Search Results (166)

Firstly, this paper reviews the fundamental theories of solid surface wettability and contact angle hysteresis. Subsequently, it further introduces four typical wettability-engineered surfaces with low hysteresis (superhydrophobic, superamphiphobic, super-slippery, and liquid-like smooth surfaces). Finally, it focuses on the latest research progress in the field of droplet manipulation on open planar surfaces with engineered wettability. To achieve droplet manipulation, the core driving forces primarily stem from natural forces guided by bioinspired gradient surfaces or the regulatory effects of external fields. In terms of bioinspired self-propelled droplet movement, this paper summarizes research inspired by natural organisms such as desert beetles, cacti, self-aligning floating seeds of emergent plants, or water-walking insects, which construct bioinspired special gradient surfaces to induce Laplace pressure differences or wettability gradients on both sides of droplets for droplet manipulation. Moreover, this paper further analyzes the mechanisms, advantages, and limitations of these self-propelled approaches, while summarizing the corresponding driving force sources and their theoretical formulas. For droplet manipulation under external fields, this paper elaborates on various external stimuli including electric fields, thermal fields, optical fields, acoustic fields, and magnetic fields. Among them, electric fields involve actuation mechanisms such as directly applied electrostatic forces and indirectly applied electrocapillary forces; thermal fields influence droplet motion through thermoresponsive wettability gradients and thermocapillary effects; optical fields cover multiple wavelengths including near-infrared, ultraviolet, and visible light; acoustic fields utilize horizontal and vertical acoustic radiation pressure or acoustic wave-induced acoustic streaming for droplet manipulation; the magnetic force acting on droplets may originate from their interior, surface, or external substrates. Based on these different transport principles, this paper comparatively analyzes the unique characteristics of droplet manipulation under the five external fields. Finally, this paper summarizes the current challenges and issues in the research of droplet manipulation on the open planar surfaces and provides an outlook on future development directions in this field. Full article

This study presents a comprehensive mathematical model of a semiconductor structure based on vanadium dioxide (VO₂), specifically in its conductive phase. The model was developed using the finite element method (FEM), enabling detailed simulation of the formation of a conductive channel under the influence of low-frequency alternating voltage (50 Hz). The VO₂ structure under investigation exhibits pronounced electric field concentration at the surface, where the field strength reaches approximately 5 × 10⁴ V/m, while maintaining a more uniform distribution of around 2 × 10⁴ V/m within the bulk of the material. The simulation results were validated experimentally using a test circuit. Minor deviations—no greater than 8%—were observed between the simulated and measured current values, attributed to magnetic core saturation and modeling assumptions. A distinctive feature of the model is its ability to incorporate the nonlinear dependencies of VO₂’s electrical properties on frequency. Analytical expressions were derived for the magnetic permeability and resistivity of VO₂, demonstrating excellent agreement with experimental data. The coefficients of determination (R²) for the frequency dependence of magnetic permeability and resistance were found to be 0.9976 and 0.9999, respectively. The current version of the model focuses exclusively on the conductive phase and does not include the thermally induced metal–insulator phase transition characteristic of VO₂. The study confirms that VO₂-based structures exhibit high responsiveness and nonlinear switching behavior, making them suitable for applications in electronic surge protection, current limiting, and switching elements. The developed model provides a reliable and physically grounded tool for the design and optimization components based on VO₂ in power electronics and protective circuitry. Full article

