Physical Science: New Insights and Developments Vol. 4

Enhanced Soft-magnetic Performance of Fe-based Composites Via Nanoparticle Doping and Hot-press Sintering for High-frequency Applications

2026-01-06T11:17:13+00:00

Soft magnetic composites (SMCs) are vital in modern power electronics, including transformers, motors, and generators, where high permeability, low core loss, and high-frequency stability are critical. This chapter presents a comprehensive study on the structural and magnetic performance of FeSi-based and Fe/Fe₃O₄-based SMCs synthesised via the hot-press sintering technique, focusing on the influence of magnetic nanoparticle doping on their soft magnetic behaviour.

In Fe–6.5 wt% Si/Fe₂O₃ SMCs, the incorporation of high-resistivity Fe₂O₃ nanoparticles effectively filled interparticle gaps and enhanced densification. All samples exhibit excellent effective permeability frequency stability, ranging from 10 kHz to 100 kHz. Furthermore, as the Fe₂O₃ content increased from 0 to 2 wt%, the effective permeability (μₑ) significantly improved from 22.32 to 30.45 (a 36.4% increase). Adding Fe₂O₃ nanopowders from 0–5 wt% also enhanced electrical resistivity from 29.55 to 50.70 mΩ.cm. This, in turn, decreased the value of P_e at f = 100 kHz and B_m=10 mT from 6.61 to 4.15 kW/cm³ (a 37.21% reduction), compared to undoped samples. Furthermore, as Fe₂O₃ content increases from 0 to 5 wt%, the power loss P_cv of the Fe₂O₃-doped Fe-6.5Si SMCs decreases from 25.63 kW/m³ to 16.13 kW/m³, a 37.0% reduction.

Similarly, in Fe–6.5 wt% Si/(Fe: TiO₂) nanocomposites, with increased doping concentration of Fe nanopowder from 0 to 1.66 vol%, both the density and electrical resistivity significantly increased from 6.72 g/cm³ to 7.11 g/cm³ (up 5.78 %) and from 29. 36 mΩ.cm to 37.16 mΩ.cm, respectively. This can be attributed to reduced interparticle voids and carrier scattering. The value of saturation magnetisation (M_s) increased first from 180.89 emu/g to 189.5 emu/g as the Fe NP content increased from 0 to 1.66 vol%, reaching a maximum value of about 189.5 emu/g for a sample with 1.66 vol% of Fe nanopowder content. Furthermore, all the composites exhibit low coercivity (<15 Oe) and excellent effective permeability frequency stability in the 0-1 MHz range. The eddy current loss at f =100 kHz and B_m=10 mT is significantly decreased from 50.09 kW/m³ to 8.168 kW/m³ (decreased by 83.69 %) as the Fe nanoparticle content increased from 0 to 1.66 vol%. However, with further increase of Fe nanoparticles from 1.66 vol% to 3.32 vol%, the value of P_e increased from 8.168 kW/m³ to 71.92 kW/m³. Furthermore, the lowest value of P_h observed in our case for a sample containing 2.49 vol% of Fe is 0.677 kW/m³.

Furthermore, Fe/Fe₃O₄–Co composites, developed via surface oxidation and Co nanoparticle doping, demonstrated superior magnetic performance. The value of M_s is significantly increased from 207 emu/g to 216 emu/g as Fe (NP) content changed from 0-1 wt%. The μ_e measured in the frequency range of 0-2 MHz initially drops first from 97.30 to 61.72 as the content changes from 0 to 1 wt%. However, with the further increase of Co nano powder content, μ_eincreased, reaching a maximum value of 237.42 (144 % compared to the sample with 0 wt% of Co NP). Moreover, the composites also exhibit excellent DC bias performance in the DC bias field range of 0-110 Oe; the % permeability for all composites is higher than 65.16 %, at 100 kOe, with a peak value of about 72.01. The Co-doped samples also showed significantly reduced total core loss and enhanced electrical resistance, which contributed to improved particle bonding and magnetic coupling. The electrical resistivity increased from 15 mΩ.cm to 55.54 mΩ.cm as the Co (NP) content changed from 0 to 1 wt%. This in turn reduced P_e from 470 kW/m³ to 396 kW/m³ at f=100 kHz and B_m=10 mT.

