Dielectric Coupling Research Articles

Catfish Effect Induced by Anion Sequential Doping for Microwave Absorption

AbstractHeteroatom doping engineering is desirable in tuning crystal structures and electrical properties, which is considered an opportunity to further develop microwave absorption materials. However, the competition mechanism and priority among doped atoms have not been revealed, which are insufficient to guide the most reasonable dielectric coupling model and design high‐performance absorbers. In this work, based on in situ N and O, ex situ S is introduced through external thermal driving, leading to fierce competition among anions. Specifically, S atoms replace pyrrole N, drive out lattice O, and create O vacancies, bringing more extensive local charge redistribution and stronger electron interaction, thus activating the defect‐induced polarization (3–6 times higher than conduction loss) in the middle/high‐frequency region. Therefore, the effective absorption bandwidth (EAB) of 9.03 GHz and the minimum reflection loss (RLmin) of −64.05 dB at a filling rate of 10 wt.% are obtained, which improves the record of carbon absorbers as reported. Through macro‐designs, i.e., multi‐layer gradient metamaterial, or utilizing other advantages, e.g., cost‐effective, stable chemical properties and wide‐angle absorption, porous carbon may possess a great application prospect in the naval field.

Aliovalent Calcium Substitution: An Effective Way to Enhance the Magnetoelectric Coupling Properties of Multiferroic BiFeO3

Kinetics of magnetoelectric coupling in bismuth ferrite (BiFeO3) with the substitution of aliovalent calcium ion is investigated. The resulting structural, dielectric, magnetic, and magnetoelectric (ME) coupling properties are explained in terms of chemical pressure originating from the substituent ion. Substitution of calcium finds to reduce the oxygen vacancies. Two important substitution concentrations find to be critical in ferroelectric (FE) and ME coupling properties. At 10 at% calcium, highest remanent polarization is obtained and maximum ME coupling coefficient is observed at 20 at%, which suggests calcium concentration between 10% and 20% can be optimized to obtain good electrical and ME coupling properties of BiFeO3. Maximum ME coupling coefficient at calcium concentration 20 at% is close to numerical calculations reported in the literature. Magnetic properties are also favorably modified by the substitution; a coupled antiferromagnetic and weak ferromagnetic ordering is obtained. Also, a variation in blocking temperature and spin relaxation is observed with respect to the substituent ion concentration.

Onset of Chirality in Plasmonic Meta-Molecules and Dielectric Coupling.

Chirality is a fundamental feature in all domains of nature, ranging from particle physics over electromagnetism to chemistry and biology. Chiral objects lack a mirror plane and inversion symmetry and therefore cannot be spatially aligned with their mirrored counterpart, their enantiomer. Both natural molecules and artificial chiral nanostructures can be characterized by their light-matter interaction, which is reflected in circular dichroism (CD). Using DNA origami, we assemble model meta-molecules from multiple plasmonic nanoparticles, representing meta-atoms accurately positioned in space. This allows us to reconstruct piece by piece the impact of varying macromolecular geometries on their surrounding optical near fields. Next to the emergence of CD signatures in the instance that we architect a third dimension, we design and implement sign-flipping signals through addition or removal of single particles in the artificial molecules. Our data and theoretical modeling reveal the hitherto unrecognized phenomenon of chiral plasmonic-dielectric coupling, explaining the intricate electromagnetic interactions within hybrid DNA-based plasmonic nanostructures.

Energy scale of dielectric coupling in antiferromagnetic insulators

To probe the energy of dielectric coupling between the dipole chains and the quasipolarons based on extension of the polaron concept, dielectric and magnetic properties of antiferromagnetic insulators, namely Ca4-xCuxTi4O12 (x = 3, 2 and 1), are investigated at different temperatures. The energy is estimated larger than 56 meV of the dipole interaction energy, but smaller than 88 meV of the dipole-chain thermal activation energy which is for the Dissado-Hill type dielectric relaxation. In particular, the quasipolaron ingredient is at least 28 meV of the total superexchange interaction which bond one singe titanium ion of the dipole chain with four quasipolarons. Then, the energy of the coupling is in the range from 84 meV to 88 meV. The experimental observation, suggests the dielectric coupling may provide an approach to obtain large permittivity in strongly-correlating systems of antiferromagnetic insulators.

