Concentration Of Magnetic Particles Research Articles

Magnetic particle imaging deblurring with dual contrastive learning and adversarial framework

Magnetic particle imaging (MPI) is an emerging medical imaging technique that has high sensitivity, contrast, and excellent depth penetration. In MPI, x-space is a reconstruction method that transforms the measured voltages into particle concentrations. The reconstructed native image can be modeled as a convolution of the magnetic particle concentration with a point-spread function (PSF). The PSF is one of the important parameters in deconvolution. However, accurately measuring or modeling the PSF in the hardware used for deconvolution is challenging due to the various environment and magnetic particle relaxation. The inaccurate PSF estimation may lead to the loss of the content structure of the MPI image, especially in low gradient fields. In this study, we developed a Dual Adversarial Network (DAN) with patch-wise contrastive constraint to deblur the MPI image. This method can overcome the limitations of unpaired data in data acquisition scenarios and remove the blur around the boundary more effectively than the common deconvolution method. We evaluated the performance of the proposed DAN model on simulated and real data. Experimental results confirmed that our model performs favorably against the deconvolution method that is mainly used for deblurring the MPI image and other GAN-based deep learning models.

Analytical modeling of a magnetoactive elastomer unimorph

Magnetoactive elastomers (MAEs) are capable of large deformation, shape programming, and moderately large actuation forces when driven by an external magnetic field. These capabilities enable applications such as soft grippers, biomedical devices, and actuators. To facilitate complex shape deformation and enhanced range of motion, a unimorph can be designed with varying geometries, behave spatially varying multi-material properties, and be actuated with a non-uniform external magnetic field. To predict actuation performance under these complex conditions, an analytical model of a segmented MAE unimorph is developed based on beam theory with large deformation. The effect of the spatially-varying magnetic field is approximated using a segment-wise effective torque. The model accommodates spatially varying concentrations of magnetic particles and differentiates between the actuation mechanisms of hard and soft magnetic particles by accommodating different assumptions concerning the magnitude and direction of induced magnetization under a magnetic field. To validate the accuracy of the model predictions, four case studies are considered with various magnetic particles and matrix materials. Actuation performance is measured experimentally to validate the model for the case studies. The results show good agreement between experimental measurements and model predictions. A further parametric study is conducted to investigate the effects of the magnetic properties of particles and external magnetic fields on the free deflection. In addition, complex shape programming of the unimorph actuator is demonstrated by locally altering the geometric and material properties.

Thermomagnetic cooling of current carrying micro-wire in ferrofluid: Two-phase approach

Thermomagnetic convection is a controlling phenomenon for heat-transfer in ferrofluids. It depends upon the magnetic field gradients, variation in magnetic susceptibility, particle concentration and temperature gradients. This article presents the effect of these parameters on cooling of a current carrying micro-wire in ferrofluid with a focus on magnetophoresis effects. A two-phase Euler-Euler model is developed. The predictions of this model are compared with experimental results and predictions from a single-phase ferrofluid model. For ferrofluid with volume fraction of φ = 0.02, the predicted average wire temperature from the Euler-Euler two-phase model is approximately 1 K lower than the measured wire temperature,while the single phase model is 5 K higher. Under identical magnetic field and heat flux conditions, variations in the particle concentration are found to have a non-negligible effect on thermomagnetic convective cooling. The maximum temperature of the wire for φ = 0.01 ferrofluid is significantly increased by 10 K and greater enhancement to cooling is observed in the case of φ = 0.04, where the inception of thermomagnetic cooling is advanced. Correspondingly, significantly different thermal and velocity fields are observed for different volume fractions. The simulations show different regimes of heat transfer. During the first few hundred milliseconds after applying electrical current, a thin boundary layer develops near the wire surface and the colder region is thermally stratified. At larger time, dispersion of ferro-particles between colder and hotter regions produces concentration gradients which affect the thermal and velocity fields. Eddies generated by thermomagnetic convection are found to form at the bottom of the vertical wire and retain their structure as they are convected upwards by natural convection. The particle concentration at the wire surface (φws) varies from 0.0188 to 0.0260 for an initial volume fraction (φ) of 0.02. This variation disturbs the thermal boundary layer and generates thermal vortices around the heated wire that differ from single-phase model predictions.

