Artykuły w czasopismach na temat „Colossal equivalent relative permittivity”
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Dong, Wen, Wanbiao Hu, Terry J. Frankcombe, Dehong Chen, Chao Zhou, Zhenxiao Fu, Ladir Cândido i in. "Colossal permittivity with ultralow dielectric loss in In + Ta co-doped rutile TiO2". Journal of Materials Chemistry A 5, nr 11 (2017): 5436–41. http://dx.doi.org/10.1039/c6ta08337d.
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Electron-pinned defect dipoles, in the form of highly stable triangle-diamond and/or triangle-linear dopant defect clusters with well defined relative positions for Ti reduction, are present in rutile In + Ta co-doped TiO2 for the colossal permittivity and low loss.
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Kotb, Hicham Mahfoz, Adil Alshoaibi, Javed Mazher, Nagih M. Shaalan i Mohamad M. Ahmad. "Colossal Permittivity Characteristics of (Nb, Si) Co-Doped TiO2 Ceramics". Materials 15, nr 13 (5.07.2022): 4701. http://dx.doi.org/10.3390/ma15134701.
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(Nb5+, Si4+) co-doped TiO2 (NSTO) ceramics with the compositions (Nb0.5Si0.5)xTi1−xO2, x = 0, 0.025, 0.050 and 0.1 were prepared with a solid-state reaction technique. X-ray diffraction (XRD) patterns and Raman spectra confirmed that the tetragonal rutile is the main phase in all the ceramics. Additionally, XRD revealed the presence of a secondary phase of SiO2 in the co-doped ceramics. Impedance spectroscopy analysis showed two contributions, which correspond to the responses of grain and grain-boundary. All the (Nb, Si) co-doped TiO2 showed improved dielectric performance in the high frequency range (>103 Hz). The sample (Nb0.5Si0.5)0.025Ti0.975O2 showed the best dielectric performance in terms of higher relative permittivity (5.5 × 104) and lower dielectric loss (0.18), at 10 kHz and 300 K, compared to pure TiO2 (1.1 × 103, 0.34). The colossal permittivity of NSTO ceramics is attributed to an internal barrier layer capacitance (IBLC) effect, formed by insulating grain-boundaries and semiconductor grains in the ceramics.
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He, Jiayang, Yanwei Huang, Guang Feng, Si Shen, Ming Yan i Heping Zeng. "Rapid Laser Reactive Sintering Synthesis of Colossal Dielectric CCTO Ceramics". Applied Sciences 10, nr 10 (19.05.2020): 3510. http://dx.doi.org/10.3390/app10103510.
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Calcium copper titanate (CCTO) ceramics were successfully synthesized using a rapid laser reactive sintering method without conventional long heat treatment times. The microstructure, dielectric properties, and impedance spectroscopy results for CCTO sintered at laser power rates of 25–85 W were investigated in detail. The X-ray diffractometry results showed that prepared CCTO is polycrystalline in a cubic structure with high purity. Scanning electron microscopy showed that CCTO sintered at 85 W has a dense microstructure with an average grain size of 30 nm. The dielectric permittivity of CCTO ceramics increased with increasing laser power over the entire frequency range and achieved a value of almost 105 in the low-frequency region. The dielectric permittivity maintained almost constant values from 102 Hz to 107 Hz, with lower dielectric loss (~0.1) from 103 Hz to 106 Hz, demonstrating good frequency stability. The impedance spectroscopy study showed that grain and grain boundary resistance decreased with rising laser power based on two parallel Resistor-Capacitance (RC) equivalent circuits in series. The activation energies for the grain boundaries were calculated from the impedance using the slope of ln σ versus 1/T and were found to be in the range of 0.53–0.63 eV. CCTO synthesized by rapid laser reactive sintering is competitive for practical applications.
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Giannoukos, Georgios, Mart Min i Toomas Rang. "Relative complex permittivity and its dependence on frequency". World Journal of Engineering 14, nr 6 (4.12.2017): 532–37. http://dx.doi.org/10.1108/wje-01-2017-0007.
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Purpose This paper aims to give a brief overview of dielectric properties, relative complex permittivity and its dependence on frequency. The significance of different approaches to complex permittivity is also discussed. Design/methodology/approach The different mechanisms of polarization are then presented. Dielectric measurements are given, and an RC parallel-equivalent circuit is used to simulate a parallel plate capacitor, and the way in which the impedance of the circuits is affected by frequency is illustrated in their respective diagrams. The way in which dielectric properties change with time is also discussed. Findings The goal of this paper is to give an overview of the characteristics of the dielectrics and how frequency affects the relative complex permittivity and to present different approaches to and equations for the relative complex permittivity, such as that of Debye, Cole–Cole, Cole–Davidson and Havriliak–Negami. In addition, three mechanisms of polarization, namely, electronic, atomic and bipolar, are presented. The most common dielectric characterization device, a capacitor with parallel plates between which the dielectric material under study is located, is also discussed. Ohmic and dielectric losses of a non-ideal capacitor are accounted for. Furthermore, this paper studies the equivalent circuits of a non-ideal parallel plate capacitor, those being a resistor and an ideal capacitor connected either in series or in parallel. Originality/value Finally, dielectric responses to both time and to stepwise excitation are given.
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Mahfoz Kotb, H., Osama Saber i Mohamad M. Ahmad. "Colossal relative permittivity and low dielectric loss in BaFe0.5Nb0.5O3 ceramics prepared by spark plasma sintering". Results in Physics 19 (grudzień 2020): 103607. http://dx.doi.org/10.1016/j.rinp.2020.103607.
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Verma, A. K., Y. K. Awasthi i Himanshu Singh. "Equivalent isotropic relative permittivity of microstrip on multilayer anisotropic substrate". International Journal of Electronics 96, nr 8 (sierpień 2009): 865–75. http://dx.doi.org/10.1080/00207210902851480.
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Jurn, Yaseen Naser, Fareq Malek, Sawsen Abdulahadi Mahmood, Wei Wen Liu, Makram A. Fakhri i Muataz Hameed Salih. "Modelling and Simulation of Rectangular Bundle of Single-Walled Carbon Nanotubes for Antenna Applications". Key Engineering Materials 701 (lipiec 2016): 57–66. http://dx.doi.org/10.4028/www.scientific.net/kem.701.57.
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This paper aims to present an effective electromagnetic (EM) modelling approach for rectangular bundle of single-walled carbon nanotubes (RB-SWCNTs), based on the electrical conductivity, relative complex permittivity and linear distribution impedance by applying General Ohm’s law for this bundle. The equivalent single conductor material (ESCM) model for personification the RB-SWCNTs is present in this paper. The main target of this modeling approach is to estimate and investigate the EM properties of RB-SWCNTs using common EM engineering tool solver CST (MWS). For this purpose, the RB-SWCNTs and ESCM dipole antennas will be designed and implemented using CST (MWS). The equivalent conductivity model, relative complex permittivity and other parameters of the RB-SWCNTs will be derived in this paper and considered as an equivalent material parameters for the ESCM. This modeling technique is expected to provide new avenues for designing different antenna structures.
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Wang, Ge, Hui Pan, Shimiao Lai, Yongjie Zhou, Li Wu, Huacheng Zhu i Yang Yang. "Dynamic Measurement of Relative Complex Permittivity of Microwave Plasma at Atmospheric Pressure". Processes 9, nr 10 (13.10.2021): 1812. http://dx.doi.org/10.3390/pr9101812.
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Complex permittivity is one of the most important parameters to characterize the interaction between microwave and medium, especially for microwave-excited plasma. It is convenient to study plasma’s dielectric properties and microwave propagation characteristics by measuring its complex permittivity. A dynamic measurement method of equivalent relative complex permittivity of microwave-excited plasma at atmospheric pressure is proposed in this paper. Firstly, a cavity based on WR-430 at a frequency of 2.45 GHz was specially designed in COMSOL. Then, the samples with different real parts of complex permittivity and loss tangent were simulated in the designed cavity to obtain their corresponding S parameters, and they were used to train the BP neural network until the error was lower than 0.001. A two-port network was built to excite the plasma. The input power, reflected power, and transmitted power could be measured by the transmission reflection method. Finally, the measured power values were converted into S parameters and used as inputs in the BP neural network. The plasma’s real parts of complex permittivity and loss tangent were obtained by inversion. The variation of plasma complex permittivity conforms to the interaction principles between microwave and plasma, which verifies the accuracy of the method.
