Distribution Of Magnetic Particles Research Articles

Development of two-stage solidification technology for implementing micro structures with liquid magnetic polymer and solid magnetic anisotropic polymer

This study presents two-stage solidification technology for fabricating micromagnetic polymer composite (MPC, polymer with magnetic particles) structures. In this process, ultra-violet (UV)-light polymer curing is used for the first stage of MPC solidification. The surface of the MPC structure is solidified in this step. Moreover, thermal polymer curing is employed for the second stage of MPC solidification. The second stage of curing was mainly for the body solidification of the MPC. The distribution of magnetic particles in MPC can be specified by applying a magnetic field during the second solidification process. Based on the presented process technologies, microstructures with liquid MPC (NdFeB particles of different wt% in liquid polymer), isotropic solid MPC and anisotropic solid MPC have been demonstrated. Microdevices with liquid MPC embedded in solid micro balls and thin layers are also demonstrated. Various tests are performed to characterize the magnetic properties of the fabricated micro MPC structures. Measurements show that the fabricated solid MPC has reasonable coercivity, as compared with bulk materials. However, the remanence and the saturation magnetization still need to be improved.

Mechanical Properties of Magneto‐Sensitive Elastomers in a Homogeneous Magnetic Field: Theory and Experiment

SummaryThe aim of this study is to present a microscopic theory which describes the mechanical behaviour of magneto‐sensitive elastomers (MSEs) under a uniform external magnetic field. For this we use a model where magnetic particles are located on the sites of the regular rectangular lattice. We introduce a structure parameter to describe isotropic, chain‐like and plane‐like particle distributions. Our theory is based on the equation for free energy as a function of strain. The magneto‐induced deformation and the shear modulus are calculated as functions of the magnetization. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. Furthermore, we have compared our result for the shear modulus to the experimental data and found good agreement.

Squeeze flow behaviors of magnetorheological plastomers under constant volume

The squeeze flow behaviors (including compressive, tensile, and oscillatory squeeze behaviors) of magnetorheological plastomers (MRPs, a kind of solidlike magnetic gels) under different experimental conditions are systematically investigated. Both compression and tension processes can be classified as elastic deformation region, stress relaxation region, and plastic flow region. A squeeze flow equation is used to describe the compressive behaviors of MRP in plastic flow region from which the compressive yield stress can be obtained and compared. The results demonstrate that both compressive yield stress and tensile yield stress are sensitive to magnetic field, particle distribution, and particle concentration. The yield stress of MRP under squeeze flow is larger than that of MR fluids due to the existence of polymer matrix. Asymmetry of hysteresis loop is found under oscillatory squeeze mode. The oscillatory squeeze behaviors of MRP are also influenced by magnetic field and particle concentration, but the influence of particle distribution is not so obvious. The related results under three operational modes are compared and qualitatively analyzed, which are helpful for further understanding the MR mechanism in the solidlike magnetic gels.

Surface Finishing of Needles for High-performance Biopsy

Realizing simultaneous internal and external surface finishing of the needle should result in significant processing time reduction. This paper clarifies the magnetic field and magnetic particle distribution specifically required to achieve the simultaneous surface finishing of 18 gauge 316 stainless steel needles, and the efficacy of the resulting simultaneous surface finishing is described. Both the inner and external surfaces of needles, 0.4–0.5μm Sa, can be simultaneously finished to around 0.01μm Sa in 5min.

Research on Distribution of Magnetic Particles Based on Magnetic Field Control Grinding Wheel

In order to solve the problem of the randomly arrangement of the diamond abrasives, a novel orderly arrangement grinding wheel was developed, which used magnetic field to control the magnetic particles to drive diamond abrasives orderly arrangement. Effects of magnetic flux density on magnetic particle distribution was studied. And effects of magnetic particle proportion on magnetic particle distribution was studied. Grinding experiments were carried out on the tungsten carbide YG8 and surface roughness after grinding was also analyzed.

Exact kinetic theory for the instability of an electron beam in a hot magnetized plasma

Efficiency of collective beam-plasma interaction strongly depends on the growth rates of dominant instabilities excited in the system. Nevertheless, exact calculations of the full unstable spectrum in the framework of relativistic kinetic theory for arbitrary magnetic fields and particle distributions were unknown until now. In this paper, we give an example of such a calculation answering the question whether the finite thermal spreads of plasma electrons are able to suppress the fastest growing modes in the beam-plasma system. It is shown that nonrelativistic temperatures of Maxwellian plasmas can stabilize only the oblique instabilities of relativistic beam. On the contrary, non-Maxwellian tails typically found in laboratory beam-plasma experiments are able to substantially reduce the growth rate of the dominant longitudinal modes affecting the efficiency of turbulent plasma heating.