Nanomagnetic Elastomers for Realizing Highly Responsive Micro- and Nanosystems.

Evolution has produced natural systems that generate motion and sense external stimuli at the micro- and nanoscales. At extremely small scales, the intricate motions and large deformations shown by these biosystems are due to a tipping balance between their structural compliance and the actuating force generated in them. Artificially mimicking such ingenious systems for scientific and engineering applications has been approached through the development and use of different smart materials mostly limited to microscale dimensions. To push the application range down to the nanoscale, we developed a material preparation process that yields a library of nanomagnetic elastomers with high magnetic particle concentrations. Through this process, we have realized a material with the highest magnetic-to-elastic force ratio, as is shown by an extensive mechanical and magnetic characterization of the materials. Furthermore, we have fabricated and actuated micro- and nanostructures mimicking cilia, demonstrating the extreme compliance and responsiveness of the developed materials.

Research on influence of polishing fluids parameters on processing effects in reciprocating magnetorheological polishing

PurposeThis paper aims to study the influence of the different parameters of magnetorheological polishing fluids (MRP fluids) on the surface roughness and material removal rate (MRR) of the workpiece surface in the reciprocating magnetorheological polishing (RMRP) process.Design/methodology/approachA series of single-factor experiments are performed to evaluate the influence of the concentration of magnetic particles, concentration of abrasive particles and size of abrasive particles on surface processing effects by using the RMRP method. Moreover, the yield stress and viscosity of MRP fluids are studied based on the Bingham plastic model by varying the MRP fluids parameters.FindingsA reasonable parameter of MRP fluids is crucial to the surface roughness and MRR of the workpiece surface, and the optimized parameters are obtained by the single-factor experiments of RMRP. The results are when the concentration of carbonyl iron particles is 40 Vol.%, the concentration of CeO2 is 5 Vol.% and the size of CeO2 is 2.5 µm in the MRP fluids, the surface roughness of the workpiece remarkably decreases to 28 nm from the initial 332 nm and the MRR of the workpiece increases to 0.118 mg/min.Originality/valueIn this study, the single-factor experiments for the different parameters of MRP fluids are studied to polish K9 glass by using the RMRP device, and the yield stress and viscosity of MRP fluids are investigated by rheological experiments, which provides reference for a reasonable selection of the MRP fluids parameter in RMRP process.

Composite magnetic properties of cobalt ferrite nanoparticles embedded in bacterial nanocellulose of different porosity levels

A simple and novel strategy for tuning the macroporous structure of bacterial nanocellulose allows for embedding nanoparticles on the template. Here, cobalt ferrite nanoparticles were co-precipitated in-situ at two templates with different porosities. Different analytical techniques like SEM, XRD, TGA, and PPMS allow for characterizing the properties of the prepared magnetic nanocomposites. After eight months of aging at room conditions, lyophilized bacterial nanocellulose preserved the macroporous structure (porosity ∼ 46%). However, rehydration and re-lyophilization of the cellulose decrease the template porosity (∼8%). The cobalt ferrite nanoparticles, growth on high and low macroporous templates, were single-crystalline and microstrain-free. The nanoparticle's shape and mean size do not change with the porosity of the template, but the cluster size does. However, the differences in porosity on templates allow tuning the nanoparticle concentration and then its magnetic interactions (in high macroporous near 63%, and low about 43%) in the nanocomposites. Magnetic data confirm the influence of the template porosity on the magnetic particle concentration. The magnetic behavior as a temperature function (effective magnetic anisotropy constant, coercive force, and reduced remanence) is dependent on the template porosity. These dissimilarities were correlated with cluster size variations, where the differences in the aggregation modify the magnetic dipolar interactions among particles.

