Large Permittivity Values Research Articles

Lattice Resonances in Transdimensional WS2 Nanoantenna Arrays

Mie resonances in high-refractive-index nanoparticles have been known for a long time but only recently have they became actively explored for control of light in nanostructures, ultra-thin optical components, and metasurfaces. Silicon nanoparticles have been widely studied mainly because of well-established fabrication technology, and other high-index materials remain overlooked. Transition metal dichalcogenides, such as tungsten or molybdenum disulfides and diselenides, are known as van der Waals materials because of the type of force holding material layers together. Transition metal dichalcogenides possess large permittivity values in visible and infrared spectral ranges and, being patterned, can support well-defined Mie resonances. In this Communication, we show that a periodic array of tungsten disulfide (WS2) nanoantennae can be considered to be transdimensional lattice and supports different multipole resonances, which can be controlled by the lattice period. We show that lattice resonances are excited in the proximity to Rayleigh anomaly and have different spectral changes in response to variations of one or another orthogonal period. WS2 nanoantennae, their clusters, oligomers, and periodic array have the potential to be used in future nanophotonic devices with efficient light control at the nanoscale.

Microwave measurement of giant unilamellar vesicles in aqueous solution

A microwave technique is demonstrated to measure floating giant unilamellar vesicle (GUV) membranes in a 25 μm wide and 18.8 μm high microfluidic channel. The measurement is conducted at 2.7 and 7.9 GHz, at which a split-ring resonator (SRR) operates at odd modes. A 500 nm wide and 100 μm long SRR split gap is used to scan GUVs that are slightly larger than 25 μm in diameter. The smaller fluidic channel induces flattened GUV membrane sections, which make close contact with the SRR gap surface. The used GUVs are synthesized with POPC (16:0–18:1 PC 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine), SM (16:0 Egg Sphingomyelin) and cholesterol at different molecular compositions. It is shown that SM and POPC bilayers have different dielectric permittivity values, which also change with measurement frequencies. The obtained membrane permittivity values, e.g. 73.64-j6.13 for POPC at 2.7 GHz, are more than 10 times larger than previously reported results. The discrepancy is likely due to the measurement of dielectric polarization parallel with, other than perpendicular to, the membrane surface. POPC and SM-rich GUV surface sections are also clearly identified. Further work is needed to verify the obtained large permittivity values and enable accurate analysis of membrane composition.

Nonlinear effects on electrophoresis of a charged dielectric nanoparticle in a charged hydrogel medium

The impact of the solid polarization of a charged dielectric particle in gel electrophoresis is studied without imposing a weak-field or a thin Debye length assumption. The electric polarization of a dielectric particle due to an external electric field creates a non-uniform surface charge density, which in turn creates a non-uniform Debye layer at the solid-gel interface. The solid polarization of the particle, the polarization of the double layer, and the electro-osmosis of mobile ions within the hydrogel medium create a nonlinear effect on the electrophoresis. We have incorporated those nonlinear effects by considering the electrokinetics governed by the Stokes-Brinkman-Nernst-Planck-Poisson equations. We have computed the governing nonlinear coupled set of equations numerically by adopting a finite volume based iterative algorithm. Our numerical method is tested for accuracy by comparing with several existing results on free-solution electrophoresis as well as results based on the Debye-Hückel approximation. Our computed result shows that the electrophoretic velocity decreases with the rise of the particle dielectric permittivity constant and attains a saturation limit at large values of permittivity. A significant impact of the solid polarization is found in gel electrophoresis compared to the free-solution electrophoresis.

Intense Cherenkov radiation from a charged particle revolving along a shifted equatorial orbit about a dielectric ball

The radiation from a charged particle uniformly revolving along a shifted equatorial orbit about a dielectric ball has been investigated. The results of numerical calculations based on exact solutions of Maxwell equations with due regard for dielectric losses of energy within the ball material testify that (a) for definite "resonant" values of the particle revolution frequency relativistic electron may generate microwave Cherenkov radiation at the first harmonic, that is approximately 900-1100 times more intensive than synchrotron radiation generated at the revolution of the same particle in vacuum and (b) in case of large values of permittivity of ball material (strontium titanate) the "resonant" radiation is generated by the revolving electron with energy of the order of 30 KeV.

