Field Generation Research Articles

Time-resolved plasmon-assisted generation of optical-vortex pulses

The microscopic mechanism of the light-matter interactions that induce orbital angular momentum (OAM) in electromagnetic fields is not thoroughly understood. In this work, we employ Archimedean spiral vortex generators in time-resolved numerical simulations using the Octopus code to observe the behind-the-scenes of OAM generation. We send a perfect circularly-polarized plane-wave light onto plasmonic optical vortex generators and observe the resulting twisted light formation with complete spatio-temporal information. In agreement with previous works, we find that emission from the plasmonic spiral branches shapes the vortex-like structure and governs the OAM generation in the outgoing electromagnetic field. To characterize the generated beam further, we emulate the emission from vortex generators with current emitters preserving the spiral geometry. We subject a point-particle system to the generated field and record the orbital angular momentum transfer between the electromagnetic field and the point particle. Finally, we probe the OAM density locally by studying the induced classical trajectory of point particles, which provides further insight into the spatio-temporal features of the induced OAM.

Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation

Patients diagnosed with cancer receive different types of treatments based on the type and the level of the tumour. An emerging treatment that differs from well-developed systematic therapies (i.e., Chemotherapy, Radiotherapy, and Immunotherapy) is Tumour Treating Field (TTF) treatment. Tumour behaviour under TTF treatment varies based on the electric field intensity; the process of exposing the tumour cells to an electric field is called electroporation. From the electrical perspective, the most efficient method for electroporation is to use a voltage pulse generator. Several pulse generator topologies have been introduced to overcome existing limitations, mitigate the drawbacks of classical generators, and provide more controllable, flexible, and portable solid-state voltage pulse generators. This paper provides a review of cancer treatment using TTF and highlights the key specifications required for efficient treatment. Additionally, potential voltage pulse generators are reviewed and compared in terms of their treatment efficacy and efficient use of electrical power.

Artificial neural networks for predicting mechanical properties of Al2219-B4C-Gr composites with multireinforcements

Artificial neural networks (ANNs) have gained prominence as a reliable model for clustering, grouping, and analysis in various domains. In recent times, machine learning (ML) models such as ANNs have proved to be on par with traditional regression and statistical models in terms of performance and usability. This study focuses on the fabrication of multicomponents-reinforced composites (Boron carbide (B4C) and Graphite (Gr)) using the stir casting technique. The addition of Magnesium to the melt enhances the wettability of B4C and Gr particles within the matrix. The microstructure and mechanical properties of the resulting Al-Mg-metal matrix composites (MMCs) are analyzed. Scanning electron micrographs reveal that B4C and Gr particles were uniformly dispersed in the matrix. X-Ray diffraction analysis confirmed the dispersion of the strengthening. The mechanical properties, including hardness, tensile, compressive, and impact strength, increased with the increase in B4C and Gr wt.%. As the percentage of B4C and Gr reinforcement wt.% increased, the load on the matrix reduced and its load-bearing capacity improved. The strain field generation rate also increased with an increase in B4C and Gr in the matrix, resulting in enhanced mechanical properties. The ANN analysis further confirmed that B4C was the more significant contributor to the mechanical properties of the composites.

Phase boundary induced drastic sensing performance enhancement of mixed-phase N-Fe2O3 (α/γ) gas sensors for acetone

The development of high-performance, portable and miniaturized metal oxide semiconductor (MOS)-based chemiresistive materials is important for portable gas sensors. Phase boundaries provide lasting inspiration and a promising avenue for designing advanced functionalities using nanomaterials. However, the impact of different phase boundaries in a single MOS on the performance of MOS-based chemiresistive gas sensors has been rarely explored. Here, we report a mixed-phase N-Fe2O3 (α/γ) gas sensor with rich phase boundaries, which exhibits an enhancement of the response up to 386 towards 50 ppm of acetone at 240 °C. This is attributed to the generation of the internal electric field (IEF) and defects originating from lattice mismatch at the N-Fe2O3 (α) – N-Fe2O3 (γ) phase boundaries, which providing more active sites for adsorption of oxygen and acetone molecules. This work clearly shows that we can optimize the gas sensing catalyst of low-cost materials by regulating the phase boundaries of nanomaterials to develop high-precision portable gas sensors.

