Changes In Dielectric Properties Research Articles

Analytical Modeling of Participation Reduction in Superconducting Coplanar Resonator and Qubit Designs Through Substrate Trenching

A strategy aimed at decreasing dielectric loss in coplanar waveguides (CPW) and qubits involves the creation of trenches in the underlying substrate within the gaps of the overlying metallization. Participation of contamination layers residing on surfaces and interfaces in these designs can be reduced due to the change in the effective dielectric properties between the groundplane and conductor metallization. Although finite element method approaches have been previously applied to quantify this decrease, an analytical method is presented that can uniquely address geometries possessing small to intermediate substrate trench depths. Conformal mapping techniques produce transformed CPW and qubit geometries without substrate trenching but a non-uniform contamination layer thickness. By parametrizing this variation, one can calculate surface participation through the use of a two-dimensional, analytical approximation that properly captures singularities in the electric field intensity near the metallization corners and edges. Examples demonstrate two regimes with respect to substrate trench depth that capture an initial increase in substrate-to-air surface participation due to the trench sidewalls and an overall decrease in surface participation due to the reduction in the effective dielectric constant, and are compared to experimental measurements to extract loss tangents on this surface.

Dielectric properties of PVA cryogels prepared by freeze-thaw cycling.

Solutions of polyvinyl alcohol (PVA) in water can form gels upon repeated freezing and thawing. These PVA cryogels have applications as biomaterials, including artificial tissue and drug delivery systems. We have studied the dielectric properties of PVA cryogels within the freeze-thaw cycles as a function of both frequency and temperature in order to understand the physical changes that take place during the thermal cycling process. Our results indicate that most of the changes in dielectric properties occur during the cooling phase of the first cycle and suggest that the solution must be cooled below a critical temperature of about 263 K for the formation of a gel that persists after thawing. The material's dielectric spectrum shows the presence of several relaxation processes. We identify one of these with the dielectric relaxation of ice and two others with motions of the PVA polymer chains. The temperature dependence of the polymeric relaxation times suggests that they are both thermally activated, with an activation energy of roughly 300 kJ/mol.

Growth inhibition of the toxic cyanobacterium Cylindrospermopsis raciborskii by extremely low-frequency electromagnetic fields

This study investigates the effects of extremely low-frequency electromagnetic fields (ELF-EMFs) on the growth and antioxidant defence enzymes of the toxic cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju. To determine resonance frequency of growth inhibition of C. raciborskii, cells were subjected to ELF square amplitude modulated waves (QAMW) with a range of frequencies (0.1, 0.3, 0.5, 0.7, 0.9 Hz) at single intensity of 100 V m–1 for 30 minutes. The results revealed that the highest growth inhibition of Cylindrospermopsis occurred upon exposure to 0.7 Hz QAMW for 30 min. ELF-EMF-exposed cultures exhibited a marked decrease in cell number, chlorophyll-a content and activity of antioxidant enzymes compared to control cultures, and this effect increased with the prolongation of exposure time. Moreover, ELF-EMF induced morphological changes in Cylindrospermopsis cells upon exposure to 0.7 Hz QAMW for 120 min, including shrinking and disintegration of cytoplasmic contents, and thickening of the cell wall. Changes in dielectric properties, as a measure of interaction of cellular constituents (e.g., plasma membrane, cell wall and cytoplasm), with electromagnetic fields were also observed for treated cells. Our results provide a new possibility for using ELF-EMFs to eliminate toxic cyanobacteria from drinking and recreational water sources.

Changes in Membrane Dielectric Properties of Porcine Kidney Cells Provide Insight into the Antiviral Activity of Glycine.

The ability to monitor the status and progression of viral infections is important for development and screening of new antiviral drugs. Previous research illustrated that the osmolyte glycine (Gly) reduced porcine parvovirus (PPV) infection in porcine kidney (PK-13) cells by stabilizing the capsid protein and preventing virus capsid assembly into viable virus particles. Dielectrophoresis (DEP) was examined herein as a noninvasive, electric field- and frequency-dependent tool for real-time monitoring of PK-13 cell responses to obtain information about membrane barrier functionality and polarization. DEP responses of PK-13 cells were compared to those of PPV-infected cells in the absence and presence of the osmolyte glycine. With infection progression, PK-13 DEP spectra shifted toward lower frequencies, reducing crossover frequencies (fCO). The spherical single-shell model was used to extract PK-13 cell dielectric properties. Upon PPV infection, specific membrane capacitance increased over the time progression of virus attachment, penetration, and capsid protein production and assembly. Following glycine treatment, the DEP spectra displayed attenuated fCO and specific membrane capacitance values shifted back toward uninfected PK-13 cell values. These results suggest that DEP can be used to noninvasively monitor the viral infection cycle and screen antiviral compounds. DEP can augment traditional tools by elucidating membrane polarization changes related to drug mechanisms that interrupt the virus infection cycle.