The Analysis on the Starting Friction Torque Increase of Magnetic Fluid Revolving Sealing

Abstract. Magnetic fluid revolving sealing is widely used in modern industry. In the process of application, it is founded that the starting friction torque is very large, particularly at lower temperature. This problem has become a key factor restricting the application of magnetic fluid rotation sealing. In this paper, the mechanism of starting torque increase is analyzed, based on the change of microstructure and its viscosity. After analysis , such conclusion is obtained , which can be described: to a certain sealing structure, the type of magnetic fluid, size distribution of magnetic particles as well as the working condition concluding temperature, magnetic field gradient and the revolving velocity of shaft is the main influence factor of starting friction torque . It is very useful to reduce the starting friction torque.

Study on Cancer Treatment using Magnetic Fluid for Medicine and Induction Heating Device

Two electromagnetic heating methods have been studied in the hyperthermic treatment of cancer: dielectric heating, and induction heating using magnetic substances. Dielectric heating devices heat even normal tissues around cancer. On the other hand, induction heating has an advantage that it can heat cancer selectively. However, so far effective induction heating has been difficult: enough heat was not generated in the body because of (1) the magnetic field generated by portable induction heating devices was not strong enough, and (2) non-existence of excellent magnetic substances, and (3) strongly invasive temperature measurement in the body. In this paper, we try to solve those problems.Firstly, we develop an effective high-power induction heating device. Secondly, we obtain an excellent superparamagnetic substance known as magnetic fluid (MF) with large magnetic particles. Thirdly, we propose a detection technique of magnetic particle distribution in the body, using X-ray CT, from which the internal body temperature can be estimated. We confirm the validity of the proposed method in vitro. Finally, we do an experiment to heat the excellent MF injected into VX-2 bearing rabbits. A significant anti-cancer effect was observed. Such results suggest that our study would be quite useful for the development of induction heating hyperthermia.

Frequency dependence of AC magnetic susceptibility over a wide range of frequencies for analyzing grain-size distribution of magnetic particles in environmental materials

Frequency dependence of AC magnetic susceptibility over a wide range of frequencies for analyzing grain-size distribution of magnetic particles in environmental materials

AN ANGLE-DEPENDENT SYNCHROTRON SELF-COMPTON MODEL FOR RELATIVISTIC JET SOURCES

We report on the development of a numerical code to calculate the angle-dependent synchrotron + synchrotron self-Compton radiation from relativistic jet sources with partially ordered magnetic fields and anisotropic particle distributions. Using a multi-zone radiation transfer approach, we can simulate magnetic-field configurations ranging from perfectly ordered (unidirectional) to randomly oriented (tangled). We demonstrate that synchrotron self-Compton model fits to the spectral energy distributions (SEDs) of extragalactic jet sources may be possible with a wide range of magnetic-field values, depending on their orientation with respect to the jet axis and the observer. This is illustrated with the example of a spectral fit to the SED of Mrk~421 from multi-wavelength observations in 2006, where acceptable fits are possible with magnetic-field values varying within a range of an order of magnitude for different degrees of B-field alignment and orientation.

Influence of Perpendicular Magnetic Field on Apparent Density and Microstructure of Magnetic Fluid

The formula for a magnetic fluid's apparent density is derived based on Bernoulli's equation of magnetic fluid, and the distribution of the magnetic fluid's apparent density is measured by the intelligent apparatus of measuring a magnetic fluid's apparent density in an applied perpendicular magnetic field. Magnetic particle chain-like alignments are observed by a transmission electron microscope (TEM). Without an applied magnetic field, the magnetic fluid's density is equal everywhere and the distribution of magnetic particles is homogeneous and unordered. When magnetic induction and magnetic induction gradient gather strength in an applied perpendicular magnetic field, the magnetic fluid's apparent density increases gradually, and more chain-like structures are formed and aligned with the direction of the magnetic field. The results of magnetic particle alignments are correspondent with the distribution of the magnetic fluid's apparent density. Both of them result from particle-particle interactions and particle-carrier liquid interactions, which are eventually controlled by the applied magnetic induction and magnetic induction gradient distribution.

