection properties. Conversely, at 270[Formula: see text]GPa, the imaginary part of permittivity indicates metallic characteristics within the electronic structure, alongside a substantial energy loss in the crystal’s real part of conductivity. Moreover, the imaginary part of conductivity unveils pronounced energy conversion between the driving electric field and current excitation, hinting at structural instability under this extreme pressure. This research contributes vital insights into the behavior of hydrocarbons under high pressure, filling crucial gaps in our understanding of their properties.

Dielectric and magnetic response of Cu-Co-Sm ferrite impregnated with graphene nanoplatelets for high-frequency device applications

This work studied a composite of graphene nanoplatelets (GNPs) impregnated copper-cobalt-samarium ferrites Cu0.5Co0.5Fe1.97Sm0.03O4/GNPs synthesized via sol-gel auto-combustion route. The structural, electrical, dielectric, and optical properties of the as-prepared composites were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), EDX, I-V characteristics, impedance measurement, raman spectroscopy, scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) analysis, and UV–visible spectroscopy. XRD confirmed that the spinel ferrites had a crystalline single-phase FCC structure with the lattice constant of around 8.33 Å, and the crystallite size range from 54.10 nm to 51.85 nm. SEM analysis confirmed the homogenous dispersion of spinel ferrites in graphene sheets, and EDX confirmed the presence of all elements in ferrite composites with GNPs. Furthermore, the spinel matrix was confirmed by the Raman and UV-visible analysis. A minimum particle size of 21.73 nm was determined using TEM, and the minimum value of activation energy (0.01 eV) was obtained from IV characteristics for ferrite composite with 2.5% GNPs. Further, our ferrite composites with GNPs demonstrated improved electroconductive properties, with conductivity ranging from 5.88×10−8S/cm to 1.04×10−6S/cm at 673 K. The real & imaginary part of permittivity, dielectric constant (ε’), and impedance (Z) were also improved with the addition of GNPs. At low frequencies, a permeability loss value of 0.81 was obtained for the ferrite composite with 5% GNPs. VSM analysis confirmed that the saturation magnetization decreased in ferrite composites with graphene nanoplatelets. The minimum value of skin depth of 1.03 mm was observed at 1.25 % GNPs. Our ferrite composites with GNPs exhibited minimal eddy current at high frequencies, making them promising candidates for high-frequency device applications.

A novel on-line microwave diagnostic for an atmospheric pressure air plasma based on an artificial neural network

Permittivity is an important aspect of the design of microwave devices. In order to design microwave devices that are more suitable for the excitation of air plasmas, this paper presents a method for the on-line measurement of the relative permittivity of an atmospheric pressure air plasma with 2.45 GHz microwaves. First, a ridged waveguide is designed and constructed to excite the air. Using the ridged waveguide, the plasma can be excited and measured simultaneously. An artificial neural network trained with simulated data is integrated into the system to invert the dielectric constant of the air plasma being measured. At a power of 786 W and an airflow rate of 1250 L/h, the real and imaginary parts of the permittivity are obtained to be −1244 and 60, respectively. The forecasted errors on the real part and the imaginary part of the relative permittivity are kept at around 5% and 3%. The Drude model is used to construct a relationship between the electronic and dielectric properties. This diagnostic method is simple to operate and has a high degree of generality. It should be useful in the design of microwave plasma devices and can greatly improve the efficiency of microwave plasma equipment.

Terahertz reconfigurable metasensor for specific recognition multiple and mixed chemical substances based on AIT fingerprint enhancement