Generation of direct current electrical fields as regenerative therapy for spinal cord injury: A review.

Electrical stimulation (ES) shows promise as a therapy to promote recovery and regeneration after spinal cord injury. ES therapy establishes beneficial electric fields (EFs) and has been investigated in numerous studies, which date back nearly a century. In this review, we discuss the various engineering approaches available to generate regenerative EFs through direct current electrical stimulation and very low frequency electrical stimulation. We highlight the electrode-tissue interface, which is important for the appropriate choice of electrode material and stimulator circuitry. We discuss how to best estimate and control the generated field, which is an important measure for comparability of studies. Finally, we assess the methods used in these studies to measure functional recovery after the injury and treatment. This work reviews studies in the field of ES therapy with the goal of supporting decisions regarding best stimulation strategy and recovery assessment for future work.

PCB Coil Enables In Situ Calibration of Magnetoelectric Sensor Systems

Abstract Accurate calibration is key for any reliable sensor system. Magnetoelectric (ME) sensors, in particular, are influenced in their operating point by external parameters such as the Earth’s magnetic field or the ambient temperature. In this paper, we introduce a new planar coil design for the generation of a magnetic test field within the plane of the ME sensor. Furthermore, we implemented a method for measuring the sensor behaviour using a short-term magnetic noise signal. The combination of the printed circuit board (PCB) coil and the accelerated sensor characterization method allows the sensor system to be calibrated at the measurement site (in situ) without the need for laboratory equipment. We can show that the presented method for calibration achieves high-quality results in 10 seconds for a sensor affected by external interference fields.

A Review of the Electromagnetic Radiation Emission and Magnetic Field Generation in Metallic Materials Under Stress

A Review of the Electromagnetic Radiation Emission and Magnetic Field Generation in Metallic Materials Under Stress

Miniaturized metachronal magnetic artificial cilia

Biological cilia, hairlike organelles on cell surfaces, often exhibit collective wavelike motion known as metachrony, which helps generating fluid flow. Inspired by nature, researchers have developed artificial cilia as microfluidic actuators, exploring several methods to mimic the metachrony. However, reported methods are difficult to miniaturize because they require either control of individual cilia properties or the generation of a complex external magnetic field. We introduce a concept that generates metachronal motion of magnetic artificial cilia (MAC), even though the MAC are all identical, and the applied external magnetic field is uniform. This is achieved by integrating a paramagnetic substructure in the substrate underneath the MAC. Uniquely, we can create both symplectic and antiplectic metachrony by changing the relative positions of MAC and substructure. We demonstrate the flow generation of the two metachronal motions in both high and low Reynolds number conditions. Our research marks a significant milestone by breaking the size limitation barrier in metachronal artificial cilia. This achievement not only showcases the potential of nature-inspired engineering but also opens up a host of exciting opportunities for designing and optimizing microsystems with enhanced fluid manipulation capabilities.

Egyptian Blue/gold nanocomposite supramarbles, a platform for IR emission enhancement

Nanotechnology manufacturing requires a unique skillset and access to that technology is not yet within the reach of many small businesses and startups. What if a specialty product could be offered as pellets or marbles, and this new platform enabled uniform nano-coatings readily handled by off the shelf standard manufacturing technologies? The platform – a supramarble (SM) – introduced in this work is a crosslinked polymer core with a coating (or corona) of hydrophobic micro- and nanoparticles. A photoactive 2-D nanoparticulate pigment, Egyptian Blue (EB) has gained tremendous popularity in sensing applications recently due to its intense near-infrared emission at ∼900 nm. Gold nanoparticles (AuNPs) have been reported to modify the spontaneous emission of other adjacent fluorophores in a remarkable way. By combining near-infrared emitting EB microparticles and AuNP decorated fumed silica (Au-FS) NPs as the corona of an SM, significant (4-fold) fluorescence enhancement is demonstrated in this work. A maximum in fluorescent intensity was shown at 70 wt% EB and 30 wt% Au-FS composite coating. The 4-fold enhancement was attributed to AuNPs’ generation of a localized electric field synergistically interacting with the fluorescent emission of EB. The influence of Au-FS on the original, intrinsic fluorescent emission wavelength of EB (∼900 nm) was also investigated.