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Bellucci, Stefano, Antonio Maffucci, Sergey Maksimenko, Federico Micciulla, Marco Migliore, Alesia Paddubskaya, Daniele Pinchera i Fulvio Schettino. "Electrical Permittivity and Conductivity of a Graphene Nanoplatelet Contact in the Microwave Range". Materials 11, nr 12 (11.12.2018): 2519. http://dx.doi.org/10.3390/ma11122519.
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This paper investigates the electrical properties in the microwave range of a contact made by graphene nanoplatelets. The final goal is that of estimating the range of values for the equivalent electrical complex permittivity of a contact obtained by integrating low-cost graphene in the form of nanoplatelets (GNPs) into a high-frequency electrical circuit. To this end, a microstrip-like circuit is designed and realized, where the graphene nanoplatelets are self-assembled into a gap between two copper electrodes. An experimental characterization is carried out, both to study the structural properties of the nanomaterials and of the realized devices, and to measure the electromagnetic scattering parameters in the microwave range by means of a microstrip technique. A full-wave electromagnetic model is also derived and used to investigate the relationship between the measured quantities and the physical and geometrical parameters. The combined use of the experimental and simulation results allows for retrieving the values of the equivalent complex permittivity. The equivalent electrical conductivity values are found to be well below the values expected for isolated graphene nanoplatelets. The real part of the electrical relative permittivity attains values comparable to those obtained with GNP nanocomposites.
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Pacini, Alex, Alessandra Costanzo i Diego Masotti. "A theoretical and numerical approach for selecting miniaturized antenna topologies on magneto-dielectric substrates". International Journal of Microwave and Wireless Technologies 7, nr 3-4 (18.05.2015): 369–77. http://dx.doi.org/10.1017/s1759078715000859.
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An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.
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Ozaki, Tamon, Noriyuki Ito, Jiro Kawai i Shuhei Nakamura. "Relative Permittivity and Conductivity of Water-treed Region in XLPE Estimated by an Equivalent Circuit". IEEJ Transactions on Fundamentals and Materials 123, nr 5 (2003): 506–12. http://dx.doi.org/10.1541/ieejfms.123.506.
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Ozaki, Tamon, Noriyuki Ito, Jiro Kawai i Shuhei Nakamura. "Relative permittivity and conductivity of water-treed region in XLPE estimated by an equivalent circuit". Electrical Engineering in Japan 148, nr 3 (2004): 7–14. http://dx.doi.org/10.1002/eej.10332.
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Kotb, Hicham Mahfoz, Hassan A. Khater, Osama Saber i Mohamad M. Ahmad. "Sintering Temperature, Frequency, and Temperature Dependent Dielectric Properties of Na0.5Sm0.5Cu3Ti4O12 Ceramics". Materials 14, nr 17 (25.08.2021): 4805. http://dx.doi.org/10.3390/ma14174805.
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NSCTO (Na0.5Sm0.5Cu3Ti4O12) ceramics have been prepared by reactive sintering solid-state reaction where the powder was prepared from the elemental oxides by mechanochemical milling followed by conventional sintering in the temperature range 1000–1100 °C. The influence of sintering temperature on the structural and dielectric properties was thoroughly studied. X-ray diffraction analysis (XRD) revealed the formation of the cubic NSCTO phase. By using the Williamson–Hall approach, the crystallite size and lattice strain were calculated. Scanning electron microscope (SEM) observations revealed that the grain size of NSCTO ceramics is slightly dependent on the sintering temperature where the average grain size increased from 1.91 ± 0.36 μm to 2.58 ± 0.89 μm with increasing sintering temperature from 1000 °C to 1100 °C. The ceramic sample sintered at 1025 °C showed the best compromise between colossal relative permittivity (ε′ = 1.34 × 103) and low dielectric loss (tanδ = 0.043) values at 1.1 kHz and 300 K. The calculated activation energy for relaxation and conduction of NSCTO highlighted the important role of single and double ionized oxygen vacancies in these processes.
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Stanciu, Cătălina A., Ioana Pintilie, Adrian Surdu, Roxana Truşcă, Bogdan S. Vasile, Mihai Eftimie i Adelina C. Ianculescu. "Influence of Sintering Strategy on the Characteristics of Sol-Gel Ba1−xCexTi1−x/4O3 Ceramics". Nanomaterials 9, nr 12 (23.11.2019): 1675. http://dx.doi.org/10.3390/nano9121675.
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Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce3+ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce3+ concentration (x = 0.05) were found to be in the proximity of the ferroelectric–paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entire investigated temperature range relative to the conventionally sintered sample of similar composition. The spark-plasma-sintered Ce-BaTiO3 specimen with high solute content (x = 0.05) showed a fine-grained microstructure and an almost temperature-independent colossal dielectric constant which originated from very high interfacial polarization.
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Packamwongsang, K., S. Noppanakeepong, N. Naranong, P. Phaewbang, P. Pleuksananon i W. Packamwongsang. "ELECTROCHEMICAL MODEL OF Euglena sanguinea Ehrenberg STIMULATED WITH MULTI-LEVEL ELECTROMAGNETIC FIELDS". ASEAN Journal on Science and Technology for Development 27, nr 2 (21.11.2017): 21–44. http://dx.doi.org/10.29037/ajstd.250.
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This research aimed at studying the property of Euglena Sanguinea Ehrenberg (E. sanguinea) before and after being stimulated by multi-level electromagnetic fields (MLEM). After the stimulation, it was found that physical properties were changed, i.e., cell membrane and components deformed. Main biochemical compositions were changed in accordance with new electrochemical equation which was estimated from FTIR bands. Moreover, the estimated electrical results before and after being stimulated, i.e., impedance and complex relative permittivity of main biochemical compositions from extraction, were then measured, simulated, and compared by means of Cole-Cole plot technique which yielded the statistic correlation 0.89 at 95% confidence level. Semi-circle impedance was related to complex relative permittivity as its value decreased with the increasing frequency. These were the information for designing the new electrical equivalent circuit model of E. sanguinea with MLEM to explain many phenomena in cell. The relationship between energy from MLEM system and bond energy of main biochemical compositions of E. sanguinea as well as between electromagnetic field behaviors of MLEM system which stimulated to cell and induced voltage transmitted through each biochemical compositions of E. sanguine were also identified.
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Packamwongsang,, K., S. Noppanakeepong,, N. Naranong,, P. Phaewbang,, P. Pleuksananon, i And W. Packamwongsang. "Electrochemical model of euglena sanguinea ehrenberg stimulated with multi-level electromagnetic fields". ASEAN Journal on Science and Technology for Development 26, nr 2 (27.11.2017): 21–44. http://dx.doi.org/10.29037/ajstd.320.
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This research aimed at studying the property of Euglena Sanguinea Ehrenberg (E. sanguinea) before and after being stimulated by multi-level electromagnetic fields (MLEM). After the stimulation, it was found that physical properties were changed, i.e., cell membrane and components deformed. Main biochemical compositions were changed in accordance with new electrochemical equation which was estimated from FTIR bands. Moreover, the estimated electrical results before and after being stimulated, i.e., impedance and complex relative permittivity of main biochemical compositions from extraction, were then measured, simulated, and compared by means of Cole-Cole plot technique which yielded the statistic correlation 0.89 at 95% confidence level. Semi-circle impedance was related to complex relative permittivity as its value decreased with the increasing frequency. These were the information for designing the new electrical equivalent circuit model of E. sanguinea with MLEM to explain many phenomena in cell. The relationship between energy from MLEM system and bond energy of main biochemical compositions of E. sanguinea as well as between electromagnetic field behaviors of MLEM system which stimulated to cell and induced voltage transmitted through each biochemical compositions of E. sanguine were also identified.
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Bifano, Luca, Alice Fischerauer i Gerhard Fischerauer. "Investigation of complex permittivity spectra of foundry sands". tm - Technisches Messen 87, nr 5 (27.05.2020): 372–80. http://dx.doi.org/10.1515/teme-2019-0121.
