Field Coupling Research Articles

Investigating transfer of coherence, direction of light propagation and Rydberg blockade in a four-level [formula omitted]-type system under linear and nonlinear interaction regimes

This theoretical study reveals that the transfer of coherence (TOC) and the direction of light propagation vector play a crucial role in transitioning from electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA) in a four-level closed and open cascade (Ξ)-type light-atom interacting systems (LAIS) under both linear as well as nonlinear interaction regimes. It is found that the amplitudes of the coherence signals are distinctly influenced by the system’s openness driven by the presence of additional dipole allowed levels not connected by the lasers and the type of interaction regimes. The effect of TOC on the EIT to EIA transition is discussed in detail by the velocity-dependent dressed state analysis and velocity mapping of the probe absorption coefficient. The findings also reveal that the efficiency of the counter-propagation scheme of the coupling fields is higher than the co-propagation scheme. Furthermore, we have estimated the Rydberg blockade effect on the probe absorption profiles for some specific velocity groups of atoms, which exhibit probe gain in the medium along with EIT and EIA patterns.

Enhancing external quantum efficiency of deep ultraviolet micro-leds through geometry design and multi-physics field coupling analysis

Abstract High-efficiency deep-ultraviolet (DUV) micro light-emitting diodes (LEDs) are explored for inspiring development in numerous fields, such as non-line-of-sight solar-blind communication, optical pumping, and maskless lithography. In this study, we performed FDTD and SimuLED calculations to investigate the optimized DUV micro-LED structure geometry for high light extraction efficiency (LEE) by designing different mesa structures, including square, hexagonal, and circular geometries of micro-LEDs emitted at a wavelength of 275 nm. The results showed that a circular mesa of 5 μm diameter achieved a LEE of 27% from the bottom and sidewall emissions of as-prepared DUV micro-LED. And both the near- and far-field transverse magnetic polarized light intensities were enhanced by a factor of 1.5 over the square and hexagonal mesas. Meanwhile, the transverse electric (TE) polarized light of the circular mesa structure was enhanced and concentrated along the normal direction. Moreover, the internal quantum efficiency (IQE) of circular mesas with varied sizes was comprehensively investigated in the interactions of the thermal and electric fields. An AlGaN-based DUV micro-LED with a diameter of 5 μm was found to obtain the highest IQE owing to a high current-density distribution and its self-heating properties, thereby achieving a sufficiently high external quantum efficiency of 26.75%. This study provides a comprehensive technical report, including electrical, thermal, and optical analyses, and a new perspective for developing high-efficiency, high-performance DUV micro-LEDs in practical applications.

Gain-assisted quantum heat engine based on electromagnetically induced transparency

We propose a scheme to realize a gain-assisted quantum heat engine (QHE) based on electromagnetically induced transparency (EIT), which consists of a three-level Λ-type atomic system interacting with two thermal reservoirs and a coupling field. The gain without inversion is induced to the system via spontaneously generated coherence (SGC) between two lower levels. The SGC has significantly affect on the system’s dynamics, resulting in an enhancement of the emission cross-section and spectral brightness of the QHE.

Coupling of biogas residue biochar and low-magnitude electric fields promotes anaerobic co-digestion of sewage sludge and food waste.

Biochar-assisted anaerobic digestion (AD) remains constrained due to the inefficient decomposition of complex organics, even with the direct interspecies electron transfer (DIET) pathway. The coupling of electrochemistry with the anaerobic biological treatment could shorten lengthy retention time in co-digestion by improving electron transfer rates and inducing functional microbial acclimation. Thus, this work investigated the potential of improving the performance of AD by coupling low-magnitude electric fields with biochar derived from the anaerobically digested biogas residue. Different voltages (0.3, 0.6, and 0.9 V) were applied at various stages to assess the impact on biochar-assisted AD. The results indicate that an external voltage of 0.3 V, coupled with 5 g/L of biochar, elevates CH4 yield by 45.5% compared to biogas residue biochar alone, and the coupled approach increased biogas production by up to 143% within 10 days. This finding may be partly explained by the enhanced utilization of substrates and the increased amounts of specific methanogens such as Methanobacterium and Methanosarcina. The abundance of the former increased from 4.0 to 11.3%, which enhances the DIET between microorganisms. Furthermore, the coupling method shows better potential for enhancing AD compared to preparing iron-based biochar, and these results present potential avenues for its broader applications.

