Dielectric and Electric Properties of Ba0.996La0.004Ti0.999O3 Ceramics Doped with Europium and Hafnium Ions

Lanthanum-modified BaTiO3 electroceramic materials have superior dielectric and piezoelectric properties. Ba0.996La0.004Ti0.999O3 (BLT4) seems to be a serious candidate for ultracondensator applications. This manuscript describes the results of hafnium and europium modification of BLT 4 ceramics. The pure and doped ceramic materials were synthesized by the conventional mixed oxide method. The microstructure of obtained samples was examined by scanning electron microscope. The investigations reveal strong correlations between the presence of admixture and the grain size, which was especially visible in the case of the hafnium dopant. The frequency and temperature dielectric characteristics measurements revealed a decrease in electric permittivity. Moreover, the impedance spectroscopy investigations showed severe changes in grains and grain-boundary resistivity, which was connected with changes in electric conductivity.

Phase field model for electrically induced damage using microforce theory

In this paper, we present a consistent derivation of the phase field model for electrically induced damage. The derivation is based on Gurtin’s microstress and microforce theory and the Coleman–Noll procedure. The resulting model accounts for Ohmic currents, includes charge conservation law and allows for finite electric permittivity and conductivity distribution in the medium. Special attention is devoted to the case when the damaged region is a codimension-two object, i.e., a curve in three dimensions. It is shown that in this case the free energy of the model necessarily includes a high-order term, which ensures the well-posedness of the problem. A special problem setting is proposed to account for the prescribed charge distribution. Local features of the phase field distribution are illustrated with one-dimensional axisymmetric numerical experiments.

The three dimensional Maxwell equations with strongly anisotropic electric permittivity

The subject matter of this work concerns the propagation of the electro-magnetic fields through strongly anisotropic media, in the three dimensional setting. We concentrate on the asymptotic behavior for the solutions of the Maxwell equations when the electric permittivity tensor is strongly anisotropic. We derive limit models and prove their well-posedness. We appeal to the variational framework and study the propagation speed of the solutions. We prove that almost all the electro-magnetic energy concentrates inside the propagation cone of the limit model.

Using Plasmonic Cloaking Method on Infinite Cylindrical Structures and its Applications

In recent years, cloaking using materials with negative electric permittivity or magnetic permeability has been studied and researched. It has been demonstrated that covering an object with a cloak that has negative electric permittivity or magnetic permeability or less than one can cause a reduction of the scattering cross section (SCS) of the object. In this paper, we have solved the problem of scattering for the object and single-layer or multi-layer cylindrical cloaks and by doing so, we have obtained the necessary fundamental equations for designing these types of cloaks in two conditions, with and without considering the effects of coupling on the mathematics of solving the problem of scattering. Using the obtained equations we have demonstrated that by using this technique reducing the level of visibility of the object is possible.

A Review on Metamaterials for Device Applications

Metamaterials are the major type of artificially engineered materials which exhibit naturally unobtainable properties according to how their microarchitectures are engineered. Owing to their unique and controllable effective properties, including electric permittivity and magnetic permeability, the metamaterials play a vital role in the development of meta-devices. Therefore, the recent research has mainly focused on shifting towards achieving tunable, switchable, nonlinear, and sensing functionalities. In this review, we summarize the recent progress in terahertz, microwave electromagnetic, and photonic metamaterials, and their applications. The review also encompasses the role of metamaterials in the advancement of microwave sensors, photonic devices, antennas, energy harvesting, and superconducting quantum interference devices (SQUIDs).

Mechanochemical Activation and Spark Plasma Sintering of the Lead-Free Ba(Fe1/2Nb1/2)O3 Ceramics

This paper investigates the impact of the technological process (Mechanochemical Activation (MA) of the powder in combination with the Spark Plasma Sintering (SPS) method) on the final properties of lead-free Ba(Fe1/2Nb1/2)O3 (BFN) ceramic materials. The BFN powders were obtained for different MA duration times (x from 10 to 100 h). The mechanically activated BFN powders were used in the technological process of the BFN ceramics by the SPS method. The measurements of the BFNxMA ceramic samples included the following analysis: Scanning Electron Microscopy (SEM), Energy Dispersive Spectrometry (EDS), DC electrical conductivity, and dielectric properties. X-ray diffractions (XRD) tests showed the appearance of the perovskite phase of BFN powders after 10 h of milling time. The longer milling time (up 20 h) causes the amount of the perovskite phase to gradually increase, and the diffraction peaks are more clearly visible. Short high energy milling times favor a large heterogeneity of the grain shape and size. Increasing the MA milling time to 40 h significantly improves the microstructure of BFN ceramics sintered in the SPS technology. The microstructure becomes fine-grained with clearly visible grain boundaries and higher grain size uniformity. Temperature measurements of the BFN ceramics show a number of interesting dielectric properties, i.e., high values of electric permittivity, relaxation properties with a diffusion phase transition, as well as negative values of dielectric properties occurring at high temperatures. The high electric permittivity values predestines the BFNxMA materials for energy storage applications e.g., high energy density batteries, while the negative values of dielectric properties can be used for shield elements against the electromagnetic radiation.