Improved Quantitative Analysis Method for Magnetic Particle Imaging Based on Deblurring and Region Scalable Fitting.

Magnetic particle imaging (MPI) is a technique for imaging magnetic particle concentration distribution. It has the advantages of high sensitivity, no signal attenuation with depth, and no ionizing radiation. Although MPI has been widely used in the biomedical field, accurate image analysis has been challenging due to its anisotropic point spread function (PSF). The purpose of this study is to propose an MPI image restoring and segmentation method to facilitate a more precise quantitative evaluation of the magnetic particle imaging in vivo. We proposed a DeRSF method that combined deblurring and region scalable fitting (RSF)to determine the imaging tracer distribution. Then a uniform erosion and scaling criterion was established based on simulation experiments to correct the segmentation results, which was further validated on phantom imaging. Finally, we imaged the MPI tracer at gradient concentrations to establish the calibration curve between the MPI signal and iron mass for iron quantification in phantom and in vivo imaging. The phantom imaging experiments showed that our method achieved improved segmentation performance. The mean value of the dice coefficients for segmentation was up to 0.86, demonstrating that our method can accurately map and quantify the distribution of the tracer. Moreover, the iron quantification on both phantom and in vivo mouse imaging was realized with the minimal error of 5.50%, by our established calibration curve. Our proposed DeRSF method was successfully used for improved MPI quantitative analysis. More importantly, this method also showed accurate quantitative results on images with different shapes and tracer concentrations in both phantom and in vivo data, which laid the foundation for the biomedical study of MPI.

The simulation of the magnetic particle deposition and the effect on the magnetic fluid sealing performance

Magnetic fluid is used for sealing because of its strong magnetic response. However, magnetic particles are aggregated at the pole tooth in the nonuniform magnetic field, which results in a change in sealing performance. This paper uses the coupling simulation of the magnetic-flow field and the diffusion equation to solve the magnetic particle concentration distribution with the different rotating speeds. The sealing performance of different magnetic particle concentration distributions is calculated using the multi-physical field coupling and the dynamic mesh method. The results show that the particle concentration inhomogeneity degree is influenced by rotating speed, particle size, and volume fractions. Besides, the increasing particle concentration inhomogeneity degree increases the sealing performance.

Magnetic particle based MRI thermometry at 0.2 T and 3 T

This study provides insight into the advantages and disadvantages of using ferrite particles embedded in agar gel phantoms as MRI temperature indicators for low-magnetic field scanners. We compare the temperature-dependent intensity of MR images at low-field (0.2 T) to those at high-field (3.0 T). Due to a shorter T1 relaxation time at low-fields, MRI scanners operating at 0.2 T can use shorter repetition times and achieve a significant T2⁎ weighting, resulting in strong temperature-dependent changes of MR image brightness in short acquisition times. Although the signal-to-noise ratio for MR images at 0.2 T MR is much lower than at 3.0 T, it is sufficient to achieve a temperature measurement uncertainty of about ±1.0 °C at 37 °C for a 90 μg/mL concentration of magnetic particles.

Magnetorheological brushes – Scarcely explored class of magnetic material

Magnetic materials such as magnetorheological (MR) fluids, and magnetorheological elastomers exhibit a broad change in their material properties, for example, viscosity and storage modulus in the presence of a magnetic field. Studies related to such MR fluid and elastomer materials are extensively available. The MR brush, meanwhile, is less frequently explored and understood. An MR brush is defined by the brush-like structures formed from chains of magnetic particles embedded within a carrier matrix, typically fluids or elastomers. In this study, we explore magnetorheological fluid (MRF) brush and magnetorheological elastomer (MRE) brush and investigate their magneto-mechanical properties. The investigation measured the stiffness and the MR response, defined as the change in properties in the presence of a magnetic field for MRF and MRE brushes. Further dependence of the magnetic effect on material and preparation parameters, mainly concentration of magnetic particles and curing flux density (for MRE brush) were investigated. The responsiveness of the brushes is compared using the Magnetorheological response index, as a proposed metric in this study. The results indicate that the MRE brush possess a greater absolute stiffness, but a lower MR response than that of the MRF brush. Both MRF and MRE brushes show an increase in the MR response with an increased concentration of magnetic fillers. MRE brush further demonstrate an enhanced MR response, which could be highly comparable to MRF brush coinciding with an increase in the magnetic flux density during the curing process. The fundamental investigation of both solid and fluid MR brushes in this study opens a new avenue in the area of magnetic materials. This new class of magnetically controllable materials could potentially be employed in applications where soft and tuneable bristle-like structures are desired.