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AbstractThis paper discusses impedance spectroscopy as a method to characterize different types of quartz sand, chromite sand, and mixtures of sand. Based on two types of measurement cells, the impedance spectra for various dry sands were measured. The spectra differ enough to allow the sands to be distinguished. The results were validated by extracting the relative permittivity from the impedance and comparing it to literature data. After that, the method could be applied with confidence to other material systems. The influence of moisture was investigated with two types of quartz sand, and typical mixtures of form sand, chromite sand, and regenerated (quartz) sand were studied. In each case, the sand composition had a distinct influence on the Nyquist plot of the impedance spectrum. Compared to results from a laboratory foundry system, the new method exhibits a much more systematic dependence on the sand composition. If one succeeds in describing the impedance spectra with an equivalent circuit model parameterized by only a few parameters, these parameters could be used to identify and classify sand mixtures in the field. This would allow one, for example, to implement feedback control strategies in foundry regeneration processes, which would stabilize the processes and improve the quality of the casting products.
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Rodriguez Barrera, Mario A., i Walter Pereira Carpes Jr. "Particle swarm optimization for the design of square loop frequency selective surfaces considering a model of dielectric effective permittivity". COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 35, nr 5 (5.09.2016): 1643–55. http://dx.doi.org/10.1108/compel-10-2015-0362.
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Purpose The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys – high frequency structure simulator commercial software simulations. Originality/value The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions.
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Crupi, Giovanni, Xiue Bao, Oluwatosin John Babarinde, Dominique M. M. P. Schreurs i Bart Nauwelaers. "Biosensor Using a One-Port Interdigital Capacitor: A Resonance-Based Investigation of the Permittivity Sensitivity for Microfluidic Broadband Bioelectronics Applications". Electronics 9, nr 2 (16.02.2020): 340. http://dx.doi.org/10.3390/electronics9020340.
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Electronics is a field of study ubiquitous in our daily lives, since this discipline is undoubtedly the driving force behind developments in many other disciplines, such as telecommunications, automation, and computer science. Nowadays, electronics is becoming more and more widely applied in life science, thus leading to an increasing interest in bioelectronics that is a major segment of bioengineering. A bioelectronics application that has gained much attention in recent years is the use of sensors for biological samples, with emphasis given to biosensors performing broadband sensing of small-volume liquid samples. Within this context, this work aims at investigating a microfluidic sensor based on a broadband one-port coplanar interdigital capacitor (IDC). The microwave performance of the sensor loaded with lossless materials under test (MUTs) is achieved by using finite-element method (FEM) simulations carried out with Ansoft’s high frequency structure simulator (HFSS). The microfluidic channel for the MUT has a volume capacity of 0.054 μL. The FEM simulations show a resonance in the admittance that is reproduced with a five-lumped-element equivalent-circuit model. By changing the real part of the relative permittivity of the MUT up to 70, the corresponding variations in both the resonant frequency of the FEM simulations and the capacitance of the equivalent-circuit model are analyzed, thereby enabling assessment of the permittivity sensitivity of the studied IDC. Furthermore, it is shown that, although the proposed local equivalent-circuit model is able to mimic faithfully the FEM simulations locally around the resonance in the admittance, a higher number of circuit elements can achieve a better agreement between FEM and equivalent-circuit simulation over the entire broad frequency going range from 0.3 MHz to 35 GHz.
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Kazemi, Maryam, Saeedeh Lotfi, Hesam Siahkamari i Mahmood Mohammadpanah. "UWB Bandpass Filter with Ultra-wide Stopband based on Ring Resonator". Frequenz 72, nr 5-6 (25.04.2018): 245–52. http://dx.doi.org/10.1515/freq-2016-0312.
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AbstractAn ultra-wideband (UWB) bandpass filter with ultra-wide stopband based on a rectangular ring resonator is presented. The filter is designed for the operational frequency band from 4.10 GHz to 10.80 GHz with an ultra-wide stopband from 11.23 GHz to 40 GHz. The even and odd equivalent circuits are used to achieve a suitable analysis of the proposed filter performance. To verify the design and analysis, the proposed bandpass filter is simulated using full-wave EM simulator Advanced Design System and fabricated on a 20mil thick Rogers_RO4003 substrate with relative permittivity of 3.38 and a loss tangent of 0.0021. The proposed filter behavior is investigated and simulation results are in good agreement with measurement results.
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Chen, Shih-Jui, Yi-Li Chen, Yu-Jui Chang, Dong-Lin Chuang, Yi-Chun Chen, Hai-Ping Tsui i Yean-Ren Hwang. "Measurement of Electrical Discharge Machining Oil Quality by Analyzing Variations in the Equivalent Relative Permittivity of the Capacitive Sensor". Sensors 20, nr 21 (2.11.2020): 6248. http://dx.doi.org/10.3390/s20216248.
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In this study, a concentration monitoring system was successfully developed. A sensor was immersed in electrical discharge machining oil, and the capacitance of the sensor changed as a function of the impurity concentration. Thus, DC voltage variations were produced via a conversion circuit. Carbon black and iron particles with different concentrations were successfully characterized. The capacitance increments were positively correlated with the particle concentration. The linear fitting results based on the impurity concentration were used to express the degree of influence of particles with different weight percentage concentrations on the increase in the overall capacitance value. An equivalent medium theory model was then developed according to the electrical characteristics of the impurities to predict different particle volume percentages.
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Braika Alameen, Sabriya Alghennai Alfitouri i Abdussalam Ali Ahmed. "Effect of dust storms on (GSM) signal north region of Libya". World Journal of Advanced Research and Reviews 14, nr 1 (30.04.2022): 504–19. http://dx.doi.org/10.30574/wjarr.2022.14.1.0351.
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Propagation mechanisms are very complex and diverse, because of the separation between the receiver and the transmitter, attenuation (reduction or loss) of the signal strength occurs. Field study will be conducted in amid north region of Libya (Bani Walid), which has high wind speed, and high attenuation loss, desert climate, and frequent dust and sand storms. This phenomenon actually influenced on wireless communication systems (GSM signal), neither the effect of the humidity on the complex permittivity nor the antenna height on the visibility, where by its effect on both attenuation and cross-polarization constants in this region. Besides the expectation of different chemical analysis of the dust and sand. These samples were collected from five location, every location had one level and sand was collected from a height of 2m, collect the meteorological data for the region of this study, e.g. visibility, wind speed and relative humidity, and height of towers from Libyana technical station. The analysis of these samples were done in two laboratories, one in university of Tripoli (AL-Fateh University), and the second in the Industrial Research Center in Tripoli. In the analysis, we were looking for the chemical and physically composition, the chemical composition of dust and sand had been got to compute complex permittivity, density, and chemical and physical properties analysis for the samples. Determine equivalent diameter, particles-size distribution, and axes ratio for collected samples; determine equivalent diameter, particles-size distribution, and axes ratio for collected samples. Compute the attenuation loss and cross-polarization discrimination (XPD) change due to the effect of sand and dust storms on wireless communication systems (GSM signal) which coverage in the studied region.
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Stoneman, Michael R., i Valerică Raicu. "Dielectric Spectroscopy Based Detection of Specific and Nonspecific Cellular Mechanisms". Sensors 21, nr 9 (3.05.2021): 3177. http://dx.doi.org/10.3390/s21093177.
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Using radiofrequency dielectric spectroscopy, we have investigated the impact of the interaction between a G protein-coupled receptor (GPCR), the sterile2 α-factor receptor protein (Ste2), and its cognate agonist ligand, the α-factor pheromone, on the dielectric properties of the plasma membrane in living yeast cells (Saccharomyces cerevisiae). The dielectric properties of a cell suspension containing a saturating concentration of α-factor were measured over the frequency range 40Hz–110 MHz and compared to the behavior of a similarly prepared suspension of cells in the absence of α-factor. A spherical three-shell model was used to determine the electrical phase parameters for the yeast cells in both types of suspensions. The relative permittivity of the plasma membrane showed a significant increase after exposure to α-factor (by 0.06 ± 0.05). The equivalent experiment performed on yeast cells lacking the ability to express Ste2 showed no change in plasma membrane permittivity. Interestingly, a large change also occurred to the electrical properties of the cellular interior after the addition of α-factor to the cell suspending medium, whether or not the cells were expressing Ste2. We present a number of different complementary experiments performed on the yeast to support these dielectric data and interpret the results in terms of specific cellular reactions to the presence of α-factor.