Terahertz (THz) fingerprint metasensing is an effective method to identify chemical substances in a rapid and non-destructive way. Currently, two main principles are used in THz metasensing: the change of the real part of permittivity causing the dip resonance frequency deviation, and the fingerprint peak of the imaginary part of permittivity causing the dip resonance splitting (absorption induced transparency, AIT). Most previous work investigated AIT detection for only single chemical substance. The suitable AIT metasensor structure are still required for simultaneously measurement of multiple and mixture chemical substances. In this manuscript, we proposed the N-order concentric rings metasensor for specific recognition multiple and mixed chemical substances based on AIT fingerprint enhancement. The structure has broadband multiple plasmonic resonance dips which are generated by near field dipole resonances. The equivalent circuit model was built to realize the reconfigurable function. Then, 5-order concentric rings structure was designed and fabricated for simultaneously specific recognition of four chemical substances (α-lactose, benzoic acid, vitamin B2 and 2, 5-dichloroanline). The influence of the real and imaginary part of the chemical substances' permittivity on AIT effect had discussed in details. Simulation results indicated that the frequency-deviation of the resonance dip can be stabilized and will not be changed when the concentration of chemical substances is over 20 mg/mL. As shifted plasmonic resonance peaks match the chemical substances’ imaginary part of permittivity fingerprint spectra, the perfect AIT effect can be realized. The metasensor can simultaneously and non-destructively conduct a specific detection of α-lactose, benzoic acid, vitamin B2 and 2,5-dichloroanline, and their mixture. The limit of detections of α-lactose, benzoic acid, vitamin B2 and 2,5-dichloroanline are 8.61 mg/mL, 6.96 mg/mL, 7.54 mg/mL and 8.35 mg/mL, respectively. Also, the sensitivity of the metasensor can reach 0.00211, 0.00208, 0.00211 and 0.00219 (unit: 1/mg/mL), respectively. By utilizing one-way analysis of variance method, the possibility of recognition error for each chemical substance is lower than 0.001. Our metasensor provides a novel and accurate platform for THz fingerprint sensing.

Highly sensitive DS-CSRR based microwave sensor for permittivity measurement of liquids

In this work, a low-cost double split complementary split ring resonator (CSRR) microwave sensor has been designed and fabricated on an FR4 substrate for permittivity characterization of liquids. This modified CSRR structure is proposed to make use of the benefits of the dielectric resonator technique compared to other types of microwave methods. The resonator structure comprises two slits in each of the rings normal to each other while maintaining one slit in each ring along the feed line for maximum excitation of the resonator. The resonator with substrate dimensions of acts like an inductance-capacitance-resistance (LCR) circuit and operates at of the industrial scientific and medical band. Eleven different liquid samples (each with of volume) covering a wide permittivity range of have been used to measure the transmission coefficient using vector network analyzer. In comparison with many recently reported works, the sensitivity of the sensor is found to be higher with average and normalized sensitivity of permittivity and respectively. Fit equations are developed for both real and imaginary parts of permittivity, and using the fit equations the permittivity of three unknown samples are determined with less than error. The sensor adopts a unique orientation of the slits to enhance the E-field intensity for better interaction of the samples with the sensor. A compact form factor, low production cost, future integration possibilities, and high sensitivity are the distinct highlights of the sensor. The sensor promises to be a potential candidate for situations that demands low-cost and highly accurate measurements and may be a good alternative to commercial sensors for dielectric characterization, concentration analysis, and impurity measurement of liquids.

Optical properties of plasmonic titanium nitride thin films from ultraviolet to mid-infrared wavelengths deposited by pulsed-DC sputtering, thermal and plasma-enhanced atomic layer deposition

We present a comparative study of the optical properties of 50 nm-thick titanium nitride (TiN) films deposited on a silicon substrate by pulsed-DC sputtering, thermal, and plasma-enhanced atomic layer deposition. Silicon was chosen as the optimal material for the complementary metal–oxide–semiconductor (CMOS) integration. Using ellipsometry and Fourier-transform infrared (FTIR) spectroscopy, broadband permittivity of the films was obtained from a series of free-space reflection measurements in the wavelength range of 210 nm to 20.0μm (∼47619–500 cm−1). Our particular focus is on the influence of the deposition method and its process temperature on the TiN plasmonic properties. We used grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, and electrical resistivity measurements to analyze the composition of thin films and to elucidate the effect of different deposition parameters on their optical properties. All measurements were carried out at room temperature and the thickness of all film samples was fixed to 50 nm to exclude the influence of these factors on the optical properties. We demonstrate that PEALD-deposited films have smoother surfaces than those deposited by the sputtering technique, while sputtered films have higher densities. In addition, by changing the temperature of both processes, it is possible to influence the stoichiometry and crystal orientation of the layers. Based on this characterization, we found out that TiN thin film deposited by pulsed-DC at 600 °C gives the best plasmonic response (high negative permittivity ϵ1 and relatively low losses associated with ϵ2, where ϵ1 and ϵ2 are the real and imaginary parts of permittivity, respectively) among all samples for the entire wavelength range under study. The same film also exhibits the excellent resistivity of 29 μΩcm. These results suggest that there is a direct relationship between stoichiometry, structural quality, and oxygen incorporation in TiN films and their plasmonic response.

