Permittivity Of Samples Research Articles

Small-sized x-band open resonator for wide-range permittivity measurements of solid-state dielectrics

A study using computer simulation of a compact two-mirror symmetric open resonator for use in the X band for measurements of the complex permittivity of flat samples was carried out. The possibilities of minimizing the dimensions of an open resonator with a loaded quality factor of about 104 are investigated. Comparative studies of various coupling elements of an open resonator with a waveguide are carried out. It is shown that coupling elements in the form of a slot on the mirror, which smoothly passes into a standard waveguide, have advantages for use in open resonator for permittivity measurements, compared with coupling elements in the form of a hole in the diaphragm at the end of waveguide on the mirror surface. It is shown that slot coupling elements make it possible to achieve in open resonators almost twice as much field magnitude than coupling elements in the form of holes.

A Mach–Zehnder Interferometer Refractive Index Sensor on a Spoof Surface Plasmon Polariton Waveguide

In this paper, we experimentally and numerically confirm a planar Mach–Zehnder interferometer (MZI) device for sensing dielectric samples based on a spoof surface plasmon polariton (SSPP) waveguide. The MZI system is constructed using two different ultrathin transmission lines with distinct dispersion units supporting SSPPs. After SSPPs propagate a certain propagation distance, a resonant dip is formed at a specific frequency due to destructive interference, whose displacement enables the SSPP to be modulated by one of the MZI arms loaded with dielectric samples. We investigate how the variations in the permittivity and thickness of dielectric samples affect the sensibility. Through an error analysis between the experimental measurements and numerical calculations, it is demonstrated that the plasmonic sensor based on the MZI has a high precision. The proposed technique is compact and robust and paves a versatile route toward the chip-scale functional devices in microwave circuits.

The ferromagnetic resonance (FMR) of SrZ hexaferrite (Sr3Co2Fe24O41), and the tuning of FMR with an external magnetic field

The hexagonal Z-type ferrite Sr3Co2Fe24O41 (SrZ) was first synthesised in 2001 and reported as being a room temperature multiferroic material in 2010, with subsequent investigations into its multiferroic properties, but little into high frequency and microwave properties, and ferromagnetic resonance frequency (FMR), which determines its ability as an electromagnetic (EM) absorber and radar absorbing (RAM) stealth material. It was shown that SrZ existed as a majority or single phase after heating in a narrow temperature range between 1170 and 1190 °C using X-ray diffraction (XRD) and measurement of magnetic hysteresis loops, with the sample appearing to be single phase SrZ at 1190 °C. We measured complex permeability and permittivity of a single phase polycrystalline ceramic sample of SrZ between 500 MHz and 8 GHz (X-band). The sample had a relatively high permittivity >17 over this entire frequency range, and it showed a strong ferromagnetic resonance (FMR) at 2.3 GHz. This FMR could also be tuned by the effect of an external magnetic field, by moving a simple bar magnet progressively closer to a toroidal sample. This incurred a very slight shift in the peak up to 2.48 GHz at distances of 2.5–10 cm from the sample – a tuning of ∼5–6% with applied magnetic fields estimated to be 0.11–0.23 T, which is not insignificant. At a close distance of 0.5 mm we got a high degree of tuning of FMR to 3.4 GHz, a large change of 1.07 GHz (= 46% increase) with an applied magnetic field estimated to be 0.40 T. Despite this, the applied field had no significant effect on permittivity over 0.5–8 GHz. Such results have never been reported before, and are significant, as this would enable tuning of the FMR via simple physical/mechanical movement of a bulk alloy magnet, effectively creating a tuneable microwave filter or absorber.