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Razzaz, Faroq, Saud M. Saeed i Majeed A. S. Alkanhal. "Ultra-Wideband Bandpass Filters Using Tapered Resonators". Applied Sciences 12, nr 7 (6.04.2022): 3699. http://dx.doi.org/10.3390/app12073699.
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In this paper, ultra-wideband bandpass filters using tapered transmission line resonators are presented. The proposed filters are based on short-circuited tapered transmission line stubs. The use of tapered transmission resonators resulted in a noticeable length reduction, a wider controlled operational bandwidth, and better stopband characteristics for filter applications. Three filters are designed with different tapered ratios using exponential tapered transmission line resonators. The other three filters are also designed using equivalent linear tapered transmission line resonators. The designed filters are simulated and fabricated on a Roger RT5880 substrate with a 2.2 relative permittivity and 0.78 mm thickness. Approximately, the same performance is obtained using either exponential or linear tapered resonators. A good agreement between the simulated and measured results is reported. The realized 112.22% fractional bandwidth filter has a return loss (S11) better than 17 dB and an insertion loss (S12) better than 1 dB over the entire UWB spectrum. Notable improvements in stopband characteristics are also achieved.
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Bica, Ioan, i Eugen Mircea Anitas. "Graphene Platelets-Based Magnetoactive Materials with Tunable Magnetoelectric and Magnetodielectric Properties". Nanomaterials 10, nr 9 (9.09.2020): 1783. http://dx.doi.org/10.3390/nano10091783.
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We fabricate hybrid magnetoactive materials (hMAMs) based on cotton fibers, silicone oil, carbonyl iron and graphene nanoplatelets (nGr) at various mass concentrations ΦnGr. The obtained materials are used as dielectric materials for manufacturing plane electrical capacitors. The equivalent electrical capacitance Cp and resistance Rp are measured in an electric field of medium frequency f, without and respectively with a magnetic field of magnetic flux density B in the range from 0.1 T up to 0.5 T. The results are used to extract the components ϵr′ and ϵr″ of the complex relative permittivity ϵr*, and to reveal the magnitude of the induced magnetoelectric couplings kx and magnetodielectric effects MDE. It is shown that ϵr′, ϵr″, kx and MDE are significantly influenced by f,B and ΦnGr. We describe the underlying physical mechanisms in the framework of dipolar approximation and using elements of dielectric theory. The tunable magnetoelectric and magnetodielectric properties of hMAMs are useful for manufacturing electrical devices for electromagnetic shielding of living organisms.
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Wang, Zhongbao, i Shaojun Fang. "ANN Synthesis Model of Single-Feed Corner-Truncated Circularly Polarized Microstrip Antenna with an Air Gap for Wideband Applications". International Journal of Antennas and Propagation 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/392843.
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A computer-aided design model based on the artificial neural network (ANN) is proposed to directly obtain patch physical dimensions of the single-feed corner-truncated circularly polarized microstrip antenna (CPMA) with an air gap for wideband applications. To take account of the effect of the air gap, an equivalent relative permittivity is introduced and adopted to calculate the resonant frequency andQ-factor of square microstrip antennas for obtaining the training data sets. ANN architectures using multilayered perceptrons (MLPs) and radial basis function networks (RBFNs) are compared. Also, six learning algorithms are used to train the MLPs for comparison. It is found that MLPs trained with the Levenberg-Marquardt (LM) algorithm are better than RBFNs for the synthesis of the CPMA. An accurate model is achieved by using an MLP with three hidden layers. The model is validated by the electromagnetic simulation and measurements. It is enormously useful to antenna engineers for facilitating the design of the single-feed CPMA with an air gap.
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Haq, Tanveerul, i Slawomir Koziel. "Rapid Design Optimization and Calibration of Microwave Sensors Based on Equivalent Complementary Resonators for High Sensitivity and Low Fabrication Tolerance". Sensors 23, nr 2 (16.01.2023): 1044. http://dx.doi.org/10.3390/s23021044.
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This paper presents the design, optimization, and calibration of multivariable resonators for microwave dielectric sensors. An optimization technique for the circular complementary split ring resonator (CC-SRR) and square complementary split ring resonator (SC-SRR) is presented to achieve the required transmission response in a precise manner. The optimized resonators are manufactured using a standard photolithographic technique and measured for fabrication tolerance. The fabricated sensor is presented for the high-resolution characterization of dielectric substrates and oil samples. A three-dimensional dielectric container is attached to the sensor and acts as a pool for the sample under test (SUT). In the presented technique, the dielectric substrates and oil samples can interact directly with the electromagnetic (EM) field emitted from the resonator. For the sake of sensor calibration, a relation between the relative permittivity of the dielectric samples and the resonant frequency of the sensor is established in the form of an inverse regression model. Comparisons with state-of-the-art sensors indicate the superiority of the presented design in terms of oil characterization reliability. The significant technical contributions of this work include the employment of the rigorous optimization of geometry parameters of the sensor, leading to its superior performance, and the development and application of the inverse-model-based calibration procedure.
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Littman, Nickolas, Steven G. O’Keefe, Amir Galehdar, Hugo G. Espinosa i David V. Thiel. "Bandwidth control of loop type frequency selective surfaces using dual elements in various arrangements". Flexible and Printed Electronics 6, nr 4 (17.11.2021): 045009. http://dx.doi.org/10.1088/2058-8585/ac361a.
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Abstract Frequency selective surfaces (FSSs) have applications across multiple disciplines due to their unique electromagnetic properties. This paper investigates the use of both rounded square loops, and simple loop type dual elements arranged in unique patterns, to control the transmission and reflection bandwidth and resonant frequencies over KU and K frequency bands supported by equivalent circuit models. The FSSs were fabricated using laser engraving to create conductive loop type elements on a thin, flexible and optically transparent Mylar substrate (relative permittivity of 2.7 and thickness of 65 μm). The frequency response of the surfaces are controlled through the element self-inductance and capacitive coupling with neighbouring elements. This work shows that different arrangements result in the formation of multiple distinct resonances. The theoretical and experimental results were in good agreement where rounded squares and dual element arrays were employed to create broadband and multiband band-stop FSSs. A polarization sensitive surface exhibited stop-bands at 12 and 16 GHz in transverse electric polarization and a stop-band at 14.4 GHz in transverse magnetic polarization. This technique can be applied to any periodic array through careful selection of the individual elements in the array, as well as their arrangement.
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Alonso, Rafael, José María García del Pozo, Samuel T. Buisán i José Adolfo Álvarez. "Analysis of the Snow Water Equivalent at the AEMet-Formigal Field Laboratory (Spanish Pyrenees) During the 2019/2020 Winter Season Using a Stepped-Frequency Continuous Wave Radar (SFCW)". Remote Sensing 13, nr 4 (9.02.2021): 616. http://dx.doi.org/10.3390/rs13040616.
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Snow makes a great contribution to the hydrological cycle in cold regions. The parameter to characterize available the water from the snow cover is the well-known snow water equivalent (SWE). This paper presents a near-surface-based radar for determining the SWE from the measured complex spectral reflectance of the snowpack. The method is based in a stepped-frequency continuous wave radar (SFCW), implemented in a coherent software defined radio (SDR), in the range from 150 MHz to 6 GHz. An electromagnetic model to solve the electromagnetic reflectance of a snowpack, including the frequency and wetness dependence of the complex relative dielectric permittivity of snow layers, is shown. Using the previous model, an approximated method to calculate the SWE is proposed. The results are presented and compared with those provided by a cosmic-ray neutron SWE gauge over the 2019–2020 winter in the experimental AEMet Formigal-Sarrios test site. This experimental field is located in the Spanish Pyrenees at an elevation of 1800 m a.s.l. The results suggest the viability of the approximate method. Finally, the feasibility of an auxiliary snow height measurement sensor based on a 120 GHz frequency modulated continuous wave (FMCW) radar sensor, is shown.
