Micron-sized Magnetic Particles Research Articles

A Singly Curved Conformal Phased Array with Integrated Particles-Based CRLH Phase Shifters

In this paper, a four unit cell micron-sized magnetic particles embedded composite right/left-handed (CRLH) transmission line metamaterial phase shifter is proposed. The variable phases are achieved by activating the micron-sized magnetic particles along the length of stub transmission lines of the CRLH transmission line structure. This causes to effectively change the inductance of stub transmission lines, which changes the phase of the RF signal. These structures can be activated in a symmetric or asymmetrical manner to obtain wide range of phase shifts. A prototype of cascaded four unit cell CRLH transmission line phase shifter with embedded silver-coated ferrites (magnetic particles) is designed, fabricated and tested for phase shifters applications. The measured phase response of the proposed phase shifter is in close agreement with the simulated phase response. Next, for the performance analysis of proposed phase shifter, a 1 × 4 conformal curved-shaped phased array operating at 5.8 GHz is fed with the four unit cell cascaded phase shifter in CST full-wave simulator. The conformal phased array with proposed integrated phase shifters was simulated for broadside pattern correction and main beam scanning at 20 degree on curved-shaped surface with different bend angles. The radiation pattern results obtained with the proposed integrated phase shifters are in close agreement with those obtained with direct excitation of the array.

Simultaneous effect of magnetic nanoparticles additive and noble metal coating on carbonyl iron-based magnetorheological fluid

Magnetorheological (MR) fluid is an intelligent fluid that is strongly influenced by an external magnetic field. These fluids are prepared by introducing micron-sized magnetic particles such as carbonyl iron into nonaqueous fluids. The main challenge in those systems containing these fluids such as shock absorbents and abrasive fluids is the instability and sedimentation of magnetic particles in the base fluid. The main aim of the study is to provide stable carbonyl iron (CI)-based magnetorheological fluids with desired efficiency and as much yield stress. In this context, we synthesized Ni-Zn ferrite nanoparticles as additives via high-energy ball milling. This is followed by coating the pristine CI particles with silver via a green-assisted coprecipitation method, using honey as a reducing agent to convert AgNO3 to Ag nanoparticles. The as-produced samples were characterized by the means of XRD, FTIR, FESEM, and TEM. Four types of prepared MR fluids were a CI based, ferrite nanoparticles additive-CI-based MR, Ag-coated CI-based MR, and a combination of the second and third states in the presence of poly alpha olefin oil as the carrier liquid and oleic acid as surfactant agent. The results revealed that the density of the Ag-coated CI was reduced to almost half the density of pristine CI particles. Furthermore, the results of the rheology test on CI-based and CI/Ni Zn ferrite MRs showed an increase in yield stress from 38,000 Pa to 46,000 Pa due to the presence of nickel-zinc ferrite particles. However, magnetorheological fluids based on carbonyl iron particles coated with silver nanoparticles showed a decrease in yield stress (29,700 Pa) because the magnetic property of CI particles has decreased by coating. Magnetorheological fluid based on carbonyl iron particles coated with silver nanoparticles and additive of nickel-zinc ferrite nanoparticles had yield stress similar to magnetorheological fluid based on iron carbonyl particles (38,000 Pa) but with more stability from 55% to 70%.

A novel magnetically oscillatory fluidized bed using micron-sized magnetic particles for continuous capture of emulsified oil droplets

Treatment of emulsions is frequently required for water environment protection and oil recovery. Breaking the emulsion structure and separating the emulsified oil are key stages. However, conventional emulsion separation methods suffer from high reagent and energy costs, and low batch capacity. In this study, a novel magnetically oscillatory fluidized bed (MOFB) was developed to realize cost-effective and continuously operated emulsion separation through the introduction of reusable micron-sized magnetic particles (MMPs) and a low-energy electromagnetic field. The emulsified oil droplets were continuously captured by MMPs in oscillatory motion driven by a periodic electromagnetic field. The constructed MOFB showed excellent separation efficiency at a high influent flow rate of 20 mL/min. And in the long-term operation of the MOFB, a higher treatment capacity for emulsified oil was obtained by the MMPs (11.1 g liquid paraffin oil /g MMPs) than by the commonly used nano-sized magnetic particles. The entire oil capture process by moved MMPs was confirmed via in situ observation using a high-speed camera. To further reveal the oil capture mechanisms, meshing and kinematics analyses were performed to construct an indicator termed dynamic bed voidage (εD). It was found that the value of εD could be regulated by the magnetic field strength and frequency, and a low value of εD (<30.3%) was crucial to maintain a highly efficient capture of emulsified oil droplets. This study provides insights into the design of a novel magnetic separator for continuous emulsion separation and promotes technological evolution toward economically competitive separation methods.