Changes in Dielectric and Mechanical Properties of Spheroplastic Containing Metallized Glass Microspheres under Compressive Deformation

The article presents experimental results of changes in the dielectric and mechanical characteristics of spheroplastics based on an organosilicon elastomer and metallized glass microspheres caused by static and shock compression. Two regions of the frequency dispersion of the dielectric constant are established that are associated with the metal coating of microspheres. It was found that both the low- and high-frequency dispersions of the complex dielectric constant decrease sharply at a relative compressive strain of no less than 70%. Possible causes of the detected change in the complex permittivity are discussed.

Plasmonic biosensor based on excellently absorbable adjustable plasmon-induced transparency in black phosphorus and graphene metamaterials

Both black phosphorus (BP) and graphene metamaterials support surface plasmon resonance that is very sensitive to the local change of dielectric properties in the system. We design a novel BP ribbons and graphene sheet hybrid structures based on tunable mid-infrared plasmon-induced transparency. The destructive interference of two excited state modes in the structure leads to a pronounced induced transparent window, and the excellent absorption of the two channels is obtained. The transmission characteristics of the hybrid structures are theoretical calculation, and the results are in good agreement with the numerical simulation curve. The dynamic adjustment function can be realized by adjusting the carrier density of BP and the Fermi level of graphene, and the excellent absorption performance not affected within the adjustment range. Moreover, we found that the optical phase is rapid flips at the plasmon resonance position. Therefore, a sensing medium layer is added on top of the structure to implement a high-sensitivity plasmonic biosensor. This work may provide potential applications to plasmonic devices based on two-dimensional metamaterial.

Ultrafast modulation of the spectral filtering properties of a THz metasurface.

We demonstrate ultrafast tuning of a plasmonic spectral filter at terahertz (THz) frequencies. The device is made of periodically spaced gold crosses deposited on the surface of an undoped silicon wafer in which transient free carriers can be optically injected with a femtosecond resonant pulse. We demonstrate the concept by measuring the transmission spectrum of a notch filter using time-domain THz spectroscopy. Proper synchronization of the THz probe and visible excitation pulses leads to an enhanced transmission at the resonance by more than two orders of magnitude. Finite-difference time-domain simulations, which are in agreement with the experimental results, show that the underlying mechanisms responsible for the resonance blueshift and linewidth broadening can be attributed to the photoinduced change in dielectric properties of the substrate. This is supported by the numerically simulated field distribution and reflection/transmission coefficients. The device can be used in future pulse shaping and ultrafast switching experiments.

Significantly improved non-ohmic and giant dielectric response in CaCu3Ti4O12 ceramics by incorporating Portland cement

The giant dielectric and nonlinear current–voltage properties of CaCu3Ti4O12 (CCTO) incorporating Portland cement (PC) were investigated. Analysis revealed that the microstructure of the CCTO/PC ceramics was highly dense. Using the microstructure analysis and theoretical calculation, the elements in PC (i.e., Al, Si, Fe, K, Cr, and Mg) can substitute into the CCTO structure, giving rise to enhanced electrical properties of the grains and grain boundaries. As a result, the giant dielectric and nonlinear current–voltage properties of CCTO/PC were significantly improved. The low–frequency loss tangent of CCTO/PC was greatly reduced, by a factor of 10, while the dielectric permittivity of the ceramics was still large (∼104) over a frequency range of 102–106 Hz. Interestingly, the nonlinear coefficient (α) and electric field breakdown (Eb) of the CCTO/PC ceramics were greatly enhanced by factors of 2 and 30, respectively. Impedance spectroscopy analysis revealed large increases in α and Eb, as well as a decrease in the loss tangent due to a significant increase in the grain boundary resistance of CCTO/PC ceramics. Changes in giant dielectric and nonlinear electrical properties can be well described by the internal barrier layer capacitor model based on space charge polarization at the internal interfaces.

Changes in mechanical and dielectric properties of silicone rubber induced by severe aging

Sheets of silicone rubber (SiR) were aged under various aging conditions to examine its effects on the mechanical and dielectric properties of SiR. Mainly by analyzing the results obtained by mid-infrared absorption spectroscopy, it has become clear that cross-linked structures with siloxane bonds are formed under all the conditions. This makes SiR hard and then brittle, but it also makes better the dielectric properties apparently. An early stage of degradation in SiR can be detected by EAB and complex electric modulus, which is defined as the reciprocal of complex permittivity. Therefore, EAB and complex electric modulus are useful to monitor the aging status of SiR.