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Tadesse, A. D., O. P. Acharya i S. Sahu. "A Compact Planar Four-port MIMO Antenna for 28/38 GHz Millimeter-wave 5G Applications". Advanced Electromagnetics 11, nr 3 (8.08.2022): 16–25. http://dx.doi.org/10.7716/aem.v11i3.1947.
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This article presents a planar four-port microstrip line-fed Multiple-Input Multiple-Output (MIMO) antenna operating at 5G millimeter-wave candidate bands of 28 GHz and 38 GHz. A rectangular-shaped patch antenna is designed as a main radiator to obtain a resonance at 28 GHz. Etching of a single-element split-ring resonator (SRR) metamaterial unit cell from the basic patch radiator introduces an additional resonance band at 38 GHz. The suggested MIMO antenna is built on Rogers RT5880 substrate material with a dimension of 14 mm × 14 mm, a thickness of 0.8 mm, and a relative permittivity of 2.2.The measured results show that the antenna achieves bandwidths of 26.6-29 GHz and 37.3-39.3 GHz, whereas greater than 25 dB of port isolation between antenna elements over both bands is obtained without applying any complex decoupling structure. The antenna’s equivalent circuit diagram is presented with the help of lumped elements to characterize its electrical responses. The investigated diversity performance parameters, which result in an envelope correlation coefficient below 0.005, diversity gain of almost 10 dB, and channel capacity loss of less than 0.35 bits/s/Hz, are all found within their conventional limits. The findings show the viability of the design for millimeter-wave 5G applications.
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Jang, Soo-Ik, Byung-Cheul Choi i Hyun M. Jang. "Phase-formation kinetics of xerogel and electrical properties of sol-gel-derived BaxSr1−xTiO3 thin films". Journal of Materials Research 12, nr 5 (maj 1997): 1327–34. http://dx.doi.org/10.1557/jmr.1997.0181.
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Chemically homogeneous BaxSr1−xTiO3 (BST with x = 0.6) multicomponent sol was synthesized using barium oxide, strontium chloride, and Ti-alkoxide (titanium isopropoxide) as starting materials. Acetylacetone (AcAc) was introduced as a chelating agent to reduce a rapid hydrolysis rate of Ti-alkoxide. Analysis of Fourier transform infrared spectroscopy (FTIR) spectra indicated that the stabilization of BST sols was achieved by the chelation of Ti-alkoxide with the enolic form of AcAc. The effective activation energy associated with the formation of perovskite phase from the xerogel was estimated by the differential thermal analysis (DTA) experiment using various heating rates. It is approximately 400 kJ/mol with the Avrami exponent (reaction order) of n = 1, suggesting that the growth of perovskite BST is diffusion-controlled. The calculated half-life time suggests that the minimum temperature for the crystallization which is practically accessible to a real processing is approximately 600 °C. The BST thin film fabricated on the “Pt(150 nm)/Ti(100 nm)/SiO2(100 nm)/Si” substrate exhibited the relative dielectric permittivity of 310 and can be represented by an equivalent circuit consisting of a resistive component originated from the bulk perovskite grain and a parallel RC component resulting from the presence of the grain boundary.
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Mackay, Tom G., i Akhlesh Lakhtakia. "Toward morphologically induced anisotropy in thermally hysteretic dielectric properties of vanadium dioxide". AIP Advances 12, nr 10 (1.10.2022): 105026. http://dx.doi.org/10.1063/5.0123882.
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The Bruggeman homogenization formalism was used to numerically investigate the dielectric properties of a columnar thin film (CTF) made from vanadium dioxide. For visible and near-infrared wavelengths, the CTF is electromagnetically equivalent to a homogeneous orthorhombic material. Over the 58–72 °C temperature range, the eigenvalues of the CTF’s relative permittivity dyadic are highly sensitive to temperature and vary according to whether the CTF is being heated or cooled. The anisotropy revealed through the eigenvalues and the anisotropy of the associated hysteresis were investigated in relation to temperature for CTFs of different porosities and columnar cross sections. When the free-space wavelength is 800 nm, the CTF is a dissipative dielectric material that exhibits temperature-dependent anisotropy and anisotropic hysteresis. In contrast, when the free-space wavelength is 1550 nm, the CTF can be a dissipative dielectric material, a hyperbolic material, or a metal-like material, depending on the temperature and the porosity of the CTF. As the porosity of the CTF decreases from 0.55 to 0.3, the anisotropy of the CTF becomes more pronounced, as does the anisotropy of the hysteresis. Only relatively modest variations in anisotropy and hysteresis arise in response to varying the columnar cross-sectional shape, as compared to the variations induced by varying the porosity.
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Hsieh, Gen-Wen, i Chih-Yang Chien. "Wearable Capacitive Tactile Sensor Based on Porous Dielectric Composite of Polyurethane and Silver Nanowire". Polymers 15, nr 18 (19.09.2023): 3816. http://dx.doi.org/10.3390/polym15183816.
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In recent years, the implementation of wearable and biocompatible tactile sensing elements with sufficient response into healthcare, medical detection, and electronic skin/amputee prosthetics has been an intriguing but challenging quest. Here, we propose a flexible all-polyurethane capacitive tactile sensor that utilizes a salt crystal-templated porous elastomeric framework filling with silver nanowire as the composite dielectric material, sandwiched by a set of polyurethane films covering silver nanowire networks as electrodes. With the aids of these cubic air pores and conducting nanowires, the fabricated capacitive tactile sensor provides pronounced enhancement of both sensor compressibility and effective relative dielectric permittivity across a broad pressure regime (from a few Pa to tens of thousands of Pa). The fabricated silver nanowire–porous polyurethane sensor presents a sensitivity improvement of up to 4−60 times as compared to a flat polyurethane device. An ultrasmall external stimulus as light as 3 mg, equivalent to an applied pressure of ∼0.3 Pa, can also be clearly recognized. Our all-polyurethane capacitive tactile sensor based on a porous dielectric framework hybrid with conducting nanowire reveals versatile potential applications in physiological activity detection, arterial pulse monitoring, and spatial pressure distribution, paving the way for wearable electronics and artificial skin.
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Anjali, M., Kumaran Rengaswamy, Abhishek Ukey, Lincy Stephen, C. V. Krishnamurthy i V. Subramanian. "Flexible metamaterial based microwave absorber with epoxy/graphene nanoplatelets composite as substrate". Journal of Applied Physics 133, nr 6 (14.02.2023): 063105. http://dx.doi.org/10.1063/5.0138171.
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Customization of substrates for the design of metamaterial absorbers gives the user a wide choice of parameters like flexibility, thickness, dielectric constant, etc. Polymer composites are attractive in this regard as they provide a variety of options to fabricate substrates with desirable properties depending on the matrix and filler materials. In this work, flexible polymer nanocomposites with different weight percentages of graphene nanoplatelets (GnP) in epoxy were fabricated and the dielectric characterization was performed. The presence of GnP increased the real part of the dielectric constant from 2.5 for 0 wt. % to 14.7 for 9 wt. % of the epoxy-GnP composites measured in X-band frequency. The substrate with 5 wt. % of GnP in epoxy having a relative permittivity of 7.3–j0.25 is chosen to design a metamaterial absorber, and the absorption studies are carried out numerically. The proposed absorber having a thickness of λ/22 is shown to have a maximum absorption of 99.8% at the frequency 9.88 GHz. Furthermore, an equivalent circuit model of the absorber is proposed and the analytical values of the circuit elements are determined. The metamaterial prototype is fabricated by coating metallic resonating structures on top of the flexible E-GnP5 substrate of thickness 1.4 mm by thermal evaporation. The performance of the fabricated absorber agrees well with the simulation results. These polymer nanocomposites with good flexibility, thermal stability, and optimum dielectric properties would be the future materials for developing conformal metamaterial absorbers for microwave applications.
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Wang, Ruonan, Yang Fang, Qianxiang Gao, Yong Li, Xihan Yang i Zhenmao Chen. "Quantitative Visualization of Buried Defects in GFRP via Microwave Reflectometry". Sensors 23, nr 14 (24.07.2023): 6629. http://dx.doi.org/10.3390/s23146629.