The Asymmetry Observed between the Effects of Photon-Phonon Coupling and Crystal Field on the Fine Structure of Fluorescence and Spontaneous Four-Wave Mixing in Ion-Doped Microcrystals.

In this paper, we explore the asymmetry observed between the effects of photon-phonon coupling (nested-dressing) and a crystal field (CF) on the fine structure of fluorescence (FL) and spontaneous four-wave mixing (SFWM) in Eu3+: BiPO4 and Eu3+: NaYF4. The competition between the CF and the strong photon-phonon dressing leads to dynamic splitting in two directions. The CF leads to static splitting in one direction under weak phonon dressing. The evolution from strong dressing to weak dressing results in spectral asymmetry. This spectral asymmetry includes out-of-phase FL and in-phase SFWM. Further, the large ratio between the dressing Rabi frequency and the de-phase rate leads to strong FL and SFWM asymmetry due to photon-phonon constructive dressing. Moreover, the experimental results suggest the analogy of a spectra asymmetry router with a channel equalization ratio of 96.6%.

Identification method for inter-turn faults in transformers based on digital twin concept

A transformer inter-turn fault identification method is proposed based on the digital twin concept to tackle the challenges of high operational complexity and low accuracy associated with traditional transformer fault identification methods. Initially, the Bald Eagle Search algorithm is employed to optimize the critical parameters of the Extreme Learning Machine (ELM), determining the optimal input layer weight and hidden layer threshold of the Extreme Learning Machine. Subsequently, leveraging the digital twin concept, a digital replica of the physical transformer is established, enabling multi-physical field coupling simulation encompassing electrical, thermal, and acoustic domains to elucidate the variation patterns of various physical parameters across different operational scenarios and fault scenarios. Furthermore, key physical characteristic parameters such as sound pressure and winding hot spot temperature are carefully selected to drive a fault identification model tailored to inter-turn faults within the framework of the digital twin concept. Through a detailed investigation using 630 kV A/10 kV transformers as a case study, the results exhibit an impressive fault identification accuracy of 95.24% for the proposed method. Comparative analysis reveals notable enhancements in fault identification accuracy of 12.22%, 7.85%, and 3.73% for ELM, Support Vector Machine and Tuna Swarm Optimization—ELM models, respectively. These findings underscore the effectiveness and practicality of the transformer inter-turn fault identification method based on the digital twin concept, offering valuable insights for the real-time monitoring and diagnosis of inter-turn faults in transformers.

Egg-tray-inspired concave foam structure on pore-scale space radiation regulation for enhancing photo-thermal-chemical synergistic conversion

Solar-to-fuel is an approach of converting concentrated solar high-temperature heat radiation to high-value chemical fuel, providing sustainable means for large-scale solar energy storage. However, the inefficient space radiation regulation and unclear photo-thermal-chemical multiphysics synergy limit solar to fuel conversion. To effectively improve photo-thermal-chemical conversion, here, we propose a novel idea of using an egg-tray-inspired concave structure in foam solar receiver-reactors for pore-scale space radiation regulation. The multiphysics field coupling model is accurately constructed to truly describe the complex radiation energy conversion process. Experimental and numerical results illustrate that, the proposed egg-tray-inspired concave structure can achieve the better radiation absorption and transmission, multi-field synergy and thermochemical conversion. The solar radiation absorption capacity can be increased by 7.05 %. The improvements reach a maximum efficiency of 3.17 % for photo-thermal conversion and 9.77 % for photo-chemical conversion. The excellent synergistic conversion of solar-to-fuel opens a new pathway towards accelerating energy transition and upgrading.

