Spherical Conductor Research Articles

Electrocatalytic oxygen reduction on nitrogen-doped porous carbon spheres prepared with resorcinol–phenolsulfonic acid–formaldehyde mixed resins

Abstract The resorcinol–phenolsulfonic acid–formaldehyde (RxPS1–xF) mixed resin spheres were prepared by the high-temperature hydrothermal synthesis. Pyrolysis of the resin spheres under NH3 atmosphere produced small, porous, conductive N-doped carbon spheres. These carbon spheres promoted electrocatalytic oxygen reduction reaction (ORR) with almost 100% four-electron reduction selectivity, and their performance was comparable to that of the state-of-the-art Pt/C catalyst.

A Hybrid Perovskite-Based Electromagnetic Wave Absorber with Enhanced Conduction Loss and Interfacial Polarization through Carbon Sphere Embedding.

Electronic equipment brings great convenience to daily life but also causes a lot of electromagnetic radiation pollution. Therefore, there is an urgent demand for electromagnetic wave-absorbing materials with a low thickness, wide bandwidth, and strong absorption. This work obtained a high-performance electromagnetic wave absorption system by adding conductive carbon spheres (CSs) to the CH3NH3PbI3 (MAPbI3) absorber. In this system, MAPbI3, with strong dipole and relaxation polarization, acts dominant to the wave absorber. The carbon spheres provide a free electron transport channel between MAPbI3 lattices and constructs interfacial polarization loss in MAPbI3/CS. By regulating the content of CSs, we speculate that this increased effective absorption bandwidth and reflection loss intensity are attributed to the conductive channel of the carbon sphere and the interfacial polarization. As a result, when the mass ratio of the carbon sphere is 7.7%, the reflection loss intensity of MAPbI3/CS reaches -54 dB at 12 GHz, the corresponding effective absorption bandwidth is 4 GHz (10.24-14.24 GHz), and the absorber thickness is 2.96 mm. This work proves that enhancing conduction loss and interfacial polarization loss is an effective strategy for regulating the properties of dielectric loss-type absorbing materials. It also indicates that organic-inorganic hybrid perovskites have great potential in the field of electromagnetic wave absorption.

Experimental study on toughening UV pre-curing adhesives for electrically conductive applications

Epoxy adhesives are not conductive materials, usually requiring the use of fillers to create electrical bridging between the joint's substrates. This work aims at the implementation of UV fixation, instead of clamping jigs, on doped joints to ensure enough contact bridging pressure during curing. As such, an UV pre-curable adhesive was mechanically characterised in terms of strength – bulk tensile test and TAST (shear) –, and fracture toughness – DCB (mode I) and ENF (mode II) tests –, in the neat state (reference). Afterwards, for the doped configurations – 5%v/v conductive spheres (Sph), 15%v/v aluminium (Al) and 10%v/v graphite (C) – only mode I and II tests were considered accessing the filler's toughening effect. The electrical conductivity of the real joints was assessed through electric discharge machining (EDM). In the end, the Sph's were deemed necessary for bond thickness control. And the Al (mode I +50 % and II +61 %) and C (mode I +25 % and II +42 %) powders presented improvements in toughening the adhesive. However, UV-fixation failed to provide enough clamping pressure, during curing, to maintain the electrical bridging necessary for EDM.

Revisit: derivation of induction heating power equation for a conductive metal sphere

AbstractCurrently, we are in the research of magnetic induction heating by using conductive metal particles. The technology (comes from a phenomenon known as the “skin effect”) generates heat produced by electrical eddy currents on metal particle’s surfaces. However, till now, the power equation to describe the energy consumption of the eddy current on a single particle surface still remains ambiguous. William R. Smythe derived this equation for metal ball. A minor error was clearly located in his derivation result. Today, similar ambiguous power equation is still adopted by researchers. In order to clarify this ambiguous situation and make our further deep study on particle-based induction heating process, in this paper, I revisit the derivation of the power equation with richful results.