Experimental Investigation of the Effect of Transient Overvoltages on XLPE-Insulated HVDC Cables

HVDC cables are subject to several types of impulses superimposed on the rated DC voltage during their service lifetime. Temporary Overvoltages (TOVs) and Superimposed Switching impulses (SSIs) are considered some of the most challenging due to the relatively long impulse duration. This paper aims at investigating experimentally the effect of TOVs and SSIs on XLPE insulation for extruded HVDC cables. 0.15-mm-thick DC-XLPE specimens, aged by applying TOVs and SSIs, are characterized using dielectric analyzer and Fourier Transform InfraRed spectroscopy (FTIR) to detect the aging effects on the insulation. Results show an increase in the imaginary part of permittivity, ε", accompanied with the appearance of additional dipolar polarization losses peaks. The amplitude and frequency of the aforementioned peaks vary with the amplitude and the number of applied TOVs and SSIs. An increase in electrical conductivity is also noticed with aging. FTIR results show absorbance peaks in the aged specimens likely due to the intramolecular bonds rupture accompanied with the formation of aging products. In summary, SSIs and TOVs cause a noticeable reduction of insulating properties in XLPE specimens. The higher the peak of the transient, the greater the aging effect.

Microwave absorption properties of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) composites

AbstractComposite of (1 − x)La0.85Ag0.15MnO3/x graphene (x = 0, 3, and 5 wt.%) and epoxy resin with a ratio of 4:1 were prepared to investigate the influence of the addition of graphene in (1 − x)La0.85Ag0.15MnO3/x graphene on real and imaginary parts of permittivity, permeability, as well as microwave reflection loss (RL), using a vector network analyzer in the 8–18 GHz of the frequency range. It is found that the value of RL is smaller at x = 3 wt.% (−20.74 dB at 14.85 GHz) and 5 wt.% (−14.81 at 16.50 GHz) compared to at x = 0 wt.% (−8.89 dB at 15.90 GHz). The result indicates that microwave absorption properties significantly improved as a result of the addition of graphene. It is suggested that the addition of graphene enhanced the dielectric loss–related mechanism such as interfacial polarization and conduction loss resulting in an improvement of microwave absorption performance for both x = 3 wt.% and x = 5 wt.% samples. It also shows that the observed enhanced microwave absorption properties may also be influenced by the resistivity of the sample as x = 3 wt.% sample exhibits enhanced microwave absorption properties and the lowest resistivity among the studied samples.

Microwave Spectroscopy Investigation of Carasau Bread Doughs: Effects of Composition up to 8.5 GHz.

Carasau bread is a flat bread, typical of Sardinia (Italy). The market of this food product has a large growth potential, and its industry is experiencing a revolution, characterized by digitalization and automation. To monitor the quality of this food product at different manufacturing stages, microwave sensors and devices could be a cost-effective solution. In this framework, knowledge of the microwave response of Carasau dough is required. Thus far, the analysis of the microwave response of Carasau doughs through dielectric spectroscopy has been limited to the dynamics of fermentation. In this work, we aim to perform complex dielectric permittivity measurements up to 8.5 GHz, investigating and modeling the role of water amount, salt and yeast concentrations on the spectra of this food product. A third-order Cole-Cole model was used to interpret the microwave response of the different samples, resulting in a maximum error of 1.58% and 1.60% for the real and imaginary parts of permittivity, respectively. Thermogravimetric analysis was also performed to support the microwave spectroscopy investigation. We found that dielectric properties of Carasau bread doughs strongly depend on the water content. The analysis highlighted that an increase in water quantity tends to increase the bounded water fraction at the expense of the free water fraction. In particular, the free water amount in the dough is not related to the broadening parameter γ2 of the second pole, whereas the bound water weight fraction is more evident in the γ2 and σdc parameters. An increase in electrical conductivity was observed for increasing water content. The microwave spectrum of the real part of the complex permittivity is slightly affected by composition, while large variation in the imaginary part of the complex dielectric permittivity can be identified, especially for frequencies below 4 GHz. The methodology and data proposed and reported in this work can be used to design a microwave sensor for retrieving the composition of Carasau bread doughs through their dielectric signature.