Effects of particle distribution on mechanical properties of magneto-sensitive elastomers in a homogeneous magnetic field

We propose a theory which describes the mechanical behaviour of magneto-sensitive elastomers (MSEs) under a uniform external magnetic field. We focus on the MSEs with isotropic spatial distribution of magnetic particles. A mechanical model is used in which magnetic particles are arranged on the sites of three regular lattices: simple cubic, body-centered cubic and hexagonal close-packed lattices. By this we extend our previous approach [Ivaneyko D. et al., Macromolecular Theory and Simulations, 2011, 20, 411] which used only a simple cubic lattice for describing the spatial distribution of the particles. The magneto-induced deformation and the Young's modulus of MSEs are calculated as functions of the strength of the external magnetic field. We show that the magneto-mechanical behaviour of MSEs is very sensitive to the spatial distribution of the magnetic particles. MSEs can demonstrate either uniaxial expansion or contraction along the magnetic field and the Young's modulus can be an increasing or decreasing function of the strength of the magnetic field depending on the spatial distribution of the magnetic particles.

Magnetoresistive-based real-time cell phagocytosis monitoring

The uptake of large particles by cells (phagocytosis) is an important factor in cell biology and also plays a major role in biomedical applications. So far, most methods for determining the phagocytic properties rely on cell-culture incubation and end-point detection schemes. Here, we present a lab-on-a-chip system for real-time monitoring of magnetic particle uptake by human fibroblast (NHDF) cells. It is based on recording the time evolution of the average position and distribution of magnetic particles during phagocytosis by giant-magnetoresistive (GMR) type sensors. We employ particles with a mean diameter of 1.2μm and characterize their phagocytosis-relevant properties. Our experiments at physiological conditions reveal a cellular uptake rate of 45 particles per hour and show that phagocytosis reaches saturation after an average uptake time of 27.7h. Moreover, reference phagocytosis experiments at 4°C are carried out to mimic environmental or disease related inhibition of the phagocytic behavior, and our measurements clearly show that we are able to distinguish between cell-membrane adherent and phagocytosed magnetic particles. Besides the demonstrated real-time monitoring of phagocytosis mechanisms, additional nano-biointerface studies can be realized, including on-chip cell adhesion/spreading as well as cell migration, attachment and detachment dynamics. This versatility shows the potential of our approach for providing a multifunctional platform for on-chip cell analysis.

Fluorescence imaging and targeted distribution of bacterial magnetic particles in nude mice

Bacterial magnetic particles (BMPs) are of interest as potential carriers of bioactive macromolecules, drugs, or liposomes. In this study, a high-pressure homogenizer was used to disrupt Magnetospirillum gryphiswaldense strain MSR-1 cells, and BMPs were purified. BMPs were labeled with fluorescence reagent 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocianin perchlorate (DiI) and injected into the tail vein of BALB/c nude mice. Distribution of fluorescence signals of DiI-BMPs in vivo was examined using a whole-body fluorescence imaging system. The result showed that fluorescence signals were detected in liver, stomach, intestine, lungs, and spleen. However, transmission electron microscopy of ultrathin sections indicated that BMPs were mainly present in liver and lungs, but not in the other organs. BMPs could be useful as carriers for targeted drug therapy of diseases of the liver or lung.

Magnetic-Field-Induced Normal Force of Magnetorheological Elastomer under Compression Status

The magnetic-field-induced normal force of magnetorheological elastomer (MRE) under compression status is studied in this paper. The influence of monotonic loading of the magnetic field, particle distribution, temperature, and cyclic loading of the magnetic field are investigated. The experimental results show that the normal force increases with increasing magnetic field and precompression force. For aligned MRE, the change of the magnetic-field-induced normal force is larger than that of isotropic MRE due to the special chainlike structure. When the temperature increases, the maximum change of the magnetic-field-induced normal force first increases and then decreases, due to the interaction of iron particles and the decreasing of the saturation magnetization of the carbonyl iron particles. If the magnetic field is circularly applied on the MRE, the normal force during unloading is smaller than that during loading due to the stress relaxation.