Mathematical simulation of radar scattering characteristics of ultra-short-pulse signals on complex shape objects

The article discusses the method of mathematical modeling of characteristics of scattering of ultrashort-pulse signals of complex shape objects, taking into account the shape of the envelope of the ultrashort-pulse radio signal and the features of radiation of an ultrawideband antenna. To estimate the reflecting properties of objects, the determination of the ultra-short-pulse radar cross section of complex shape objects with their radar location by non-harmonic signals is given. The mathematical model of radar scattering characteristics of location objects under ultra-short-pulse signals takes into account the shape of the envelope of the signal generated by a transmitter of a single-chip microchip NVA 6100 with duration of 300 ps and obtained through direct measurements. The electric scattering field of a location object in the frequency domain is determined on the use of a polygonal model of the object and asymptotic methods of diffraction theory. The transfer function of the Vivaldi antenna to radiation obtained by numerical modeling using the method of moments was used in the electric field calculations. Verification of the developed mathematical model was carried out on the basis of determining the ultra-short pulse radar cross section of perfect electric conductive sphere. A diagram of the ultra-short-pulse radar cross section of the GPS satellite was obtained, taking into account the radiation of the ultra-short-pulse signal by the Vivaldi antenna. The diagram of ultra-short pulse radar cross section of GPS satellite does not contain interference maxima and minima, and the averaged values ultra-short radar cross section of GPS satellite from lateral angles are on average 3..8 times less than radar cross section at the center frequency of the spectrum. The mathematical model of radar scattering characteristics of location objects under ultra-short-pulse signals is intended for preliminary estimates of the ultra-short-pulse radar cross section at an early step of designing ultra-wideband radars. The obtained estimates of the ultra-short-pulse radar cross section of the GPS satellite make it possible to identify the main features in the scattering of ultra-short-pulse signals at the location of extended targets.

Analysis of Scattering characteristics of PEMC sphere by vortex Bessel beams

Generalized Lorenz-Mie theory (GLMT) is well known to analyze the scattering characteristics of spherical surfaces and metamaterials such as perfect electromagnetic conductor (PEMC) sphere. Also, metamaterials are explored very well when illuminated by electromagnetic waves/beams and their characteristics depend upon propagation and scattering response. So, in this manuscript, vortex Bessel beam (VBB) interaction from PEMC sphere has been investigated. The VBB interaction with material particles is of quite interesting due to association of orbital angular momentum (OAM) with them. By employing the Integral localized approximation (ILA) method, the beam‐shape coefficients (BSCs) regarding VBB are obtained. Computations for the scattering efficiency QSca and extinction efficiency QExt for PEMC sphere by considering the co‐polarized and cross‐polarized scattering components are presented and analyzed. Moreover, the influences of OAM mode number, electromagnetic admittance parameter, and diffraction angle are discussed. Numerical results have applications regarding transfer of OAM of VBB to PEMC sphere and associated applications in light manipulation and scattering, optical tweezers, metamaterial fields, and remote sensing.

The resistive limit response of an ellipsoidal conductor: a magnetostatic formulation

Interpreting transient electromagnetic (TEM) anomalies in terms of conductive rectangular plates is effective in many situations. However, not all conductors are thin and planar. Triaxial ellipsoid conductors are an attractive alternative: geometrically simple (corner-free), mathematically tractable at early and late time limits, and able to encompass shapes ranging from discs to elongate lenses to equi-dimensional pods. Accordingly a fast magnetostatic algorithm has been developed to compute the resistive limit (RL) response of a ellipsoidal conductor, which may also be permeable. The algorithm has been validated against new analytic resistive limit solutions for spherical and spheroidal conductors and against 3D multigrid finite difference modelling for a triaxial ellipsoidal conductor. A uniformly conductive ellipsoid supports three fundamental current modes in the resistive limit, an independent mode for excitation parallel to each of the principal axes. The RL current density increases linearly with radial distance from the ellipsoid centre. A formula for the time constant of an oblate spheroid has been derived for excitation parallel to its rotational axis, namely τ 3 ≈ σ μ 0 bc / ( 4 + 6 c / b ) , where σ is the conductivity and c and b are respectively the minor and major radii.