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Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it is indispensable to carry out effective quantitative nondestructive testing (NDT) of internal defects buried within GFRP structures. Along with the development of composite materials, microwave NDT is promising in non-intrusive inspection of defects in GFRPs. In this paper, quantitative screening of the subsurface impact damage and air void in a unidirectional GFRP via microwave reflectometry was intensively investigated. The influence of the microwave polarization direction with respect to the GFRP fiber direction on the reflection coefficient was investigated by using the equivalent relative permittivity calculated with theoretical analysis. Following this, a microwave NDT system was built up for further investigation regarding the imaging and quantitative evaluation of buried defects in GFRPs. A direct-wave suppression method based on singular-value decomposition was proposed to obtain high-quality defect images. The defect in-plane area was subsequently assessed via a proposed defect-edge identification method. The simulation and experimental results revealed that (1) the testing sensitivity to buried defects was the highest when the electric-field polarization direction is parallel to the GFRP fiber direction; and (2) the averaged evaluation accuracy regarding the in-plane area of the buried defect reached approximately 90% by applying the microwave reflectometry together with the proposed processing methods.
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Nepeina, Kseniia, Elena Bataleva i Pavel Alexandrov. "Electromagnetic Monitoring of Modern Geodynamic Processes: An Approach for Micro-Inhomogeneous Rock through Effective Parameters". Applied Sciences 13, nr 14 (10.07.2023): 8063. http://dx.doi.org/10.3390/app13148063.
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This study focuses on microscale anisotropy in rock structure and texture, exploring its influence on the macro anisotropic electromagnetic parameters of the geological media, specifically electric conductivity (σ), relative permittivity (ε), and magnetic permeability (μ). The novelty of this research lies in the advancement of geophysical monitoring methods for calculating cross properties through the estimation of effective parameters—a kind of integral macroscopic characteristic of media mostly used for composite materials with inclusions. To achieve this, we approximate real geological media with layered bianisotropic media, employing the effective media approximation (EMA) averaging technique to simplify the retrieval of the effective electromagnetic parameters (e.g., apparent resistivity–inversely proportional to electrical conductivity). Additionally, we investigate the correlation between effective electromagnetic parameters and geodynamic processes, which is supported by the experimental data obtained during monitoring studies in the Tien Shan region. The observed decrease and increase in apparent electrical resistivity values of ρk over time in orthogonal azimuths leads to further ρk deviations of up to 80%. We demonstrate that transitioning to another coordinate system is equivalent to considering gradient anisotropic media. Building upon the developed method, we derive the effective electric conductivity tensor for gradient anisotropic media by modeling the process of fracturing in a rock mass. Research findings validate the concept that continuous electromagnetic monitoring can aid in identifying natural geodynamic disasters based on variations in integral macroscopic parameters such as electrical conductivity. The geodynamic processes are closely related to seismicity and stress regimes with provided constraints. Therefore, disasters such as earthquakes are damaging and seismically hazardous.
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YOSSIFON, G., I. FRANKEL i T. MILOH. "Macro-scale description of transient electro-kinetic phenomena over polarizable dielectric solids". Journal of Fluid Mechanics 620 (10.02.2009): 241–62. http://dx.doi.org/10.1017/s002211200800459x.
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We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable dielectric solids following the application of a ‘weak’ transient electric field. To obtain a macro-scale description in the limit of narrow electric double layers (EDLs), we have derived a pair of effective transient boundary conditions directly connecting the electric potentials across the EDL. Within the framework of the above assumptions, these conditions apply to a general transient electro-kinetic problem involving dielectric solids of arbitrary geometry and relative permittivity. Furthermore, the newly derived scheme is applicable to general transient and spatially non-uniform external fields. We examine the details of the physical mechanisms involved in the relaxation of the induced-charging process of the EDL adjacent to polarizable dielectric solids. It is thus established that the time scale characterizing the electrostatic relaxation increases with the dielectric constant of the solid from the Debye time (for the diffusion across the EDL) through the ‘intermediate’ scale (proportional to the product of the respective Debye- and geometric-length scales). Thus, the present rigorous analysis substantiates earlier results largely obtained by heuristic use of equivalent RC-circuit models. Furthermore, for typical values of ionic diffusivity and kinematic viscosity of the electrolyte solution, the latter time scale is comparable to the time scale of viscous relaxation in problems concerning microfluidic applications or micro-particle dynamics. The analysis is illustrated for spherical micro-particles. Explicit results are thus presented for the temporal evolution of electro-osmosis around a dielectric sphere immersed in unbounded electrolyte solution under the action of a suddenly applied uniform field, combining both induced charge and ‘equilibrium’ (fixed charge) contributions to the zeta potential. It is demonstrated that, owing to the time delay of the induced-EDL charging, the ‘equilibrium’ contribution to fluid motion (which is linear in the electric field) initially dominates the (quadratic) ‘induced’ contribution.
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Fomin, D. G., N. V. Dudarev, S. N. Darovskikh i V. K. Baranov. "The Investigation of the Volumetric Strip-Slot Transition with U-Shaped Slot Resonator". Ural Radio Engineering Journal 4, nr 3 (2020): 277–92. http://dx.doi.org/10.15826/urej.2020.4.3.002.
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The application of volumetric strip-slot transition for the implementationof wireless devices with contactless frequency-selective transmission of microwave signals is relevant. This is due to the compactness of volumetric strip-slot transition achieved by the multilayer arrangement of its functional parts and of its electrical frequency-selective characteristics. At the same time the volumetric-modular design allows the replacement of its individual components which provides high functional flexibility of the device. Reducing of weight and dimensions of the volumetric strip-slot transition while maintaining its electrical characteristics is possible due to well-known methods used in microwave technology: 1) using of substrates with a high value of the relative permittivity, 2) due to the transition to higher frequency ranges. The authors of this paper present the third method for reducing of weight and dimensions of the volumetric stripslot transition by using a U-shaped slot resonator. The development of the equivalent circuit of the volumetric strip-slot transition and calculation of all its lumped elements are also presented. The values of such lumped elements as linear capacitance of the strip line, linear inductance of the strip line, characteristic impedance of the slot transmission line were determined. The value of the inductive inhomogeneity occurred when the slot resonator bends by 90 degrees was calculated and its S-parameters in the frequency range were simulated. Numerical electrodynamics simulation was performed to confirm the validity of the results of circuit simulation. Then the experiment research of the sample of the volumetric strip-slot transition with the U-shaped slot resonator was carried out. The theoretical and experimental results of the conducted researches of volumetric strip-slot transition with the U-shaped slot resonator are in good qualitative and numerical agreement with each other. The use of the U-shaped slot resonator provides an opportunity to achieve a 36% reduction of weight and dimensions parameters of the volumetric stripslot transition while maintaining its electrical characteristics.
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Shihzad, Waleed, Sadiq Ullah, Ashfaq Ahmad, Nisar Ahmad Abbasi i Dong-you Choi. "Design and Analysis of Dual-Band High-Gain THz Antenna Array for THz Space Applications". Applied Sciences 12, nr 18 (14.09.2022): 9231. http://dx.doi.org/10.3390/app12189231.
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In this paper, a high-gain THz antenna array is presented. The array uses a polyimide substrate with a thickness of 10 μm, a relative permittivity of 3.5, and an overall volume of 2920 μm × 1055 μm × 10 μm, which can be employed for THz band space communication and other interesting applications. The dual-band single-element antenna is designed in four steps, while operating at 0.714 and 0.7412 THz with −10 dB bandwidths of 4.71 and 3.13 GHz, providing gain of 5.14 and 5 dB, respectively. In order to achieve a high gain, multiple order antenna arrays are designed such as the 2 × 1 antenna array and the 4 × 1 antenna array, named type B and C, respectively. The gain and directivity of the proposed type C THz antenna array are 12.5 and 11.23 dB, and 12.532 and 11.625 dBi at 0.714 and 0.7412 THz, with 99.76 and 96.6% radiation efficiency, respectively . For justification purposes, the simulations of the type B antenna are carried out in two simulators such as the CST microwave studio (CSTMWS) and the advance design system (ADS), and the performance of the type B antenna is compared with an equivalent circuit model on the bases of return loss, resulting in strong agreement. Furthermore, the parametric analysis for the type C antenna is done on the basis of separation among the radiating elements in the range 513 to 553 μm. A 64 × 1 antenna array is used to achieve possible gains of 23.8 and 24.1 dB, and directivity of 24.2 and 24.5 dBi with good efficiencies of about 91.66 and 90.35% at 0.7085 and 0.75225 THz, respectively, while the 128 × 1 antenna array provides a gain of 26.8 and 27.2 dB, and directivity of 27.2 and 27.7 dBi with good efficiency of 91.66 and 90.35% at 0.7085 and 0.75225 THz, respectively. All the results achieved in this manuscript ensure the proposed design is a feasible candidate for high-speed and free space wireless communication systems.