Effects of High-collision Plasma on Radiation Protection of Human Brain

Objective: The purpose of this paper is to find a reasonable composite structure of electromagnetic protection device, especially the distribution characteristics of plasma parameters and operation conditions. Methods: Due to its high collision frequency, the high-pressure discharge plasma can be usedas a filling medium to take the electromagnetic protection effect. The strategies and algorithmsare presented to solve the propagation characteristics of electromagnetic wave (EMW) in plasma with complex dielectric constant. When the real and imaginary part of permittivity are of the same order of magnitude, the imaginary part value will impact on the feature of plasma dielectric constant, also affect the behavior of propagation of EMW. The propagation process of EMW in virtual human brain (VHB) model is investigated by finite difference time domain method. By optimizing the layout of plasma layer and air layer, an effective phase regulator is constructed, and the reflected wave amplitude is greatly reduced. Results: The simulation results show that plasma makes the amplitude of the electromagnetic fields in VHB decrease to different degrees. their maximum average decrease is about 25% and the corresponding reduction of SAR value is more than 40% in the frequency range of 1.8-3.6GHz. Conclusion: The existence of plasma can make the scalp and muscle possess the excellent performance in resisting the incident of EMW, so that the amplitude of the electromagnetic field inside the brain body is small, so as to effectively protect the brain tissue. These research results have good reference value and engineering applicability for the structure design of protection equipment with high frequency of EMW.

Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>

Perovskite manganese La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub> (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (<i>T</i>) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at <i>T</i> ≥ 600 <sup>o</sup>C. The average grain size was ~15 nm at the calcination temperature (T<sub>cal</sub>) = 600 <sup>o</sup>C and it increased to ~1 μm when T cal increased up to 1200 <sup>o</sup>C. <i>M</i>-<i>H</i> curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing <i>T</i><sub>cal</sub>. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ <i>f</i> ≤ 18GHz. The complex permittivities (ε', ε") increased significantly in samples calcined above 800 <sup>o</sup>C because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the <i>M</i><sub>S</sub> value increased significantly. As the <i>T</i><sub>cal</sub> increased, the height of the μ' and μ" spectra also gradually increased. The large values of ε', ε" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.

Influence of Dielectric Plate Parameters on the Reflection Coefficient of a Planar Aperture Antenna

In this article, an aperture antenna excited by a waveguide with a circular cross-section and covered with a dielectric plate was analyzed via simulation calculation and verified via measurements. The influence of the geometrical and electromagnetic parameters of the dielectric plate on the reflection coefficient S11 of the antenna opening was systematically analyzed. The geometrical parameters taken in this analysis are the thickness d and the width/length h1/h2 of the dielectric plate. The electromagnetic parameters used in this analysis are the real and the imaginary part of permittivity (εr, tan δ) and the electrical conductivity of the dielectric plate (σ). The simulation calculation and analysis included other structural and electromagnetic parameters of the dielectric plate (density of the radome material, relative permeability, and magnetic loss tangent (ρ, µr, and tan δµ, respectively)), but the results show that in the range of real values of these parameters for the materials used for the dielectric plate, they had no significant influence on the reflection coefficient. The results show that impedance-matched antennas with very low values of the reflection coefficients S11 at the resonant frequency can be realized by changing the geometrical and electromagnetic parameters of the dielectric plate material. The results are presented for a circular aperture antenna on a planar grounded plane with a dielectric plate on the opening, and the achieved lowest values of the S11 parameter were −45.17 dB (simulated) and −43.93 dB (measured) at the frequencies of 1.7820 GHz and 1.7550 GHz, respectively. The estimated values of the dielectric plate parameters in this case are thickness d = 11.08 mm (0.67 λ); width × length of grounded plane and dielectric plate h1 × h2 = 423 × 450 mm2 (2.51 × 2.67 λ); relative permittivity 2.5, tan δ = 0.09, μr = 1, tan δμ = 0.00, ρ = 1200 kg·m−3; and electrical conductivity σ = 0 S/m. The simulation calculation results were verified by measuring the reflection coefficient S11 on the created laboratory model of the aperture antenna with the dielectric plate and showed a very good match.