Polyphenol modification of graphene-stabilized emulsions to form electrically conductive polymer spheres

HypothesisPolyphenols, specifically tannic acid, should increase the hydrophilicity of graphene when added during the interfacial exfoliation through π-π stacking. Following Bancroft’s rule, increasing the hydrophilicity of graphene will result in a phase inversion of water-in-oil emulsions stabilized by graphene. Polymerization of the oil phase will then lead to graphene-coated spheres rather than graphene-stabilized polyHIPEs. ExperimentsOptical particle sizing, microscopy, contact angle, and electrical conductivity measurements were performed to determine the mechanism of sphere formation in graphene-stabilized emulsions modified with tannic acid. Studies focused on the effect of graphite flake size, graphite concentration, tannic acid concentration, and oil phase composition. Particle sizing and scanning electron microscopy examined the spheres' size, shape, and surface morphology. Contact angle measurements gave insight into the change in graphene surface energy. Conductivity studies examined the graphene shell surrounding the spheres. FindingsAdding tannic acid to graphene-stabilized emulsions induced a phase change from water-in-oil to oil-in-water. Contact angle measurements confirmed greater hydrophilicity of graphene in the presence of tannic acid. However, very high tannic acid concentrations led to a decrease in the stability of the emulsion. Varying the graphite flake size and concentration resulted in morphology and conductivity changes. Dilution of the monomer phase produced hollow microcapsules.

Constructing highly stable and biomimetic supercapacitor materials of 2D MoS2 coupled with NiCoLDH @chitosan carbon microsphere

Due to the growing demand for clean and renewable energy, the effective utilization of renewable resources in energy storage and has been concerned. And high specific capacitance and stable electrochemistry for energy storage devices are challenging to develop. Learning from unique structure of goniastrea coral, we design to construct three-dimensional layered conductive electrodes material made of MoS2@chitosan carbon spheres (MNCCS) composite. The NiCoLDH nanosheets construct on the surface of conductive chitosan carbon spheres to effectively form open permeable channels and rich conductive networks, improves the efficient energy storage and electrochemical stability. MoS2 is strongly coupled with NiCoLDH nanosheets through heterointerface, which resembles tentacles on the surface of coral, exposing more active sites to efficiently trap ions. Besides, the obtained material possesses favorable heterojunction interface and defects, which provide sufficient available electroactive sites and numerous storage charge area. Hence, The MNCCS presents an outstanding specific capacitance of 2605.9 F g−1 at 1 A g−1. Notably, a supercapacitor fitted with MNCCS electrode and CCS electrode achieves high specific capacitance (234.4 F g−1 at 1 A g−1), the maximum energy density of 77.0W h kg−1 at highest power density of 667.4W kg−1, along with the excellent cycling stability of 90.8% retention over 10,000 cycles. This work provides a new perspective for fabricating high-performance and stable supercapacitors electrode material for clean energy storage.

Analytical Method of Eddy-Current Field Induced by Moving Conductor in Gradient Magnetic Field

Electromagnetic field analyses of conductors moving in magnetic fields have been widely applied in scientific research and industrial production. In this paper, an equivalent model is proposed to solve the eddy-current field of an arbitrarily-shaped conductor moving in gradient magnetic field. As an example, the analytical model of a spherical conductor moving axially with air-core cylindrical coils is solved. First, the induced eddy-current density inside the conductor ball is derived by using the Ohm’s law of moving conductor. Next, the eddy current inside the conductor ball is equivalent to coaxial current-loops and regarded as excitation source in the newly established boundary-value problem. Then in experiments, the induced voltages of pick-up coil are in good agreement with the theoretical values, which can verify the analytical methods and results of this paper. Furthermore, the time-difference between the zero-crossing points of induced voltage curve is inversely proportional to the moving speed, and the amplitude of induced voltage is proportional to conductor conductivity. The analytical methods proposed in this paper can be used to solve the eddy-current fields induced by arbitrarily-shaped conductors moving in gradient magnetic fields directly, and do not need to calculate the governing equations and boundary conditions containing velocity terms.

