Field Density Distribution Research Articles

Effects of fiber dosage, loading orientation and stress on frequency response of enhanced Carbon Nano-Fiber Aggregates

Nanomaterial additives have been broadly used in cement and concrete-based sensors to measure the stress and strain in the structure. Most of the studies focused on measuring the resistivity of sensors with Direct Current (DC) or relatively low-frequency. In this work, the impedance responses of enhanced Carbon Nano-Fiber Aggregates (CNFAs) at different frequencies are rigorously studied and utilized as a tool for real-time structural health monitoring (SHM). The CNFA impedance measurements at different measurement frequencies provide an extra dimension (frequency dimension) to allow the characterization of different phenomena and multimodal measurements simultaneously. First, a comprehensive physical model is established to understand the frequency responses of the CNFA impedance. Second, COMSOL Multiphysics is used to simulate the frequency responses of the CNFA impedance, which provides more insights into the electric field and current density distribution. The impedance of CNFAs decreased with the increased dosage of carbon nanofibers (CNFs). Third, experimental studies are reported in detail. The electrical impedance variation (EZV) of the CNFA in parallel orientation is 151% higher than that of perpendicular orientation at the frequency of 2612 Hz and uniaxial compression stress of 4.65 MPa. The strain-EZV curve obtained from the response spectrum is linear for frequencies ranging from 98 Hz to 463.9 kHz. The strain-EZV curve for 5625 Hz has a linear fit with the gauge factor of 147.78. At 1000 Hz, the CNFA exhibited a repeatable behavior up to 9.35 MPa and detection limit up to the stress of 18.62 MPa.

Flux tubes in full QCD at high temperature

Chromoelectric and chromomagnetic field and energy density distributions produced by a quark-antiquark pair have been investigated in the presence of dynamical fermions in the close vicinity to the deconfinement phase transition. In our lattice simulation we have used highly improved staggered quark action and tree level improved Symanzik gauge (HISQ/tree) action on the lattices of two different sizes, exploiting the Gradient flow method for noise reduction. We find that, in full QCD with dynamical quarks, the dynamical fermions widen the flux tube in a short separation range of about R = 1 fm, after which an hadronization takes place due to the suppression by the dynamical fermions. Energy density and width of the flux tube vanish at about R = 1.8 fm and R = 1.5 fm, respectively, at all temperatures. The present results also suggest that the flux tube structure still persists in the deconfined phase and it melts gradually after certain temperature value is reached above the critical temperature.

A novel selective thermophotovoltaic emitter based on multipole resonances

Thermophotovoltaic systems can harvest electric energy from heat sources with a potential efficiency exceeding the Shockley–Queisser limit due to the selective emission of an elaborate thermal emitter. In this work, a two-dimensional nanodisks/thin-film metamaterial is proposed as a wavelength-selective emitter, which can coordinate well with the photovoltaic cell in a thermophotovoltaic system. Compared to conventional emitters based on surface plasmon polaritons, the emittance peaks of the proposed emitter are realized by the excitations of both electric dipole and anapole modes in silicon nanodisks, which can be easily tailored due to the non-dispersive optical constants of dielectric materials. Meanwhile, the effect of polarization and polar angle on the emittance spectra is also investigated, suggesting that the proposed emitter has high emittance and efficiency not only in the normal direction but also at large oblique angles. Electromagnetic field and current density distributions reveal that the coupling between multipole resonances and the bottom tungsten layer can induce a magnetic dipolar resonance. Therefore, the wavelengths of both emittance peaks are sensitive to the period paralleled to the incident electric field. Besides, the anapole-induced mode can couple with the lattice resonance, resulting in higher emittance. Moreover, the proposed emitter is successfully fabricated, and the measured spectra agree well with the theoretical results. The fundamental understanding and insights obtained here will facilitate the active design and application of novel multipole-based emitters in enhancing energy conversion.