STUDY OF FOUR YOUNG TeV PULSAR WIND NEBULAE WITH A SPECTRAL EVOLUTION MODEL

We study four young Pulsar Wind Nebulae (PWNe) detected in TeV gamma-rays, G21.5-0.9, G54.1+0.3, Kes 75, and G0.9+0.1, using the spectral evolution model developed and applied to the Crab Nebula in our previous work. We model the evolution of magnetic field and particle distribution function inside a uniformly expanding PWN considering a time-dependent injection from the pulsar and radiative and adiabatic losses. Considering uncertainties in the interstellar radiation field (ISRF) and their distance, we study two cases for each PWN. Because TeV PWNe have a large TeV gamma-rays to X-rays flux ratio, the magnetic energy of the PWNe accounts for only a small fraction of the total energy injected (typically a few x 10^{-3}). The gamma-ray emission is dominated by inverse Compton scattering off the infrared photons of the ISRF. A broken power-law distribution function for the injected particles reproduces the observed spectrum well, except for G0.9+0.1. For G0.9+0.1, we do not need a low energy counterpart because adiabatic losses alone are enough to reproduce the radio observations. High energy power-law indices at injection are similar (2.5 -- 2.6), while low energy power-law indices range from 1.0 to 1.6. The lower limit of the particle injection rate indicates that the pair multiplicity is larger than 10^4. The corresponding upper limit of the bulk Lorentz factor of the pulsar winds is close to the break energy of the broken power-law injection, except for Kes 75.

Models of frequency-dependent susceptibility of rocks and soils revisited and broadened

SUMMARY Mathematical models of the frequency-dependent susceptibility in rocks, soils and environmental materials have been adapted to measurements performed with multiple operating frequencies (465, 976, 3904, 4650, 15 616, 100 000 and 250 000 Hz) on the basis of log-normal volume distribution of magnetic particles. The XFD parameter depends, in addition to the amount of SP particles, also on the operating frequencies, whose values should be therefore also presented. The model curves of the XFD parameter versus arithmetical mean (μ) of the logarithms of grain volume are roughly bell-like shaped. The width and peak position of these curves is controlled by mean and standard deviation of the logarithmic volume distribution. Magnetic susceptibility contributions from paramagnetic minerals, and from ferrimagnetic particles not belonging to a unimodal SP/SD volume distribution, tend to decrease the XFD parameter. Therefore, low XFD values do not therefore necessarily indicate low amount of SP particles, but can also be indicative of the presence of the paramagnetic fraction. A new parameter XR is introduced based on susceptibility measurements at three operating frequencies; it is insensitive to dia- and paramagnetic fractions and helps us to differentiate between wide and narrow size distributions of ferromagnetic particles. A new XFB parameter is introduced that originates through normalizing the XFD parameter by the difference of natural logarithms of operating frequencies and related to the decade difference between the frequencies. It is convenient for comparison of the Bartington MS-2 Susceptibility Meter data with the MFK1-FA Kappabridge data.

Characterization of Flexibly Linked Shape Memory Polyurethane Composite with Magnetic Property

A flexibly cross-linked shape memory polyurethane (SMPU) was converted to a magnetic polymer by making a composite with a ferromagnetic particle (Fe3O4). The flexibly cross-linked SMPU has already displayed excellent mechanical and shape memory properties; the design of a magnetically responsive material allowed for a unique and novel SMPU. Among the three different composite preparation methods (melt-mixing, solvent blending, and in situ reaction mixing), the melt-mixing method was the best and attained even distribution of magnetic particles and high mechanical and shape memory properties. Differential scanning calorimetric and infrared results showed that the polymer structure was not affected by melt-mixing. In tensile testing, the maximum stress of the composite reached 39 MPa, and the strain at break also increased to 2495%. Shape recovery exhibited maximums as high as 99% and displayed similar values after repetitive shape recovery test cycles. Finally, the magnetic property of SMPU was characterized by a superconducting quantum interference device magnetometer and demonstrated in the magnetic attraction test. The potential applications of the magnetic and flexible SMPU are discussed.

Magneto‐sensitive Elastomers in a Homogeneous Magnetic Field: A Regular Rectangular Lattice Model

AbstractA theory of mechanical behaviour of the magneto‐sensitive elastomers is developed in the framework of a linear elasticity approach. Using a regular rectangular lattice model, different spatial distributions of magnetic particles within a polymer matrix are considered: isotropic, chain‐like and plane‐like. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus, G, for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. At the same time, with increasing magnetic field the Young's modulus, E, for tensile deformation along the magnetic field decreases for both chain‐like and isotropic distributions of magnetic particles and increases for the plane‐like distribution of magnetic particles. magnified image

Numerical Analysis of the Polishing Process of Inner Tube Wall Using Micron-Size Particles in Magnetic Fluids

Distribution and behaviour of micron-size magnetic particles and nonmagnetic particles in magnetic fluids in the polishing process of inner wall of small tube is investigated numerically by using the particle method based on the simplified Stokes dynamics. In this study, it is shown that chain-like clusters of both magnetic particles and those of nonmagnetic abrasive particles are formed between the two magnetic poles. The clusters are strongly held during the polishing process. The clusters of the nonmagnetic abrasive particles are surrounding the clusters of magnetic particles and they are combined with each other.