Electromechanical properties and photoluminescence of Er3+-doped PMN-33PT single crystal

Based on the successful growth of large-sized Er3+-doped PMN-PT single crystal, the phase composition, electromechanical properties and photoluminescence of [001]C-oriented Er3+-doped PMN-33PT crystal were investigated in detail. The results show that the crystal coexists in rhombohedral and monoclinic phases at room temperature. The crystal possesses excellent piezoelectric (d33 ∼ 2103 pC/N), dielectric (ε33T ∼ 7589), and electromechanical coupling properties (k33 ∼ 0.91), accompanied by a higher phase transition temperature and larger coercive field compared with that of PMN-33PT single crystal. This indicates an improved electromechanical performance induced by Er3+ doping. Additionally, the crystal achieves upconversion and downconversion luminescence, and a strong dependence of the upconversion emission on temperature is demonstrated. Furthermore, a comparable optical temperature sensing performance based on the fluorescence intensity ratio of the upconversion luminescence is verified. These results demonstrate a promising multifunctional material. The electro-optical coupling performance of the Er3+-doped PMN-33PT crystal is under evaluation.

The study of CoFe2O4/Ba0.85Ca0.15Zr0.1Ti0.9O3-laminated composite ceramic on dielectric, relaxation, ferroelectric, and magnetoelectric coupling properties

The study of CoFe2O4/Ba0.85Ca0.15Zr0.1Ti0.9O3-laminated composite ceramic on dielectric, relaxation, ferroelectric, and magnetoelectric coupling properties

Optical properties, dielectric relaxor behavior, impedance and modulus spectroscopy of 0.8BiFeO3-0.2CaTiO3 composite

0.8BiFeO3-0.2CaTiO3 (0.8BFO-0.2CTO) was synthesized by the sol-gel route. Structural characterization was performed by X-ray diffraction which confirms the rhombohedral structure. FESEM analysis reveals the irregular grains that are inhomogenous and slightly dense. Temperature-dependent dielectric permittivity shows a dielectric anomaly near the magnetic phase transition temperature (TN) of BiFeO3 as well as relaxor-type ferroelectric properties. The PE loop confirms the presence of ferroelectricity in the sample. Frequency-dependent ac conductivity exhibits low frequency dispersion and was well explained by Jonscher power law. The obtained fitting parameters A (pre-exponential factor that indicates polarizability) and n (dimensionless frequency exponent) show maxima and minima at the transition temperature. The electrical properties were further analysed by impedance and modulus spectroscopy. According to these analysis, the relaxation time was distributed and does not follow the Debye type behaviour. Nyquist plots had been used to estimate grain and grain boundary contributions. A typical negative temperature coefficient of resistance (NTCR) behaviour was apparent due to the decrement in bulk and grain boundary resistances as the temperature increases. The temperature-dependent relaxation time revealed Arrhenius's behaviour. 0.8BFO-0.2CTO exhibits absorption and shows a transmittance of 40–44% in the visible region of spectra. The obtained value of Eg was ∼2.26 eV, which implies the application in ultrafast optoelectronic devices. The good ability of absorption in visible region, high transmittance, the increase of extinction coefficient with wavelength, and low band gap makes 0.8BFO-0.2CTO an extraordinary material for optical devices application. The sample also shows a decrease in magneto-capacitance and increase in magneto-impedance which reflects the presence of strong magneto dielectric coupling in 0.8BFO-0.2CTO at room temperature.

Direct evidence of mutual control of ferroelectric polarization and magnetization in Y-type hexaferrite BaSrCo2Fe12-Al O22 ceramics

Hexaferrites that exhibit the intrinsic and strong magnetoelectric (ME) coupling effect have been considered the most promising candidate for single-phase multiferroics. Currently, the strong ME coupling effect in this system was widely reported in single crystal form, while it is rare in polycrystalline one. In this work, Y-type hexaferrite BaSrCo2Fe12-xAlxO22 (x = 0.0, 0.3, 0.6 and 0.9) ceramics were manufactured with conventional solid-state reaction. Their magnetic, dielectric, and ME coupling properties were systematically surveyed. It was revealed that Al doping could result in a high magnetic transition temperature of ~ 345 K for x = 0.9. Also, the ferroelectric polarization and abnormal magnetodielectric properties were significantly enhanced which could be maintained down to 200 K. Most interestingly, the sample x = 0.9 displayed strong direct and converse ME coefficients of ~ 400 ps/m and ~ 900 ps/m at 150 K, respectively. Therefore, these results reveal that Al doping can broaden our understanding of the Y-type hexaferrite in room-temperature multiferroics.