A low-frequency rotational electromagnetic energy harvester using a magnetic plucking mechanism

Energy harvesting from rotational motion, such as vehicle tires and rotational devices, remains a challenge because of the difficulty of balancing the harvesting frequency range and the power-generation density and efficiency. Traditional energy harvesters using the mechanism of magnetic plucking and piezoelectric conversion cannot overcome the inherent disadvantages of the output power and the strictness of the application conditions. In this study, a low-frequency rotational electromagnetic energy harvester using a nonlinear magnetic plucking configuration is proposed. Using the novel structure to pluck a cylindroid generating magnet in each rotational motion, the resetting effect provides a new way to stabilize the output voltage and improve the energy harvesting performance. Two design factors for controlling the resetting effect were studied theoretically and experimentally. The finite element method based on the Maxwell stress tensor not only helps in understanding the magnetic field density distribution in the energy harvesting process but also reveals the resetting mechanism. Simulating a vehicle tire with a diameter of 0.6 m rotating at a speed of approximately 20 km/h, it was experimentally validated that the maximum average output power across all the rotating frequencies (0.5–5.0 Hz) reached 13.13 mW under certain excitation conditions in the experiment, which is increased by 215.9% compared with the harvester without the resetting effect. The great performance under different application conditions demonstrated that the proposed electromagnetic energy harvester has a great potential in energy harvesting from low-frequency rotational motions.

Boson stars in Palatini gravity

We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter ξ. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of boson stars in Palatini gravity are fairly similar to those found in general relativity. Major differences are observed for negative values of the coupling parameter which results in a repulsive gravitational component for high enough scalar field density distributions. Adding self-interactions makes the degeneracy between and general relativity even more pronounced, leaving very little room for observational discrimination between the two theories.

Spatial Mapping of Electrostatic Fields in 2D Heterostructures.

In situ electron microscopy is an effective tool for understanding the mechanisms driving novel phenomena in 2D structures. However, due to practical challenges, it is difficult to address these technologically relevant 2D heterostructures with electron microscopy. Here, we use the differential phase contrast (DPC) imaging technique to build a methodology for probing local electrostatic fields during electrical operation with nanoscale spatial resolution in such materials. We find that, by combining a traditional DPC setup with a high-pass filter, we can largely eliminate electric fluctuations emanating from short-range atomic potentials. Using a method based on this filtering algorithm, a priori electric field expectations can be directly compared with experimentally derived values to readily identify inhomogeneities and potentially problematic regions. We use this platform to analyze the electric field and charge density distribution across layers of hBN and MoS2.

Lightning Current Performance of Conventional and Enhanced Rod Ground Electrodes

The correct operation of surge arresters under lightning and switching transient conditions requires that grounding be effective at high frequencies as well as at power system frequency. Effective high frequency grounding also limits the electrocution risk to substation personnel due to transient ground potential rise. This article assesses the performance of high frequency electrodes at typical lightning impulse current magnitudes. The enhancement of such electrodes by addition of bonded horizontal arms in cross and star arrangement is also investigated. The effective impulse resistances for electrodes having lengths up to 4.8 m are calculated over a range of impulse current magnitudes at the same location. The results obtained indicate that, for low impulse current magnitudes, the preionization electrode's resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) falls with increasing rod length, a behavior reflected in the measured dc resistance. The presence of horizontal enhancement was found to reduce <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> in all cases. The occurrence of soil ionization in the immediate vicinity of the electrode resulted in a reduced postionization resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) at higher currents, tending toward a common asymptotic value independent of both the length of the rod and the presence of electrode enhancements. The observed behavior is supported by numerical simulation of electric field and current density distributions, indicating that the high current performance of a grounding rod is heavily influenced by soil ionization and breakdown in high-field regions at the electrode extremities.

Dynamic Characteristics of a YBCO Bulk Above an Electromagnet Guideway

For high-temperature superconducting (HTS) maglev, an electromagnet guideway unit (EMGU) that can form an electromagnet guideway (EMG) with a small gap, or even no gap, between EMGUs has been designed. The longitudinal magnetic fields along a single EMGU and two EMGUs arranged in a line were first investigated through measurement and simulation. The experimentally measured data validated the simulation results from a three-dimensional (3D) EMGU model implemented in COMSOL Multiphysics, indicating that the model is reliable and can be used for further studies. The dynamic responses of a high-temperature superconducting (HTS) bulk above a single EMGU and two EMGUs arranged in a line, including the dynamic levitation force (LF) and traveling directional force (TDF), under different operating conditions were investigated through experiment and simulation using a segregated H-formulation model. The magnetic field and current density distributions inside the superconductor are affected by the external magnetic field generated by the EMGU and are responsible for the dynamic characteristics. Finally, the segmented instant excitation (SIE) mode was investigated through simulation, which shows it is feasible by coordinating the currents of EMGUs.

Magnetic-resonance-based measurement of electromagnetic fields and conductivity in vivo using single current administration-A machine learning approach.

Diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) is a newly developed technique that combines MR-based measurements of magnetic flux density with diffusion tensor MRI (DT-MRI) data to reconstruct electrical conductivity tensor distributions. DT-MREIT techniques normally require injection of two independent current patterns for unique reconstruction of conductivity characteristics. In this paper, we demonstrate an algorithm that can be used to reconstruct the position dependent scale factor relating conductivity and diffusion tensors, using flux density data measured from only one current injection. We demonstrate how these images can also be used to reconstruct electric field and current density distributions. Reconstructions were performed using a mimetic algorithm and simulations of magnetic flux density from complementary electrode montages, combined with a small-scale machine learning approach. In a biological tissue phantom, we found that the method reduced relative errors between single-current and two-current DT-MREIT results to around 10%. For in vivo human experimental data the error was about 15%. These results suggest that incorporation of machine learning may make it easier to recover electrical conductivity tensors and electric field images during neuromodulation therapy without the need for multiple current administrations.

Enhanced Heat Dissipation in Gallium Nitride-Based Light-Emitting Diodes by Piezo-phototronic Effect.

As a new generation of light sources, GaN-based light-emitting diodes (LEDs) have wide applications in lighting and display. Heat dissipation in LEDs is a fundamental issue that leads to a decrease in light output, a shortened lifespan, and the risk of catastrophic failure. Here, the temperature spatial distribution of the LEDs is revealed by using high-resolution infrared thermography, and the piezo-phototronic effect is proved to restrain efficaciously the temperature increment for the first time. We observe the temperature field and current density distribution of the LED array under external strain compensation. Specifically, the temperature rise caused by the self-heating effect is reduced by 47.62% under 0.1% external strain, which is attributed to the enhanced competitiveness of radiative recombination against nonradiative recombination due to the piezo-phototronic effect. This work not only deepens the understanding of the piezo-phototronic effect in LEDs but also provides a novel, easy-to-implement, and economical method to effectively enhance thermal management.

Plasmonic modes at inclined edges of anisotropic two-dimensional materials

Confined modes at the edge arbitrarily inclined with respect to optical axes of nonmagnetic anisotropic 2D materials are considered. By developing the exact Wiener-Hopf and approximated Fetter methods we studied edge modes dispersions, field and charge density distributions. The 2D layer is described by the Lorentz-type conductivities in one or both directions, which is realistic for natural anisotropic 2D materials and resonant hyperbolic metasurfaces. We demonstrate that, due to anisotropy, the edge mode exists only at wave vectors exceeding the nonzero threshold value if the edge is tilted with respect to the direction of the resonant conductivity. The dominating contribution to field and charge density spatial profiles is provided by evanescent 2D waves, which are confined both in space near the 2D layer and along the layer near its edge. The degree of field confinement along the layer is determined by wave vector or frequency mismatch between the edge mode and continuum of freely propagating 2D modes. Our analysis is suitable for various types of polaritons (plasmon, phonon, exciton polaritons, etc.) at large enough wave vectors. Thanks to superior field confinement in all directions perpendicular to the edge these modes look promising for modern plasmonics and sensorics.

Thermal-electromagnetic coupling simulation study of high efficiency and energy saving application of induction motor for offshore oil platform

The load of the offshore oil platform is mostly pump unit, Asynchronous motor with cage rotor has simple structure, reliable operation, and inexpensive. But it has a huge shortcoming of its low efficiency. When the output power is constant, improving efficiency is to decrease loss of the motor. This paper discusses some methods of energy saving and low consumption of the pump unit to improve the efficiency. Direct drive pump can completely eliminate transmission loss, eliminate bearing of centrifugal pump impeller pump, reduce friction, and thus reduce mechanical loss. The rotor copper loss and stator copper loss will be reduced by using copper squirrel cage and multi-wound motor, so the efficiency of the motor will be improved. If all the pump unit of the offshore oil platform is turned into this low consumption motor, it will save a lot of energy and greatly improve the efficiency of the load. Today, motors are widely found in various devices and their analysis involves the coupling of multiple physical fields. One of the most serious problems for some large motors is the heating problem, which generates various losses during motor operation, and these losses are eventually converted into thermal energy and emitted in the form of heat. The operating temperature of the motor has a great influence on the insulating material of the motor. Afterwards, a method of thermal-electromagnetic coupling simulation of the motor is carried out with a pump unit in the offshore oil platform as an example, and the magnetic line distribution, magnetic field density distribution cloud diagram and water pump temperature distribution of the motor are obtained, which are the basis of the electromagnetic design of the water pump and the design of the heat dissipation system.