INCLUDING THE OWN FIELDS OF QUANTUM EMITTERS IN DESCRIBING GENERATION REGIMES

The paper discusses three different modes of electromagnetic field generation by an ensemble of quantum emitters placed at the radiation wavelength in the one-dimensional case. The excitation of the resonator field is considered, which, as a rule, is determined by the geometry of the system, with and without taking into account the eigenfields of the emitters. The superradiance mode of the same ensemble of emitters is also analyzed. Since the main indicator of generation is the level of energy output from the system, the position of the maximum of this indicator determines the operating point of the device. Taking into account the intrinsic field of the emitters enhances the generation intensity and significantly changes the position of the operating point.

A Reversed Inverse Faraday Effect

The inverse Faraday effect is a magneto‐optical process allowing the magnetization of matter by an optical excitation carrying a non‐zero spin. In particular, a right circular polarization generates a magnetization in the direction of light propagation and a left circular polarization in the opposite direction to this propagation. Herein, it demonstrates that by manipulating the spin density of light, i.e., its polarization, in a plasmonic nanostructure, a reversed inverse Faraday effect is generated. A right circular polarization will generate a magnetization in the opposite direction of the light propagation, a left circular polarization in the direction of propagation. Also, it demonstrates that this new physical phenomenon is chiral, generating a strong magnetic field only for one helicity of the light, the opposite helicity producing this effect only for the mirror structure. This new optical concept opens the way to the generation of magnetic fields with unpolarized light, finding application in the ultrafast manipulation of magnetic domains and processes, such as spin precession, spin currents, and waves, magnetic skyrmion or magnetic circular dichroism, with direct applications in data storage and processing technologies.

A Measuring System for HTS Wires and Coils Properties at Low Temperatures

The use of high temperature superconducting materials (HTS) in various applications, requires knowledge of their critical parameters like critical current, critical magnetic field and critical temperature, in DC applications like high magnetic field generators, superconducting magnetic energy storage system (SMES), magnetic resonance imaging (MRI), magnets for particle accelerators, SC Maglev trains and other applications. Also, these parameters are important for specific properties in alternating current applications like fault current limiters, transformers, generators, motors, and power transmission lines. An important characteristic that needs to be tucked into consideration for AC applications is the power losses that occur in the HTS superconducting materials, which limits the maximum performance that the superconducting materials can attain for these applications. In order to measure these characteristics, which depend on the type of material used, but also on the temperature and other parameters, it is necessary to use an appropriate setup device that allows both obtaining the working temperature range (4.2 K to 300 K and other necessary parameters like high vacuum 10-6 mbar, high current supply (500 A), high magnetic field measurement system (1-10 T), etc. For the cryogenic cooling of the entire system, a closed cycle Gifford-McMahon type cryocooler is used, with two cooling stages, stage I at 50 K and second stage at 4.2 K (liquid Helium temperature). The set-up system used for measurement of the parameters of HTS superconducting materials (YBCO, BSCCO or MgB2) and the various coils made with them, is described in this article together with its functional parameters and some experimental results obtained by testing an YBCO coils system. The maximum generated magnetic flux density was 5 T in the centre of the coils system.

Superchirality induced enhanced circular dichroism spectroscopy via multi-beam superposition

Circular dichroism (CD) spectroscopy is a typical technique to detect the chirality of an object. Due to the mismatch between light wavelength and the size of molecules, CD signal generally tends to be very weak in natural materials. In this work, we demonstrate the generation of superchiral field in free space through multi-beam superposition, without plasmonic/dielectric substrate that required in traditional methods. Through a systematic study of the superposition effect of up to six beams of light, we found that even achiral light fields can obtain optical chirality through superposition, and circularly polarized light fields can most effectively enhance the optical chirality density in the interference field. Generally, a maximal superchiral factor equivalent to the number of superposed beams can be achieved through optimizing the orientation of the illumination. However, when the number of superposed beams is more than three, the initial phase of superposed beams would play a significant role in determining the characteristics of the interference field, which must be carefully treated in modulating both the shape and the optical chiral density of the synthesized subwavelength chiral hotspot. Furthermore, we demonstrate that this technique is suitable to combine optical tweezers and CD spectroscopy. Based on three-beam superposition configuration, we explore the optical force and CD effects from single chiral nanoparticle, which are introduced into the optical standing wave formed by a flat mirror. It is found out that the nanoparticle can be stably trapped by the superchiral hotspot and gives rise to 2.92-fold enhancement of CD signal. This work may serve as a guideline for establishing applications in chirality sorting, chiral imaging, and CD spectroscopy.