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Varshney, Atul, Vipul Sharma, Issa Elfergani, Chemseddine Zebiri, Zoran Vujicic i Jonathan Rodriguez. "An Inline V-Band WR-15 Transition Using Antipodal Dipole Antenna as RF Energy Launcher @ 60 GHz for Satellite Applications". Electronics 11, nr 23 (23.11.2022): 3860. http://dx.doi.org/10.3390/electronics11233860.
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This article demonstrates the design and development of WR-15 transition using an antipodal microstrip dipole antenna at a frequency of 60 GHz for space applications. An inline microstrip line to rectangular waveguide (MS-to-RWG) transition is proposed for the V-band (50–75 GHz) functioning. The RF energy is coupled and launched through an antipodal dipole microstrip antenna. Impedance matching and mode matching between the MS line and dipole are achieved by a quarter wave impedance transformer. This results in the better performance of transitions in terms of insertion loss (IL > −0.50 dB) and return loss (RL < −10 dB) for a 40.76% relative bandwidth from 55.57 GHz to 65.76 GHz. The lowest values of IL and RL at 60 GHz are −0.09 dB and −32.05 dB, respectively. A 50 μm thick double-sided etched InP substrate material is used for microstrip antipodal dipole antenna design. A back-to-back designed transition has IL > −0.70 dB and RL < −10 dB from 54.29 GHz to 64.07 GHz. The inline transition design is simple in structure, easy to fabricate, robust, compact, and economic; occupies less space because the transition size is exactly equal to the WR-15 length; and is prepared using an InP substrate with high permittivity of 12.4 and thickness of 50 μm. Thus, the devices have the lowest insertion loss value and lowest return loss (RL) value, of <−31 dB, as compared to earlier designs in the literature. Therefore, the proposed design has the lowest radiation loss (because of thickness) and highest transmission (about 97% power). Easy impedance matching using only a single-step quarter-wave transformer between the antipodal dipole antenna and 50 Ω microstrip line (avoiding the multi-sections’ demand and microstrip line’s tedious complexity) is needed. Since, when the InP dielectric substrate is inserted in WR-15, the waveguide becomes a dielectric-filled waveguide (DFWG), and its characteristics impedance reduces to 143 Ω from 505 Ω at an operating frequency of 60 GHz. In the proposed transition, no ridge waveguide or waveguide back-short is utilized in WR-15. The microstrip line did not contain any via, fence, window, screw, galvanic structure, post, etc. Hence, the transition is suitable for high-data-rate 5G communications, satellite remote sensing, missile navigation, MIC/MMIC circuits’ characterization, and mm-wave applications. The electrical equivalent model of the proposed design has been generated and validated using an RF circuit simulator and was found to have excellent matching.
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Karnajit Singh, Hodam, Prajna P. Mohapatra, Subingya Pandey i Pamu Dobbidi. "Unlocking the potential of hexaferrite–spinel ferrite composites: Microstructure-induced colossal permittivity and relaxation phenomena". Journal of Applied Physics 134, nr 19 (15.11.2023). http://dx.doi.org/10.1063/5.0168293.
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The solid-state synthesized dense ceramic composite, consisting of M-type hexaferrite Ba0.5Sr0.5Fe12O19 and inverse spinel ferrite Ni0.3Co0.2Zn0.5Fe2O4 (NCZFO) with varying concentrations, demonstrates the presence of apparent colossal permittivity along with dielectric relaxation behaviors at the higher frequency regions for all the composites. This phenomenon manifests as a giant dielectric permittivity of approximately 105 at 1 kHz, gradually decreasing to around 103 at 1 MHz at room temperature. It can be attributed to the Maxwell–Wagner interfacial polarization, which arises from the presence of different conductivity regions within the microstructures of the composite. The dielectric permittivity and the activation energy are also increased with higher NCZFO content, indicating an intricate microstructure influencing the electrical response by impacting charge carrier movement and ion migration. The presence of both Fe and Co cation defects and oxygen vacancies enhanced non-uniformity in the microstructure with different conductivity regions. The appearance of relaxation peaks in the higher frequency region can be attributed to inhomogeneity in the microstructure. In conjunction with the equivalent circuit analysis, the Nyquist plot confirmed that the electrical response at a lower frequency primarily arises from grain boundaries. The departure from ideal Debye-type relaxation behavior in the electrical response is also confirmed by impedance analysis. Furthermore, the step-like increase in AC conductivity with frequency suggests that the electrical response observed at a lower frequency is not intrinsic. Rather, it indicates the depletion of insulating grain boundaries due to diffusive ion motions resulting from defects. This observation reinforces that the high dielectric permittivity observed in the composite is not an inherent characteristic of the constituent materials. Instead, it arises from the microstructure and the influence of defects within the material.
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Ramírez-González, Julia, Derek Clark Sinclair i Anthony Roy West. "Impedance and Dielectric Spectroscopy of Functional Materials: A Critical Evaluation of the Two Techniques". Journal of The Electrochemical Society, 6.11.2023. http://dx.doi.org/10.1149/1945-7111/ad09fa.
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Abstract Impedance and dielectric spectroscopies are closely-related techniques for measuring electrical properties of materials. The techniques differ in two ways. First, impedance measurements are usually made over several decades of frequency (ie broadband) whereas most dielectric measurements are made at fixed frequency. Second, time constants that control semicircles in impedance complex plane plots and peaks in permittivity or tan δ spectroscopic plots are not the same. In impedance data, time constants represent conducting components and parallel resistance-capacitance (RC) combinations; in permittivity data they represent dielectric processes and series RC combinations. Differences between the techniques are confined to data analysis procedures and interpretation. Using broadband data, it is possible to (i) determine the best equivalent circuit to fit experimental data, (ii) unambiguously evaluate and assign resistance, capacitance and time constant parameters to regions of the material being measured and (iii) quantify departures from ideality using constant phase elements, CPEs. The advantages of using broadband measurements are highlighted with two examples: calcium copper titanate, CCTO which is often, erroneously, described as a giant or colossal dielectric; lead magnesium niobate, PMN, the classic relaxor ferroelectric whose characteristic properties are controlled entirely by the presence of non-ideality, represented by a CPE, in its equivalent circuit.
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Teranishi, Takashi, Hideki Matsui, Shinya Kondo i Akira Kishimoto. "Spinodal decomposition-derived giant polarization in TiO2–SnO2 generated from a metastable phase". Journal of Applied Physics 133, nr 17 (2.05.2023). http://dx.doi.org/10.1063/5.0144782.
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Spinodal decomposition (SD) was incorporated into Nb-doped metastable TiO2–SnO2 to achieve giant interfacial polarization. The dielectric characteristics were analyzed using an equivalent circuit involving electron migration, where the SD bulk is given by the universal dielectric response relation. Both the Nb–TiO2 and the Nb–SnO2 layers showed semiconductive behaviors. With increasing SD treatment temperature, the SD volume fraction increased, as did cation interdiffusion at the SD interface, resulting in a large dielectric loss. The optimal SD temperature was determined as 1100 °C, where the Maxwell–Wagner capacitance showed a very high value of 44.6 μF corresponding to the permittivity at the lowest frequency exceeding 106. Such colossal polarization was considered due to an accumulation of trapped electrons at the Schottky barrier at SD layers with different conductivities.