Improving the efficiency of machine learning in simulating sedimentary heavy metal contamination by coupling preposing feature selection methods

Sediment cores were collected from Taihu Lake in China. The chronology was determined by radionuclide. Heavy metals and magnetic properties of each core slice were assessed, respectively. The concentrations of most heavy metals in sediments surged at 20 cm from the surface, accompanying the increase in the concentrations of single-domain magnetic particles. This may be resulted from the influence of anthropic activities on the lake's environment after the 1970s. Two feature selection methods, random forest (RF) and maximal information coefficient (MIC), were combined with support vector machine (SVM) model to simulate heavy metals, with the inclusion of selected magnetic and physicochemical parameters. Compared with the modeling results obtained with the full set of parameters, a reasonable simulation performance was obtained with RF and MIC. RF performed better than MIC by increasing the R2 of simulation models for Cd, Cr, Cu, Pb, and Sb. For heavy metals with high ecological risks (As, Cd, Cr, Hg, Pb, Sb), the correlation coefficients for observed and predicted data ranged from 0.73 to 0.97 with only 14–27% of the parameters selected by RF as input variables. The RF-RBF-SVM enabled heavy metal predictions based on the magnetic properties of the lake sediments.

Robust hydrogen-bonding interactions from deep eutectic solvent enabling high magneto-responsive performances

In this study, magnetorheological fluids (MRFs) with a choline chloride/glycerol deep eutectic solvent (DES) as the carrier liquid were elaborately developed and studied. Because of the strong hydrogen bonding interactions between the DES and the functional groups on the surfaces of the magnetic particles, the mechanical properties and sedimentation stability of the MRF were improved significantly. The influence of the hydrogen bond donor (HBD) type and water content of DES, the hydrogen bond acceptor (HBA):HBD ratio, and the concentration of magnetic particles on the magnetorheological (MR) properties was investigated. It was found that, except for the HBA:HBD ratio, these factors had a significant influence on the properties. The results showed that DES is an efficient carrier liquid, capable of forming MRFs with Fe3O4-based or carbonyl iron particles, and it showed more excellent MR properties compared with silicone oil-based MRFs. This paper demonstrates the design and fabrication of a new type of eco-friendly, high-performance MRF enabling the future development of efficient MRFs based on the modulation of chemical or molecular interactions.

Effect of Magnetic Microparticles on Cultivated Human Corneal Endothelial Cells.