Entropy optimized Ferro-copper/blood based nanofluid flow between double stretchable disks: Application to brain dynamic

Researchers and scientists were inspired by the enormous reactions from industry about heat transformation enhancements due to the entropy generation. The entropy generation shows as a extremes for complex mechanisms like solid state physics, two-phase flows, electro-magnetic air conditioning, and economic evaluation of manufacturing processes, as well as biological technologies chemistry, including biochemistry. We note here that many thermal mechanisms are related to the irreversibility system. The current work focused on the entropy generation impacts in viscous magnetized mono-nanofluids flow between stretchable rotating disks. Ferro and copper are considered as nanoparticles and Blood as a base fluid. The Darcy-Forchheimer porous medium and joule heating effects are considered. For simplifying the current analysis, suitable transformation were introduced in the mathematical description to renovate the partial differential equations (PDE’s) into coupled ordinary ones. To solve the resulting ODEs well-known numerical algorithm bvp4c is used in Matlab in the light of Lobatto-IIIA formula. The consequence of sundry parameters against velocity components, pressure field, temperature distribution and entropy generation are described graphically.

Investigation of intense pulsed ion beam generation by a magnetically insulated ion diode at a reduced impedance

The intense pulsed ion beam (IPIB) generation was investigated at reduced impedance of a magnetically insulated ion diode. The main goal of our research was to obtain IPIB with adjustable parameters at low current densities. The diode impedance was varied by the external magnetic field current by setting the delay of the accelerator's trigger relative to the launch of the magnetic field generator. The B-applied ion diode adjustably generated IPIB with a current density in the range from 25 to 4 A/cm2. In the matched mode the accelerator generates the ion beam with a current density of about 100 A/cm2. Obtained results of the IPIB current density adjustment allows to irradiate samples in a single vacuum cycle without the change of charging voltage of both magnetic field and accelerating voltage generators. Gold films with a thickness of 10 nm deposited on fluorine-doped tin oxide (FTO)/glass substrates were irradiated to demonstrate the applicability of obtained IPIB for irradiation of thin coatings without their deterioration. Single shot of IPIB with current density of 20 A/cm2 transformed Au film to spherical micro-particles, while after irradiation at the same fluence with 5 pulses of IPIB with current density of 4 A/cm2 Au coating was preserved as a film.

All-plasmonic-metal chiral nanostructures fabricated by circularly polarized light

Chiral plasmonic nanostructures, which would be applied to enantioselective sensors and metasurfaces, can be prepared in an enantioselective manner by irradiation with circularly polarized light (CPL). However, their resonance sites have been covered with non-plasmonic, dielectric moieties. Here, we prepared all-silver chiral plasmonic nanostructures on a glass plate in one-step by irradiating 380–450 nm right- or left-CPL to an aqueous solution containing Ag+ and citrate ions. Achiral or racemic Ag nanoparticles with anisotropic geometry are deposited on a glass plate by photochemical electron transfer from citrate to Ag+ in the initial phase. The deposited nanoparticles are grown into chiral structures under CPL via generation of an electric field with chiral distributions. An achiral Ag nanoplate array was also grown under 600–700 nm CPL into chiral nanostructure arrays on the basis of hot electron reduction of Ag+.

APPLICATION OF THE METHOD OF DISCRETE SINGULARITIES TO THE CALCULATION OF THE EVOLUTION OF SURFACE GRAVITY WAVES OVER BOTTOM IRREGULARITIES

