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Aggregate structures of magnetic particles at θtime = 45° for RB = 5 and ξ = 10: aλ = 10 and bλ = 16. A stronger magnetic interaction strength (λ = 16) leads to a weaker tendency of the reorientation of the magnetic moments toward the field direction and also a weaker tendency of the formation of chain-like clusters along the field direction. It is noted that the yellow dot implies the direction of the magnetic moment of each particle
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In the present study, we concentrate on the results of the unexpected characteristic that the stable particle cluster formation induces a decrease in the degree of heating effect in an alternating magnetic field, by means of Brownian dynamics simulations. If chain-like clusters are stably formed in the system, whether or not a large heating effect...
Citations
... With the continuous development of society, the future development trend of rail transit will have the characteristics of energy saving, environmental protection, safety and comfort, fast, and convenience. In addition to technological innovations in existing rail transportation vehicles, rail transit in the twenty-first century, it is also necessary to vigorously develop new rail transportation vehicles, and the maglev train was born [1]. At the same time, with the continuous development of superconducting materials, combining superconducting materials and magnetic levitation trains makes the maglev train faster, develops operational reliability, high safety, low loss and noise, and is comfortable and environmentally friendly [2]. ...
In order to reduce the levitation energy consumption and increase the levitation air gap, a simulation study of the electrochemistry superconducting magnetic levitation system based on the H equation is proposed. Through finite element simulation, the magnetic field distribution, current distribution, force, and other characteristics of the magnetic suspension system in the superconducting gravimeter are obtained; the relationship between the force of the superconducting ball in the magnetic field and the height of the suspension body and the current of the suspension coil is analyzed; and the penetration rate, the magnetic gradient, penetration depth, and maximum magnetic induction intensity of the superconducting spherical surface of the single-coil electrochemistry superconducting magnetic levitation system are obtained by simulation calculation. Simulation results show that, at 1 s, we start to use 0.2 s, 0.4 s, 0.6 s, and 0.8 s time, respectively, to pass current into the floating coil until it reaches 4.4 A. The magnetic gradient of the electrochemistry superconducting magnetic levitation system using a single coil is too large to meet the requirements of gravity measurement, the penetration depth is much smaller than the thickness of the superconducting sphere, and the maximum magnetic field on the surface of the superconducting sphere is much smaller than the critical magnetic field value of the superconducting material, and no loss will occur. The critical magnetic field value of the superconducting sphere is much smaller than that of the superconducting sphere. The critical magnetic field value of the material will not quench, which verifies that the H equation can simulate the superconducting magnetic levitation system well and has a high simulation accuracy and efficiency.
... In contrast, other studies attribute this effect to Brownian mobility restriction [17], [20]. Nevertheless, in [21] the decline in the effect of Brownian dynamics on NPs heating was studied; it was concluded that the magnetic moment of each constituent particle could sufficiently respond to the change in the magnetic field when the particle-field interaction is significantly more dominant, which leads to a larger area of the hysteresis loop, hence a better heat production performance. Therefore, a more considerable efficacy in producing heat could solve most of the above-described problems, either improving the nanoparticles' behavior, which is the line of research followed by most scientific community, or improving energy delivery from the exciting magnetic field, which is the main aim of this work. ...
This article shows the use of a high-frequency Full-Bridge inverter to design an alternating magnetic field generator for experimental studies on anti-cancer treatment with magnetic nanoparticles. In magnetic hyperthermia, nanoparticles are used to raise the pathological cancerous cell’s temperature high enough to induce their death by apoptosis, but not as high as to destroy them by thermal ablation of the whole tissue volume, consequently leaving healthy cells alive. Conventionally, sinusoidal alternative magnetic fields are used to heat the nanoparticles, which can be more easily produced than other waveforms. However, there are no theoretical nor experimental reasons to chose the sinusoidal waveform. This work aims to develop an improved power system to study the effect of different waveforms of the magnetic field on the heat production when exciting magnetic nanoparticles, aiming at demonstrating that other waveforms can be much more efficient in producing heat than conventional sinusoids. To prove our hypothesis, we designed an inverter able to generate four waveforms at high frequencies and a fifth sinusoidal signal derived by a resonant capacitor, in the range of 100 kHz to 1 MHz and up to 10 mT of peak intensity. Also, we used SiC devices to process high currents at high switching frequencies efficiently. Additionally, to enhance the system efficiency, Zero-Voltage Switching is used to reduce switching losses and minimize electromagnetic noise and interference. The experimental results obtained with non-sinusoidal waveforms have shown a remarkable performance improvement compared to classical sine wave excitation. The nanoparticles’ heat dissipation depends on the applied alternating magnetic field’s signal slope, signal frequency, and peak field intensity. We conclude that further work deserves to be done to find the optimum work conditions in function of the used particle and biological environment, to test if this type of magnetic field generator could overcome the conventional system’s performance.
