Change In Permittivity Research Articles

Electromagnetic measurements of composites containing barium strontium titanate or nickel zinc ferrite inclusions from 1 to 4 GHz

Composites with barium strontium titanate (BST) or nickel zinc ferrite (NZF) spherical inclusions mixed in a silicone matrix were manufactured at volume fractions ranging from 5% to 25%. The dielectric and magnetic parameters were measured from 1 to 4 GHz using a coaxial airline. The relative permittivity increased from 2.74 ± 0.01 for the polydimethylsiloxane (PDMS) host material to 7.45 ± 0.33 after combining PDMS with a 25% volume fraction of BST inclusions. The relative permittivities of BST and NZF composites were relatively constant across all measured frequencies. The relative permeability of the composites increased from 1.001 ± 0.001 for PDMS to 1.43 ± 0.04 for a 25% NZF composite at 1 GHz. The relative permeability of the 25% NZF composite decreased from 1.43 ± 0.05 at 1 GHz to 1.17 ± 0.01 at 4 GHz. The NZF samples also exhibited low dielectric and magnetic loss tangents from 0.005 ± 0.01 to 0.091 ± 0.015 and 0.037 ± 0.001 to 0.20 ± 0.038, respectively, for all volume fractions, although the dielectric loss tangent did increase with volume fraction. For BST composites, all volume fraction changes of at least 5% yielded statistically significant changes in permittivity; no changes in BST volume fraction yielded statistically significant changes in permeability. For NZF composites, the change in permittivity was statistically significant when the volume fraction varied by more than 5% and the change in permeability was statistically significant for variations in volume fraction greater than 10%. The DC electrical breakdown strength of NZF composites decreased exponentially with increasing volume fraction of NZF, while BST composites exhibited no statistically significant variation with volume fraction.

A planar microwave resonator with odd resonance for calibration in permanent moisture sensing applications

A cylindrical dual-mode planar microwave ring resonator for a permanent moisture sensor is presented. The ring is design for TMn10 fundamental (odd-mode) resonance, and optimized to sustain stability (suitable for calibration reference against environmental interference) using Ansys high-frequency structure simulator. An even-mode resonance is perturbed by etching a step-impedance stub on the upper 0.5λ ring. The equations for the TMn10 mode resonance and its mode splitting are stated. The equivalent circuits of the ring, odd-, and even-modes are derived. The even-mode is set to capture the response of the permanent moisture withholding hydrophilic polyvinyl alcohol (PVA)–polyaniline (PANI) 0.26 mm-thick films. The in-lab made films are produced by infusing certain concentrations of PANI into pure PVA. On-spot measurements using a vector network analyzer (VNA) and time-based continuous data acquisitions using LabVIEW on NI PXIe–1075 VNA are done to confirm repeatability of the obtained results. A measured permanent moisture response of 180 MHz is confirmed for 50% PANI with a thickness (hfilm) of 0.55 mm. The sources of permanent moisture withholding capability of the films are investigated. Structural observation of the residue films, its permittivity changes, and morphological structural imagery confirmed the sources of permanent response.

Effect of BaTiO3 nanowire on effective permittivity of the PVDF composites

With the increasing application of barium titanate (BaTiO3) in polyvinylidene fluoride (PVDF), the evaluation of its dielectric properties has attracted the attention of many frontier scholars. In this paper, from the theoretical point of view, the effects of the aspect ratio and the concentrations of BaTiO3 nanowires on macroscopic dielectric properties were studied by the finite element method. Depending on the calculation results, some conclusions had been obtained: First, it was found that the effect of higher aspect ratios of nanowires on the effective permittivity of the composites was not significant when the aspect ratio of the nanowire filler exceeded 20. Second, when the permittivity of the BaTiO3 nanowires reaches about 3000, as the permittivity of the filler increases, the rate of change of the effective permittivity of the composite material gradually slows down, which indicates that nanowires with higher permittivity have little influence on the effective permittivity of the composites. Finally, by comparing with permittivity data of BT/PVDF composites in the literature, it was found that the simulation results have good consistency with the experimentally measured values. The above-mentioned results have shown that the composite may exhibit good dielectric properties at a low concentration (<30 vol. %) and low permittivity filler. Moreover, the electrostatic field can roughly represent the electric field of a low-concentration composite under a certain electric field strength.