Experimental Study on the Variation of Soil Dielectric Permittivity under the Influence of Soil Compaction and Water Content

The dielectric permittivity of common soils is mainly controlled by water content and porosity, while the latter is closely related to the characteristics of compaction. By studying the changes in dielectric permittivity of soil samples with different soil water content and compaction levels, the influence of the controlling factors on the relationship model between soil water content and dielectric permittivity can be evaluated. In this paper, network analyzer was used to measure the dielectric permittivity of 7 groups of soil samples with gravimetric water content ranging from 8.09% to 14.52% and dry density ranging from 1.61 g/cm3 to 1.96 g/cm3. The results show that the dielectric permittivity increases with the increase of water content and dry density, and the effect of water content on permittivity is more significant for soils with higher dry density. Furthermore, when the water content is less than or equal to the optimal water content, Topp formula and the complex refractive index model (CRIM) can better predict the soil dry density. When the water content approaches the saturated state of soil, there is a deviation between the predicted value and the actual value. At last, the modified Topp formula and the complex refractive index model (CRIM) can accurately predict soil compactness. This provides an important basis for rapid detection of water content and compactness of highway subgrade soil by ground penetrating radar.

Deep neural network for retrieving material's permittivity from S‐parameters

AbstractThis research proposed a deep neural network (DNN) model employing a multilayer feedforward artificial neural network to characterize the relative permittivity and loss tangent of a solid sample in a broad frequency range from 1 to 10 GHz. The method exploited a grounded coplanar waveguide as a measurement fixture, and a vast amount of data was obtained from full‐wave simulations. The latter was used to train the proposed DNN model. We performed parametric studies to examine optimal DNN hyperparameters and improve the efficiency of the material property retrieval process. The proposed model was validated by retrieving the relative permittivity and loss tangent of a known substrate. The results show good agreement with the known reference values with a slight error of 1.2%.

An Improved Split-Ring Resonator-Based Sensor for Microfluidic Applications.

This study proposes an ultrahigh-sensitivity split-ring resonator-based microwave sensor for retrieving the complex permittivity of liquid samples. An interdigital capacitor structure was used to expand the sensing area and the sensitivity. A defected ground structure and A parallel dual split-ring resonator were introduced to improve the quality factor. A polydimethylsiloxane microfluidic channel substrate was placed above the interdigital capacitor structure. The channel route coincided with the interdigital gap to fully utilize the strong electric field. Ethanol-water solutions with varying ethanol fractions were injected into the channel as the testing liquid. It was demonstrated that the variation in resonant frequency can be used to retrieve the dielectric properties of liquid samples. The proposed sensor used a small liquid volume of ~0.68 μL and provided values in good agreement with the reference data.

Determination of Broadband Complex EM Parameters of Powdered Materials: 2. Ilmenite‐Bearing Lunar Analogue Materials

AbstractWe present systematic measurements of the frequency‐dependent complex dielectric permittivity of lunar regolith analogue samples with increasing amounts of the mineral ilmenite along with Bayesian model fits using a one‐pole Cole‐Cole model. We use these results to calculate a lower bound for the attenuation of radar signals in dB/m based on ilmenite content. We compare our measurement results with previous efforts to use Earth‐based radar maps to calculate the effect of ilmenite on radar attenuation and find that they are in agreement. We also revisit the ilmenite‐dependent loss tangent relationships of Carrier III et al. (1991) and demonstrate the significant frequency‐dependent effect of ilmenite content on signal attenuation as well as the effect of minor variations in loss tangent for depth‐to‐feature determinations. The results presented here are the first systematic laboratory measurements investigating the effect of ilmenite on radar attenuation and show future promise for the application of dielectric spectroscopy, or the identification of materials based on their electromagnetic properties in the radar and microwave range.