Intracellular Delivery of Micron-Sized Magnetic Particles through a Virus Infection Pathway.

Micron-sized magnetic particles (M-MPs) have low toxicity, strong magnetic signals, and long-term retention capability, which are significant advantages for their application in biomedical imaging. Unfortunately, M-MPs are only internalized by few cell types, such as macrophages and phagocytes, and because of this lack of active intracellular delivery, their applications are restricted. The emergence of self-assembled virus-like particles (VLPs) offers a viable approach to drive M-MPs into cells, although the specific mechanism has not been revealed. In this study, we investigated in detail the intracellular pathway of M-MPs mediated by VLPs using a fluorescence co-localization method. The results indicated that the intracellular movement of M-MPs was consistent with the virus infection pathway, specifically caveolae-dependent endocytosis, transportation through microtubules, and accumulation in the endoplasmic reticulum. This study provides experimental support for the active transport of M-MPs into other cell types, thereby further extending their applications.

Investigation of a non-Newtonian MR fluid flow between parallel plates by developed CFD code for different numerical schemes

Magnetorheological (MR) fluids are composed of a solution of micron-sized magnetizable particles dispersed in a carrier fluid, typically oil. Thus, the MR fluids are classified as smart fluids by showing variable apparent viscosity under a precisely controllable external magnetic field. This feature of the MR fluids gave the possibility to use them in the MR dampers to control variational damping forces. In this work, an MR damper on relatively small scales is considered to investigate the MR fluid flow behavior through the piston annuli where the magnetic field exists. This work mainly focuses on the numerical solutions of the flow variables in a magnetically excited non-Newtonian flow medium by comparing analytical results for various Reynolds numbers. The Herschel–Bulkley (HB) viscous model is used for the non-Newtonian characteristic of the MR fluid. For the numerical modeling of the HB viscous model, the regularized approaches are used to avoid numerical errors. However, contrary to the actual HB model, the regularized models can be incapable to give true apparent viscous values at very low shear rates depending on the regularization parameters. Thus, the present study aims to give a better understanding of choosing the optimal regularization parameters for the studied flow conditions. The second part of the study discusses the numerical discretization schemes aiming to present their performances while changing the Reynolds number between 0.002 and 1. In this manner, a Computational Fluid Mechanics (CFD) solver has been developed for two-dimensional geometries which are meshed with structured grids by using six different discretization schemes including two of the most known total variation diminishing (TVD) schemes. For simplicity of the problem, a two-dimensional parallel plates geometry and a constant magnitude of the magnetic field intensity along the piston annuli are assumed. The study also summarizes the CFD technique by evaluating the physical meaning of the flow field variables.

A continuum magneto-mechanical model for magnetorheological elastomers

Magnetorheological elastomers (MREs) consist of micron-sized magnetizable particles embedded in a rubber matrix. Properties of these magneto-sensitive materials are changed reversibly upon application of external magnetic fields. They exhibit highly non-linear magneto-mechanical response which allows developing new devices and applications. However, the coupled magneto-mechanical behavior makes mathematical modeling of MREs quite complicated. So development of a reliable constitutive framework is essential for further understanding of this coupled behavior as well as simulation of the systems that utilize MREs. In this paper, a finite strain continuum model is developed for MREs where the effect of magnetization on material stiffness is directly introduced in the material shear modulus. It is shown that this approach simplifies the constitutive models and also perceives the magnetic saturation of MREs. Moreover, the coupled effects of magnetization, deformation and particle-chains orientation on the mechanical response are also taken into account in the introduced parameter. This reduces the number of material parameters, the required experimental tests for parameters identification and also simplifies the mathematical formulation of the developed constitutive equations which is beneficial for numerical formulations. A systematic two-step method is then introduced for material parameters identification which assures uniqueness of the parameters set. The predictive capabilities of the proposed model are examined via available mechanical and magneto-mechanical experimental data on both isotropic and anisotropic MRE samples at different configurations of magnetic field and loading with respect to the preferred direction of the samples. It is shown that the model can well predict the magneto-mechanical response of MREs at different deformation modes and magnetic fields.