Graphene nanoplatelets (GNPs): a source to bring change in the properties of Co-Ni-Gd-ferrite/GNP nanocomposites.

The nanocomposites of Co0.5Ni0.5Gd0.03Fe1.97O4/graphene nanoplatelets (CNGF/GNPs) were synthesized by a cost-effective sol-gel auto combustion (SGAC) route. The X-ray diffraction analysis confirmed the cubic structure of the as-prepared nanocomposites, and a crystallite size of 32.28 nm was observed for the 7.5 wt% GNPs. Irregular and unique nanoparticles consisting of short stacks of graphene sheets having a platelet shape were confirmed by the morphological analysis of the as-prepared nanocomposites. Raman analysis revealed a spinel crystal structure along with a new vibrational mode due to the GNPs. The energy bandgap was 3.98 eV for the composite with 7.5 wt% GNP concentration. It was observed that the percentage temperature coefficient of resistance (TCR%) rapidly decreased with an increase in temperature both in low- and high-temperature ranges. Dielectric studies carried out in the frequency range 104-107 Hz confirmed that the graphene-added composites had high values for both the real and imaginary parts of permittivity at low frequencies. A decrease in saturation magnetization with an increase in GNP concentration was observed compared with the pure CNGF samples. Hence, the as-prepared composites are useful for application in high-frequency devices as well as spintronics.

Temperature denpendent microwave absorption properties of SrFe12O19 in X-band

Researchers are currently focusing on the electromagnetic and microwave absorption properties of SrFe12O19 hexaferrites. The high-temperature absorption (more than 573 K) is highly demanded in various including the military, national defense, aviation, and other fields. SrFe12O19 has good thermal stability at high temperature, and it has large coercivity, which also determines that it has good stability in magnetic properties and is not easy to be affected by the environment. Thus, it is necessary to explore the magnetic characteristics of SrFe12O19 hexaferrites at high temperatures. SrFe12O19 hexaferrites were fabricated by the molten salt method and their microstructure, high-temperature electromagnetic properties, and microwave properties were investigated in detail. The complex permeability and permittivity of SrFe12O19 were measured at varying temperatures (293–673 K) in the X band. While the real parts of permittivity and permeability increased with the increasing temperature, the imaginary parts of permittivity and permeability did not change significantly with increasing temperature. The calculated absorption properties displayed that as temperature increased from 293K to 623K, the frequency of the RL peaks moved to a low-frequency direction, and the sample’s minimum value of RL could be smaller than -10dB across the whole X band. The results indicate that SrFe12O19 particles have better absorption properties and can be used in high-temperature environments. These particles can be possibly used in many particular fields.

Advanced Ti3C2Tx MXene‐modified cement nanocomposites toward high efficiency electromagnetic functional materials for green buildings

AbstractThe proliferation of electronic devices and wireless communication is leading to serious electromagnetic (EM) interference. In this work, Ti3C2/cement composites were developed as high efficiency EM functional materials by introducing exfoliated Ti3C2Tx MXene with cement for green buildings with EM shielding function. In the composites, few‐layered Ti3C2 MXene were dispersed homogeneously throughout the cement matrix. The EM properties of the composites were studied as a function of the MXene content. With increasing MXene content, real and imaginary part of permittivity was significantly improved owing to the polarization and electrical conduction caused by the MXene phase. Composites with 15 wt.% MXene showed good EM absorbing properties with a maximum effective absorbing bandwidth of 2.67 GHz. Strong EM shielding can be achieved when MXene content increased to 25 wt.%. The EM shielding effectiveness of such composites was higher than 22.0 dB, and the dominating shielding mechanism was EM absorption. This work finds new materials for the development of advanced green buildings with EM shielding function.