A metamaterial based microfluidic sensor for permittivity detection of liquid

The electromagnetic (EM) behavior of a microwave sensor has specific relationship with the physical properties of the materials to be detected, e.g. the concentration of solution and the permittivity of gas. The microwave sensor can detect changes of EM response in real time, and obtain the material properties with low sample consumption, high efficiency and dispersion characteristics. This work presents a microfluidic sensor using spiral resonators and plasmonic metamaterials with confined EM fields for intensive resonance. Two microfluidic chips with spiral channels engraved in polydimethylsiloxane are also adopted to enhance the interaction between the EM fields and the carried liquids at resonance frequencies. The permittivity of liquid samples can be detected through the shift of resonance frequency. A prototype of the sensor is fabricated and tested with several regular solutions and organic solvents, showing a good performance in terms of low liquid consumption (8 μl), good sensitivity (410 MHz frequency offset when ϵr changes from 1 to 36.7) and low cost.

Multiple Spoof Plasmonically Induced Transparency for Sensing Applications

We design a pair of resonators to realize multiple spoof plasmonically induced transparency (PIT) with high-Q group delays, which show potential in sensing applications. To reveal the mechanism of the multiple spoof PIT scheme, we deduce mathematical equations of a simplified model composed of multiple harmonic oscillators, and we further propose an equivalent-circuit model to analyze the metamaterials in an intuitive way. A prototype consisting of a broadband stub resonator and a spoof localized surface-plasmonic resonator is further fabricated to detect the complex permittivity of high-lossy liquids and solid samples in microwave bands. Experimental results show that the group-delay-based sensor can work well even when high-order modes are weakly excited, and the trade-off between sensitivity and properties of samples is discussed. The proposed double-resonator scheme with multiple spoof PIT is universal, and we design a metasurface working in terahertz bands to show that the concept can be widely used in various surface-sensing applications.

Enhanced the Cu2+ doping on the structural, optical and electrical properties of zinc oxide (ZnO) nanoparticles for electronic device applications

Zinc oxide (ZnO) and Cu doped ZnO Nano particles (NP's) were synthesized through chemical route (sol gel & Co-precipitation) to reveal their structural, electrical and optical properties. The synthesized NP's have been characterized by X-Ray diffraction (XRD), Fourier transform infrared rays (FTIR) spectroscopy, Ultra violet visible (UV–V) spectroscopy and impedance spectrometry techniques. XRD pattern revealed the formation of hexagonal structure of ZnO NP's. However size variation of ZnO NP's was observed with addition of Cu contents. SEM analysis revealed that nanorods have been made due to Cu doping in ZnO NP's. FTIR spectroscopy determined the presence of Cu contents in the synthesized samples while UV-technique shown the absorption peaks in the range of 200–800 nm range. The band gap energy decreases with increasing Cu content was observed. The microwave dielectric properties (i.e. relative permittivity & tangent loss) of the Cu doped samples were observed to be decrease with resonant frequency.

Structural and Electrical Properties of Glass-Ceramic Ferroelectric Composite Materials

Introduction. Materials exhibiting high dielectric permittivity are relevant for use in modern ultrahigh-frequency electronics. Among them, ferroelectrics with high dielectric nonlinearity present particular interest. The electrical strength of ferroelectric materials can be increased using modern composite structures based on mixing ferroelectries and linear dielectrics - materials exhibiting simultaneously low dielectric permittivity and high electrical strength. This approach provides for the opportunity of creating new multicomponent materials with previously unattainable properties and adjusting their component composition, inclusion size and electrical properties across a wide range. In this work, on the basis of porous potassium-iron-silicate glass (KFS) obtained by ion exchange, glass-ceramic materials containing barium titanate were synthesized for use at ultrahigh frequencies.Aim. Production of glass composites by low-temperature sintering of pre-synthesized BaTiO3 (BTO) and potassium-iron-silicate glass, as well as characterization of their structural and electrical properties at ultrahigh frequencies (microwave).Materials and methods. The crystal structure and phase composition of the obtained films were studied by X-ray diffraction using a DRON-6 diffractometer by the emission spectral line CuKα1 (λ = 1.5406 Å). The dielectric permittivity (ε) of microwave samples was evaluated by the Nicholson-Ross method at room temperature using an Agilent E4980A LCR-meter.Results. According to X-ray diffraction analysis, the synthesized samples are a mixture of KFS glass, ferroelectric BaTiO3 and dielectric barium polytitanates; the ratio of the latter determines the electrical properties of the composites. Depending on the content of barium titanate, the studied samples demonstrate a dielectric constant from 50 to 270 at a dielectric loss level of 0.1...0.02. The samples subjected to annealing in an oxygen medium showed an increase in dielectric permittivity by 10.25 % and an increase in controllability with a decrease in dielectric losses by an average of two times.Conclusion. The composite composition of 70 wt % BTO /30 wt % KFS was found to be the most promising in terms of structural and electrical properties. This composite showed an increase in dielectric permittivity by 25 % and a significant increase in nonlinearity, at the same time as reducing losses by more than two times as a result of annealing in an oxygen medium.