Bidisperse magneto-rheological fluids consisting of functional SPIONs added to commercial MRF

Magnetorheological fluids (MRFs) are smart materials with a reversible and fast transition from a liquid to a semi-solid state when an external magnetic field is applied (magnetorheological effect). The sedimentation of micron-sized magnetic particles in commercial MRFs is a crucial problem limiting the long-term use in industrial applications. Here, we develop a new MRF based on commercial 140-CG LORD® with the addition of surface functional superparamagnetic iron oxide nanoparticles (SPIONs). These new bidisperse MRFs are comprised of either poly(acrylic acid) (PAA) coated SPIONs or lauric acid (LA) coated SPIONs and micron-sized fatty acid-coated magnetic particles of the commercial MRF. SPIONs have specific coatings to interact with the fatty acid coating of the micron-sized Fe-particles. Sedimentation behaviour and the magnetorheological properties of these bidisperse MRFs with 6–12wt% SPION were examined. Bidisperse MRFs improved the stability and redispersibility of MRFs. Bidisperse MRFs with 12wt% SPION-PAA showed similar or better magnetorheological behaviour than the commercial MRF despite lower content of the micron size Fe-particles. Hence, a combination of magnetizable nano and micron-sized particles and utilization of correct surface chemistry that allows their favourable interaction improves the stability of MRFs without sacrificing magnetic response but even by improving it.

Investigation of shear-induced physical and chemical transformations of Fe microparticles in hydrocarbon- and fluorocarbon-based magnetorheological fluids

Aging of magnetorheological fluids (MRFs) during the operation of mechanical devices is accompanied by degradation of both the particles and the fluid components. This study has shown that collisions among micron-size magnetic iron particles under shear can result in nanoscale changes to surface topography. Moreover, it has shown that shear-induced collisions can lead to redistributions among different oxidation state species in surface and near sub-surface regions of the particles. The redistributions among oxidation states and chemical species is the result of interfacial reactions that can involve adventitious oxygen, catalysis and other energetic processes that can act on either or both, the host fluid medium and additives introduced to stabilize the MRF. The interfacial chemistry is complex, inviting studies that couple macroscale processes (shear events in a clutch mechanism) with nanoscale inquiry into the effects of such processes. This study examined the chemical and morphological states of MRF particles subjected to continual shear loading in a rotary clutch device over well-defined periods of time for both hydrocarbon and fluorocarbon-based host fluids. New insights into chemical transformations, on and beneath, particle surfaces provide reference for better durability assessment, MRF formulation, and device design in the future. X-ray photoelectron spectroscopy iron, fluorine, oxygen and carbon depth profiles provided insight into the evolving oxidation states of the MRF particles. Over time, fluorine and oxygen insinuate themselves into the particle where they give rise to a host of different oxidized iron species. Simultaneously, the iron content of the surface diminishes. Scanning electron microscopy revealed how the particles transform from nascent nearly spherical shape prior to shear to irregular morphology in the clutch mechanisms. Transmission electron microscopy revealed carbon-rich residues with embedded nanoparticle fragments in aged MRF particle samples, suggesting that MRF particle surfaces may have served as reaction interfaces.

Temperature effect on viscoelastic properties of anisotropic magnetorheological elastomers under compression

Magnetorheological elastomers (MREs) are a class of smart materials composed of an elastomer and micron-sized magnetic particles. Besides the loading amplitude and frequency, the elastic and rheological properties of MREs are also dependent on the external magnetic field and temperature. Previous studies focused on the influences of external magnetic field, strain amplitude and frequency on the dynamic properties, however, the temperature effect was rarely reported. In this paper, dynamic mechanical analysis (DMA) tests were carried out to investigate the viscoelastic properties of the anisotropic MRE samples under various temperatures and magnetic fields. A transition behavior of the anisotropic MRE samples was observed at about 50 °C for the dynamic modulus. The storage modulus initially decreased with the increasing of the temperature up to 50 °C and then increased or maintained a stable value when the temperature increased up to 60 °C. The time-temperature superposition (TTS) principle was extended to construct the dynamic modulus master curve of the MREs by using the horizontal shift factor and the vertical shift factor. The good correlations between the measured and predicted data were confirmed by performing statistical analysis for the goodness of fit. The constructed master curve and shift factors can be used to predict the viscoelastic properties of the MREs beyond the DMA experiment’s range of temperatures and frequencies.

Modeling of particle-capture mechanism of axial magnetic filter in bounded flow field with variable viscosity

The capture mechanism of micron-sized magnetic particles from a surfactant-containing suspension is examined in an axial magnetic filter with a bounded flow field by using the particle trajectory model. The effects of change in the suspension viscosity to the suspension flow velocity are modeled. Analytical and numerical solutions for the particle trajectory model are obtained for a laminar flow regime. It is evaluated that the magnetic particles in the suspension, subjected to a viscosity change, are captured in a gradient magnetic field formed by a magnetized external ferromagnetic wire and the capturing of particles gets harder due to condensation of surfactant layers.