Nanoparticles/Parabolic Nanobowl Hybrid Structure as a Surface-Enhanced Raman Scattering Substrate: Insights Using the FDTD Method

Nanobowl structures are commonly used as substrates for surface-enhanced Raman scattering (SERS) detection due to their high plasmonic activity. In this work, we introduce and investigate a superenhancing potential structure, nanoparticles (NPs) in a parabolic nanobowl (PNB). Moreover, the optimal parameters of the NPs in the PNB structure are obtained and the origin of plasmon enhancement is analyzed. The electric field distribution and the electromagnetic field enhancement factor MSERS of the PNB structure are obtained via the finite-difference time-domain (FDTD) method. We found that the electric field enhancement originated from the coupling of the surface plasmon polariton (SPP) within the PNB and the interstitial local surface plasmon resonance (LSPR) of the nanoparticles. By manipulating the curvature of the PNB, the size of the NPs, and the materials of the NPs in PNB structures, the plasmon resonance of both NPs and the PNB became strongest. When the curvature of the PNB is 2.9 μm–1, the wide-range enhancive electromagnetic field generated at the bottom of the PNB couples best with the LSPR of the NPs. The NP size is recommended to be in the range of 46–56 nm. For the choice of materials, it is found that the maximum enhancement is on the order of 1010 when noble metals Au and Ag are used as the materials of the PNB and NPs. Since the permittivity imaginary part of Si is closer to zero, a maximum enhancement factor reaching 1011 magnitude is obtained when Si is used as the material of the PNB. These results indicate that the PNB structure shows powerful SERS enhancement and is expected to be applied to the detection of environmental pollutants, such as microplastics.

The impact of indium ion on structural, magnetic, and electrodynamic traits of Co-Ni nanospinel ferrites

Indium doped cobalt–nickel nano-spinel ferrites, Co0.5Ni0.5Fe2-xInxO4 (x ≤ 0.10) (NSFs), have been fabricated through solution-combustion (SC) approach and characterized for structural, magnetic morphological behavior. XRD (X-ray powder diffraction) affirmed that all NSFs have a single phase without any impurities. SEM (Scanning Electron Microscope) along with EDX (Energy dispersive X-ray), TEM (Transmission Electron Microscope), HR-TEM (High-Resolution Transmission Electron Microscope) analyses, and elemental mappings confirmed the morphology and chemical composition of all products, respectively. The crystallite size has decreased from ∼50 nm to ∼19 nm, while the lattice constant has been seen to vary because of the replacement of Fe3+ ions by In3+ ions. The fitting of room temperature Mössbauer spectra provided the hyperfine parameters, and it was found that the In3+ ions occupy the A site. The isomer shift values are associated with the characteristics of the high spin Fe3+ charge state. The magnetic behaviors of produced nanospinel ferrites (NSFs) were assessed through M vs. H loops registered at 10 and 300 K. It was found that the pristine as well as In3+ ions substituted Co-Ni NSFs exhibit ferrimagnetic nature at both temperatures. In addition, considerable variations in the magnetic parameters were noticed with respect to the level of the substituent element. The values of Ms at both 10 and 300 K increased up to x = 0.03 and then decreased with a further increase in the indium content. Unlike the variations in Ms and Mr, the Hc values at both 10 and 300 K are found to reduce almost linearly with the indium concentration (x). The variations in different magnetic parameters were explained based on the cation distribution, magnetic moments, ionic radii, magnetocrystalline anisotropy, structural and morphological changes, etc. It was predicted that In3+ ions tend to substitute Fe3+ ions at the Td (A) sites for x ≤ 0.03 and then start to partially substitute Fe3+ ions at the Oh (B) sites as x reaches above 0.03. Such a prediction in combination with the variations in the entire magnetic moment could explain the observed variations for Ms values. The reduction in Hc values was mainly ascribed to a drop in the anisotropy constant. Electrodynamic properties were investigated as S-parameters (S11-S21) in the 33–50 GHz frequency range. Main parameters such as real and imaginary parts of permittivity and permeability vs. frequency were calculated based on the standard model. A good correlation between the indium content and high-frequency properties was determined. It was observed the decrease of the electrical and magnetic losses with the increase of the indium concentration due to the diamagnetic origin and differences between Fe3+/In3+ ionic radii of the substituent.