Design and Analysis of Junctionless Based Symmetric Nanogap-Embedded TFET Biosensor

In the present paper, symmetrical configuration of dual material double gate dielectric modulated junctionless TFET (DM DG JLTFET) for biosensor applications is explored. The JLTFET consists of Si material with an intensely doped n-type substrate. In this work, the JLTFET utilizes the dielectric modulation method which aids the bio-transistor to recognize neutral and charged analytes (biomolecules). A double metal gate structure is designed by employing two dissimilar metal gate electrodes to reduce short channel impact on device characteristics. The proposed device includes a nanogap region (cavity) which is framed for biomolecules to immobilize. Surface potential and their sensitivity are examined for neutral and charged-neutral analytes. The effects of structure parameters such as nanogap region length and fill-in factor have been analyzed through simulation. The paper examines the behavior of DM DG JLTFET for biological molecules sensing via change in relative permittivity and charge density. The proposed device shows noticeable sensitivity results for charged biomolecules (especially for positively charged analytes). The present work has analyzed the different parameters affecting the sensitivity of the biosensor which includes structural geometric variations like change in cavity length, cavity thickness and fill-in factor. The sensitivity of the neutral biomolecules having higher dielectric constant is observed higher; the surface potential sensitivity of the Gelatin (k = 12) is estimated as 3.75 × 10 3 which is 45%, 55%, and 135% higher than the sensitivity of Keratin (k = 7), Bacteriophage T7 (k = 6), and Glucose Oxidase (k = 3), respectively at the cavity length of 7 nm.

Non-invasive determination of blood glucose level using narrowband microwave sensor

The diabetic patients use invasive technique to monitor their Blood Glucose Level (BGL) on a regular basis. This paper mainly presents a system that estimates BGL noninvasively using microwave techniques. A narrowband microstrip antenna resonating at 1.3 GHz is used as a microwave sensor. If human finger containing a specific value of the BGL is placed on a radiating patch of narrowband microstrip patch antenna, microwave sensor structure, then the near field of this radiating patch antenna structure gets interact with human finger and results change in electrical characteristics of the antenna. These electric changes are in relation to blood permittivity changes due to variation in BGL value. The change in electric characteristics of narrow band antenna microwave structure results corresponding frequency shift. The dataset of more than 200 individuals are generated where corresponding frequency shifts for various BGLs are recorded. The prepared dataset provided linear relationship between reference BGL and corresponding frequency shift. Regression analysis for BGL estimation resulted coefficient of determination with value 0.75. The significant improvement in this coefficient of determination is obtained by subband frequency analysis, which resulted in close approximation with expected value. The Surveillance Error Grid (SEG) and Mean Absolute Relative Difference (MARD) analyses are performed on prepared dataset to validate and verify clinical acceptance of microwave based non-invasive BGL estimation system. The developed antenna model has the MARD value of 4.204% and existing split ring resonator non-invasive antenna has 12.5% MARD value for the whole dataset.

Negative permittivity behavior in Ti3AlC2-polyimide composites and the regulation mechanism

With the rapid development of metamaterials, percolating composites with negative dielectric constant have become a research hotspot in recent years. In this work, Ti3AlC2-polyimide percolating composites were prepared by mechanical mixing and pressure forming, and their microstructure and dielectric properties were investigated in detail. By controlling the Ti3AlC2 content, an electrical percolation phenomenon appears with the formation of Ti3AlC2 conductive network. The conductive mechanism changed from hoping conduction to metal-like conduction. Above the percolation threshold (68%–72%), real permittivity changes from positive to negative and mainly due to the damped motion of the free electrons. The Drude model analysis showed that the negative permittivity resulted from the plasma-like oscillation of free electrons. The equivalent circuit analysis indicated that the generation of negative permittivity was closely related to the appearance of inductance. This work provided a simple and effective strategy for regulating negative permittivity and promoted its application.