An active microfluidic sensor based on slow-wave substrate integrated waveguide for measuring complex permittivity of liquids

In this paper, a microfluidic sensor based on slow-wave substrate integrated waveguide (SW-SIW) is proposed to measure the complex permittivity of liquids and it achieves an ultrahigh quality factor of 51156, which is much higher than previous reported designs. The proposed sensor consists of three-layer dielectric substrates and an active circuit. The traditional SIW has the fundamental mode of TE101, whose electric field is concentrated inside the SIW structure. The SW-SIW, which is evolved from traditional SIW structure, has the characteristic of relatively small electrical size due to large equivalent capacitance and the capability to confine the electrical field density further. The internal rows of blind via holes are connecting the top layer of second substrate to the bottom layer of third substrate. In order to further reduce the electrical size, an air cavity is formed in second substrate around blind via holes as it can increase the equivalent capacitance of SW-SIW resonator. The air cavity has an important impact on the resonant frequency of the sensor, and the electrical size could be reduced by enlarging the air cavity. In this paper, an appropriate air cavity is adopted with comprehensive consideration of detection sensitivity and electrical size. The polydimethylsiloxane (PDMS) microfluidic substrate is embedded in first substrate. When the resonator is excited, the electric field is confined above the surface of blind vias. The electric field varies with the volume fraction of aqueous solution injected into the microfluidic channel, and the resonant frequency and quality factor alter correspondingly. The variations in the resonant frequency and quality factor are applied to retrieve the complex permittivity of liquid samples. The proposed sensor is fabricated and tested, it has a dimension of 0.678λ0 × 0.432λ0 (λ0 is the wavelength in free space at 3.7 GHz), and the peak sensitivity and unloaded quality factor are about 2.5 % and 51156, which are improved by 67 % and 5015 % than traditional SIW sensor, respectively. In particular, the sensitivity of measuring loss tangent of liquid sample is improved by several times to hundreds of times with the loss tangent range from 0.1 to 0.9 than other reported sensors. The measured data has a good agreement with the reference complex permittivity.

Graphene Based Wideband Electromagnetic Absorbing Textiles at Microwave Bands

The design and realization of graphene based wideband electromagnetic (EM) absorbing textiles are becoming of primary interest. Hence, the development of new conductive coatings to be cast onto commercial textiles is crucial. In this article, we propose new graphene based absorbing textiles that conjugate outstanding EM absorbing properties at radiofrequency with low-weight, flexibility, cost-effectiveness, and washability. With this purpose, an innovative production process of polyvinylidene fluoride (PVDF) coatings filled with graphene nanoplatelets (GNPs) is developed for the production of radar-absorbing coated textiles, which are fully characterized in terms of morphological, electrical, and EM absorbing properties. In particular, the complex dielectric permittivity of the coated textiles including different amounts of GNPs is assessed through the measurement of the complex permittivity of a benchmark sample, the consequent estimation of the average GNP size and the prediction by simulations of the effective complex permittivity of graphene based coatings loaded with different GNP amounts. Such predicted data are crucial to design radar absorbing textiles with minimum bandwidths at −10 dB of 5 GHz and reflection coefficients below −5 dB over all the frequency range from 8 up to 18 GHz. These textiles are then produced and characterized in terms of reflection coefficient in free space against a plane wave with normal incidence. The obtained results demonstrate the full satisfaction of the design requirements. In fact, the produced samples show a reflection coefficient with a bandwidth at −10 dB up to 77% of the resonant frequency.