Dual-band and polarization-independent metamaterial terahertz narrowband absorber.

A dual-band terahertz metamaterial narrowband absorber is investigated based on a single simple windmill-shaped structure. The proposed metamaterial absorber achieves near-perfect absorption at 0.371 THz and 0.464 THz. The full width at half-maximum is 0.76% and 0.31% relative to absorption frequency. The multireflection interference theory is used for analyzing the absorption mechanism at low absorption frequency. The theoretical predictions of the decoupled model have excellent agreement with simulation results. By investigating the absorber's distribution of electric field and surface current density at high absorption frequency, the absorber's near-perfect absorption at the high absorption frequency originating from the magnetic resonance formed between the top metal structure and the bottom metal plane is explained. Besides, the absorber proposed is independent of the polarization angle. It is significant to various applications such as narrowband thermal radiation, photoelectric detection, biological sensing, and other fields.

Analysis of Imaging Quality of New Laser Communication System on Missile in the Aerodynamic Environment

We study the influence of altitude and speed on aero-optic imaging quality degradation of new laser communication system “Multi-Aperture Transmission and Diversity Reception” of surface-to-air missile. The 3D modeling and meshing of surface-to-air missile are obtained by ANSYS software. The density field distribution around the optical system was analyzed by FLUENT and the nonuniform refractive-index field around is calculated, in view of the Gladstone–Dale relation. The point spread function (PSF), Strehl ratio (SR), encircled energy, and modulation transfer function (MTF) are provided for the imaging quality evaluation of optical system. The altitude ranges from 0 to 20 km, and the speeds of missile are 5 and 3 Ma. The results show that, at the constant speed, with increase in the altitude, the refraction index and the radius of dispersion spot including 80% energy are gradually decreasing; the SR results and the curve of MTF are gradually increasing, and the PSF is concentrated. At the constant altitude, with increase in the speed, the aerodynamic flow field becomes more and more complex. Therefore, the higher the altitude, the better the receiving quality, and the smaller the speed, the better the receiving quality.

The Diffraction by the Half-plane with the Fractional Boundary Condition

In this article, there is considered the electromagnetic plane wave diffraction by the half-plane with fractional boundary conditions. As a mathematical tool, the fractional calculus is used. The theoretical part is given based on which the near field, Poynting vector and energy density distribution are calculated. Interesting results are obtained for the fractional order between marginal values, which describes a new type of material with new properties. The results are analyzed.

Plasmon nanoparticle effect to improve optical properties of perovskite thin film

Noble metal material, size, period and position are key parameters to affect optical absorption property of perovskite thin film, which was numerically investigated in this paper by finite element method. It demonstrates that Al nanoparticles show larger enhancement ability of light absorption than that of Au and Ag under AM1.5 illumination with the same geometry parameter. The light absorption enhancement after introducing Al nanopheres is optimized by nanosphere size, period and position being placed either on top (case I), in perovskite layer (case II), or simultaneously on top and in perovskite layer (case III), which mechanism isdiscussed in terms of the corresponding electric field and power loss density distributions. The maximal light absorption enhancement is revealed to ∼1.41 fold that of without Al nanosphere case. The SiO2, Al2O3 and TiO2 dielectric-nanoshell encapsulating effects on incident light trapping ability and photocurrent of the above optimized case are discussed as well. The present work holds great promise for choosing appropriate plasmonic material, size, period and position to facilitate designing perovskite solar cells and photo detectors.

Broadband terahertz absorber based on Dirac semimetal with tunable working bandwidth

A broadband metamaterial absorber (MA) based on bulk Dirac semimetal (BDS) with the property that the working bandwidth can be tuned is proposed. By changing the pattern on the top layer, the working band is expanded from narrowband to broadband. Interestingly, the working band over 90% absorption can be continuously changed from 0 to 3.4 terahertz (THz) when the Fermi energy level (EF) varies from 10 to 80 meV. The absorption mechanism of this broadband and tunable absorber is demonstrated and verified by the impedance matching theory, electric field, and power loss density distributions. Moreover, the proposed absorber is robust to the incident angle θ from 0°to 50°. Due to the symmetry structure, the designed absorber achieved the excellent property of polarization insensitivity. This proposed tunable broadband absorber may have a potential application in THz imaging and optoelectronic devices.