Enhanced magnetoelectric response of cofired ceramic layered composites by adjusting the grain boundary conductivity of the magnetostrictive component

Magnetoelectric composites provide large enough room-temperature functional responses to enable a range of novel technologies, like uncooled high-sensitivity magnetic sensors. Magnetoelectricity in these composites appears as a product property of the piezoresponses of two elastically coupled ferroic phases. Coefficients then depend not only on the magnetostriction and piezoelectricity of the components, but also on interface quality. Different composite approaches are under development, among which cofired ceramic layered structures of ferrimagnetic spinel and ferroelectric perovskite oxides stand out because direct bonding between phases is attained, which facilitates miniaturization. An aspect rarely investigated is the role of the electrical characteristics of the magnetostrictive material beyond their effect on ferroelectric poling. We report here a three-fold enhancement of magnetoelectric coefficients by the only adjustment of the grain boundary conductivity of the spinel oxide. Significant differences in poling level are ruled out, and the effect is related with changes in the composite effective permittivity.

Continuously tunable substrate integrated coaxial line bandpass filters with liquid crystal technology

AbstractThis letter introduces two continuously tunable bandpass filters with substrate integrated coaxial line (SICL) and liquid crystal (LC) technologies. The tunability of the filters is a kind of electric tuning, achieved by the permittivity changing of the LC material filled in the SICL cavities. The SICL resonator and the electric and magnetic coupling between the resonators are investigated. Then, fourth‐order direct‐coupled and cross‐coupled tunable filters (Filter I and II) with center frequency of 6.5 GHz are designed, fabricated, and measured. The experimental results show that the continuous tuning ranges are 220 and 280 MHz for Filter I and II, respectively. Furthermore, the insertion losses of the Filter I and II are 3.93–4.78 dB and 3.65–4.3 dB over the whole tuning range.

Age-dependence of electromagnetic power and heat deposition in near-surface tissues in emerging 5G bands

With the development of 5th generation (5G) mobile networks people of different ages will be exposed in the upper part of the microwave spectrum. From the perspective of non-ionizing radiation dosimetry, an accurate analysis of age-dependent electromagnetic power deposition and resulting heating is required. In this study, we evaluate the effect of age on exposure at 26 GHz and 60 GHz. A near-surface tissue model illuminated by a plane wave is used to asses the exposure considering both frequency-independent and frequency-dependent limits. The age-related variation of the skin thickness and tissue electromagnetic properties has been considered. Moreover, the blood flow decrease rate has been taken into account to assess the age-dependent heating. Our results demonstrate that the overall variations of the power density, specific absorption rate (SAR) and heating in the near-surface tissues are limited to about 10–15%. These variations are mainly due to the tissue permittivity and blood flow change with age. In contrast to the transmitted power density that increases with age, the peak SAR decreases at both frequencies. The peak steady-state heating increases from 5 to 70 years old by roughly 11% at 26 GHz and 13% at 60 GHz.

Investigating the influence of the grain size and distribution on the macroscopic dielectric properties of Antarctic firn