Electric mountain bikes (eMTBs) demand compact, high-torque motors capable of handling steep terrain and variable load conditions. Surface-mounted permanent magnet synchronous motors (SPMSMs) are widely used in this application due to their simple construction, ease of manufacturing, and cost-effectiveness. However, SPMSMs inherently lack reluctance torque, limiting their torque density and performance at high speeds. While interior PMSMs (IPMSMs) can overcome this limitation via reluctance torque, they require complex rotor machining and may compromise mechanical robustness. This paper proposes a surface-inset PMSM topology as a compromise between both approaches—introducing reluctance torque while maintaining a structurally simple rotor. The proposed motor features inset magnets shaped with a tapered outer profile, allowing them to remain flush with the rotor surface. This geometric configuration eliminates the need for a retaining sleeve during high-speed operation while also enabling saliency-based torque contribution. A baseline SPMSM design is first analyzed through finite element analysis (FEA) to establish reference performance. Comparative simulations show that the proposed design achieves a 20% increase in peak torque and a 33% reduction in current density. Experimental validation confirms these findings, with the fabricated prototype achieving a torque density of 30.1 kNm/m³. The results demonstrate that reluctance-assisted torque enhancement can be achieved without compromising mechanical simplicity or manufacturability. This study provides a practical pathway for improving motor performance in eMTB systems while retaining the production advantages of surface-mounted designs. The surface-inset approach offers a scalable and cost-effective solution that bridges the gap between conventional SPMSMs and more complex IPMSMs in high-demand e-mobility applications. Full article

With the widespread application of DC technology in data centers, renewable energy, electric transportation, and high-voltage direct current (HVDC) transmission, DC rectangular busbars are becoming increasingly important in power transmission systems due to their high current density and compact structure. However, space constraints make the deployment of conventional sensors challenging, highlighting the urgent need for miniaturized, non-contact current measurement technologies to meet the integration requirements of smart distribution systems. This paper proposes a field-source inversion-based contactless DC measurement method for rectangular busbars. The mathematical model of the magnetic field near the surface of the DC rectangular busbar is first established, incorporating the busbar eccentricity, rotation, and geomagnetic interference into the model framework. Subsequently, a magnetic field–current inversion model is constructed, and the DC measurement of the rectangular busbar is achieved by performing an inverse calculation. The effectiveness of the proposed method is validated by both simulation studies and physical experiments. Full article

The temperature variations of interconnected coaxial connectors in RF circuits are strongly influenced by the contact surface characteristics and the ferromagnetic properties of the electroplated materials. In this study, specially structured N-DIN connectors with either magnetic or non-magnetic plating were designed. A dedicated high-frequency, high-power RF experimental platform was set up to monitor and measure the temperature and power of the connectors. Finite element analysis (FEA) was employed to simulate the current density and temperature distribution across the samples. Furthermore, an equivalent circuit model of the central conductor was established by integrating electrical contact theory with the magnetic hysteresis effect. Based on the voltage–temperature (V–T) relation and the derived magnetic field–magnetoresistance (H–M) relation, a predictive model for the temperature rise of the central conductor was formulated. Experimental results demonstrated good agreement with simulation predictions, validating the proposed model and highlighting the critical role of plating material properties in high-power RF connectors’ thermal effect. Full article

Wireless power transfer (WPT) is recognized as a critical technology to advance carbon neutrality in transportation by alleviating charging challenges for electric vehicles and accelerating their adoption to replace fossil fuel. To ensure durability under traffic loads and harsh environments while avoiding vehicle obstructions, WPT primary circuits should be embedded within pavement structures rather than surface-mounted. This study systematically investigated the optimization of magnetite-modified asphalt material composition and thickness for enhancing electromagnetic coupling in WPT systems through integrated numerical and experimental approaches. A 3D finite element model (FEM) and a WPT platform with primary-side inductor–capacitor–capacitor (LCC) and secondary-side series (S) compensation were developed to assess the electromagnetic performance of magnetite content ranging from 0 to 25% and pavement thickness ranging from 30 to 70 mm. Results indicate that magnetite incorporation increased efficiency from 80.3 to 84.7% and coupling coefficients from 0.236 to 0.242, with power loss increasing by only 0.25 W. This enhancement is driven by improved equivalent permeability, which directly enhances magnetic coupling efficiency. A critical pavement thickness of 50 mm was identified, beyond which the reduction in transmission efficiency increased significantly due to magnetic flux dispersion. Additionally, the nonlinear increase in power loss is partially attributed to the significant rise in hysteresis and eddy current losses at elevated magnetite content levels. The proposed design framework, which focuses on 10% magnetite content and a total pavement thickness of 50 mm, achieves an optimal energy transfer efficiency. This approach contributes to sustainable infrastructure development for wireless charging applications. Full article

