Magnetic Permeability

Vitreous coatings can be used as a means for the corrosion protection of metals and alloys due to their excellent dielectric properties. Their use is of particular interest in the case of highly aggressive media (different pH levels, temperatures up to 600 °C). However, ceramic coatings exposed to aggressive agents and thermal cycles can experience devitrification and spalling problems, with the consequent loss of their protective properties.The present study uses the electrochemical impedance spectroscopy technique to characterize, in a non-destructive way, the appearance of surface defects induced by the effect of temperature and chemical attack on a vitreous enamel deposited on steel. By means of analysis of the impedance diagrams obtained, a relationship is established between the loss of the coating's protective properties and the mechanism by which the corrosion process takes place.

We present an improved version of the Jiles-Atherton model for least square identification. We first use a simplified anhysteretic magnetization model to provide simple estimates of the initial parameters. Then we perform a normalization of sensitivity functions to improve the convergence of the Levenberg-Marquardt algorithm, leading to the emergence of optimal parameters. Experimental trials validate our method.

The influence was studied of applying an external magnetic field on the microstructure and on the microwave magnetic and dielectric properties of thin-film absorbing structures containing two types of magnetic fillers. The frequency spectra between 7 and 17 GHz were obtained of the complex magnetic permeability μ* and the complex dielectric permittivity ε*. A strong dependence was established of the

A model describing the development of dendritic structure and the resulting gradient of flow resistance to interdendritic liquid is presented. The Hagen–Pousielle version of D’Arcy’s equation for flow through a porous structure is developed as a function of cooling rate and liquid volume fraction. Applied to finite elements in a unidirectionally cooled casting model, permeability gradient, feeding flow-rate required to prevent porosity, and mushy-zone liquid pressure drop at this flow rate are evaluated for the simple Fe–2Cr–0.5C and Al–5Cu castings exhibiting asymptotic and linear temperature profiles, respectively. The model shows permeability of the dendritic structure in the mushy zone dropping sharply, approaching the root of solidification front (solidus). Also shown is the effect of relative magnitude of primary and secondary arm spacing. If secondary dendrite arm spacing approaches primary arm spacing, the permeability for flow normal to primary dendrite arms approaches or even surpasses the permeability for flow parallel to primary dendrite arms.

Fast precise moisture measurement in mineral process plants, has long been a difficult problem. In this master thesis a foundation for a new way of measurement using transmission line theory, is laid out. Macroscopic electro-magnetic properties of the measured sample can be linked to those of the individual constituents of the sample. Thus one is believed to be able to do a precise estimate of the amount of moisture in a sample. In our case the samples are moist magnetite concentrate.
The characterization of sample macroscopic electro-magnetic properties is done by using a coaxial cell, performing frequency spectra measurement. In this master thesis, the electrical behavior that links the measured data to the macroscopic electro-magnetic properties is examined. It exists two setups, one inductive and one capacitive.
The DC resistivity of the moist magnetite concentrate is determined and some interesting phenomena, suggested to be self potential were discovered. This phenomenon is in general known from geochemistry of mineral rich clays. This made the measurements of resistivity tricky to perform, some measurements were achieved and a new relation between moisture of the moist magnetite concentrate and resistivity is presented.
Studies have been performed on the history of attempts of solving this problem, as well as current relevant research. Reference samples have been prepared in a geotechnical laboratory. Impedance frequency behavior of the measurement equipment is measured and presented, with different curves for different moisture content. From these measurements it is obvious that the moisture affects the impedance of the measurement equipment and thus it is possible to use this method to measure moisture content, if one can determine the electrical model which describes the measurement system.
A few equivalent circuits of transmission lines have been discussed, and one was chosen to represent the purely coaxial part of the coaxial cell. Other parts have been modeled with other elements of AC theory.
A new electrical model for the coaxial probe is proposed, based on LC resonances. Some Comsol FEM simulations have been performed on the coaxial cell, as well as on electric property sensors. Ideas to designs of electrical sensors are discussed. It is mainly the geometry which has been investigated.
First it was proposed that a phenomenon of resonance occurs at the interface of the bottom and coaxial part of the cell, LC resonance. The resonance effect has later been investigated and identified as quarter wavelength resonance, due to the length of the measurement cell and change of wave velocity due to wave propagation in MUT.
Simulations of proposed circuit equivalents in Orcad with PSpice have given some correlation with measured data for dry and non-conducting samples.
There is still work to be done, to complete an accurate mathematical model of the system.