... There is a growing consensus that Brown relaxation provides a negligible contribution to heating by J o u r n a l P r e -p r o o f nanoparticles embedded in cells or tissues [208,255,256]. To achieve significant heating from Brownian relaxation requires very large coupling of the magnetization to the lattice to generate adequate torque [257,258]. Serantes et al. demonstrated that heating by Brown rotation comparable to Néel reversal is achievable, but only with favorable conditions that require significantly lower frequencies (<<100 kHz) than currently used [263]. ...
... Recent efforts to describe magnetic heating have yielded improvements that incorporate nanoparticle polydispersity (i.e. size), dipole-dipole interactions, and other complexities encountered in biological systems [169,[188][189][190][199][200][201][202][203][206][207][208]233,234,[252][253][254][255][256][257][258][259][260][261][262][263]. An aspect of more recent attempts is a recognition that the (re-)orientation of the nanoparticles by Brownian motion alters the local energy relationship among interacting nanoparticles. ...
Significant research and preclinical investment in cancer nanomedicine has produced several products, which have improved cancer care. Nevertheless, there exists a perception that cancer nanomedicine ‘has not lived up to its promise’ because the number of approved products and their clinical performance are modest. Many of these analyses do not consider the long clinical history and many clinical products developed from iron oxide nanoparticles. Iron oxide nanoparticles have enjoyed clinical use for about nine decades demonstrating safety, and considerable clinical utility and versatility. FDA-approved applications of iron oxide nanoparticles include cancer diagnosis, cancer hyperthermia therapy, and iron deficiency anemia. For cancer nanomedicine, this wealth of clinical experience is invaluable to provide key lessons and highlight pitfalls in the pursuit of nanotechnology-based cancer therapeutics. We review the clinical experience with systemic liposomal drug delivery and parenteral therapy of iron deficiency anemia (IDA) with iron oxide nanoparticles. We note that the clinical success of injectable iron exploits the inherent interaction between nanoparticles and the (innate) immune system, which designers of liposomal drug delivery seek to avoid. Magnetic fluid hyperthermia, a cancer therapy that harnesses magnetic hysteresis heating is approved for treating humans only with iron oxide nanoparticles. Despite its successful demonstration to enhance overall survival in clinical trials, this nanotechnology-based thermal medicine struggles to establish a clinical presence. We review the physical and biological attributes of this approach, and suggest reasons for barriers to its acceptance. Finally, despite the extensive clinical experience with iron oxide nanoparticles new and exciting research points to surprising immune-modulating potential. Recent data demonstrate the interactions between immune cells and iron oxide nanoparticles can induce anti-tumor immune responses. These present new and exciting opportunities to explore additional applications with this venerable technology. Clinical applications of iron oxide nanoparticles present poignant case studies of the opportunities, complexities, and challenges in cancer nanomedicine. They also illustrate the need for revised paradigms and multidisciplinary approaches to develop and translate nanomedicines into clinical cancer care.