Broadband tunable terahertz metasurface absorber based on complementary-wheel-shaped graphene

We present a simple design for a broadband tunable terahertz metasurface absorber (MSA), which is composed of a periodic array of complementary-wheel-shaped (CWS) graphene sheets and a lossy polyimide layer backed with a ground-plane. Numerical simulation results show that the absorbance of the proposed MSA achieves over 90% for the frequency range of 1.77 THz to 4.16 THz with the relative bandwidth of about 80.6% when E f = 1.0 eV, and the absorbance is up to 93.6% and 99.8% at 2.07 and 3.83 THz. The proposed MSA is polarization-insensitive and wide-angle for both transverse-electric (TE) and transverse-magnetic (TM) waves. Fabry-Perot interference theory is used to analyze the mechanism of the MSA, and the theoretical results are agreement well with simulations. The absorption performance of the MSA can be flexibly adjusted by changing the Fermi energy level of the graphene. The simulated absorbance of the MSA can be adjusted from 19% to nearly 100% by changing the E f from 0.1 eV to 1.0 eV, which is consistent well with theoretical calculation. In addition, absorption properties of the MSA are also can be adjusted by changing the geometrical parameters of the unit-cell structure. Due to its simple structure and strong tunability, the proposed MSA has potential application prospects in the fields of tunable filtering, detection, sensing and so on. • A broadband tunable terahertz metasurface absorber (MSA) was proposed. • The absorbance of MSA is greater than 90% from 1.77 THz to 4.16 THz with the relative bandwidth of about 80.6% when Fermi energy level Ef = 1.0 eV. • Physics origin of MSA is studied by field and power loss density distributions and Fabry-Perot interference theory. • The absorption performance of the proposed MSA can be adjusted by changing the Fermi energy level and structure parameters.

Electrokinetic transport and distribution of antibacterial nanoparticles for endodontic disinfection.

To assess a novel, noninvasive intervention capable of mobilizing charged antibacterial nanoparticles to the apical portions of the root canal system, utilizing the principles of electrokinetics. Experiments were conducted in three stages. Stage-1: A computer model was generated to predict and visualize the electric field and current density distribution generated by the proposed intervention. Stage-2: Transport of chitosan nanoparticles (CSnp) was evaluated qualitatively using a transparent microfluidic model with fluorescent-labelled CSnp. Stage-3: An ex vivo model was utilized to study the antimicrobial efficacy of the proposed treatment against 3-week-old monospecies E.faecalis biofilms. Scanning electron microscopy (SEM) was also utilized in this stage to confirm the deposition of CSnp. The results of the computer simulations predicted an electric field and current density that reach their maxima at the apical constriction of the root canal. Correspondingly, the microfluidic experiments demonstrated rapid, controlled CSnp transport throughout the simulated root canal anatomy with subsequent distribution and deposition in the apical constriction as well as periapical regions. Infected root canals when subjected to the novel treatment method resulted in a mean bacterial reduction of 2.1 log CFU. SEM analysis revealed electrophoretic deposition of chitosan nanoparticles onto the root canal dentine walls in the apical region. The findings from this study demonstrate that the combination of cationic antibacterial nanoparticles with a low-intensity electric field results in particle transportation (electrophoresis) and deposition within the root canal. This results in a synergistic antibiofilm efficacy and has the potential to enhance root canal disinfection.

Numerical simulation of temperature field and pressure field of the fracture system at Zhangzhou geothermal field

Zhangzhou geothermal field is one of the highest temperature in southeastern coastal areas in China. Zhangzhou geothermal field is an uplift-fracture type geothermal resource, and there are several deep fractures in the geothermal field, controlling water flow and heat transfer. Presently there is no systematic study of the characteristics of the temperature field, pressure field and water density distribution in the geothermal field, and there is no systematic analysis of the main factors affecting the temperature field. In this work, geological features of the fracture system are considered, and a conceptual model of the fracture system is established. Based on these, the distribution of the temperature field, pressure field and water density field at Zhangzhou geothermal field are numerically studied, the controlling effect of the fracture system on the temperature field is analyzed, and the main factors affecting the temperature field, pressure field and water density field are discussed. The results indicate that the temperature field and water density field at Zhangzhou geothermal field are strongly controlled by the fracture system, and the zone of high-temperature and low-density is confined within the fracture system. Main factors affecting the temperature field and water density field include the permeability of the fracture zone, the thermal conductivity of rocks and the water recharge rate. Higher fracture zone permeability will reduce the temperature and increase the water density in the center of the fracture system. Higher water recharge rate will increase the temperature and reduce the water density in the center of the fracture system.