This study is based on the analysis of detailed measurements of firn dielectric properties performed in Antarctica through coring down to 106 m. Dielectric measurements in the frequency band (0.4–2.5 GHz) have been carried out using an open−resonator probe. Density was also measured for the same samples. The experimental results confirmed the well−known dependence of the real part of permittivity ε′ on depth and density, showing an increase of ε′ with density. The imaginary part also increases with depth with a rather complex dependence on frequency, probably due to the presence of salts or impurities.The analysis of the experimental data was performed by implementing 3D and 2D full wave numerical models, to simulate a mixture of firn crystals at prescribed densities, corresponding to the measured densities on the ice cores. The numerical analysis of the ensemble of inclusions showed that the usual symmetric formulae used for modeling ice dielectric properties agree with the average results of the simulation, but they are not able to explain the spreading of the measured data at given density.A dielectric model was then developed allowing for quantification of the dependence of dielectric properties on density, by combining two models: one consisting in firn crystals into an air host, the other assuming the presence of air inclusions into a homogeneous firn host. The weighted equation is based on the volume fraction. A simple geometric shape (ellipsoidal) is assumed for both ice crystals and air inclusions. This kind of shape is reasonable for the purpose of the dielectric study. The result is a mixture, smoothly changing from firn particles in air (low density) to air bubbles in an ice matrix (high density).A statistical analysis has been accomplished to investigate the dependence of the dielectric properties on the geometrical arrangement of the inclusions. For that purpose, a large number of simulations with different arrangements (micro−states) giving rise to the same average density (macro−states) has been carried out. The permittivity change due to micro−state variability appears to be at least two−three times the model variation due to density alone, and comparable to the measured variability at a given depth, suggesting that firn structure has a significant effect on the dielectric properties.

Permittivity of (40 nm and 80 nm) alumina nanofluids in ethylene glycol at different temperatures

This article studies the effective permittivity of alumina nanofluids (aluminium oxide) in ethylene glycol. Two nanoparticle sizes (40 nm and 80 nm) were considered and the measurements were carried out at various concentrations (up to 2% in volume) and at six different temperatures (from 298.15 K to 348.15 K). An empirical equation is proposed that allows to obtain the permittivity value at any concentration or temperature in the studied ranges. The influence of the volume fraction, nanoparticle size and the temperature on relative permittivity is shown. When compared to the previous published values for alumina (40 nm) in water, current results show the influence of the base fluid. The enhancement of permittivity was calculated, and its behaviour was analysed. Smaller sized particles have the highest values of permittivity and enhancement. Theoretical models in the study of permittivity are applied. The poor predictions of classical models are attributed to the positive behaviour of the permittivity change on mixing for these nanofluids. The contributions to permittivity from ethylene glycol and nanoparticles are separated in two distinct terms in the variable index equation. The permittivity change on mixing calculated from this equation points out that the nanoparticles are the main responsible for the unusual permittivity increment in these colloids.

Electrical characterization of phytoplankton suspensions using impedance spectroscopy

This study used impedance spectroscopy measurements to extract the electrical properties of phytoplankton cells in suspension. Experimental measurements were acquired, and the single-shell model was applied to extract the specific membrane capacitance, cytoplasm permittivity, and conductivity of assumingly spherical cells in suspension utilizing Maxwell’s mixture theory of a controlled volume fraction of cells. The impedance of suspensions of algae was measured at different frequencies ranging from 3 kHz to 10 MHz and impedance values were compared to investigate differences between two types of cells by characterizing their change in cytoplasm permittivity and specific membrane capacitance. Differentiation between healthy control and nitrogen-depleted cultured algae was attempted. The extracted specific membrane capacitances of Chlamydomonas and Selenastrum were 15.5 ± 3.6 and 40.6 ± 12.6 mF m− 2 respectively. Successful differentiation based on the specific membrane capacitance of different algae species was achieved. However, no significant difference was noticed between nitrogen-abundant and nitrogen-depleted cultures.

Numerical Simulation of Subsurface Penetrating Radar in Isidis Planitia on Mars for China’s First Mission to Mars

The water ice exploration mission is an important scientific target of China’s first Mission to Mars. The high frequency full polarimetric subsurface penetrating radar (SPR) system onboard the landing rover can carry out high-resolution imaging of the near-surface area of Mars, which is an important tool for detecting the presence of shallow water ice and soil structure. At present, most of the radar detection simulations are based on low-frequency antennas to analyze the geological structure of Mars down to several kilometers, with low resolution, which is difficult to detect the subsurface structure in the near-surface accurately. Considering topographic relief, interface roughness, subsurface rock, water ice, and permittivity changes at different layers, a three-dimensional near-surface model in the Isidis Planitia on Mars is established. The interpretation of the forward simulation results is of reference value for future Mars exploration missions.