To investigate effects of magnetic microparticles on movement of magnet controlled human corneal endothelial cells (HCECs). Immortalized HCEC line (B4G12) and primary culture of HCECs were exposed to two commercially available magnetic micro- or nanoparticles, SiMAG (average size 100 nm) and fluidMAG (average size <1000 nm). Cell viability assays and reactive oxygen species production assays were performed. Cellular structural changes, intracellular distribution of microparticles, and expression levels of proteins related to cellular survival were analyzed. Ex vivo human corneas were exposed to microparticles to further evaluate their effects. Magnetic particle-laden HCECs were cultured under the influence of a neodymium magnet. No significant decrease of viability was found in HCECs after exposure to both magnetic particles at concentrations up to 20 µg/mL for 48 hours. However, high concentrations (40 µg/mL and 80 µg/mL) of SiMAG and FluidMAG significantly decreased viability in immortalized HCECs, and only 80 µg/mL of SiMAG and FluidMAG decreased viability in primary HCECs after 48 hours of exposure. There was relative stability of viability at various concentrations of magnetic particles, despite a dose-dependent increase of reactive oxygen species, lactate dehydrogenase, and markers of apoptosis. Ex vivo human cornea study further revealed that exposure to 20 µg/mL of SiMAG and fluidMAG for 72 hours was tolerable. Endocytosed magnetic particles were mainly localized in the cytoplasm. The application of a magnetic field during cell culture successfully demonstrated that magnetic particle-loaded HCECs moved toward the magnet area and that the population density of HCECs was significantly increased. We verified short-term effects of SiMAG and fluidMAG on HCECs and their ability to control movement of HCECs by an external magnetic field. A technology of applying magnetic particles to a human corneal endothelial cell culture and controlling the movement of cells to a desired area using a magnetic field could be used to increase cell density during cell culture or improve the localization of corneal endothelial cells injected into the anterior chamber to the back of the cornea.

Self-assembly and magnetorheological performance of Fe3O4-based liquid-crystalline composites

A new class of Fe3O4-based liquid-crystalline composites (Fe3O4@ILCPs) were constructed via a self-assembly process by using polyetheramine, liquid-crystalline monomer 3,3′-bis((cholesteryloxy)carbonyl)-[1,1′-biphenyl]-4,4′-dicarboxylic acid (BSI), adipic acid and magnetic nanoparticles Fe3O4. The cholesterol-based BSI content in the Fe3O4@ILCPs was varied in order to decipher the relationships between structure and thermal and magnetorheological properties on a molecular level. The increase in BSI component resulted in more rigid mesogens in ILCPs, as reflected by an increase in glass-transition temperature and isotropization temperature in differential scanning calorimetry analysis. The magnetorheological performance revealed that the Fe3O4@ILCPs-based magnetorheological fluids (MRFs) showed Bingham flow characteristics in the presence of external magnetic field. Under the same silicone oil carrier fluid and fixed magnetic field strength, the higher the content of magnetic particles was, the stronger the aggregation was between the Fe3O4@ILCPs particles and, as a result, the greater the shear stress and viscosity were. The Fe3O4@ILCP-1-based MRFs exhibited the highest shear stress and viscosity among the three MRFs (Fe3O4@ILCP-1, Fe3O4@ILCP-2 and Fe3O4@ILCP-3-based MRFs) at a fixed shear rate suggested that Fe3O4@ILCP-1 containing more bulky ionic mesogen is favorable for liquid crystal orientation and synergistically interactions with magnetic particle Fe3O4 alignment induced by magnetic field. The sedimentation measurements suggested that MRFs showed good sedimentation stability due to the network structure of Fe3O4@ILCPs particles and the reduction of density mismatch between carrier fluid and magnetic nanoparticles.

Recovery of heavy medium in coal washing plant using a flat plate magnetic separator and optimization of flow and magnetic fields

Heavy medium coal washing technique can achieve deep coal desulfurization and ash reduction. It is an important approach that can ensure clean and efficient utilization of coal. Heavy medium coal washing technique is affected by the efficient and high-quality recovery of heavy medium. While, it has the poor recovery due to the finer particle size and weaker magnetic property using the drum magnetic separator. In this study, the recovery of heavy medium was performed using a flat magnetic separator based on a plane extrusion magnetic system. The effect flow field and magnetic field on the recovery of the heavy medium were theoretically discussed, and the mechanism was clarified. The main results demonstrated that the plane extrusion magnetic system had a high magnetic field strength with B > 0.5 T, and the magnetic field distance was greater than 30 mm with B > 0.2 T. Additionally, the leakage of magnetic field lines was less regardless of the position of the magnetic poles. The magnetic system was suitable for plate installation. A fluid domain height changes from 40 cm to 60 cm during the recovery cycle had a significant effect on the magnetic field strength, and an increase in the fluid domain height extended the motion trajectory of the magnetic particles. A flow velocity changes from 1.2 m/s to 2.0 m/s directly affected the competitive forces intensity. However, the competitive intensity was significantly less than that of the magnetic force, and an increase in the flow field velocity slightly affected the motion trajectory of magnetic particles. The effect of the magnetic particle concentration on the motion trajectory of magnetic particles was unclear due to the stable magnetic properties of the heavy medium. The theoretical and experimental analysis confirmed that the thin flow field film separation space of the flat plate magnetic separator and the magnetic field characteristic of the plane extrusion magnetic system, could be beneficial to the separation of finer particle size and weaking magnetic susceptibility. Additionally, the counterbalance relationship between the magnetic and competitive forces fulfilled the requirements of the high-efficiency magnetic separation of the heavy medium.