Magnetoencephalography (MEG) is a non-invasive neuroimaging technique that measures weak magnetic fields generated by neural electrical activity in the brain. Traditional MEG systems use superconducting quantum interference device (SQUID) sensors, which require cryogenic cooling and employ a dense array of sensors to capture magnetic field maps (MFMs) around the head. Recent advancements have introduced optically pumped magnetometers (OPMs) as a promising alternative. Unlike SQUIDs, OPMs do not require cooling and can be placed closer to regions of interest (ROIs). This study aims to optimize the layout of OPM-MEG sensors, maximizing information capture with a limited number of sensors. We applied a sequential selection algorithm (SSA), originally developed for body surface potential mapping in electrocardiography, which requires a large database of full-head MFMs. While modern OPM-MEG systems offer full-head coverage, expected future clinical use will benefit from simplified procedures, where handling a lower number of sensors is easier and more efficient. To explore this, we converted full-head SQUID-MEG measurements of auditory-evoked fields (AEFs) into OPM-MEG layouts with 80 sensor sites. System conversion was done by calculating a current distribution on the brain surface using minimum norm estimation (MNE). We evaluated the SSA’s performance under different protocols, for example, using measurements of single or combined OPM components. We assessed the quality of estimated MFMs using metrics, such as the correlation coefficient (CC), root-mean-square error, and relative error. Additionally, we performed source localization for the highest auditory response (M100) by fitting equivalent current dipoles. Our results show that the first 15 to 20 optimally selected sensors (CC > 0.95, localization error < 1 mm) capture most of the information contained in full-head MFMs. Our main finding is that for event-related fields, such as AEFs, which primarily originate from focal sources, a significantly smaller number of sensors than currently used in conventional MEG systems is sufficient to extract relevant information. Full article

This paper proposes a two-dimensional (2D) generalized equivalent magnetic network (GEMN) model suitable for surface-mounted permanent magnet electric machines (SPEMs). The model divides the SPEM into eight types of regions: stator yoke, stator tooth body, stator tooth tips, stator slot body, stator slot openings, air gap, rotor permanent magnets, and rotor yoke. Each region is subdivided radially and tangentially into multiple 2D magnetic network units containing radial and tangential magnetic circuit parameters, forming a regular magnetic network covering all regions of the SPEM. The topology of this magnetic network remains unchanged during rotor rotation and can accommodate various surface-mounted permanent magnet structures including Halbach arrays, which enhances the generality of the model significantly. The proposed model can be used to calculate the 2D magnetic flux density distribution, winding electromotive force, electromagnetic torque, stator iron loss, and permanent magnet demagnetization in the influence of magnetic saturation, stator slotting, and current harmonic. Comparative analysis with the accurate subdomain method (ASDM) and finite element method (FEM) demonstrates that the GEMN model achieves a good balance between computational speed and accuracy, making it particularly suitable for efficient electromagnetic performance evaluation of SPEMs. Full article

The development of efficient and sustainable electrocatalysts for optimizing methanol oxidation reactions (MORs) in direct methanol fuel cells (DMFCs) is crucial for the innovation of clean electrode energy technologies. This study highlights the synthesis and characterization of magnesium ferrite (MgFe₂O₄) and magnesium-based metal–organic framework (Mg-MOF) composites, utilizing cost-effective and scalable methods such as co-precipitation and ultrasound-assisted synthesis. The composite material, prepared in a 1:1 ratio, demonstrated enhanced catalytic performance due to the synergistic integration of MgFe₂O₄ and Mg-MOF. Comprehensive structural and morphological analyses, including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), the Brunauer–Emmett–Teller (BET) technique, and X-ray photoelectron spectroscopy (XPS), confirmed the successful formation of the composite. Also, the modification of magnetic properties, particularly the values of coercive force (Hc), led to a significant enhancement in electrical and catalytic performance. The material exhibited mesoporous characteristics and an improved surface area. Electrochemical evaluations revealed superior MOR activity for the composite electrode, achieving a current density of 31.5 mA∙cm⁻² at 1 M methanol with an onset potential of 0.34 V versus Ag/AgCl, measured at a scan rate of 100 mV/s. Remarkably, the composite electrode showed a 75% improvement in current density compared to its components. Additionally, the composite exhibited a low overpotential of 350 mV and favorable Tafel slopes of 22.54 and 4.27 mV∙dec⁻¹ at high and low potentials, respectively, confirming rapid methanol oxidation kinetics on this electrode. It also demonstrated excellent stability, retaining 97.4% of its current density after 1 h. Electrochemical impedance spectroscopy (EIS) further revealed a reduced charge transfer resistance of 9.26 Ω, indicating enhanced conductivity and catalytic efficiency. These findings underscore the potential of MgFe₂O₄/Mg-MOF composites as cost-effective and high-performance anode materials for DMFCs, paving the way for sustainable energy solutions. Full article