Dielectric and optical properties of alumina and silica nanoparticles dispersed poly(methyl methacrylate) matrix-based nanocomposites for advanced polymer technologies

Dielectric behaviour of the polymer nanocomposite (PNC) films comprise alumina (Al2O3) and silica (SiO2) nanoparticles (1, 3, and 5 wt%) dispersed in poly(methyl methacrylate) (PMMA) matrix was investigated in the frequency span of 20 Hz to 1 MHz at 30 °C and also with temperature variation (30–60 °C) for the 3 wt% nanofillers containing PNC films. Some changes in the dielectric permittivity and electrical conductivity were observed with the increase of nanofiller content, frequency variation, and rise in temperature of these films. Electric modulus spectra confirmed a broad relaxation peak at the lower frequencies for the Al2O3 loaded PNC films which attribute to the PMMA bulky side ester groups rotation, whereas this relaxation was not observed for the SiO2 filled PNC films in the same experimental frequency range. The UV–Vis absorbance, transmittance, and reflectance spectra of these PNCs showed a gradual variation with the increase of Al2O3 and SiO2 contents in the films. The energy bandgap decreases, whereas the Urbach energy, refractive indices, and optical conductivity enhance with the increase of filler concentration in these composites. The X-ray diffraction (XRD) study revealed the predominantly amorphous nature of these materials and the homogeneity of the hybrid was evidenced by their SEM images. The energy dispersive X-Ray (EDX) mapping revealed the purity of these hybrid composites. The results demonstrated that these PNC films are low permittivity polymeric nanodielectrics (PNDs), and their controllable optical parameters with the filler contents could be technologically important in the design and development of some advanced microelectronic and optoelectronic devices.

Study of the Complex Permittivity of a Polyurethane Matrix Modified by Nanoparticles

This study presents the influence of various types of nanoparticle (NP) fillers incorporated into a polyurethane (PU) (VUKOL 022) matrix and its subsequent changes in complex permittivity. Two types of surface modification of SiO2 fillers were investigated. The frequency dependence of the real and imaginary parts of complex permittivity was measured within the frequency range of 1 mHz to 1 MHz using the capacitance method. The 1 wt.% NPs in PU caused an increase (MgO, TiO2, n-SiO2, and f-SiO2) or a decrease (d-SiO2) in the real permittivity. The $\alpha $ -relaxation and intermediate dipolar effect were observed at the temperature dependence of the imaginary permittivity. The change in permittivity by various surface modifications of SiO2 and other nanofillers was discussed based on the multi-core model. Moreover, the NPs caused a shift in the local maximum of the permittivity, which was a result of the interfacial polarisation and a charge multiplication of the $\alpha $ -relaxation process.

О распространении видеоимпульсных сигналов в диссипативных средах

The results of the numerical solution of the problem of propagation of an electromagnetic video pulse signal of nanosecond duration in a dissipative medium are presented for use in the deep georadar data interpretation. Based on the developed scheme for integrating Maxwell's equations, the results of numerical modeling of the propagation of electromagnetic pulses of various shapes without approximations, usually used in the traditional solution of GPR problems, including the separation of temporal and spatial variables of the electromagnetic field and neglect of the rapid field change in comparison with the processes occurring in the medium, are obtained. The influence of the pulse shape on the shape of the electromagnetic echo signal is considered for various models of the medium close to real conditions, including those with a gradient change in electrical conductivity and permittivity. The influence of the distribution of electrical conductivity of the medium is studied.