Carbon sequestration assessment using varying concentrations of magnetotactic bacteria

• Magnetic techniques provide indirect and non-destructive identification of magnetosomal magnetic nanoparticles. • The magnetic properties of the nanoparticles depend on the quantity of the bacterial cells. • Carbon content of magnetotactic bacteria could be related to the global carbon cycle. Carbon cycling processes on Earth are many and complex, and several continental and oceanic environments remain poorly studied. Consequently, major uncertainties affect carbon-cycling models which limit our ability to understand and predict climate dynamics. The first assessment of carbon sequestration for magnetotactic bacteria (MTB) was carried out in this study. MTB produce magnetosomes which are intracellular organelles containing nanometer-sized, membrane-bound magnetite crystals. These crystals are arranged into single or multiple chains within the cell, which enable MTB to align themselves along a magnetic field (magnetotaxis). MTB are well known in the biological sciences, and their magnetic remains are widely studied in earth sciences as magnetofossils. Rock magnetic techniques provide indirect and non-destructive identification of magnetosomes in a sample. It is very crucial to understand the magnetic response of different types of magnetosomes produced by distinct MTB species with varying concentrations. Magnetic properties of lysed and whole MTB cells, the cultured Magnetovibrio blakemorei strain MV-1 T and Magnetofaba australis strain IT-1, with concentrations varying from 10 2 to 10 9 per sample are presented here. Magnetic properties of quantified bacterial magnetite depend largely on the quantity of MTB cells rather than on the bacterial species or cell type (lysed or whole). Magnetic values are significantly higher for the samples containing 10 7 cells or higher, FORC diagrams have no measurable magnetic fingerprint for the samples containing less than 10 7 cells. Therefore, unmeasurable magnetic signals may compromise detection of lower magnetic particle concentrations in a sample. This study estimates the carbon content of MTB cells and discusses its relationship to the global carbon cycle.

Magnetic Response Detects the Strength of Carrageenan Network.

The effect of carrageenan concentration on the magneto-rheological effect of magnetic gels with a magnetic particle concentration of 50 wt.% was investigated under a magnetic field of 50 mT by dynamic viscoelastic measurements. The change in the storage modulus for magnetic gels due to the magnetic field was 3.0 × 103 Pa at a carrageenan concentration of 1.0 wt.% and increased with the concentration. The modulus change showed a maximum of 2.3 × 104 Pa at ~2.0 wt.% and became lower at higher concentrations. This is an interesting phenomenon, which was first observed in this study. The critical strain, the strain where the storage modulus intersects the loss modulus in the strain dependence of the modulus, was much higher than that for carrageenan gels, indicating a strong interaction between the magnetic particles and carrageenan. At 0 mT, the critical strain for the magnetic gels increased remarkably with decreasing the concentration, indicating that magnetic gels have a structure that does not flow easily at concentrations below 1.75 wt.%. It is considered that the structure hardly flows, hindering the movement of particles. At high concentrations, the SEM photographs showed both a particle network of magnetic particles and a dense carrageenan network. It can be considered that the movement of magnetic particles was hindered due to these factors at high concentrations.