A Triple-Quasi-TEM-Resonance Dielectric Cavity for Bandpass Filter Design

This letter presents a triple-quasi-TEM-resonance dielectric cavity for compact bandpass filter design. The proposed dielectric cavity is silver coated and has three blind holes which form three distinct quasi-TEM mode resonators. The external coupling structure for the resonator is realized by tapping hole. The inter-resonator couplings are realized and controlled by slots on the outer surfaces of the dielectric block. A three-pole filter with two controllable transmission zeros is designed and implemented. The measured results agree well with the simulated results, verifying the proposed triple-resonance dielectric cavity structure and coupling mechanisms.

A Versatile and Shelf-Stable Dielectric Coupling Medium for Microwave Imaging

To develop a new class of emulsions using a protein-based emulsifier as the coupling fluid for microwave imaging systems. In this paper, we provide a theoretical basis for engineering shelf-stable dielectric fluids, a step-by-step formulation method, and measurements of complex dielectric properties in the frequency range of 0.5-3 GHz, which can be applicable for many of the recent microwave imaging systems. This medium was primarily designed for long-term stability while providing a controllable range of complex dielectric permittivities given different fractions of its constituents. Consequently, this emulsion shows dielectric stability in open air throughout a 7-day experiment and temperature insensitivity over the range of 0 ° C to 60 ° . This control over dielectric permittivity enables formulations that tune the background-to-target contrast to the linearizable regime of iterative inverse scattering algorithms. Accordingly, the emulsion conductivity can also be controlled and reduced to maintain the required signal-to-noise ratio within the dynamic range of the imaging system. The new formulation overcomes the practical challenges of engineering coupling fluids for microwave imaging systems, e.g., temporal stability, non-toxic, low sensitivity to temperature variation, and easy formulation from readily available and inexpensive materials. The achieved properties associated with this new fluid are of particular benefit to microwave imaging systems used in thermal therapy monitoring.

The second production of RSD (AC-LGAD) at FBK

In this contribution we describe the second run of RSD (Resistive AC-Coupled Silicon Detectors) designed at INFN Torino and produced by Fondazione Bruno Kessler (FBK), Trento. RSD are n-in-p detectors intended for 4D particle tracking based on the LGAD technology that get rid of any segmentation implant in order to achieve the 100% fill-factor. They are characterized by three key-elements, (i) a continuous gain implant, (ii) a resistive n-cathode and (iii) a dielectric coupling layer deposited on top, guaranteeing a good spatial reconstruction of the hit position while benefiting from the good timing properties of LGADs. We will start from the very promising results of our RSD1 batch in terms of tracking performances and then we will move to the description of the design of the RSD2 run. In particular, the principles driving the sensor design and the specific AC-electrode layout adopted to optimize the signal confinement will be addressed.

High-Performance Semitransparent Organic Solar Cells: From Competing Indexes of Transparency and Efficiency Perspectives.

Semitransparent organic solar cells (ST‐OSCs) offer potentially more opportunities in areas of self‐powered greenhouses and building‐integrated photovoltaic systems. In this work, the effort to use a combination of solution‐processable gold nanobipyramids (AuNBPs)‐based hole transporting layer and a low/high dielectric constant double layer optical coupling layer (OCL) for improving the performance of ST‐OSCs over the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT) is reported. The fabrication and characterization of the ST‐OSCs are guided, at design and analyses level, using the theoretical simulation and experimental optimization. The use of a low/high dielectric constant double layer OCL helps enhancing the visible light transparency while reflecting the near‐infrared (NIR) photons back into the photoactive layer for light harvesting. NIR absorption enhancement in the ST‐OSCs is realized through the AuNBPs‐induced localized surface plasmon resonance (LSPR). The weight ratio of the polymer donor to nonfullerene acceptor in the bulk heterojunction is adjusted to realize the maximum NIR absorption enhancement, enabled by the AuNBPs‐induced LSPR, achieving the high‐performance ST‐OSCs with a high PCE of 13.15% and a high AVT of 25.9%.

Removal of multi-pollutants in flue gas via a new approach based on dielectric barrier discharge coupling MnCu/Ti oxidation

A dielectric barrier discharge (DBD) coupling MnCu/Ti oxidation and postpositioned wet electrostatic precipitator (WESP) system was built. The experimental results showed that WESP can significantly enhance the simultaneous conversion efficiency(ηC) of NO, SO2 and Hg0 by the DBD coupling MnCu/Ti reactor. The best simultaneous removal efficiency(ηR) of NO, SO2 and Hg0 reached 94.5%, 100% and 100%, respectively. The ratio of catalyst active component (Mn/Cu) and catalyst filling amount were optimized. The effects of catalyst active component ratio, filling amount, flue gas component and energy density (SED) on the ηC of NO, SO2 and Hg0 were determined. The effect of sodium humate (HA-Na) in the cleaning water on the ηR was also illustrated. Besides, we clarified the absorption mechanism and how WESP corona discharge oxidized NO, SO2 and Hg0, as well as the removal of NO2, SO2, and SO3 by HA-Na. Product analysis showed that NO2, SO2 and SO3 were converted into NO3- and SO42-, part of HgO was converted into Hg2+ in the cleaning water, and a small amount of Hg(NO3)2 and HgSO4 were converted into Hg2+, NO3- and SO42-.