Broadband Dielectric Properties of Ex Vivo Bovine Liver Tissue Characterized at Ablative Temperatures

To investigate the thermal and frequency dependence of dielectric properties of ex vivo liver tissue - relative permittivity and effective conductivity - over the frequency range 500 MHz to 6GHz and temperatures ranging from 20 to 130°C. We measured the dielectric properties of fresh ex vivo bovine liver tissue using the open-ended coaxial probe method (n = 15 samples). Numerical optimization techniques were utilized to obtain parametric models for characterizing changes in broadband dielectric properties as a function of temperature and thermal isoeffective dose. The effect of heating tissue at rates over the range 6.4-16.9°C/min was studied. The measured dielectric properties were used in simulations of microwave ablation to assess changes in simulated antenna return loss compared to experimental measurements. Across all frequencies, both relative permittivity and effective conductivity dropped sharply over the temperature range 89 - 107°C. Below 91°C, the slope of the effective conductivity changes from positive values at lower frequencies (0.5-1.64GHz) to negative values at higher frequencies (1.64-6GHz). The maximum achieved correlation values between transient reflection coefficients from measurements and simulations ranged between 0.83 - 0.89 and 0.68 - 0.91, respectively, when using temperature-dependent and thermal-dose dependent dielectric property parameterizations. We have presented experimental measurements and parametric models for characterizing changes in dielectric properties of bovine liver tissue at ablative temperatures. The presented dielectric property models will contribute to the development of ablation systems operating at frequencies other than 2.45GHz, as well as broadband techniques for monitoring growth of microwave ablation zones.

A study on the effect of PVDF on the structural and transport properties of polyaniline

The polymer composite of electrically conducting polyaniline with polyvinylidene fluoride is prepared to study the electrical conductivity and structural modifications. The electrical conductivity studies were made by varying frequency from 100 Hz to 5 MHz at room temperature. The AC conductivity remained almost constant at lower frequencies and for higher frequencies the conductivity increased. The PAni-PVDF composite exhibited better conductivity in comparison to the pure samples. The changes in dielectric properties against frequency variations were studied and exponential reduction in dielectric loss at very low frequencies was observed. The structural and morphological studies were carried out using XRD, FTIR, and SEM.

Multiresponsive Spin Crossover Driven by Rotation of Tetraphenylborate Anion in an Iron(III) Complex

Dynamic molecular materials, which involve mechanical motions in crystals, usually exhibit tunable properties related to conformational polymorphs. Herein, we describe a solvent-free molecular crys...

The effect of UV irradiation on the dielectric properties of bionanocomposites with fillers of biological origin and metal nanoparticles

In this paper, information is given about the investigation of the dielectric properties of bionanocomposites modified with fish bones (FBs) and scales and metal nanoparticles (Al, Fe) with 50–80 nm dimension before and after ultraviolet (UV) irradiation, depending on the temperature, the irradiation time and the volume content of fillers. The investigations of dielectric permittivity and dielectric loss were carried out in the temperature range 300–390 K, the time of irradiation with UV rays were 50, 100, 70 and 150 h, and the filler contents were 3, 5, 7, 10, 15 vol.% and nanoparticles 1 vol.% Al (Fe). It was found that the dielectric constant of UV-irradiated biocomposites with FB additives increases and the dielectric loss decreases. An increase in dielectric constant is also observed with an increase in the volume content of a biological origin filler. Note that the effect of UV irradiation causes the appearance of a new region of dielectric loss in the temperature-dependent tan[Formula: see text] of the polyethylene. However, in modified samples after irradiation, under the same conditions, the change in dielectric properties is much less pronounced than in the initial ones, i.e. the dielectric constant increases monotonically, and the value of tan[Formula: see text] in the maximum of the new loss region is much smaller. Moreover, the effect of the additive is manifested in slowing down the process of LDPE oxidation in the irradiation zone, since the main losses of the polyethylene are primarily caused by the relaxation of the carbonyl groups. Thus, the observed dependences of [Formula: see text] and tan[Formula: see text] on the time of exposure to UV rays are explained by a change in the physical structure of the polymer matrix and the boundary layer of the components composition under the action of charges formed during irradiation.

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr0.7Ti0.3)O3 to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.