The numerical technique for simulation of viscous non-linear interactions between a solitary wave and a non-regular bottom was developed. It couples the boundary integral method used to determine the free surface deformations and the vortex scheme for integrating the fluid dynamic equations. To verify the model, a series of test calculations was carried out, where the obtained results were compared with our own experimental data and results known from similar studies by other authors. A good coincidence of the free surface elevation, as well as the velocity fields during the passage of a solitary wave over a thin submerged plate, was obtained. Systematic calculations of the interaction of a solitary wave with a submerged step in a wide range of wave amplitudes and step heights were performed. It is shown that when a wave emerges from deep water into the shallows, its evolution is determined by energy losses due to reflection, dispersion effects, and the generation of a vortex field. The dynamics of the wave on the submerged step depends on the coefficient of interaction, which is the ratio of the wave amplitude to the water depth above the step. Four types of wave behavior are possible above the step. Those are the weak interaction, when the wave gently splits into transmitted and reflected solitons; fission with development of two solitons behind the irregularity; fission with the generation of a dispersion chain of waves in the shallow water; and the collapse of a wave. The obtained critical value of the coefficient of interaction, at which the solitary wave is always breaking, is about 0.8, which is in congruence with the experimental data. Studies of patterns of vorticity generated by a solitary wave at the edge of a submerged step revealed two oppositely directed vortices with a horizontal axis, the scale of which is proportional to the water depth in a shallow channel. Their dynamics causes intensive exchange processes between deep water and shallows, as well as water flows from the bottom to the top and water mixing. The obtained data make it possible to predict in advance the development of processes and dangers caused by long nonlinear waves reaching the shelf.

Axial Movement Effect on Voltage and Current Behaviors of Insert No-Insulation REBCO Pancake Coil

In 2017, an insert 12-stacked no-insulation (NI) rare-earth barium copper oxide (REBCO) magnet was used in the generation of a world-record DC magnetic field of 45.5 T. The experiment demonstrated its high thermal stability; however, NI REBCO pancake coils are facing mechanical problems. In such an ultra-high field, strong electromagnetic forces work on insert REBCO coils, in particular during sequential normal-state transitions. Strong forces may cause insert REBCO coils to deform and move. Some research revealed that some deformations and movements affected the coil voltages and the screening currents. Whereas, the coil movement in an ultra-high field has not been studied yet. Voltages and currents are induced by the movement of insert coils, and there is a possibility of degrading the coil stability. In this paper, we have investigated the electromagnetic behaviors during sequential normal-state transition, considering the coil movement due to strong axial forces. The electromagnetic behaviors are simulated using a radially-subdivided partial element equivalent circuit (PEEC) model coupled with mechanical movement analysis.

Entropy: An Inspiring Tool for Characterizing Turbulence-Combustion Interaction in Swirling Flames via Direct Numerical Simulations of Non-Premixed and Premixed Flames.

This article focuses on entropy generation in the combustion field, which serves as a useful indicator to quantify the interaction between turbulence and combustion. The study is performed on the direct numerical simulations (DNS) of high pressure non-premixed and premixed swirling flames. By analyzing the entropy generation in thermal transport, mass transport, and chemical reactions, it is found that the thermal transport, driven by the temperature gradient, plays a dominant role. The enstrophy transport analysis reveals that the responses of individual terms to combustion can be measured by the entropy: the vortex stretching and the dissipation terms increase monotonically with the increasing entropy. In high entropy regions, the turbulence behaves as the "cigar shaped" state in the non-premixed flame, while as the axisymmetric state in the premixed flame. A substantial increase in the normal Reynolds stress with the entropy is observed. This is due to the competition between two terms promoted by the entropy, i.e., the velocity-pressure gradient correlation term and the shear production term. As a result, the velocity-pressure gradient correlation tends to isotropize turbulence by transferring energy increasingly from the largest streamwise component to the other smaller normal components of Reynolds stress and is dominated by the fluctuating pressure gradient that increases along the entropy. The shear production term increases with the entropy due to the upgrading alignment of the eigenvectors of strain rate and Reynolds stress tensors.

Field Measurements of Prototype Superconducting Magnet for a Compact Heavy-Ion Therapy Synchrotron

A synchrotron using superconducting magnets has been designed for a next-generation heavy-ion therapy system at National Institutes for Quantum Science and Technology. The maximum central field and ramp rate of their magnets are 3.5 T and 0.7 T/s, respectively, and a field homogeneity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">–4</sup> unit is required. To verify field generation and thermal characteristics, a prototype superconducting magnet was fabricated. This first prototype was designed as a short-straight model with a length of 400 mm and a cross section equal to that of a full-scale magnet. The magnet was conduction-cooled at cryogenic temperatures and energized up to a nominal current of 265 A. Its central field was then measured by hall sensors. Descriptions of the design and fabrication of the first prototype magnet and the results of the magnetic-field measurements are reported in this paper.