Halit S. Gokturk

Percolation in magnetic composites

Electric and magnetic properties of composite materials consisting of low density polyethylene filled with powdered ferromagnetic materials were investigated. The volume fractions of the fillers were varied from 10% up to the theoretical maximum packing fractions, i.e. between 0.70 and 0.77, so that the percolation phenomenon could be investigated. The ferromagnetic fillers used were HyMu 800 (a nickel-iron-molybdenum alloy), MnZn ferrite and NiZn ferrite. The particle sizes and size distributions of the fillers were well characterized by image analysis techniques. Based on the particle size distribution the maximum loading levels of fillers as permitted by geometric considerations were calculated. The properties of the composites characterized included: volume and surface resistivities, dielectric constants, electrical loss factors and magnetic permeabilities.

Electric and magnetic properties of a thermoplastic elastomer incorporated with ferromagnetic powders

The electric and magnetic properties of a composite material consisting of a thermoplastic elastomer incorporated with iron powder and nickel-iron alloy powder are investigated. The volume fraction of the powder filters ranges from 0.1 to 0.5. The composites are characterized in terms of their volume and surface resistivities, permittivities and electric loss factors and magnetic permeabilities 0 and magnetic loss factors. With the addition of the ferromagnetic powders, the volume and surface resistivity values of the composites decrease by more than seven orders of magnitude, the permittivity values increase tenfold and magnetic permeability values increase by a factor of about six. The ferromagnetic powders are more effective in contributing the electric and magnetic properties the composite at higher loading levels. The frequency variations of AC electric and magnetic properties are also measured in the range 20 Hz to 1 MHz. >

Enhancement of the relative magnetic permeability of polymeric Composites with hybrid particulate fillers

Composites with high relative magnetic permeability values can be used in many industrial applications, especially if they can be shaped using conventional polymer-processing technologies. In this study, various hybrid composite systems (i.e., particles with differing aspect ratio, size, and magnetic permeability embedded into a polymeric binder) were prepared in an attempt to reach high relative permeability values without the use of high pressures or sintering. It was determined that an interaction effect between the different types of fillers exists and enhances the relative magnetic permeability value of the composite in relation to the use of single type of magnetic filler. Relative magnetic permeability values of over 100 were achieved. Such relative magnetic permeability values represent a significant increase in the magnetic permeability over available magnetic composites prepared using similar processing techniques. The significant gains in magnetic permeability were realized by altering the maximum packing fraction, and ultimately the percolation threshold of the composite, by using low and high aspect ratio particles simultaneously in the formulation of the magnetic composites.

Granular magnetic composites employing cobalt based amorphous alloys in a polymeric host

Cobalt based soft ferromagnetic amorphous alloys have unique properties which make these materials good candidates to be employed in magnetic composites prepared by dispersing granules of the alloy in a polymeric host. These alloys have excellent soft magnetic properties which are minimally affected by external stresses induced during the processing operations involved in the preparation of such a composite. Continuous ribbons of a cobalt based amorphous alloy, Metglas 2705M, were cut into large aspect ratio flakes and blended into a polyethylene host in volume fractions ranging from 0.001 to 0.15. The relative magnetic permeability values of the composites increased with increasing volume fraction of the amorphous alloy, reaching a value of 26 at the volume fraction 0.15. The magnetic properties of the composites exhibited two distinguishing features: The permeability values of these composite samples were found to vary only slightly, about 10%, as a function of frequency in the range 10 Hz–100 kHz; the ...

Development of Mathematical Tools to Determine Optimum Enclosure Designs for Controlling Electromagnetic Fields

Electromagnetic fields are present wherever sources of currents are found. Conventional shielding against these electromagnetic fields is accomplished by using com plete ferromagnetic enclosures. Maxwells equations govern the phenomenon of electro magnetic fields in discontinuous media, and analytical solutions in the presence of enclo sures of arbitrary shapes are not available. Hence, Maxwells equations are solved numerically using the finite element method in conjunction with the magnetic scalar potential approach. The test case for the verification of the numerical code is a long cylin drical ferromagnetic shell placed in a transverse uniform magnetic field for which an ana lytical solution is derived here. The comparison of analytical and numerical solutions vali dates the accuracy of the numerical code. As expected the magnetic field inside the complete enclosure varies inversely to the relative permeability of the enclosure. Using this approach, enclosures of different shapes can be designed.

Relative Magnetic Permeability of Injection Molded Composites as Affected by the Flow Induced Orientation of Ferromagnetic Particles

Publisher Summary The objective of this chapter is to experimentally examine the effects of processing on the orientation distributions of ferromagnetic fibers in injection molded composites and to elucidate the effects of the resultant fiber orientation distributions on the magnetic properties of the injection moldings. Furthermore, the effects of the concentration and the aspect ratio of the ferromagnetic particles are also investigated. Magnetic properties of composites are influenced by concentration, fiber length, and orientation of the ferromagnetic particles, which are incorporated into a polymeric binder. Since fibers are anisotropic their preferential orientation will impart anisotropy in the composite material properties. Anisotropic magnetic composites are produced by injection molding of suspensions consisting of a high-viscosity polymeric binder and various fillers in two custom designed molds, which produced differences in fiber orientation distributions. The magnetic properties of the composites are characterized in terms of their relative permeability values and related to their microstructure. It is determined that composites with a higher degree of orientation generate higher permeability values. Quantitative data, which link orientation distribution functions to magnetic permeability values of composites, are provided for the first time. It is also shown that various processing conditions and die diameter influence the orientation, hence the permeability. These findings can be utilized to tailor injection moldings with desired relative magnetic permeability values for various industrial applications.