Enhanced Generation of Reactive Oxygen Species via Piezoelectrics based on p-n Heterojunctions with Built-In Electric Field.

Tuning the charge transfer processes through a built-in electric field is an effective way to accelerate the dynamics of electro- and photocatalytic reactions. However, the coupling of the built-in electric field of p-n heterojunctions and the microstrain-induced polarization on the impact of piezocatalysis has not been fully explored. Herein, we demonstrate the role of the built-in electric field of p-type BiOI/n-type BiVO4 heterojunctions in enhancing their piezocatalytic behaviors. The highly crystalline p-n heterojunction is synthesized by using a coprecipitation method under ambient aqueous conditions. Under ultrasonic irradiation in water exposed to air, the p-n heterojunctions exhibit significantly higher production rates of reactive species (·OH, ·O2-, and 1O2) as compared to isolated BiVO4 and BiOI. Also, the piezocatalytic rate of H2O2 production with the BiOI/BiVO4 heterojunction reaches 480 μmol g-1 h-1, which is 1.6- and 12-fold higher than those of BiVO4 and BiOI, respectively. Furthermore, the p-n heterojunction maintains a highly stable H2O2 production rate under ultrasonic irradiation for up to 5 h. The results from the experiments and equation-driven simulations of the strain and piezoelectric potential distributions indicate that the piezocatalytic reactivity of the p-n heterojunction resulted from the polarization intensity induced by periodic ultrasound, which is enhanced by the built-in electric field of the p-n heterojunctions. This study provides new insights into the design of piezocatalysts and opens up new prospects for applications in medicine, environmental remediation, and sonochemical sensors.

One-dimensional SERS nanoprobes based on cellulose nanocrystals and their biomaging performance

Surface enhanced Raman scattering spectroscopy (SERS) technology has received increasing attention in the bioimaging field. Herein, based on the support of cellulose nanocrystal (CNC) with thiol groups, one-dimensional (1D) "hot spot" structure was constructed by the self-assembly of gold nanoparticles (AuNPs) via Au-S bonding. Silica shell was subsequently coated on the CNC loaded with AuNPs to fabricate core-shell SERS nanoprobe, which was further successfully applied for the SERS imaging of Hela cells. Owing to the presence of silica shell, the nanoprobe exhibited excellent water-dispersible stability in phosphate buffer salt solution (PBS). Moreover, the silica shell effectively protected both the "hot spot" structure and the adsorbed Raman reporter of 4-mercaptobenzoic acid from external interference, thereby improving the signal stability of SERS nanoprobe. In addition, the plasma coupling of electromagnetic field between AuNPs and silica significantly enhanced the Raman signal of "hot spots". The SERS nanoprobe possessed good biocompatibility even at relatively high concentrations, and successfully achieved bioimaging of Hela cell using the Raman signal at 1580 cm−1 channel.

Thermodynamics of charged black holes in Maxwell-dilaton-massive gravity* *Supported by the National Key Research and Development Program of China (2020YFC2201400). D. C. Zou is supported by the National Natural Science Foundation of China (12365009), and the Natural Science Foundation of Jiangxi Province, China (20232BAB201039)

Considering the nonminimal coupling of the dilaton field to the massive graviton field in Maxwell-dilaton-massive gravity, we obtain a class of analytical solutions of charged black holes, which are neither asymptotically flat nor (A)dS. The calculated thermodynamic quantities, such as mass, temperature, and entropy, verify the validity of the first law of black hole thermodynamics. Moreover, we further investigate the critical behaviors of these black holes in the grand canonical and canonical ensembles and find a novel critical phenomenon never before observed, known as the "reverse" reentrant phase transition with a tricritical point. It implies that the system undergoes a novel "SBH-LBH-SBH" phase transition process and is the reverse of the "LBH-SBH-LBH" process observed in reentrant phase transitions.