This paper proposes a tri-band wide-angle polarization-insensitive absorber operating in the C-band and Ku-band, based on the design concept of metal–dielectric–metal. The absorber achieves absorption efficiencies of 99.05%, 99.3%, and 97.9% at 4.23 GHz, 7.403 GHz, and 14.813 GHz, respectively. The first two absorption frequencies are in the C-band, while the third absorption frequency is in the Ku-band, both of which are commonly used in satellite communication. The designed absorber consists of three differently sized regular hexagonal rings. To analyze the interaction mechanism between the electromagnetic wave and the absorber, we applied the theory of impedance matching and equivalent media to analyze the metamaterial properties of the absorber. In addition, the equivalent circuit model of the absorber has been analyzed. We then determined the existence of coupled electromagnetic resonances between the top and bottom surfaces by analyzing the distribution of the electric field, magnetic field, and surface currents on the absorber. By varying the polarization angle and incident angle of the incoming wave, we found that the absorber exhibits polarization insensitivity and wide-angle absorption characteristics. The TE and TM waves maintain more than 90% absorption efficiency up to incident angles of 50° and 60°, respectively. The absorber’s thickness is 1.07 mm, which is 0.0154 times the wavelength corresponding to the lowest resonant frequency ${(\lambda }_0)$, and the edge length of the subunit’s regular hexagon is 7.5 mm (0.108${\lambda }_0$), making the absorber sub-wavelength in scale while maintaining its compactness. The proposed absorber operates in the C-band and Ku-band, and can be applied in the field of satellite communications, achieving functions such as electromagnetic shielding and stealth. Full article

Superconducting spherical shells have important application value or potential in various fields, such as inertial navigation, gravity measurement, and nuclear fusion. Depending on the needs of the applications, the thickness of the superconducting shell may vary from micrometers to nanometers. We report an investigation into the superconducting properties of ${\mathrm{MgB}}_2$ spherical shells deposited on 1 mm diameter Si₃N₄ spheres, with the shell thickness varying from approximately 200 nm to 720 nm. The upper critical field $H_{c2}$, the lower critical field $H_{c1}$, and the superconducting critical current density $J_c$ were determined from electrical resistance, initial magnetization, and magnetization hysteresis loop measurements, respectively. As the shell thickness decreased, it was observed that $H_{c2}$ was enhanced, $H_{c1}$ declined, and $J_c$ rose. This systematic evolution of the superconducting properties is suggested to have arisen from a reduction in the grain size with a decrease in the shell thickness, as shown by surface morphology images of the shells. A reduction in the grain size leads to increased grain boundaries and scattering strength, which decrease the electron diffusivities, thereby enhancing $H_{c2}$ and suppressing $H_{c1}$ as the shell thickness diminishes. The proliferation of grain boundaries would also provide more effective flux pinning in the shell, giving rise to an improvement in $J_c$. Our study demonstrated a close correlation between the microstructure, specifically, the grain size, and the superconducting properties in ${\mathrm{MgB}}_2$ spherical shells and the effectiveness of tuning them by varying the thickness of the shell. Moreover, it also revealed that the superconducting properties of the fabricated spherical shells, particularly their evolutions with the shell thickness, were critically influenced by the multiband superconductivity of ${\mathrm{MgB}}_2$. These findings would provide a helpful reference for fabricating ${\mathrm{MgB}}_2$ superconducting shells with desired thicknesses and properties, enabling them to better meet the requirements of applications in various fields. Full article