Single-domain magnetic particles have unique and excellent magnetic properties and are widely used in biomedical applications, but there are many mechanisms for their response to external magnetic fields. Different models apply under various conditions, which challenges researchers who want to choose a suitable model for their studies. Based on this situation, this paper comprehensively summarizes the mechanisms and models of magnetic loss of single-domain magnetic particles in an external magnetic field. Notably, this paper comprehensively summarizes the non-equilibrium kinetic model of the response of single-domain superparamagnetic particles to external magnetic fields. In this paper, the mechanism for hysteresis loss of single-domain ferromagnetic particles and a model for its calculation are presented, the Stoner–Wohlfarth (SW) model based on equilibrium state and the statistical mechanics model based on non-equilibrium state are introduced; then, the mechanism for the relaxation loss of single-domain superparamagnetic particles and a model for its calculation are introduced, and the linear response model based on equilibrium state and the statistical mechanics model based on non-equilibrium state are introduced in a general way. Lastly, the development of single-domain superparamagnetic particles is briefly prospected. This review provides a convenient reference for researchers to explore the magnetic properties of single-domain magnetic particles and promotes their application and development in the field of biomedicine.
We have investigated the behavior of magnetic rod-like particles and their relationship with the heat generation effect for both alternating and rotating magnetic fields, by means of Brownian dynamics simulations. As a common feature for both type of magnetic field variations, in the case of significantly strong particle-particle interaction strengths, densely-packed clusters are formed, which do not contribute to the heat generation. For the case of the alternating magnetic field, in the intermediate frequency range, linear thick chain-like clusters are formed and the constituent rod-like particles themselves tend to rotate to follow the change in the field. In contrast, for the case of the rotating field, linear clusters rotate as a whole body to respond to the magnetic field rotation. In both type of magnetic field variations, the magnetic interactions between the constituent particles in a cluster tend to function to suppress the relaxational motion of the rod-like particles, which, as a result, leads to increase in the heat generation effect in certain situations. In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect, whereas in contrast, in the lower frequency region the alternating magnetic field yields the larger heating effect.
Highlights
• The behavior of magnetic rod-like magnetic particles has been elucidated in the case of an alternating and a rotating magnetic field.
• The magnetic interactions between the constituent particles in a cluster tend to suppress the relaxation motion of the rod-like particles.
• The frequency and strength of a time-dependent magnetic field have complex influences on the heating effect.
• In a relatively large frequency region, the rotating applied magnetic field gives rise to a larger heat generation effect.
• In a relatively lower frequency region, the alternating magnetic field is superior to the rotating field.
We have addressed the aggregation phenomena of a cubic haematite particle suspension in an alternating magnetic field in order to investigate the regime change in the aggregate structure. Brownian dynamics simulations have been performed for a quasi-two-dimensional system with an alternating magnetic field applied in the plane of the system. In a weak alternating field, the cubic particles aggregate to form closely-packed structures tending to an aligned face-to-face configuration with increasing magnetic particle-particle interaction strength. In a closely-packed cluster, the orientation of the magnetic moment of a constituent particle tends to be more strongly influenced by the magnetic interaction between neighbouring particles and less influenced by the direction of the alternating magnetic field. As the strength of the applied field is increased, the particle moments become more restricted to the direction of the alternating field and the closely-packed structures transform into elongated aggregates with an offset face-to-face configuration. As the direction of the alternating magnetic field switches from the positive to the negative x-direction, the elongated aggregates tend to collapse temporarily and when the orientation of the moments is again strongly restricted to the switched field direction, elongated aggregate structures with offset face-to-face contact are re-formed in the system.
Highlights of the present paper
• We have investigated a regime change in the internal structure of cubic particle aggregates in an alternating magnetic field.
• As the magnetic field strength is increased, closely-packed aggregates with an aligned face-to-face configuration transform into elongated aggregates with an offset face-to-face configuration.
• We have clarified that the elongated aggregates collapse temporarily and then re-form when the direction of the alternating magnetic field switches.
• We have suggested that the frequency of the magnetic field may be used as a means for controlling the local internal structure of particle aggregates.