Enhanced transmission via a sub-wavelength hole aperture coupled to a high-permittivity resonator

One order of magnitude enhanced transmissivity was demonstrated by microwave scattering parameter measurements of a sub-wavelength single hole aperture (λ/20) coupled to a high-permittivity ferroelectric cube (εr = 120). It was shown that the large permittivity value allows the concentration of the impinging electromagnetic wave on a millimetre scale, compatible with the deep sub-wavelength millimetre-sized aperture without involving surface plasmon mode propagation as in optics. The transmission enhancement explained by a tight coupling between the dielectric resonator and the sub cut-off aperture was experimentally verified by considering coupling distance and hole size as parameters.

Electrical properties of resin monomers used in restorative dentistry

ObjectivesThe application of an electric field has been shown to positively influence the impregnation of the resin monomers currently used in dentin bonding systems during hybrid layer formation. This study presents an experimental characterization of the electrical properties of these monomers with the aim of both correlating them to their chemical structures and seeking an insight into the mechanisms of the monomer migration under an applied electric field. MethodsSome common monomers examined were TEGDMA (triethyleneglycoldimethacrylate), HEMA (2-hydroxyethyl methacrylate), UDMA (urethane dimethacrylate), 2-MP (bis[2-(methacryloyloxy)ethyl] phosphate, TCDM di(hydroxyethyl methacrylate) ester of 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic anhydride) and Bis-GMA [2,2-bis(4-2-hydroxy-3-methacryloyloxypropoxyphenyl)propane]. A customized cell produced for the measurement of the electrical properties of monomers was manufactured and electrical conductivity and permittivity of resin monomers were measured. ResultsThe permittivity of the tested monomers is largely affected by electrical frequency. The large values of permittivity and dielectric losses observed as frequency decreased, indicate a dominant effect of ionic polarization, particularly evident in materials showing the highest conductivity. Permittivity and conductivity of the tested monomers showed a similar behavior, i.e. materials with the lowest permittivity also show small values of conductivity and vice versa. SignificanceThe results of the present study revealed a good correlation between electrical properties and Hoy solubility parameters and, in particular, the higher the polar contribution (polar forces plus hydrogen bonding) the higher the permittivity and conductivity. The most relevant outcome of this study is that the electrophoretic mechanism prevails on the electroendoosmotic effect in determining the monomer migration under the application of electric fields.

Theory of broadband dispersion of permittivity of biological cell suspensions

The classical Pauly-Schwan electrical model of the biological cell is generalized by considering the diffusion processes that occur due to the selective (with respect to ions of different signes of charges) conductivity of surface cell structures (cytoplasmic membrane and electrical double layer). The analytical theory of the dispersion of the permittivity of biological cell suspensions that cover a broad frequency band that includes three typical (for these systems) dispersion regions α, β, and γ is constructed using the generalized model, whereas the classical model describes only β and γ regions. Very large values of permittivity and their complete stipulation by the ionic selectivity of surface structures, which are characteristic for the region of α dispersion, predetermine the unique sensitivity of low-frequency dielectric spectrum to the effective conductivity of the membrane of a living cell, which can find important applications in biology and medicine.

Property engineering in BaTiO3 films by stoichiometry control

BaTiO3 thin films were prepared on metallic foil substrates using chemical solution deposition. The impact of A to B site cation ratios on the phase assemblage and microstructural and dielectric properties was investigated by characterizing a sample set that includes stoichiometric BaTiO3 and 1, 2, 3, 4, and 5 mol% excess BaO. Each composition was subjected to a high-temperature anneal step with maximum dwell temperatures of 1000, 1100, and 1200 °C for 20 h. Excess barium concentrations greater than 3% lead to dramatic grain growth and average grain sizes exceeding 1 μm. Despite the large deviations from stoichiometry and the 20 h dwell time at temperature, x-ray diffraction, and high-resolution electron microscopy analysis were unable to detect secondary phases until films with 5% excess barium were annealed to 1200 °C. Thin films with 3% excess barium were prepared on copper substrates and annealed at 1060 °C, the practical limit for copper. This combination of BaO excess and annealing temperature produced an average lateral grain size of 0.8 μm and a room-temperature permittivity of 4000. This is in comparison to a permittivity of 1800 for stoichiometric material prepared using identical conditions. This work suggests metastable solubility of BaO in BaTiO3 that leads to enhanced grain growth and large permittivity values. This technique provides a new solid-state means of achieving grain growth in low thermal budget systems.