Development of a Measurement System to Characterize Dielectric Materials in Cryogenic Temperature

It is very desirable to measure both the dielectric breakdown voltage and the dielectric losses in insulating materials at cryogenic temperatures, in order to improve the project of superconducting devices. In this work, we present the project of a measuring system that allows measuring the dielectric breakdown voltage, the loss tangent, and the electric permittivity of dielectric materials samples rated to operate at 77.4 K (liquid nitrogen bath), industrial frequency of 50-60Hz, and voltages up to 13.8 kV. Such system uses the same electrodes and chamber for all those kinds of measurements, in compliance with the standards of those tests. Only the external power and measurement circuits must be changed in order to perform the respective characterization. The project of that measurement system has been validated by computational simulation of a virtual prototype, using a commercial finite element method software package.

A Systematic Material Characterization Method via Near-Field Scanning Microwave Microscopy

Accurate measurement of material dielectric property is essential for engineers to synthesize microwave devices. This article proposes a systematic material characterization method via the coaxial resonator (CR)-based near-field scanning microwave microscopy (NFSMM) with an arbitrary tip shape, from the modeling method to the inversion algorithm. The effective interaction region in the CR-based NFSMM is investigated and determined, which contributes most to the contrast capacitance caused by the tip-sample interaction. Then the Huygens’ principle is applied in the forward solver of NFSMM when the samples under test are homogeneous. The relative error of our model is less than 2.1% in numerical validations. Based on the proposed forward solver, a dielectric characterization method via the conjugate gradient (CG) algorithm is proposed and verified with experimental results. The retrieved permittivity of unknown samples matches well with that measured by the transmission line method, and the discrepancy between the two results is less than 3%. The proposed systematic method is promising to provide a new pathway to quantitatively determine the dielectric property of homogeneous samples.

Study of the structural, ferroelectric and dielectric properties of BaTiO3 co-doped with Sn4+ and Cr3+

In the present work, we studied the effect of Sn4+ and Cr3+ doping on the structural, ferroelectric, and dielectric properties of BaSnxCryTi1−(x+y)O3. The materials were prepared by a combination of high-energy mechanical milling and solid-state reactions. The X-Ray Diffraction (XRD) analysis and Rietveld refinements confirmed the presence of a single tetragonal phase for the pure and doped samples. The SEM study revealed that the microstructure is highly susceptible to the addition of both dopants, causing an evident grain refinement. On the other hand, the addition of Sn4+ and Cr3+ had a strong influence on ferroelectric properties, as observed by the pinching of the ferroelectric hysteresis loops. The addition of Sn4+ increases the remnant and maximum polarization, as the Cr3+ doping promoted the contrary effect. Co-doping with Sn4+ and Cr3+ resulted in a maximum energy storage value of 0.2574J/cm3 with a efficiency of up to 65%, overcoming the values of pure BT. The relative permittivity of all doped samples remained in values of ∼1000, just a little below the permittivity of pure BT.