Large magnetoelectric effect in BaFe12O19-(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 particulate composite

Multiferroic composites with a large magnetoelectric response are gaining attractive interests for the design of magnetoelectric (ME) functional devices. In this work, the particulate ME composites (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3–xBaFe12O19 (x=0, 0.1, 0.2, 0.3, 0.4 and 1) were prepared, and their structural, dielectric, magnetic, ferroelectric, piezoelectric properties and magnetoelectric coupling were systematically investigated. The composites consisted of only two chemically separated phases with well-bonded interface. Dielectric and impedance analyses indicated the co-contribution of grain and grain boundary to polarization. Well-saturated ferroelectric and magnetic hysteresis loops demonstrated multiferroic nature. ME response was investigated elaborately by employing magnetically induced polarization, together with measuring ME voltage coefficient and magnetodielectric value. Specifically, a large ME coefficient of 26.78 ​mV/cm·Oe was achieved for x=0.3, which is higher than that in single-phase BaFe12O19 and its coupled composites.

Improving the comprehensive energy storage performance of composite materials through the coupling effect of AgNbO3/PVDF nanocomposite

AbstractCeramic‐polymer nanocomposites with high energy storage density can achieve excellent energy storage performance and have a wide range of application prospects. Currently, it has been shown that the coupling effects have a great impact on improving the performance of dielectric composites, but increasing the breakdown strength of polymer nanocomposite is still a tremendous challenge to the achievement of high energy density under high voltages. The aim of this paper is to further investigate this problem and obtain AgNbO3/PVDF flexible composites by introducing a small amount of AgNbO3 ultrafine powder prepared by hydrothermal method into poly(vinylidene fluoride) (PVDF). The interfacial coupling effect within this nanocomposite with the coupling effects of nonlinear dielectric materials improves its energy storage capacity and electrical strength resistance. The energy density of the 2 wt% AgNbO3/PVDF composite film was raised to 16.5 J/cm3 at the electric breakdown strength of 391.7 MV/m, and its energy storage capacity is two to three times that of AgNbO3 lead‐free antiferroelectric ceramics. Finite element simulations showed the further enhancement of breakdown strength was ascribed to the local electric field and to the AgNbO3 ultrafine powder which blocked the breakdown path in the nanocomposites and coupling effects occurred with PVDF. Hence, the AgNbO3 ultrafine powder has a positive effect on improving the energy storage performance of flexible composites. The effects of nonlinear dielectric material coupling effects and interfacial coupling effects on the dielectric properties of composite dielectric materials are further investigated, which are important for the development of flexible high energy storage capacitors.

Ni/CNTs and carbon coating engineering to synergistically optimize the interfacial behaviors of TiO2 for thermal conductive microwave absorbers

With the coming of 5G era, endowing the microwave absorbers with a light weight and a high thermal conductivity is crucial yet challenging. Combining dielectric/magnetic components with the abundant heterointerfaces has been considered as a promising approach for the development of functional materials with excellent microwave absorption (MA) performances. Herein, we successfully constructed a hierarchical hetero-nanobrush architecture with carbon-coated TiO2 as a backbone decorated by Ni-catalyzed carbon nanotubes (TiO2@C-Ni/CNTs) for excellent MA and thermal management application, and investigated the influence of the Ni/CNTs content on its MA property. CNTs and the well-distributed Ni nanoparticles on top can promote dielectric behaviors and magnetic performances of composites, which is beneficial to the formation of dielectric and magnetic coupling network. Furthermore, the multiple core-shell structures included in TiO2@C-Ni/CNTs composites have the vast heterogeneous interfaces, which can result in multiple relaxation and effective interfacial polarization. Under the synergic action of the conductive loss, interface polarization, and three-dimensional spatial network structure, as-synthesized TiO2@C-Ni/CNTs nanobrushes possess superior MA performances with the minimum reflection loss (RL) of −32.3 dB at 17.3 GHz with a thickness of 1.6 mm and the broadest effective absorption bandwidth (EAB) of 5.5 GHz with a thickness of 1.8 mm. Furthermore, the thermal conductivities and diffusivities of the TiO2@C-Ni/CNTs/nature rubber hybrids are also effectively enhanced. This work provides an idea to design magnetic-dielectric composite nanostructures for MA and thermal management materials.