A Novel Radar Processing Tool for Estimating the Permittivity Profile of the Shallow Lunar Ejecta: A Case Study at the Von Kármán Crater

<p>On 3<sup>rd</sup> of January 2019, the Lunar probe Chang’E-4 landed at Von Kármán (VK) crater at South-Pole Aitken (SPA) crater. The transient cavity of SPA has been estimated at 840-1400 km, which implies that the SPA basin excavated through the Lunar’s crust and into the mantle. Due to that, the geology of the area has attracted a lot of interest, since mantle materials can provide useful insights on the mineralogical composition of the upper mantle and the formation of the Moon.</p><p>Lunar Penetrating Radar (LPR) has been applied for both satellite and in situ measurement configurations resulting to fruitful insights regarding the dielectric structure of the Moon. The Yutu-2 rover from the Chang’E-4 mission is equipped with a low-frequency (60 MHz) and two high-frequency (500 MHz) antennas. Previous research [1] using the high-frequency data from the Yutu-2 rover, concluded that a homogenous ~12 m weathered layered overlays the ejecta from the near-by Finsen crater. This model is based on typical hyperbola-fitting and the lack of layers on the measured radagram for the first ~150 ns [1].   </p><p>Typical hyperbola-fitting is not suitable for complex media with varying permittivity with depth. To mitigate that, we propose a novel interpretation tool that fits multiple hyperbolas simultaneously by estimating the optimum one-dimensional permittivity profile. The suggested scheme is successfully validated via a series of numerical experiments and subsequently applied to the data acquired by the Yutu-2 rover during the first two Lunar days of the mission. Four distinct layers were identified in the first ~12 m that were previously non-visible due to their smooth dielectric boundaries. This differs from previous results [1] where the first ~12 m are assumed homogeneous, part of the weathered fine-grained regolith of the Finsen crater. Based on these results, we suggest a new stratigraphic model in which the ejecta of VK L' (~ 5.5 m) were deposited on top of the Finsen ejecta. Space weathering degraded the first ~1.5 m of the ejecta decreasing its density and electric permittivity. The ejecta from VK L were subsequently deposited on top of the weathered layer creating a top layer with ~6 m width. The long weathering process, from early Eratosthenian till now, gave rise to a ~3 m of loose Lunar soil with low electric permittivity. The suggested model is consisted with the LROC NAC images [2], the expected Lunar weathering rates [3] and the mineralogical content of the area [2].</p><p><strong>References </strong></p><p>[1] Zhang, L., Li, J., Zeng, Z., Xu, Y., Liu, C., & Chen, S, (2020), Stratigraphy of the Von Kármán crater based on Chang’E-4 lunar penetrating radar data. Geophysical Research Letters, 47.</p><p>[2] Huang, J., Xiao, Z., Flahaut, J., Martinot, M., Head, J., Xiao, X., & et al. (2018), Geological characteristics of Von Kármán crater, northwestern South Pole-Aitken basin: Chang’E-4 landing site region, Journal of Geophysical Research: Planets, 123, 1684-1700.</p><p>[3] Gou, S., Yue, Z., Di, K., Cai, Z., Liu, Z., & Niu, S. (2021), Absolute model age of Lunar Finsen crater and geologic implications, Icarus, 354, 114046.</p>

Location of agate geodes in Permian deposits of Simota gully using the GPR

The article describes the establishment of the location of agate geodes using the GPR method in the area of the Simota gully (Lesser Poland Voivodeship). Agates (a multicolored variety of gemstone of chalcedony group) have multifaceted values that informed their study. Traditional methods of geode location are less reliable, hence the attempt to use the GPR method. Measurements were taken at two study test sites with subsurface geology of weathered melaphyre and pyroclastic deposits using a GPR system (ProEx). A high-frequency antenna (1.6 GHz) was used along with the pre-established profiles of lengths of 6-m and 10-cm intervals. Furthermore, simple soil tests using the soil sampler tool were made prior to the GPR measurement. The GPR results show significant high attenuation of the electromagnetic energy interpreted to be due to clay components of the regolith. Advanced signal processing procedures (such as the attribute of the signal) were used on the data for better enhancement that aided interpretation. Other anomalies depicted on the radargrams were thought to be the presence of roots, pieces of melaphyres-targeted agates. Furtherance to ascertain the reflection coefficients as recorded on the GPR data, in situ samples (root pieces, melaphyres, agates) taken were tested in the laboratory for electric permittivity property. Based on the interpretation results, several agate geodes were dug out from the ground.