In the present study, we have addressed a dispersion composed of magnetic cubic particles in an alternating magnetic field to investigate the time change in the local internal structure of particle aggregates by means of quasi-two-dimensional Brownian dynamics simulations. An alternating magnetic field is applied along the x-direction. In the situation of a relatively weak magnetic field, if the magnetic particle-particle interaction strength is small, single particles remain in the system. The magnetic moments of single particles follow the change in the switched direction of the alternating magnetic field. As the magnetic particle-particle interaction strength is increased, particles aggregate to form closely-packed structures with a perfect face-to-face configuration. Since the orientation of the magnetic moments of constituent particles is strongly restricted due to the influence of the magnetic particle-particle interaction between neighboring particles, they do not follow the change in the alternating magnetic field direction. As the magnetic particle-field interaction strength is increased, closely-packed structures tend to collapse, and loosely-packed structures are formed in the system. As the magnetic particle-field interaction strength is further increased, the magnetic moments of constituent particles are restricted to the direction of the alternating magnetic field. Therefore, the aggregates with an offset face-to-face configuration are formed along the magnetic field direction. If the alternating magnetic field switches from the positive x-direction to the negative x-direction, the aggregates with an offset face-to-face configuration collapse temporarily because the magnetic moments reorient in the switched direction of the alternating magnetic field. After that, the orientation of the magnetic moments is strongly restricted to the switched magnetic field direction, and aggregates with an offset face-to-face configuration are re-formed in the system.
In the present study, by means of quasi-two-dimensional Brownian dynamics simulations, we have addressed the physical phenomena of a suspension composed of cubic haematite particles in a rotating magnetic field in order to elucidate the relationship between aggregate structures and their response to a rotating magnetic field. In the case of a relatively weak magnetic particle-particle interaction, single particles remain without aggregating to form specific clusters, and the magnetic moment of single particles tends to follow a change in the direction of the rotating magnetic field. In the case of a strong magnetic particle-particle interaction, closely-packed clusters with a face-to-face configuration tend to form in the system, although the individual magnetic moments of the constituent particles do not follow the change in the magnetic field direction. As the magnetic field strength is increased, closely-packed structures are transformed into aggregate structures with an offset face-to-face configuration. In this situation, the magnetic moments of constituent particles are strongly restricted to the magnetic field direction, and the aggregates themselves may significantly rotate to follow the change in the orientation of the rotating magnetic field.
The present study addresses the physical phenomena of a suspension composed of magnetic spherical particles in a rotating magnetic field in order to elucidate the influence of particle aggregation phenomena on the heat production from Brownian relaxation by means of Brownian dynamics simulations. In the case of a weak magnetic particle-particle interaction, particles do not aggregate to form specific cluster configurations. In this situation, the magnetic moment of each particle quickly inclines toward the field direction, and single particles do not give rise to a sufficiently large heating effect. With an increasing magnetic interaction between particles, chain-like clusters tend to form in the system and function to offer a larger resistance to the orientation of the magnetic moments, which leads to an increase in the heating effect. In the case of a significantly strong magnetic particle-particle interaction, the particles tend to aggregate to form stable ring-like clusters where the magnetic moments of the constituent particles are not able to be so responsive to the rotating magnetic field and this leads to a decrease in the heating effect.
Highlights of the present paper
• The characteristics of particle aggregation have been clarified.
• The relationship between the strength of the magnetic particle-particle interaction and the frequency of the rotating magnetic field on the aggregation phenomena has been clarified.
• The response of the particle aggregates to an applied rotating magnetic field has been clarified.
• The relationship between the performance of the degree of heat production and the internal structure of magnetic particle configurations has been clarified.
We have proposed a new repulsive layer model for describing the interaction between steric layers of coated cubic particles. This approach is an effective technique applicable to particle-based simulations such as a Brownian dynamics simulation of a suspension composed of cubic particles. 3D Brownian dynamics simulations employing this repulsive interaction model have been performed in order to investigate the equilibrium aggregate structures of a suspension composed of cubic haematite particles. It has been verified that Brownian dynamics employing the present steric interaction model are in good agreement with Monte Carlo results with respect to particle aggregate structures and particle orientational characteristics. From the viewpoint of developing a surface modification technology, we have also investigated a regime change in the aggregate structure of cubic particle in a quasi-2D system by means of Brownian dynamics simulations. If the magnetic particle–particle interaction strength is relatively strong, in zero applied magnetic field the particles aggregate in an offset face-to-face configuration. As the magnetic field strength is increased, the offset face-to-face structure is transformed into a more direct face-to-face contact configuration that extends throughout the whole simulation region.