Magnetic multiwalled carbon nanotube (MWCNTs) nanocomposites have been created by the assembly of Mg-Ni-Ti substituted barium ferrite nanoparticles onto surface of MWCNTs. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to demonstrate the successful attachment of ferrite nanoparticles to MWCNTs. Vibrating sample magnetometer (VSM) confirms the relatively strong dependence of saturation of magnetization and coercivity with the volume percentage of MWCNTs. Reflection loss evaluations indicated that the nanocomposites display a great potential application as wide-band electromagnetic wave absorbers.

A seven-element array of Yagi-Uda antennas was constructed at a frequency of 500 MHz to measure the electrosusceptibility of plane waves. The element weightings are determined by a near-field synthesis technique which optimizes the uniformity of the field throughout a rectangular test volume in the near field of the array. The amplitude and phase of the electric field were measured throughout the test volume with a short dipole probe, and it is found that the agreement with the theory is excellent.

The time-domain EM induction response of non-magnetic and magnetic targets can be approximated using a conductive permeable prism composed of six faces of conductive plates, each face being composed of a set of conductive ribbons. The effect of magnetic permeability is included by the use of two "apparent flux gathering" coefficients, and two "effective magnetic permeability" coefficients, in the axial and transverse directions. These four magnetic property coefficients are a function of physical properties and geometry of the target, but are independent of prism orientation relative to a transmitter. The approximation algorithm is computationally fast, allowing inversions for target parameters to be achieved in seconds. The model is tested on profiles acquired with a Geonics EM63 time-domain EM metal detector over a non-magnetic copper pipe target, and a steel artillery shell in horizontal and vertical orientations. Results show that this approximation to a permeable prism has a capability of fitting geometric, conductivity and magnetic parameters at both early and late sample times. The magnetic parameters show strong change from early to late times on the EMI decay curve, indicating that the magnetic properties of the target have non-linear characteristics. It is proposed that these magnetic parameters and the nature of their non-linearity may carry additional discrimination information for distinguishing between intact munitions and scrap in UXO studies.

A generalized model to recover the magnetic permeability μ of linear magnetic medium thin films from magnetic force microscopy (MFM), data under magnetostatic conditions is developed. In the mathematical treatment, where no assumption is made about the symmetry of the stray field, shape or magnetization for the MFM tip, we are lead to an inverse problem by entailing a nonlinear system of equations and obtain from the experimental data both physical magnitudes wanted: the thickness of the film bμ and μ. On the other hand, relations between superconducting and magnetic thin films are obtained, solving the problem of calibration functions and allowing to recover for a superconducting material the London penetration depth λ as well as the film thickness bλ.

The possibility of decomposing the quasi-static hysteresis loop to the contributions of the rotational magnetization (DR) and the domain wall movement (DWM) is demonstrated experimentally and modelled theoretically by the hyperbolic T model. Although the method of decomposition described here is quite general for ferromagnetic materials, it is ideally applicable to the Finemet-type nanocrystalline alloys because of the presence of

A flake-shaped Sendust/acryl suspension is tape cast and the effect of the viscosity of the suspension on the magnetic permeability of the resulting composite is investigated. The real part of the permeability of the composite is inversely proportional to the viscosity of the suspension, indicating that the lower the viscosity of the suspension, the higher the permeability of the composite. The viscosity of the suspension is controlled by adding a small amount of surfactant; an anionic surfactant is most effective for lowering the viscosity at a given concentration range. It is thought that using a suspension with a relatively low viscosity improves the permeability of the resulting composite due to the easy alignment of the flake-shaped filler with the plain direction of the sheet.

In this work, tunability of the microwave properties of Magneto-Dielectric Polymer Nanocomposites (MDPNCs) has been demonstrated for the first time. Particularly, permeability, permittivity and loss factor were tuned by an externally applied DC magnetic field with strength achievable by commercial permanent magnets. The considerable tunability, ease of manufacturing, compatibility with multilayer RF laminates and substrate implementation make this material well-suited for use in tunable microwave circuits. Two custom-built microstrip test fixtures using multi-layer substrates were employed to extract the permeability, permittivity and loss tangent of MDPNCs using S-parameter measurements.

ABSTRACT Some microwave passive components (such as circulators, isolators,  ... etc) still use bulk magnetic materials. A method for the dielectric and magnetic characterization of multi-layer materials in the microwave range is presented as well as its reliability and its domain of validity. It allows to determine the elements of the permeability tensor of gyromagnetic slab. This method of material characterization can be implemented at various microwave bands by changing the geometrical dimensions of the rectangular waveguide.

Metamaterials are emerging as engineered material structures that can be fabricated toward specific magnetic and/or electrical characteristics. Research in the field of negative refractive index and metamaterials has produced demonstrations of artificial magnetic resonances ...