Effect of carbon black with large particle size on dynamic mechanical analysis of magnetorheological elastomers (MREs)

Magnetorheological elastomers (MREs) are composite materials consist of micron-sized magnetizable particles and a polymer matrix. In this work, we chose the most suitable carbon black (CB) by comparing MR effect of MREs with three kinds of CB (N330, N660, N990). To improve magneto-rheological (MR) effect, MREs with different contents of CB were prepared. MRE samples were fabricated under a constant magnetic field. The rheological properties including MR effect, damping ratio were measured with rotational rheometer. The effect of loading parameters such as shear strain, frequency and magnetic field on the shear modulus and damping ratio of MREs were observed. The experimental results show that N990 is better at improving MR effect than N330 and N660. N990 improve the damping performance of MREs. The magneto-rheological properties increase with the increase of N990 content. This type of MREs with varied stiffness and damping have potential as semi-active control devices for smart damping materials.

On the theory of hysteretic magnetostriction of soft ferrogels

The paper deals with theoretical study of hysteretic magnetostriction of soft ferrogels – composite materials, consisting of the micron-sized magnetizable particles embedded into gel matrices. It is supposed that initially, before application of an external magnetic field, the particles are homogeneously and isotropically distributed in an elastic matrix. The theoretical explanation of the hysteresis phenomena is based on the conception that, under the field action, the particles rearrange into the linear chain-like aggregates. The typical length of the chains is determined by the competition between the force of magnetic attraction of the particles and the force of elastic deformation of the matrix.

Desorption of harmful hydrocarbon compounds in soil using micron-sized magnetic particles and high-frequency magnetic fields

This research looks at the use of high frequency (HF) magnetic fields to desorb/reduce harmful chemical compounds within gasoline and diesel that commonly leak out of underground storage tanks. Using a multi-strand coil design, measured magnetic fields of over 3 kilo-amperes per meter are generated at an optimal frequency of 117 kHz without skin-depth losses, and without the use of expensive super-conductors or liquid-cooled mechanisms. This high frequency magnetic field is successfully used in non-contact-based magnetic heating and desorption of Gasoline and Diesel mixed with sand, water and easily-dispersible, benign micrometer-sized iron filings, used as a magnetic absorber. Gas chromatography (GC) tests done on magnetically-heated Gasoline-soil and Diesel-soil mixtures show desorption/reduction of gasoline and diesel by 44% and 51% respectively, but desorption/reduction of harmful BTEX compounds and other chemical irritants within Gasoline and Diesel by 28–66% after only 80 minutes of magnetic heating. Review of remediation/desorption methods show magnetic fields fare favorably in comparison to other methods that require longer treatment period or the use of secondary pollutants at reducing hydrocarbon and BTEX compounds in them.

Experimental Investigation of Static Properties of Magnetorheological Elastomer

Magnetorheological elastomer (MRE) is a type of smart material made of natural or synthetic rubber filled with micron-sized magnetic particles. Its shear modulus and elasticity can be controlled by applying an external magnetic field. In this study, a mounting system model is used to obtain displacement transmissibility factor. In the experimental analysis, three different MRE samples are manufactured by varying the percentage of magnetic particles. The experimental investigations are carried out to characterize the quasi-static properties of these MREs by attaching them with universal testing machine in compression and tensile mode. In both modes, different currents and velocities are applied to the samples. From the experimental results, a proportional relationship has been observed among the resisting force from MREs and applied excitation current, displacement and velocity. In most cases, the force has increased with the increasing percentage of magnetic particles in the sample. However, the highest force is obtained from the sample with 30% magnetic particles, at 2 A current and velocity of 4 mm/min. The results observed in this research would be useful for vibration control in applications such as engine mounting system.

Magnetic microscopic imaging with an optically pumped magnetometer and flux guides

By combining an optically pumped magnetometer (OPM) with flux guides (FGs) and by installing a sample platform on automated translation stages, we have implemented an ultra-sensitive FG-OPM scanning magnetic imaging system that is capable of detecting magnetic fields of ∼20 pT with spatial resolution better than 300 μm (expected to reach ∼10 pT sensitivity and ∼100 μm spatial resolution with optimized FGs). As a demonstration of one possible application of the FG-OPM device, we conducted magnetic imaging of micron-size magnetic particles. Magnetic imaging of such particles, including nano-particles and clusters, is very important for many fields, especially for medical cancer diagnostics and biophysics applications. For rapid, precise magnetic imaging, we constructed an automatic scanning system, which holds and moves a target sample containing magnetic particles at a given stand-off distance from the FG tips. We show that the device was able to produce clear microscopic magnetic images of 10 μm-size magnetic particles. In addition, we also numerically investigated how the magnetic flux from a target sample at a given stand-off distance is transmitted to the OPM vapor cell.