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Bonnell, Randall, Daniel McGrath, Andrew R. Hedrick, Ernesto Trujillo, Tate G. Meehan, Keith Williams, Hans‐Peter Marshall i in. "Snowpack relative permittivity and density derived from near‐coincident lidar and ground‐penetrating radar". Hydrological Processes 37, nr 10 (październik 2023). http://dx.doi.org/10.1002/hyp.14996.
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AbstractDepth‐based and radar‐based remote sensing methods (e.g., lidar, synthetic aperture radar) are promising approaches for remotely measuring snow water equivalent (SWE) at high spatial resolution. These approaches require snow density estimates, obtained from in‐situ measurements or density models, to calculate SWE. However, in‐situ measurements are operationally limited, and few density models have seen extensive evaluation. Here, we combine near‐coincident, lidar‐measured snow depths with ground‐penetrating radar (GPR) two‐way travel times (twt) of snowpack thickness to derive >20 km of relative permittivity estimates from nine dry and two wet snow surveys at Grand Mesa, Cameron Pass, and Ranch Creek, Colorado. We tested three equations for converting dry snow relative permittivity to snow density and found the Kovacs et al. (1995) equation to yield the best comparison with in‐situ measurements (RMSE = 54 kg m−3). Variogram analyses revealed a 19 m median correlation length for relative permittivity and snow density in dry snow, which increased to >30 m in wet conditions. We compared derived densities with estimated densities from several empirical models, the Snow Data Assimilation System (SNODAS), and the physically based iSnobal model. Estimated and derived densities were combined with snow depths and twt to evaluate density model performance within SWE remote sensing methods. The Jonas et al. (2009) empirical model yielded the most accurate SWE from lidar snow depths (RMSE = 51 mm), whereas SNODAS yielded the most accurate SWE from GPR twt (RMSE = 41 mm). Densities from both models generated SWE estimates within ±10% of derived SWE when SWE averaged >400 mm, however, model uncertainty increased to >20% when SWE averaged <300 mm. The development and refinement of density models, particularly in lower SWE conditions, is a high priority to fully realize the potential of SWE remote sensing methods.
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Boroujeni, Saman Naseri, Bjørn Maribo-Mogensen, Xiaodong Liang i Georgios M. Kontogeorgis. "On the estimation of equivalent conductivity of electrolyte solutions; The effect of relative static permittivity and viscosity". Fluid Phase Equilibria, grudzień 2022, 113698. http://dx.doi.org/10.1016/j.fluid.2022.113698.
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Zhao, Biyao, Jinshun Bi, Yue Ma, Jian Zhang, Yan Wang, Linjie Fan, Tingting Han, Yundong Xuan, Viktor Stempitsky i Mengxin Liu. "The impacts of localized backside etching on proton radiation response in SOI passive devices". Japanese Journal of Applied Physics, 17.01.2023. http://dx.doi.org/10.35848/1347-4065/acb40f.
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Abstract In this work, the effect of high-energy proton irradiation on the radiofrequency (RF) properties of silicon-on-insulator (SOI) substrates is investigated. The localized backside etching (LBE) structure is introduced for RF properties improvement and proton irradiation hardening. It is observed that after the 50 MeV proton irradiation with a fluence of 1×1012 p/cm2, the attenuation, crosstalk, and relative permittivity significantly decrease for conventional SOI substrates. In contrast, LBE substrates are less sensitive to proton irradiation and simultaneously exhibit better RF performance. The enhancement of the LBE structure on irradiation tolerance is qualitatively characterized by the equivalent circuit model parameter extraction.
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Takahashi, Ken M. "Moisture Intrusion in Sio2/Epoxy Interfaces". MRS Proceedings 153 (1989). http://dx.doi.org/10.1557/proc-153-187.
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SummaryIn-situ interfacial impedance measurements were used to study the effects of moisture at 80 °C on the interface between oxidized silicon and a diglycidyl ether of bisphenol A (DGEBA) epoxy cured with diethylene triamine (DETA). Using two electrode configurations, admittances attributable to bulk and interfacial conduction processes were distinguished. Bulk impedance measurements followed Randles behavior; conduction in the bulk epoxy was ionic, and was diffusion controlled at low frequencies. Equivalent circuit models were used to demonstrate that an apparent interfacial conduction process was caused by distributed current leakage into the silicon subphase, not a true interfacial conduction path that would indicate water adsorption or interfacial aggregation. However, transitions in diffusivity and bulk epoxy permittivity behavior above a 70-80% relative humidity threshold were observed. Effective epoxy permittivity (∈c) jumped to values indicative of a water cluster induced Maxwell-Wagner relaxation. The humidity threshold corresponds to a level that has been associated with adhesion loss in epoxies. It appears that epoxy adhesion losses result from bulk epoxy property changes at high humidity rather than interfacial bond displacement or delamination.
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Takahashi, Ken M. "Moisture Intrusion in Sio2/Epoxy Interfaces". MRS Proceedings 154 (1989). http://dx.doi.org/10.1557/proc-154-259.
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In-situ interfacial impedance measurements were used to study the effects of moisture at 80 ° C on the interface between oxidized silicon and a diglycidyl ether of bisphenol A (DGEBA) epoxy cured with diethylene triamine (DETA). Using two electrode configurations, admittances attributable to bulk and interfacial conduction processes were distinguished. Bulk impedance measurements followed Randles behavior; conduction in the bulk epoxy was ionic, and was diffusion controlled at low frequencies. Equivalent circuit models were used to demonstrate that an apparent interfacial conduction process was caused by distributed current leakage into the silicon subphase, not a true interfacial conduction path that would indicate water adsorption or interfacial aggregation. However, transitions in diffusivity and bulk epoxy permittivity behavior above a 70–80% relative humidity threshold were observed. Effective epoxy permittivity (εc) jumped to values indicative of a water cluster induced Maxwell-Wagner relaxation. The humidity threshold corresponds to a level that has been associated with adhesion loss in epoxies. It appears that epoxy adhesion losses result from bulk epoxy property changes at high humidity rather than interfacial bond displacement or delamination.
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Bobzin, Kirsten, Wolfgang Wietheger, Elisa Burbaum, Tim Hosenfeldt, Nazlim Bagcivan, Mehmet Öte, Björn Müller, Carsten Kunde i Anna-Lena Elsner. "Comparison of Ceramic Insulation Coatings via Impedance Spectroscopy". Journal of Thermal Spray Technology, 22.04.2022. http://dx.doi.org/10.1007/s11666-022-01395-z.
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AbstractAlumina is often used for electrical insulation. However, different material systems promise to increase the insulation due to their material characteristics. Because of the process properties including high cooling rates, thermally sprayed coatings generally differ from sintered material, which also effect the electrical properties. Within this study, different thermally sprayed coatings are analyzed via impedance spectroscopy to evaluate the capacitive and the electrical insulation behavior. Besides comparing the frequency-dependent resistance, equivalent circuit diagrams were used to calculate the relative permittivity of the coatings. X-ray diffractograms reveal the phase stability of the coatings during thermal spraying. X-ray diffraction was additionally conducted to classify the systems and the respective effects. In particular, the investigated mullite-based coatings exhibit slightly increased impedance values compared to conventionally used alumina-based coating systems.
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Milsom, John Andrew. "Why are the Electric and Magnetic Fields in an Electromagnetic Wave Propagating through a Conductor not in Phase?" European Journal of Physics, 26.07.2023. http://dx.doi.org/10.1088/1361-6404/aceadf.
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Abstract Intermediate and advanced texts in electromagnetic theory frequently discuss infinite plane waves propagating through conducting media. They find that the magnetic field has a phase delay (relative to the electric field) that can be as large as π/4 rad depending upon the ratio of the conductivity to the product of the angular frequency and the permittivity σ/(ωε). The expressions given to calculate this phase delay are unnecessarily complicated and provide minimal physical insight. We provide a simple expression for the phase delay and then illustrate how to interpret it by first considering Ampere's Law and Faraday's Law separately and then coupling them together. In the classroom, this provides an excellent educational opportunity for our students since we make analogies between the phase shifts associated with Ampere's Law and equivalent phase shifts in driven oscillators and alternating current RC circuits.