A Novel Sensor-Integrated Aperture Coupled Microwave Patch Resonator for Humidity Detection

Wireless sensor elements integrated with miniaturized antennas are useful in various applications such as wearable chemical and environmental sensors and Internet-of-Things (IoT) sensor nodes. A major problem in antenna operation is detuning of the antenna bandwidth due to loading by the sensor element. In this article, we report on the integration of an interdigitated capacitor (IDC), acting as a sensor, into an aperture coupled patch (ACP) antenna, such that weak coupling is established between the IDC and the rectangular patch resonator. Because of low mutual coupling, during the sensing process the antenna is not detuned out of its operational bandwidth and its performance is not compromised by the presence of the sensor and vice versa. A sensing material (barium titanate film) is deposited on the IDC located at the edge of the microstrip line used to slot-feed the ACP antenna. A change in the material permittivity is transduced into a variation of resonant frequency of the antenna. We describe the design and fabrication of the IDC sensor-integrated ACP antenna and demonstrate the measured sensing performance at different temperatures and relative humidity concentrations.

Design of a microstrip patch sensor antenna for the measurement of permittivity

This paper presents a new high gain Microstrip Patch Sensor Antenna for the measurement of permittivity. The proposed antenna uses a copper (annealed) patch imposed over the FR-4 substrate. Here several thin rectangular slots are loaded along the radiation side and two circular slots in the mid of the patch. The constructed design offers Return loss = −29.13 dB, Gain = 6.26 dBi at resonant frequency 2.33 GHz. This proposed antenna is aimed to increase the sensitivity by measuring the permittivity of material and is also employed for wireless application. The design also shows a non-linear frequency shift with the change of relative permittivity of the Material Under Test (MUT). Computer simulation technology software (CST) has been used to execute this design, simulation, and perform analysis. The proposed antenna can be employed for measuring humidity, Salinity determination of seawater, temperature, and other characteristics simultaneously. This antenna is expected for measuring permittivity for both solid and liquid materials.

Bending control and stability of functionally graded dielectric elastomers

A rectangular plate of dielectric elastomer exhibiting gradients of material properties through its thickness will deform inhomogeneously when a potential difference is applied to compliant electrodes on its major surfaces, because each plane parallel to the major surfaces will expand or contract to a different extent. Here we study the voltage-induced bending response of a functionally graded dielectric plate on the basis of the nonlinear theory of electroelasticity, when both the elastic shear modulus and the electric permittivity change with the thickness coordinate. The theory is illustrated for a neo-Hookean electroelastic energy function with the shear modulus and permittivity varying linearly across the thickness. In general the bending angle increases with the potential difference, and this enables the material inhomogeneity to be tuned to control the bending shape. We derive the Hessian criterion that ensures stability of the bent configurations in respect of a general form of electroelastic constitutive law specialized for the considered geometry. This requires that the Hessian remains positive. For the considered model we show that the bent configuration is stable until the voltage reaches the value for which the cross section of the bent configuration forms a complete circle.

Near-field sensor array with 65-GHz CMOS oscillators for rapid detection of viable Escherichia coli

In this study, the growth of Escherichia coli was monitored using a complementary metal-oxide-semiconductor (CMOS) near-field sensor array. Each of the 1488 integrated elements, arranged in a 3 mm square, has a resonator that oscillates at 65 GHz. The effective capacitance of the resonator is altered by changes in the dielectric properties of the sensor surface, which shifts the resonance frequency. Growth curves of E. coli at different initial concentrations (OD600 = 0.01, 0.03, and 0.05) were monitored. A suspension with initial turbidity of OD600 = 0.05 was cultured in a medium, and the sensor successfully distinguished between viable E. coli and heat-treated dead E. coli in 20 min. Moreover, the apparent suppression of growth was observed in the presence of 500 μg/mL streptomycin. As the sensor is composed of arrayed elements, and the area of sensitivity distribution of the element is larger than the size of one bacteria, the variation in the output value of each element may reflect the number and movement of bacteria. This study revealed that the presence of viable E. coli could be rapidly confirmed by using the change in permittivity caused by the displacement of media by E. coli near the sensor surface.