Occurrence and Distribution Patterns of Magnetic Particles Within Stalagmite Growth Laminae

AbstractThe concentrations of magnetic particles in stalagmites depend greatly on the regional hydrologic condition, and thus can act as an important proxy for paleoclimate reconstruction. The central axis region of a stalagmite is usually selected for such magnetism study. However, little is known about the distribution and influence factors of exogenetic magnetic particles within the growth laminae. In this study, the occurrence and variations of magnetic particles along the growth laminae of three shape stalagmites were investigated by a set of magnetic measurements, including isothermal remanent magnetization (IRM) acquisition curves and low‐temperature magnetic analysis. The results show the main magnetic remanence carrier is detrital magnetite/maghemite, coexisting with small amounts of hematite and goethite. The distribution of soft magnetic particles along the growth laminae showed different patterns among the three shape stalagmites (dome, cone, and candle). For the dome shape stalagmite, the soft magnetic particle concentrations in all studied growth layers showed an increasing trend from center to edge. Similar patterns were also appeared in the bottom growth layers of the cone and candle shape stalagmites. This edge enrichment of magnetic particles is caused by drip water washing effect. However, such enrichment pattern became weaker or even inverse in the top growth layers of the cone and candle shape stalagmites, indicating that the shapes of stalagmites could also affect the surface distribution of soft magnetic minerals. These uneven distributions of magnetic particles imply that the central axis region of a stalagmite may not always be the optimal specimen for environmental magnetism study.

Mechanical Force Acting on Ferrogel in a Non-Uniform Magnetic Field: Measurements and Modeling.

The development of magnetoactive microsystems for targeted drug delivery, magnetic biodetection, and replacement therapy is an important task of present day biomedical research. In this work, we experimentally studied the mechanical force acting in cylindrical ferrogel samples due to the application of a non-uniform magnetic field. A commercial microsystem is not available for this type of experimental study. Therefore, the original experimental setup for measuring the mechanical force on ferrogel in a non-uniform magnetic field was designed, calibrated, and tested. An external magnetic field was provided by an electromagnet. The maximum intensity at the surface of the electromagnet was 39.8 kA/m and it linearly decreased within 10 mm distance from the magnet. The Ferrogel samples were based on a double networking polymeric structure which included a chemical network of polyacrylamide and a physical network of natural polysaccharide guar. Magnetite particles, 0.25 micron in diameter, were embedded in the hydrogel structure, up to 24% by weight. The forces of attraction between an electromagnet and cylindrical ferrogel samples, 9 mm in height and 13 mm in diameter, increased with field intensity and the concentration of magnetic particles, and varied within 0.1–30 mN. The model provided a fair evaluation of the mechanical forces that emerged in ferrogel samples placed in a non-uniform magnetic field and proved to be useful for predicting the deformation of ferrogels in practical bioengineering applications.

Effect of Volume Fraction on Shear Mode Properties of Fe-Co and Fe-Ni Filled Magneto-Rheological Elastomers.

In this research, the synergistic behavior of magnetorheological elastomers containing nickel and cobalt along with iron particles as magnetically polarizable fillers is examined experimentally under dynamic shear loading. Two different types of magnetorheological elastomer were fabricated having equal proportions of iron and nickel in one kind, and iron and cobalt in the other. The concentrations of magnetic particles in each type are varied from 10% to 40% and investigated for several frequencies, displacement amplitude, and magnetic field values. A test assembly with moveable permanent magnets was used to vary magnetic field density. Force displacement hysteresis loops were studied for dynamic response of magnetorheological elastomers (MREs). It was observed that MREs showed a linear behavior at low strains while nonlinearity increased with increasing strain. The percentage filler content and frequency increased the MRE stiffness whereas it decreased with displacement amplitude. The computed maximum magnetorheological (MR) effect was 55.56 percent. While MRE with iron and cobalt gave the highest effective stiffness, MRE with iron and nickel gave the highest MR effect.