Enhanced magnetoelectric coefficient (α) in the modified BiFeO3–PbTiO3 system with large La substitution

Magnetoelectric coupling coefficient (α) values of 0.88mV∕cm∕Oe at 200Oe and magnetocapacitive effects are reported in solid-solution BF–LF–PT with large La substitution (50:50 in BF). Enhancement of magnetic, dielectric, and ferroelectric properties is also observed. The solid solution shows relaxor behavior with large permittivity values (∼30000), large remnant polarization (∼61μC∕cm2), and symmetric but nonsaturating M-H loop with Mr∼0.25emu∕g.

Electrorotational studies of the cytoplasmic dielectric properties of Friend murine erythroleukaemia cells

Electrorotation (ROT) spectra of Friend murine erythroleukaemia DS19 cells were measured in the frequency range 10 kHz-100 MHz as a function of suspension osmolality and cell differentiation treatment with hexamethylene bisacetamide (HMBA). A minimization program was employed to curve-fit the measured spectra using a single-shell dielectric model, allowing the derivation of cellular interior conductivity and permittivity (valid for the frequency range 10-100 MHz) and the cytoplasmic membrane capacitance (its dependence on the cell differentiation state and suspension osmolality having been reported earlier). Following HMBA treatment, DS19 cells exhibited a slight increment in average interior permittivity and a decrement in interior conductivity, although the changes were not statistically significant. For both untreated and HMBA treated samples, the average interior conductivity increased and permittivity decreased with increasing suspension osmolality. Of significance was that the average permittivity of cell interiors was larger than that of pure water. The electrorotation spectra of freshly prepared cell nuclei were measured, and the derived nuclear dielectric parameters were employed in numerical simulations to investigate the effects of nuclei on the ROT spectra of intact cells. Other cellular internal structures such as mitochondria were also analysed using theoretical simulations. It was concluded that the derived large permittivity values did not result from cell nuclei or mitochondria, and, instead, we suggest that they may arise from the combined effects of several cytoplasmic organelles.

A moment method solution of a volume-surface integral equation using isoparametric elements and point matching (TE scattering)

Three integral equations for TE (transverse electric) scattering by dielectric cylinders having large values of permittivity are examined. A moment-method solution of the volume-surface integral equation is developed employing isoparametric elements and point matching. The solution is shown to be accurate and stable than the traditional solutions using pulse basis, particularly in the case of scatterers having large refractive indices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low‐frequency permittivities of skarns and associated rocks

The lossy dielectric properties of dry heterogeneous skarns and associated rocks vary significantly when the real (ε′) and quadrature (ε″) permittivity responses are measured between 1 Hz and 160 kHz. Ores containing iron oxides and/or sulfides show very large permittivity values and high loss tangents with some dc conductivity. Unmineralized skarns manifest large ε′ and moderate ε″ values. Country rock, limestones, and granitoids show relatively low permittivities. The dielectric responses are ascribed generally to Maxwell‐Wagner mechanisms. No clear, convincing correlations are apparent between petrological characteristics and dielectric properties, but as iron and titanium content increases, so does the imaginary permittivity. Both real and imaginary permittivities are strongly influenced by density, and this effect must be removed before the effects of mineralogy can be observed.

Characteristics of the surface and features of the propagation of radio waves in the atmosphere of Venus from data of bistatic radiolocation experiments using Venera 9 and 10 satellites

The results of the investigation of two regions of Venus by bistatic radiolocation are presented. The experiments were carried out at wavelength λ 0 = 32 cm. Maps of the distribution of reflectivity were obtained and characteristics of the relief, dielectric permittivity, soil density, and refraction attenuation in the atmosphere were measured. The value of the dispersion of small-scale slopes in the observed regions, γ, varies between 0.4 and 2.2°. There are some features on the reflectivity maps. Some of these features may correspond to mountain slopes with values in the range 2 to 8°. Corresponding changes of relief heights are contained in the interval 0.8 to 2.6 km. The features are found within the region (in the venerocentric IAU system): −26.5 to 25.0° latitude and 220.0−239.2° longitude. One area was revealed with large values of permittivity in the range 6.5–7.5, and soil density between 2.7 and 2.9 g/cm 3. The center of this area is located at −23.5° latitude and 230.4° longitude. The extent of this region is 80 km. The results of measurements of the refraction angle and the refraction attenuation of radio waves are in good agreement with the parameters of the atmosphere of Venus received from the Soviet landers.