Root-induced changes in soil thermal and dielectric properties should not be ignored

There is a lack of quantitative understandings on root-mediated changes of soil physical properties. Here we investigated the influences of maize roots on soil heat capacity (C), thermal conductivity (λ) and dielectric constant (ε) of the root zone. Root-zone soil cores were collected at different depths and horizontal positions from the eighth leaf to milk stage of maize, and C, λ and ε of the samples were measured with the thermo-TDR technique. Improved C, λ and ε models that included the influences of roots were developed and validated. The patterns and magnitudes of root effects on C, λ and ε generally followed the configurations of root distribution. On average, the presence of roots caused increases in soil C, λ and ε by 8.8%, 7.1% and 13.6%, respectively. For the root-zone soils, root influences on thermal properties and dielectric constant were significant and could be described quantitatively by using the proposed models.

Compatibility of Printed Photopolymers With Nine-Month Immersion in Common High Voltage Insulation Oils

To enable the use of additively manufactured polymer materials as structural and insulating components within high-voltage pulsed power systems, a better understanding of material compatibility with common pulser material environments is required. This work examines the effect of long-duration contact of printed polymeric components with three high-voltage insulating oils (Shell Diala S2 ZX-A, Luminol TRi, and Royco 602) at room temperature (~25 °C). Test pieces printed using stereolithography (SLA) were evaluated for changes in dielectric strength, mechanical properties, and composition after submersion in insulating oil for a nine-month duration. Gas chromatography–mass spectrometry (GC–MS) was used for compositional analysis on neat and polymer-exposed oils to identify compositional changes that occurred in the oil over the course of the exposure period.

Study on the Change of Dielectric Properties and Chemical-Mechanism during Coal Low-Temperature Oxidation

The study aims to investigate the variation of the coal dielectric properties during coal low-temperature oxidation and the effect of oxidation product on the coal dielectric properties. Four different types of coal were prepared under low-temperature oxidation condition, and the coal dielectric properties were measured with an impedance analyzer at frequencies ranging between 20 Hz and 30 MHz. The oxygen-containing functional groups in oxidized coal samples were semi-quantitatively evaluated using Fourier transform infrared spectroscopy. Low-temperature oxidation stage of coal spontaneous combustion could be predicted according to the change of coal dielectric properties in the process of temperature rise. It was found that the dielectric constant of coal with high water content decreased exponentially with temperature. For coal sample with low water content, the dielectric properties changed piecewise linearly with temperature. Coal dehydration was considered to be the reason for the decrease of the dielectric constant from 30 °C to 120 °C. The increase of the relative content of oxygen-containing functional groups, especially carbonyl compounds, could be the reason for the rise of the coal dielectric constant from T2 to T3.

Separation of Phases and Charge States in Relaxor Ferroelectric PbCo1/3Nb2/3O3

The permittivity, conductivity, electric polarization, and features of high-resolution X-ray diffraction scattering of a relaxor ferroelectric PbCo1/3Nb2/3O3 have been investigated in the temperature range 5–350 K. Continuous correlated temperature changes in dielectric properties and electric polarization have been revealed, which were not typical of relaxor ferroelectrics. These changes can be attributed to local polar domains, which were induced in the original crystal matrix. In such domains, the charges (valences) of Co and Nb ions were continuously changed.

Simulation of nanodielectrics: nanoparticle and interphase effects on electric field distributions

Nanodielectrics have been regarded as a class of material system that can provide significantly improved chemical, mechanical and dielectric properties over conventional microcomposites. This is due to the presence of a high volume fraction of the interphase between nanoparticles and polymers. However, precise effects of nanodielectrics are not well understood, leading to difficulties in interpreting the dielectric behaviours of nanodielectrics. In the current work, effects of nanoparticle distributions, interparticle distances, nanoparticle sizes, interphase permittivities and interphase thicknesses on the possible electric field variations within a nanodielectric model have been simulated using Finite Element Method Magnetics (FEMM) 4.2. The results demonstrate that different nanoparticle and interphase configurations lead to different effects on the electric field intensity within the nanodielectric model. Mechanisms leading to changes in dielectric properties based on the observed electric field variations are discussed.

Degradation of Mechanical and Dielectric Properties of Flame‐Retardant Ethylene Propylene Rubber by Thermal Aging

Thermal degradation was performed at 175, 200, and 250 °C from 100 to 2000 h on flame‐retardant ethylene propylene rubber (FR‐EPR) with the same compositions as those used in the insulation of a safety‐related cable in nuclear power plants. For these samples, indenter modulus (IM), elongation at break, tensile strength, and complex permittivity were measured to clarify mechanical and dielectric properties. Fourier transform infrared absorption and differential scanning calorimetric spectra were also measured to determine structural changes. As a result, it was found that FR‐EPR becomes hard by oxidation and crosslinking, and that it becomes brittle as the degradation becomes more severe. In addition, such changes in mechanical properties by the aging occur much earlier than the changes in dielectric properties. Regarding this, IM is a good indicator to examine the degradation degree of FR‐EPR. © 2020 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.