Analysis of light scattering of a Gaussian beam by a perfect electromagnetic conductor (PEMC) sphere

Analysis of light scattering of a Gaussian beam by a perfect electromagnetic conductor (PEMC) sphere

Spatial distribution of electric field measurement system: straight characterization of one or more original electric field sources in association with a new triaxial sensor

Several original point charge like electric field sources and a new tri-axial capacitive based electric field sensor have been designed to be associated together to build a new instrument able to characterize the electrical properties of the environment. The paper presents two fundamental features of the target electric imaging instrument: the characterization of the constituent parts of the system and the validation of the low-level data processing functions. The original electric field sources are composed of several conductive spheres with conical support so that they can be assimilated to point charges. The various arrangements of the sources can generate monopolar or multipolar electric fields. The tri-axial sensor is is integrated in a 2D scanning setup and used to map simultaneously the three components of the electric field generated by original electric field sources composed of several conductive spheres. The measured electric field images are compared to images calculated with an analytical model using the method of image charges. The agreement between measured electric field images and model validates both the original design of the sources and the geometrical features of the sensor which opens the door to application such as the detection of non-conductive buried object and smart detection with autoconfiguration.

Mathematical Modeling of Brain Swelling in Electroencephalography and Magnetoencephalography

In the present paper, the forward problem of EEG and MEG is discussed, where the head is modeled by a spherical two-shell piecewise-homogeneous conductor with a neuronal current source positioned in the exterior shell area representing the brain tissue, while the interior shell portrays a cerebral edema. We consider constant conductivity, which assumes different values in each compartment, where the expansions of the electric potential and the magnetic field are represented via spherical harmonics. Furthermore, we demonstrate the reduction of our analytical results to the single-compartment model while it is shown that the magnetic field in the exterior of the conductor is a function only of the dipole moment and its position. Consequently, it does not depend on the inhomogeneity dictated by the interior shell, a fact that verifies the efficiency of the model.

Effects of head modeling errors on the spatial frequency representation of MEG

Objectives. We aim to investigate the effects of head model inaccuracies on signal and source reconstruction accuracies for various sensor array distances to the head. This allows for the assessment of the importance of head modeling for next-generation magnetoencephalography (MEG) sensors, optically-pumped magnetometers (OPM). Approach. A 1-shell boundary element method (BEM) spherical head model with 642 vertices of radius 9 cm and conductivity of 0.33 S m−1 was defined. The vertices were then randomly perturbed radially up to 2%, 4%, 6%, 8% and 10% of the radius. For each head perturbation case, the forward signal was calculated for dipolar sources located at 2 cm, 4 cm, 6 cm and 8 cm from the origin (center of the sphere), and for a 324 sensor array located at 10 cm to 15 cm from the origin. Equivalent current dipole (ECD) source localization was performed for each of these forward signals. The signal for each perturbed spherical head case was then analyzed in the spatial frequency domain, and the signal and ECD errors were quantified relative to the unperturbed case. Main results. In the noiseless and high signal-to-noise ratio (SNR) case of approximately ≥6 dB, inaccuracies in our spherical BEM head conductor models lead to increased signal and ECD inaccuracies when sensor arrays are placed closer to the head. This is true especially in the case of deep and superficial sources. In the noisy case however, the higher SNR for closer sensor arrays allows for an improved ECD fit and outweighs the effects of head geometry inaccuracies. Significance. OPMs may be placed directly on the head, as opposed to the more commonly used superconducting quantum interference device sensors which must be placed a few centimeters away from the head. OPMs thus allow for signals of higher spatial resolution to be captured, resulting in potentially more accurate source localizations. Our results suggest that an increased emphasis on accurate head modeling for OPMs may be necessary to fully realize its improved source localization potential.

Correction: Laguerre–Gaussian Beam Scattering by a Perfect Electromagnetic Conductor (PEMC) Sphere

Correction: Laguerre–Gaussian Beam Scattering by a Perfect Electromagnetic Conductor (PEMC) Sphere

Radiation force and torque on an absorptive electromagnetic conductor sphere by an arbitrary-shaped optical polarized beam

The optical radiation force (ORF) and optical spin torque (OST) on an absorptive electromagnetic conductor (AEMC) sphere by an arbitrary-shaped optical polarized beam are investigated in the framework of the generalized Lorenz–Mie theory (GLMT). The analytical expressions of ORF and OST are derived, and both of them are decomposed into three components (co-polarized, cross-polarized, and interference components) due to the unique “optical rotation” effect of the AEMC. The ORF and OST exerted on both a PEMC and an AEMC sphere by an Airy beam are discussed, and the impact of the losses Mi of AEMC is focused on. Besides, the influence of particle size parameter ka and admittance parameter M on the ORF and OST are also mainly analyzed. The optical pulling force built on this system is paid attention to and discussed. And the impact of the polarization states of the incident beam on the ORF and OST is also discussed. Furthermore, the comparison of ORF that the Airy beam interacts with a dielectric sphere and an AEMC sphere is studied emphatically. The findings in this manuscript will take effect on particle manipulation, optical spanners, optical tweezers, and metamaterial field.