The results highlight that optimal nanopowder doping combined with hot pressing promotes favourable microstructural evolution, leading to significant enhancement in the magnetic and electrical properties of Fe-based soft magnetic composites and optimises the balance between permeability and core loss. This design strategy enables the development of high-density, low-loss, and frequency-stable Fe-based SMCs, making them highly suitable for next-generation high-power, high-frequency, and energy-efficient electronic applications.

Development of a Composite Material Made of Sand and Molten Polyethylene Using a Scheffler Solar Concentrator

2026-01-06T11:21:30+00:00

The production of composite materials with a polyethylene matrix and sand reinforcement, through matrix melting, is energy-intensive. The melting temperature (approximately 200°C) of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) is achieved through solar concentration. The plastic melting unit in SAABA, Burkina Faso, uses 8 m² Scheffler concentrators, each with a common cubic receiver. The reflective facets are made of glass mirrors, self-adhesive mirror film, and aluminum mirrors. The average available power of 1.80 kW, obtained with an average solar irradiance of 623 W/m², is sufficient for melting.

In the production of composite materials, the matrix is composed solely of high-grade thermoplastics. The higher the matrix grade, the more fluid the material is during processing. The grade indicates the viscosity index of a material. The development of composite materials not only provides a solution for the recovery of plastic waste but also contributes to significantly reducing the ever-increasing volume of plastic waste, especially LDPE and HDPE, in developing countries.

Fractional Differential Equations Involving the Spherical Bessel Function j\(_0\): Analytical Solutions Via Laplace Transform

2026-01-06T11:26:47+00:00

This work addresses the resolution of fractional differential equations whose nonhomogeneous part is given by the spherical Bessel function \(J_0 (x)\). By using the fractional derivative in the sense of Caputo and the Laplace transform, a general analytical solution is obtained in terms of the generalised hypergeometric functions \( _2 F_3\), revealing a recurrent structure in the solutions. Furthermore, particular cases for integer and fractional orders are presented, highlighting the appearance of special functions such as the sine integral and Fresnel functions. The results confirm the close relationship between fractional calculus and Bessel functions, proposing new perspectives for applications in mathematical physics.

Effect of Prandtl Number on Magnetohydrodynamics Natural Convection in Open Square Cavity with heated Circular Cylinder for various Inclination Angle

2026-01-06T11:34:30+00:00

The presence of magnetic field on the convective heat transfer and the natural convection fluid flow are of paramount importance in scientific and engineering research. Several numerical and experimental methods have been developed to investigate flow characteristics inside the cavities with and without obstacle. Magnetohydrodynamics (MHD) natural convection and fluid flow in a two-dimensional open and inclined square cavity with a heated circular cylinder were considered in this study. The opposite wall to the opening side of the cavity was first kept at constant heat flux q, at the same time, the surrounding fluid interacting with the aperture was maintained at an ambient temperature \(T_\infty\). The top and bottom wall was kept at low and high temperatures, respectively. As a result, a natural convection is formed in the cavity due to the buoyancy force and temperature difference in the cavity. The governing equations for mass, momentum and energy conservation are expressed in a normalised primitive variables formulation. To the best knowledge of the authors there was no earlier work using these parameters and boundary conditions. The objectives of this study are to find out the characteristics of the streamlines and isotherms inside the cavity. The streamlines and isotherms are produced, heat transfer parameter Nu are obtained for various Prandtl numbers Pr = 0.72, 2, 5, 7 and inclination angles from 0°, 5°, 20°, 35°, 50° for fixed Hartmann number 60. The results are presented in graphical as well as tabular form. As a result, it is found that heat flux is an increasing function of Prandtl number Pr, while the Rayleigh number is 10000, and heat flux is maximum when the inclination angle is 5°. It is observed that fluid moves counterclockwise around the cylinder. Various recirculations are formed around the cylinder, and one small vortex is formed into the flow field for 50° inclination and Pr = 0.72 near the cylinder. Almost all the isotherm lines are concentrated at the right lower corner of the cavity. The present result agrees with the existing heat transfer and boundary layer theory.