Numerical simulation of multi-field coupling in geothermal reservoir heat extraction of enhanced geothermal systems

The coupled analysis of multi-field heat and mass transfer in geothermal reservoirs is a pivotal concern within the realm of geothermal rock exploitation. It holds significant implications for the assessment of thermal energy capacity and the formulation of reservoir optimization strategies in the context of geothermal rock resources. Parameters governing production, along with fracture network characteristics (such as injection well temperature, injection well pressure, fracture width, and fracture network density), exert an influence on enhanced geothermal systems (EGS) heat production. In this study, aiming to comprehend the dynamic heat generation of EGS during prolonged exploitation, a coupling of various fields including permeation within the rock formations of geothermal reservoirs and the deformation of these rocks was achieved. In this study, we formulated the governing equations for the temperature field, stress field, and permeability field within the geothermal reservoir rock. Subsequently, we conducted numerical simulations to investigate the heat transfer process in an enhanced geothermal system. We analyzed the effects of injection well temperature, injection well pressure, primary fracture width, and secondary fracture density on the temperature distribution within the reservoir and the thermal power output of the production well. The research findings underscore that ill-conceived exploitation schemes markedly accelerate the thermal breakthrough rate of production wells, resulting in a diminished rate of geothermal resource extraction from the geothermal reservoir rock. Variations in influent well temperature and secondary fracture density exhibit an approximately linear impact on the output from production wells. Crucially, injection well pressure and primary fracture width emerge as pivotal factors influencing reservoir output response, with excessive widening of primary fractures leading to premature thermal breakthrough in production wells.

Fractional and Unitary Electric Charges I: Classical Foundations of Quantum Effects

Numerical value of the atom’s electrical/electromotive charge emerges naturally upon expressing its definitive e-m oscillation frequency ν as an exponent of eight, 8ν  (‘octave quantum’). This simple procedure realizes, for each element, accurate values of the established quantum numbers. It is revealed that unlike others, the spin quantum number ±½ is not an ‘octave quantum’, it actually turns out an exponent of a field coupling that manifests atomic mass. Octave quanta of frequencies of atoms of the second and third (invisible unknown) elements of nature’s chemical periodicity, “blackton” Bl and “boston” Bs, (8⅓, 8⅔)  manifest observational fractional one-third 1/3  and two-third 2/3  electrical charges normally associated with ‘quarks’. Based on the concept of ‘octave quantum’ the author uses periodic arrangement of the chemical elements to present a unique account of established quantum numbers, it facilitates a deeper insight into factors responsible for unusual valences commonly encountered among transition elements. It is concluded that the ease with which the procedure reproduces established quantum numbers strongly suggests an intrinsic classical origin of observational quantum characteristics.

Research on multi-scale hysteresis constitutive model of giant magnetostrictive materials considering multi-field coupling

The magnetization and magnetostrictive strain of giant magnetostrictive materials exhibit a complex nonlinear trend under the coupling of multiple fields, including magnetic field, temperature field, and prestress field. To enhance prediction accuracy, we propose a three-dimensional magnetic-thermal-force coupled nonlinear multi-scale hysteresis vector model. This model is derived from the principles of thermodynamics and continuum mechanics, taking into account the interactions among magnetic domains, grains, polycrystals, and macroscopic scales. It combines the volume-averaging principle of magnetic domain microscopy with the generalized Jiles-Atherton hysteresis model. The predicted hysteresis magnetization and magnetostrictive strain curves obtained from this model are in good agreement with experimental results. By analyzing the predicted hysteresis magnetization and magnetostrictive strain under different conditions, we demonstrate that our proposed model can comprehensively describe the effects of temperature and prestress on the multi-field coupled hysteresis behaviors of giant magnetostrictive materials. Moreover, it provides theoretical guidance for both macroscopic and microscopic optimization in designing active devices incorporating super magnetostrictive materials.