Measurements of electromechanical impedance to determine effects of pressure and temperature on underwater acoustic transducers

Underwater electroacoustic transducers can be subjected to large static pressures, wide range of temperature, and high operational electric fields causing internal heating. These conditions can adversely impact the performance of transducers including transmit output source level, reliability, survivability, useable bandwidth, tuning and matching to the amplifier, and efficiency. A low cost electroacoustic impedance measurement system was implemented with an air-pressurized mechanical transformer using SCUBA tanks to investigate transducer properties to 1,500 PSI. Subsequently, a water pressurized tank was used to 10 000 psi (or 7000 m of equivalent depth). A variety of underwater cylindrical transducers were tested and the changes in electromechanical properties (dielectric constant, capacitance, loss-tangent, mechanical compliance, piezoelectric d-constant, and effective coupling constant) were measured dynamically using the impedance methods. An analytical model was developed with a GUI to predict acoustic performance and tuning for different operational (depth, temperature, and drive level) conditions. Cylindrical transducers of oil-filled and polyurethane filled designs were shown to have moderate changes in electromechanical properties to pressures of 10 000 psi.

Measurement of complex shear viscosity up to 3 GHz using an electrodeless AT-cut quartz transducer

An experimental method is proposed to determine the frequency-dependent complex shear viscosity of liquids based on the quartz crystal microbalance with dissipation method. An AT-cut quartz transducer without metal electrodes is immersed in a sample liquid and the transducer is electrically coupled to the circuit through the dielectric response of the sample itself. After correcting for the apparent change in the resonance properties due to the dielectric coupling of the sample, our method is able to determine the viscosity of liquids of high polarity and low viscosity at frequencies as high as 3 GHz. The method was then applied to ethylene glycol and the viscoelastic relaxation in the GHz regime was observed. Furthermore, it was also applied to room-temperature ionic liquids to show that the dielectric correction of the resonance properties is valid for conductive liquids.

An improved BP neural network‐based calibration method for the capacitive flexible three‐axis tactile sensor array

Flexible tactile sensing based on capacitive sensing has become a research hotspot in recent years because of its low energy consumption, high performance and wide application prospects. However, the axis error caused by the coupling deformation of the dielectric will seriously affect the accuracy of the sensor. In this paper, a capacitive flexible three-axis tactile sensor array is modelled and simulated, and a neural network-based calibrator for the three-axis sensor array is proposed, which can be used to calibrate the simulated measurement data. The simulation results show that even though the correlation coefficient of linear regression for each axis is very close to 1, the effect of dielectric nonlinear coupling distortion cannot be eliminated. The calibration method based on the neural network can effectively suppress the nonlinear coupling distortion of the dielectric, and reduce the measurement coupling rate of the sensor model from 26% to 1%. At the same time, in order to ensure the measurement accuracy and robustness of different units in the sensor array, the input layer of the calibrator is expanded, and the data set containing capacitance information and two-dimensional location information is used for training. The experimental results show that the proposed calibration method combining two-dimensional position information training accurately calibrates the capacitive flexible three-dimensional tactile sensor array.

Giant Functional Properties in Porous Electroceramics through Additive Manufacturing of Capillary Suspensions

Dedicated hierarchical structuring of functional ceramics can be used to shift the limits of functionality. This work presents the manufacturing of highly open porous, hierarchically structured barium titanate ceramics with 3-3 connectivity via direct ink writing of capillary suspension-type inks. The pore size of the printed struts (∼1 μm) is combined with a printed mesostructure (∼100 μm). The self-organized particle network, driven by strong capillary forces in the ternary solid/fluid/fluid ink, results in a high strut porosity, and the distinct flow properties of the ink allow for printing high strut size to pore size ratios, resulting in total porosities >60%. These unique and highly porous additive manufactured log-pile structures with closed bottom and top layers enable tailored dielectric and electromechanical coupling, resulting in an energy harvesting figure of merit FOM33 more than four times higher than any documented data for barium titanate. This clearly demonstrates that combining additive manufacturing of capillary suspensions in combination with appropriate sintering allows for creation of complex architected 3D structures with unprecedented properties. This opens up opportunities in a broad variety of applications, including electromechanical energy harvesting, electrode materials for batteries or fuel cells, thermoelectrics, or bone tissue engineering with piezoelectrically stimulated cell growth.