Pair trajectories of uncharged conducting spheres in an electric field

In this paper, we study the role of electrostatic forces on pair trajectories of two uncharged conducting spheres subject to an external electric field. We consider the hydrodynamic interactions between the spheres as they move relative to one another. Previous studies have shown that electric-field-induced forces on a two-sphere system are always attractive, except for the configuration when the line joining the centers is perpendicular to the external electric field. In the current study, we derive the asymptotic form of the interparticle force induced by the electric field in the lubrication limit for arbitrary size ratios. The attractive electric force diverges as the separation approaches zero. Thus, our calculation shows that the electric-field-induced forces can overcome the continuum lubrication resistance and allow finite time contact between the surfaces of two spherical conductors. We calculate the asymptotic variation of interparticle separation using the near-field asymptotic expressions for the electric-field-induced forces, exploring the role of hydrodynamic interactions in interparticle motion parallel and perpendicular to the electric field.

Modelling the electromagnetic response of a sphere located in a layered earth

Estimating the electromagnetic response of a conductive sphere in a layered earth is of great interest in terms of both modelling and interpretating data acquired via geophysical electromagnetic methods where the target is at some distance from the source and receiver. This is particularly the case when using Airborne Electromagnetic Method (AEM) where the source and receiver are located at some height above the subsurface. This problem can be solved by utilising field expansions representing derivatives of cylindrical functions, which describe the fields propagating in the layered earth, and spherical functions, which describe the fields reflected by the sphere. Furthermore, these representations allow the development of relationships between cylindrical and spherical functions. These functions and subsequent relationships have been used to develop an algorithm for estimating the electromagnetic response of a conductive sphere in an isotropic layered earth. Software based on this algorithm has been tested on both synthetic and field data. The field data presented were collected with the AEM AirTEM system over the Reid-Mahaffy test site, Ontario, Canada. Results from these tests prove the importance and utility of integrating the sphere in a layered earth model in the AEM interpretation toolbox.

Alternativni teorijski model zemljinog EM polja zasnovan na hipotezama o dve komponente polja

Introduction/purpose: The paper describes an alternative theoretical model of the Earth's EM field based on two-component field hypotheses. The paper consists of several parts, one part of which is a model showing the rotation of the magnetically conducting sphere of magnetization M in a foreign magnetic field. The last part defines theoretical models for the calculation of the components of the electromagnetic field of electrically conductive, dielectric and magnetically conductive spheres which are exposed to the influence of a foreign electromagnetic field. Methods: In the work, the responses of electrically conductive, dielectric and magnetically conductive spheres to the influence of external EM fields were investigated using the analytical method. Results: The obtained solutions in the form of analytical formulas will be applied to research the impact of the Sun's EM field on the planets and especially on the Earth. Conclusion: The resulting formulas of the electric and magnetic field strength and induction and their solutions can be applied to electrically conductive, dielectric and magnetically conductive spheres. In comparison to already known formulas, they are simple and have higher accuracy.

On the Field Energy of Two Charges With Application to Electric Dipoles

This paper revisits the topic of electrostatic field energy due to a pair of the electric charges. Not only point-like charges but also charged spheres of radius R are studied. The self-energies as well as the interaction field energy are discussed in full detail. By combining two alternative didactic paths (one mathematical and the other based on energy conservation principles), it is shown that the interaction field energy (which is a volume integral of the energy density over the infinite space) is always equal to the potential energy, regardless of the nature of the electrical charges. For these two characteristic cases of electric charges (i.e., point-like and uniformly charged spheres), the location and the amount of the major part of the interaction field energy is discussed; the relevant factoids are documented in the form of two compact theorems in the Appendix. The case of non-uniformly charged spheres (i.e., spherical conductors) is also discussed to some extent. In addition to this general presentation, the particular case of the electric dipole is discussed, as a special case, accompanied with many numerical results.