Magnetic polymeric conduits are developing as revolutionary materials in regenerative medicine, providing exceptional benefits in directing tissue healing, improving targeted medication administration, and facilitating remote control via external magnetic fields. The present article offers a thorough examination of current progress in the design, construction, and functionalization of these hybrid systems. The integration of magnetic nanoparticles into polymeric matrices confers distinctive features, including regulated alignment, improved cellular motility, and targeted medicinal delivery, while preserving structural integrity. Moreover, the incorporation of multifunctional attributes, such as electrical conductivity for cerebral stimulation and optical characteristics for real-time imaging, expands their range of applications. Essential studies indicate that the dimensions, morphology, surface chemistry, and composition of magnetic nanoparticles significantly affect their biocompatibility, degrading characteristics, and overall efficacy. Notwithstanding considerable advancements, issues concerning long-term biocompatibility, biodegradability, and scalability persist, in addition to the must for uniform regulatory frameworks to facilitate clinical translation. Progress in additive manufacturing and nanotechnology is overcoming these obstacles, facilitating the creation of dynamic and adaptive conduit structures designed for particular biomedical requirements. Magnetic polymeric conduits, by integrating usefulness and safety, are set to transform regenerative therapies, presenting a new avenue for customized medicine and advanced healthcare solutions. Full article

A number of computer experiments have investigated the effectiveness in terms of accuracy of the method for simultaneously determining the distributions of electrical conductivity and magnetic permeability in the subsurface zone of planar conductive objects when modeling the process of eddy-current measurement testing by surface probes. The method is based on the use of surrogate optimization, which involves the use of a high-performance neural network proxy-model of probe by means of a deep learning as part of the target quadratic function. The surrogate model acts as a carrier and storage of a priori information about the object and takes into account the influence of all the main factors essential in the formation of the probe output signal. The problems of the surrogate model’s cumbersomeness and mitigation of the “curse of dimensionality” effect are solved by applying techniques for reducing the dimensionality of the design space based on the PCA algorithm. We investigated options for compromise solutions regarding the dimensionality of the PCA-space and the accuracy of obtaining the desired material properties profiles by the optimization method. The results of modeling the inverse measurement problem indicate a fairly high accuracy of profile reconstruction. Full article

We propose a non-magnetic transparent heating film based on silver nanowires (Ag-NWs) for application in spin-exchange relaxation-free (SERF) magnetic field measurement devices. To achieve ultra-high sensitivity in atomic magnetometers, the atoms within the alkali metal vapor cell must be maintained in a stable and uniform high-temperature environment. Ag-NWs, as a transparent conductive material with exceptional electrical conductivity, are well suited for this application. By employing high-frequency AC heating, we effectively minimize associated magnetic noise. The experimental results demonstrate that the proposed heating film, utilizing a surface heating method, can achieve temperatures exceeding 140 °C, which is sufficient to vaporize alkali metal atoms. The average magnetic flux coefficient of the heating film is 0.1143 nT/mA. Typically, as the current increases, a larger magnetic field is generated. When integrated with the heating system discussed in this paper, this characteristic can effectively mitigate low-frequency magnetic interference. In comparison with traditional flexible printed circuits (FPC), the Ag-NWs heating film exhibits a more uniform temperature distribution. This magnetically transparent heating film, leveraging Ag-NWs, enhances atomic magnetometry and presents opportunities for use in chip-level gyroscopes, atomic clocks, and various other atomic devices. Full article

Micromagnetic stimulation (μMS) is a promising branch of neurostimulation but without some of the drawbacks of electrical stimulation. Microcoil (μcoil)-based magnetic stimulation uses small micrometer-sized coils that generate a time-varying magnetic field, which, as per Faraday’s Laws of Electromagnetic Induction, induces an electric field on a conductive surface. This method of stimulation has the advantage of not requiring electrical contact with the tissue; however, these μcoils are not easy to operate. Large currents are required to generate the required magnetic field. These large currents are too large for standard test equipment to provide, and additional power amplifiers are needed. To aid in the testing and development of micromagnetic stimulation devices, we have created a compact single-unit test setup for driving these devices called the µCoil Driver. This unit is designed to drive small inductive loads up to ±8 V at 5 A and 10 kHz. Full article