Hysteresis of the magnetic properties of soft magnetic gels.

We present results of an experimental and theoretical study of the magnetic properties of soft magnetic gels consisting of micron-sized magnetizable particles embedded in a polymer matrix. Experiments demonstrate hysteretic dependences of composite magnetization on an applied magnetic field and non-monotonic, with maximum, dependence of the sample susceptibilities on the field. We propose a theoretical approach which describes the main physical features of these experimental results.

S0520304 ナノ・マイクロ粒子混合系MR流体のMR効果向上と粒子カラム挙動

Magnetorheological (MR) fluids are suspensions of micron-sized magnetic particles dispersed into carrier oils, and behave like a Bingham fluid with magnetic-field responsive yield stress. In this research, bidisperse MR suspensions consisting of micro (6.6 μm) and nano (110 nm) iron particles dispersed into silicone oil were fabricated to investigate the enhancement of the MR effects in close relation to the magnetic field-induced particle cluster structures in the static condition and particle column behavior in the shear flow mode. The static particle cluster structures formed in the suspensions under applied magnetic fields were visualized using an optical microscope in a transmission mode, and the particle column behavior in the shear mode was visualized using a hand-made shear flow device and a digital video system with a micro-lens. The MR effects of the bidispersed MR suspensions changed significantly as a function of the solid fraction of nano-particles. Interestingly, the field-induced shear stress was significantly enhanced when the solid fraction of nano-particles was 25%. As well known, the particle chains formed roughly along to the applied magnetic field were observed for the MR suspension containing the micron-sized iron particles. The enhancement of the MR effects can be attributed to the static formation of distinct and wide particle cluster chains reinforced with nano-particles, and the breaking and reconnection of many thicker particle columns in the shear flow mode.

Magnetodeformation and elastic properties of ferrogels and ferroelastomers

The work deals with a theoretical study of magnetoelastic properties of soft composite materials, consisting of a polymer matrix filled with micron-sized magnetizable particles (ferrogels and ferroelastomers). The systems with a homogeneous gas-like spatial distribution of particles in the matrix are considered. The impact of the particles magnetic interaction on the macroscopic elastic characteristics of the composites is studied. Analysis shows that this interaction increases elastic moduli of the materials. This effect must be especially significant for the composites with soft gel matrix.

On the theory of rheological properties of bimodal magnetic fluids

This work deals with the theoretical study of rheological properties of a suspension of micron-sized magnetizable particles in a nanodisperse ferrofluid. In recent years, these systems have been synthesized by several teams in order to enhance technological properties of traditional magnetic fluids. We suppose that the micron-sized particles, under the action of an applied magnetic field, form linear chain-like aggregates. Analysis shows that the presence of the ferrofluid can significantly increase the magnetoviscous effect in the suspension of the particles. Unlike the traditional models of magnetorheological suspensions (MRSs) with chains, we have studied the effect of mutual magnetization of particles in chains. Estimates show that this effect significantly increases macroscopical viscous stress in the suspensions and that is why it must be taken into account for theoretical descriptions and interpretation of experiments on the rheological properties of magnetic suspensions.

Plate-like iron particles based bidisperse magnetorheological fluid

Magnetorheological (MR) properties are experimentally investigated for bi-dispersion suspension of plate-like iron magnetic particles dispersed in carrier liquid to see the influence of small size particle on large size MR fluid. As a first step, structural, magnetic, and morphology of two different micron size magnetic particles are described in details. The three different weight fractions of MR fluid samples are then prepared, followed by measuring their magneto-viscous and visco-elastic properties. In the steady-state shear, the Bingham yield stress obtained by extrapolating the shear stress to the zero shear rate increases by augmenting the weight fraction of small micron size magnetic particles and the strength of magnetic field. In the oscillatory strain sweep test at an angular frequency of 10 rad s−1, a transition from visco-elastic solid to visco-elastic liquid is observed and a strong chain formation is proposed to explain the mechanism for transition. The storage modulus also increases with increasing weight fraction. From the frequency sweep test, the storage modulus is seen as independent of frequency, but depends on the magnetic field strength and weight fraction. The magneto-viscous sweep test indicates that both shear modulus and complex viscosity are independent with weight fraction at a high magnetic field. This experimental study reveals some very important physical parameters, rheological properties, and storage modulus of the plate-like iron particles based on MR fluid. The formation of less compact because of the anisotropy in iron particle creates weak sedimentation and good redispersibility of MR fluid. The results presented in this work are the key factors for devising how mechanical applications operated under static and dynamic conditions.