Real and imaginary permittivity measured by thermal noise dielectric spectroscopy

This paper demonstrates that both real and imaginary parts of dielectric permittivity in a kHz frequency range can be determined from the thermal noise voltage spectra. The proposed method, termed as thermal noise dielectric spectroscopy, relies on the set of calibration measurements of gauge resistors and capacitors. This method has a great potential for investigations of strongly nonlinear dielectric materials whenever the initial permittivity is of interest because the thermal noise method probes the permittivity by an almost zero electric field. Here, we tested this method by measuring dielectric spectra of 100 nm thin film of paraelectric SrTiO3 in a thermal noise setup in which the film is effectively probed by voltages of the order of nanovolts. For the sake of comparison, the permittivity of the same SrTiO3 thin film has been also measured using the standard impedance analyzer with the probing AC voltage of 10 mV. Agreement between methods is remarkable for both real and imaginary parts of the permittivity. Results strongly suggest that the proposed technique is broadly applicable for investigation of the frequency and temperature dependence of the complex permittivity of nanoscale dielectric materials.

Additive manufacturing of nanocellulose/polyborosilazane derived CNFs-SiBCN ceramic metamaterials for ultra-broadband electromagnetic absorption

• Defect-rich CNFs were developed as electromagnetic absorbents. • Metamaterials were developed by the combination of 3D printing and PDC route. • Cole-Cole circle plots indicates the materials possess strong polarization capability. • Ultra-broad EAB of 32.4 GHz was achieved by multi-scale design. Electromagnetic absorption materials that possess efficient absorption performance and broad absorption bandwidth are needed to combat the electromagnetic interference (EMI). SiBCN ceramic-based metamaterials modified with defect-rich carbon nanofibers (CNFs) were developed by combining the additive manufacturing technique and polymer derived ceramic route. Meta-structures were patterned by additive manufacturing of preceramic polymer and followed by thermolysis of the green bodies. Defect-rich CNFs were in-situ generated by thermolysis of nanocellulose introduced into the preceramic green bodies. When the content of cellulose is 6.0 wt% and the annealing temperature is 1200 °C, the real and imaginary part of permittivity can reach as high as 17.0 and 7.0, respectively. Cole-Cole circle plots indicates that the CNFs-SiBCN ceramics possess strong polarization capability due to the defect-rich structure of CNFs. At the thickness of 1.8 mm, the minimal reflection loss (RL min ) can reach −20.0 dB while the effective absorption bandwidth reached 2.85 GHz. Through multi-scale (nano and macro) designing, a simulated ultra-broad effective absorption bandwidth of 32.4 GHz from 7.6 GHz to 40 GHz was achieved, where the RL min reached −46.0 dB at the frequency of 26.8 GHz. This work finds innovative route for the development of ceramic-based broadband electromagnetic absorption materials and new application for the polymer derived ceramics.

Microstrip sensor and methodology for the determination of complex anisotropic permittivity using perturbation techniques

In this work, a sensor in microstrip technology and a methodology for measuring the real part and the imaginary part of the complex uniaxial permittivity of solid anisotropic samples are presented. The sensor is based on a pair of parallel lines coupled resonators and a cleft arranged in the coupling region which allows to hold the samples under test (SUTs). The proposed methodology relates the change in the even/odd resonance frequency with the real part of the permittivity in the vertical/horizontal direction, and the change in the Q factor of the even/odd mode with the imaginary part of the permittivity in the vertical/horizontal direction. The methodology was successfully verified with the characterization, at 2.43 GHz of anisotropic samples of printed PLA, Diclad 880, and RO4350B using the knowns materials: RT5870, PTFE and RO4003.