Novel Technique of Gap Waveguide Cavity Resonator Sensor with High Resolution for Liquid Detection

This article proposes a novel microfluidic sensor designed with a highly accurate Q-factor for liquid detection. The proposed sensor is developed and implemented with a gap waveguide cavity resonator (GWCR) approach. The GWCR approach is formed from the two metallic plates denoted as upper and lower plates. These plates are separated by an array of metallic pins attached to the lower plate, leading to high electric field concentration. A microfluidic channel is created at the midpoint of each plate to place the holder of liquid under test (LUT). The GWCR provides a high electric field, which increases Q-factor and is shown to exhibit a significant improvement in sensitivity and linearity. To characterise and evaluate the dielectric properties of the fluid, the LUT is placed inside a hairlike glass, which passes through the microfluidic channels. The LUT perturbs the electric field distribution inside the GWCR, known as the perturbation principle. The relation between the LUT and the electric field changes the electric field behaviours in terms of resonant frequency, Q-factor, and transmission coefficient. The analysis of these changes in the electric field behaviours leads to identifying the dielectric properties of the LUT. The anonymous dielectric characteristics of LUT, permittivity, and loss tangent formulas are derived utilising the polynomial fitting approach. The measurement outcomes reveal that the stated sensor can measure the permittivity and loss tangent for both LUT samples, such as ethanol and methanol, at 6.1 GHz and 23.4°C.

Dielectric properties of hot-pressed Poly(vinylidene fluoride)/Functionalized carbon nanotube composites

This work reports the structural and dielectric properties of poly(vinylidene fluoride) (PVDF) composites with functionalized carbon nanotube (FCNT) prepared by the hot pressing method. XPS, SEM, TEM, and TGA techniques were employed to understand the extent of functionalization of CNT with acid treatment. Permittivity, Electric Modulus, and AC conductivity measurements of hot pressed samples are compared with samples prepared by the solvent casting method. It was found that the PVDF-FCNT composites were formed with more γ phases. Hot pressing the samples increases the overall polar phases, especially the β phase. The permittivity, electric modulus, and AC conductivity studies reveal the dielectric behavior and conductivity changes with hot pressing samples.

Two-channel dual-band microwave EBG sensor for simultaneous dielectric detection of liquids

A compact and dual band Electromagnetic band gap structure (EBG) based on microwave sensor is implemented for multi-sensing and simultaneous dielectric characterization of the liquids. Proposed sensor consist of two different size of EBG patch with stack arrangement are electrically coupled with suspended microstrip transmission line operating at industrial, scientific and medical (ISM) bands 2.45 GHz and 5.80 GHz. A two polypropylene (pp) pipe with dielectric constant 2.2 and inner diameter of 4 mm are inserted in the electric field region of EBG patches to carry the liquid under test. The numerically developed sensor models for both bands are experimentally verified through the fabricated sensor for various binary mixture of water and ethanol. The calculated complex permittivities of different samples are with good agreement to reference one.

Impedance spectroscopy and giant permittivity study of [formula omitted] spinel ferrite as a function of frequency and temperature

Spinel ferrites especially zinc ferrites are of enormous importance in technological applications such as chemical sensors, electrical appliances, microwave industries. Their properties are subject to different studies to investigate the involved mechanisms. The present research work undertakes the study of the conductivity and dielectric permittivity of ZnFe2O4 spinel ferrite as a function of frequency and temperature. Thus, we prepared zinc ferrite spinel by the solid-state reaction route. The structural analysis by X-ray diffraction and scanning electronic microscopy shows that the obtained sample is pure, single-phase composed of prismatic grain of crystallites with a size of 72 nm. The impedance, dielectric permittivity and conductivity of zinc ferrite sample were studied in the frequency range 40 Hz–10 MHz and in the temperature range 300–700 K. Dc conductivity is found thermally activated with an activation energy of 236 meV, indicating an electronic conduction process. The variation of the conductivity with frequency follows power low at low frequency and Drude low at high frequency. Such mechanism change is explained by the increase of free carrier density. Three-relaxation process are identified from impedance spectroscopy analysis. Their associated relaxation times are thermally active and the activation energy of the one associated with grain is close to the one obtained from conductivity, indicating the intra grain conduction dominates transport mechanism. Finally, the compound shows a high dielectric constant in a wide range of frequency, making it suitable for super capacitor application