Extended Study on the Design and Experimental Evaluation of an Ultrasonic Generator for the Inactivation of Gram-Positive and Gram-negative Bacteria

2026-04-04T10:49:17+00:00

Ultrasonic waves, which operate at frequencies above the threshold of human hearing, are capable of generating mechanical effects and acoustic cavitation phenomena in liquid media. These effects can induce significant damage to the cellular structures of microorganisms. Although several studies have reported the effectiveness of ultrasonic waves in bacterial inactivation, investigations into the influence of ultrasonic frequency variation on bacterial mortality, particularly in relation to differences in cell wall characteristics, remain limited. This study presents the design and experimental implementation of an ultrasonic generator utilising an IC 555 timer as the source of ultrasonic waves for bacterial inactivation. The developed system operated within a frequency range of 40–65 kHz and was experimentally tested using suspensions of Gram-positive and Gram-negative bacteria with identical initial concentrations. The Gram-positive bacterium used was Staphylococcus aureus, while the Gram-negative bacterium was Escherichia coli. The bacterial suspensions were exposed to ultrasonic waves at different frequencies and irradiation distances for a constant exposure time of 10 minutes. The effectiveness of the ultrasonic treatment was assessed by calculating the percentage of bacterial mortality and the average reduction in bacterial count (CFU/mL). The results indicate that bacterial mortality increases as the ultrasonic frequency rises for both types of bacteria. Under the same irradiation conditions, Gram-negative bacteria consistently showed higher mortality rates than Gram-positive bacteria. For Gram-positive bacteria at 5 cm, mortality increased from 34.3% to 43.5%, while average mortality rose from 42.6 to 65.0 CFU/mL. Gram-negative bacteria showed higher susceptibility, with mortality increasing from 50.3% to 63.6% and average mortality from 49.3 to 96.3 CFU/mL at the same distance. Furthermore, decreasing the irradiation distance improved the efficiency of bacterial inactivation for both bacterial groups. Future studies should focus on measuring ultrasonic power and monitoring temperature changes during exposure to provide a more comprehensive understanding of the inactivation mechanism.

Self-Assembly Processes of Polymer Cobalt Microwire Composites Synthesised by Chemical Deposition with Hydrazine

2026-04-10T12:19:36+00:00

Magnetic micro- and nanomaterials with controlled morphology and size are of significant importance for the fabrication of nanoscale devices and advanced functional materials. Among these, cobalt-based microstructures are particularly attractive due to their pronounced magnetic dipole moments and strong response to external magnetic fields, which induce alignment along the field direction. A comparative study of self-organisation processes in magnetic polymer microwire composites doped with cobalt microwires was conducted. The microwires were synthesised by chemical deposition using hydrazine in an external magnetic field and compared with commercial cobalt microwires. Self-organisation arises from the diffusion and polarisation of magnetic nanoparticles stimulated by a constant magnetic field. It was studied using nuclear magnetic resonance (NMR) and magnetometry. Magnetisation inversion is accompanied by an increase in magnetic susceptibility, enhancement of the NMR echo signal intensity, and acceleration of the transverse relaxation rate of two-pulse echoes. A weakening of these effects was observed in cobalt micropowder-based polymer composites. The echo signal amplification effect in the case of synthesised microwires is much greater than that of commercial nanowires, which may be due to the lower pinning force of domain walls and their greater mobility in them. The resulting polymer composites show promise for practical applications.