Microwave heating of oil shale based on multiphysics field coupling: Positioning of the waveguide

Microwave heating has proven widespread applications in oil shale pyrolysis; however, the impact of waveguide port positioning on the microwave reactor's thermal performance remains underexplored. This work establishes a 3D coupled model that incorporates electromagnetic, thermochemical, and fluid dynamics effects employing multiphysics modeling methodology. The thermochemical characteristics of an oil shale sample under microwave irradiation are quantified for a broad range of waveguide port positions, specified via Latin hypercube sampling, which ensures the randomness of the port coordinates. The cavity field strength exhibits markedly high sensitivity to the waveguide positioning: the standard deviation of the cavity-averaged electromagnetic intensities for all considered positions is found to be 30.42% greater compare to the associated mean. The best port position yields a temperature rising rate an order of magnitude higher than the worst positioning, for which kerogen pyrolysis does not appear to be even activated in the same initial stage. The ranking of waveguide positions identified based on the temperature rising rate aligns well with the analysis of microwave utilization efficiency. The study offers insights for optimized microwave reactor design with enhanced oil shale thermal treatment.

Rock Breaking Mechanism and Process Optimisation of Jet Cutting Basic Roof Rock under Submerged Jet Condition

The destruction of rock under the condition of a close submerged jet has become a hot topic of scientific research and engineering application in the past decade. With the unremitting efforts of a large number of experts and scholars around the world, gratifying progress has been made in the research of computational fluid dynamics (CFD) on the internal and external flow fields of the jet nozzle, the theoretical derivation of rock mechanics on the fracture initiation and propagation criteria of hydraulic fracturing, and the numerical simulation of jet erosion mechanism under the coupling of fluid and solid fields, however, for the rock mechanics hydraulic fracturing cutting engineering scale of non-oil drilling fracturing technology, the research on the fluid-solid coupling boundary conditions of fracturing fluid and hard dense rock under the flow state conditions of the submerged field inside and outside the borehole is not sufficient. In the calculation of the fluid-solid coupling boundary flow field under the non-submerged jet state, the control equation with Reynolds number between 2300-4000 shall be selected, while it belongs to the laminar flow state in the stage of hole sealing and pressurised fracturing. Therefore, Von-Mises equivalent plastic stress is selected in the mechanical model to calibrate the failure state of the rock-solid boundary, and the control equations of laminar flow and turbulent flow are selected to calibrate the fluid boundary. The mechanism of different stages of rock breaking by hydraulic fracturing jet can be further analysed in detail, and Comsol 6.0 multi-physical field simulation software is selected for verification. The research results will help deepen the understanding of rock breaking mechanism by jet and optimise the selection of parameters for field construction.

Coupling of Electric and Flow Fields to Enhance Ion Transport for Energy-Efficient Electrochemical Tap-Water Softening.

Electrochemical-induced precipitation is a sustainable approach for tap-water softening, but the hardness removal performance and energy efficiency are vastly limited by the ultraslow ion transport and the superlow local HCO3-/Ca2+ ratio compared to the industrial scenarios. To tackle the challenges, we herein report an energy-efficient electrochemical tap-water softening strategy by utilizing an integrated cathode-anode-cathode (CAC) reactor in which the direction of the electric field is reversed to that of the flow field in the upstream cell, while the same in the downstream cell. As a result, the transport of ions, especially HCO3-, is significantly accelerated in the downstream cell under a flow field. The local HCO3-/Ca2+ ratio is increased by 1.5 times, as revealed by the finite element numerical simulation and in situ imaging. In addition, a continuous flow electrochemical system with an integrated CAC reactor is operated for 240 h to soften tap water. Experiments show that a much lower cell voltage (9.24 V decreased) and energy consumption (28% decreased) are obtained. The proposed ion-transport enhancement strategy by coupled electric and flow fields provides a new perspective on developing electrochemical technologies to meet the flexible and economic demand for tap-water softening.

Dynamic characteristics testing and modeling in electromagnetic-thermal-force coupling of electromagnetic devices using parallel finite element simulation

Electromagnetic systems of Electromagnetic devices involve multiphysics coupling of electromagnetic fields, electrical circuits, mechanical motion, and temperature fields. When the digital prototype model has a large number of meshes, the commercial finite element software also has the disadvantage of long computation time in the simulation of dynamic characteristics of electrical apparatus. This paper proposes a transmission line method (TLM) based digital modeling method for the electromagnetic-thermal-force coupling to test and evaluate the static and dynamic characteristics of electromagnetic devices more accurately and efficiently. The case study is developed on a direct current (DC) contactor, and the dynamic characteristics testing and modeling in the electromagnetic-thermal-force coupling of the contactor are investigated. The numerical results of the finite element method (FEM) model for the electromagnetic system of the contactor are compared with the commercial FEM software Altair Flux and the experimental results, which demonstrate the exceptional accuracy of the proposed digital modeling method for the multiphysics coupling of the DC contactor. Meanwhile, the dynamic characteristics of the DC contactor at different ambient temperatures are measured and evaluated, and the comparison with the experimental measurements shows the applicability of the proposed digital prototype model at different ambient temperatures. Compared with the conventional Newton-Raphson (NR) iteration, when dividing fine mesh and extremely fine mesh, the TLM parallel computing significantly improves the efficiency of solving the dynamic characteristics of multiphysics coupling by about 35 % and 44 % with the same computational accuracy, respectively. The dynamic characteristics evaluation method combined with digital modeling technology and experimental measurements proposed in this paper demonstrates high accuracy and solving efficiency, making a notable contribution to the field of design and optimization of electromagnetic devices.

Suppression of the Ferromagnetic Boundary Coupling and Precision Control of Magnetic Field with the Self-Shielding Method

Suppression of the Ferromagnetic Boundary Coupling and Precision Control of Magnetic Field with the Self-Shielding Method

Simulation method for filling stage in liquid composite molding based on a two-phase flow volume of fluid model

Liquid composite molding (LCM) is a process for manufacturing fiber-reinforced resin matrix composites. The chemical rheological properties of resin in the filling stage of LCM will produce a non-isothermal flow process that includes multi-field coupling of thermal field, flow field, and chemical field. During the filling stage, the resin is injected into a closed mold pre-laid with a fiber at a certain temperature and pressure to flow continuously and undergo a curing chemical reaction. The viscosity of resin changes constantly under the influence of temperature and the curing reaction, which affects the flow of resin. The simulation of this multi-field coupling filling stage in LCM can provide an effective reference for the design of process parameters. The simulation method of the filling stage in LCM is studied in this paper. The mathematical model of the filling stage is derived based on the air–resin two-phase flow volume of the fluid model. Based on the secondary development of the ANSYS FLUENT software, the mathematical model is solved to realize the simulation. The parameters of an alkali-free glass fiber plain weave fabric are measured and the calculation model of thermosetting resin viscosity is established by designed experiments, which are applied in simulation. The filling stage experiment of LCM is designed to verify the accuracy of simulation results. Meanwhile, by comparing with the traditional simulation method, it is found that the data error obtained by the simulation method in this paper is significantly reduced.

Resonant inductive coupling network for human-sized magnetic particle imaging.

In magnetic particle imaging, a field-free region is maneuvered throughout the field of view using a time-varying magnetic field known as the drive-field. Human-sized systems operate the drive-field in the kHz range and generate it by utilizing strong currents that can rise to the kA range within a coil called the drive field generator. Matching and tuning between a power amplifier, a band-pass filter, and the drive-field generator is required. Here, for reasons of safety in future human scanners, a symmetrical topology and a transformer called an inductive coupling network are used. Our primary objectives are to achieve floating potentials to ensure patient safety while attaining high linearity and high gain for the resonant transformer. We present a novel systematic approach to the design of a loss-optimized resonant toroid with a D-shaped cross section, employing segmentation to adjust the inductance-to-resistance ratio while maintaining a constant quality factor. Simultaneously, we derive a specific matching condition for a symmetric transmit-receive circuit for magnetic particle imaging. The chosen setup filters the fundamental frequency and allows simultaneous signal transmission and reception. In addition, the decoupling of multiple drive field channels is discussed, and the primary side of the transformer is evaluated for maximum coupling and minimum stray field. Two prototypes were constructed, measured, decoupled, and compared to the derived theory and method-of-moment based simulations.