Effect of Ti Doping on the Structural and Optical Properties of ZnO:Ti Thin Films Prepared by Electrodeposition

2026-04-10T12:23:22+00:00

Thin films of metal oxides from Group II elements have demonstrated significant potential for applications across various fields of science and technology. Among them, zinc oxide (ZnO) stands out due to its excellent properties, making it highly suitable for diverse technological applications. Titanium (Ti), a quadrivalent cation, can be incorporated into ZnO as an interstitial dopant, acting as a scattering centre and modifying its properties. In this study, a cost-effective electrodeposition method was employed to synthesise titanium-doped zinc oxide (ZnO:Ti) thin films with varying Ti concentrations, in order to investigate their effects on optical and structural properties. The films were deposited on fluorine-doped tin oxide (FTO) conductive glass substrates using a three-electrode system, with FTO as the working electrode, a platinum rod as the counter electrode, and Ag/AgCl as the reference electrode. Zinc acetate and titanium powder digested with hydrogen fluoride served as sources of Zn, O, and Ti ions, respectively. The deposited thin films of ZnO:Ti were characterised for their optical and structural properties using Uv-Vis spectrometry and X-ray diffraction technique, respectively. The results of the characterizations shown that the optical properties of the films, such as transmittance, refractive index, extinction coefficient and bandgap energy, were influenced by Ti doping. The transmittance (%) was found to decrease for the film (10 ml ZnO:Ti) deposited at the highest Ti concentration in the VIS region, but increased to the highest value in the NIR region. The bandgap energy of the deposited thin films was found to decrease with the concentration of Ti doping. The obtained values were (2.73 – 3.20 eV) for undoped ZnO and (2.73 – 3.18 eV), (2.80 - 3.0 eV), 2.81 eV and 2.60 eV for 4ml, 6ml, 8ml and 10ml ZnO:Ti, respectively. The X-ray diffraction analysis indicated that the fabricated films have crystalline structures which are also influenced by Ti doping. The crystallite size of the films was found to increase while micro-strain decreased as the doping concentration increased, which enhanced the crystal structure for device applications. These findings suggest that ZnO:Ti thin films are promising candidates for applications in transparent thin-film transistors (TTFTs), liquid crystal displays (LCDs), light-emitting diodes (LEDs), transparent electrodes in solar cells, and other optoelectronic devices.

Thermal Analysis of Laminar Natural Convection Over an Immersed Curved Geometries

2026-04-16T10:23:32+00:00

The investigation on natural convective heat transfer of two-dimensional density-invariant and unsteady laminar fluid flow along curved surfaces is significant in order to enhance the effectiveness in various engineering systems. Curved surfaces are often encountered in various engineering systems, such as in heat exchangers, electronic cooling systems, and energy systems, where the curvature of the surfaces plays a significant role in affecting the heat transfer characteristics. This research investigation offers insights into the behavior of fluid flow and temperature distribution along curved surfaces in laminar flow conditions. In this study, the continuity, the momentum and thermal energy equations are non-dimensionalized, discretized and the solutions of the dimensionless governing equations approximated using finite-difference method. The model equations are applied to generate numerical simulations in order to explore the effect of curvature, surface roughness, and flow parameters such as temperature gradient and thermal conductivity on resistance to motion as well as the rate of material degradation due to frictional wear and tear. The aim is to investigate how curvature influences the flow separation, heat transfer enhancement or reduction and boundary layer developments. For easier and comprehensive interpretation of results, the findings are precisely presented graphically. It is noted that the flow regime as well as thermal exchange behavior are greatly influenced by the geometry of the surface. The curved surface introduces convolutions in both flow developments and heat transfer phenomena. The study conclusively established that the dissipation of heat within the boundary layer increases with increase in the length of the curvature. The findings of this research will significantly contribute to the optimization of thermal management strategies in systems with curved surfaces. This will assist Engineers in making appropriate designs and estimate improvements in equipment that require less resistance to the motion especially in engineering fields such as aerospace, hydrospace, automotive and industrial heat exchange processes.