Power losses model of a foil winding

A semi-analytical method for calculating foil winding power losses is presented in the article. The short-circuit losses of foil type windings are somehow greater in comparison to the other types of windings consisting of rectangular conductors or magnet wires. The main reason for higher losses is related to eddy currents induced by the magnetic field passing through the foil surface

Magnetic Fluids’ Heating Power Exposed to a High-Frequency Rotating Magnetic Field

Magnetic fluids are superparamagnetic materials that have recently been the subject of extensive research because of their unique properties. Among them is the heating effect when exposed to an alternating magnetic field, wherein the objective is to use this property in medicine as an alternative method for the treatment of tumors in the body. The heating effect characterization for the alternating magnetic field (AMF) has been studied widely, whilst for the rotational magnetic field (RMF), no systematic study has been done yet. In this article, we present the characterization of the heating power of magnetic fluids in a high-frequency rotational magnetic field. The results show similar behavior of heating power or specific absorption rate characteristics as in AMF

Computation of a magnetic liquid free surface shape in a homogeneous magnetic field

Doktorska naloga obravnava problematiko izračuna oblike proste površine magnetne tekočine v homogenem in statičnem magnetnem polju. Če magnetno tekočino, ki je stabilna koloidna suspenzija magnetnih nanodelcev, izpostavimo zunanjemu magnetnemu polju, ki presega določeno kritično vrednost, se bodo na prosti površini tekočine ustvarile konicam podobne oblike. Razporeditev in višina konic bo odvisna od jakosti magnetnega polja, kot tudi od lastnosti tekočine. V nalogi sta teoretično in numerično obravnavana dva primera, in sicer primer osamljene konice v dvodimenzionalni osno simetrični postavitvi ter centralne konice v heksagonalnem periodičnem vzorcu, ki je vpeta v tri-razsežnostni prostor. V prvem primeru je vodilna enačba magnetno razširjena nelinearna Young-Laplaceova enačba, pri tem obliko proste površine opisuje polinomska funkcija v valjnem koordinatnem sistemu. Drugi primer temelji na energijskem funkcionalu, ki zajema magnetno, gravitacijsko in površinsko energijo. V tem primeru je površina aproksimirana z valovnimi funkcijami oziroma z vsoto treh ravninskih valov, katerih valovni vektorji so v kartezičnem koordinatnem sistemu krajevno premaknjeni za 2/3. Računska strategija je zastavljena na način, da se najprej ovrednoti magnetno polje v prostoru, za kar je uporabljena metoda končnih elementov in nato deformacija proste površine, pri tem je v slednjem postopku naloga zastavljena kot optimizacijski problem, ki se v primeru osamljene konice v 2D prostoru rešuje s pomočjo algoritma diferenčne evolucije, v primeru centralne konice v heksagonalni razporeditvi pa z uporabo kombinacije algoritma diferenčne evolucije in Ritzove metode. Rezultati numeričnega modela deformacije proste površine magnetne tekočine so primerjani z računskimi in merjenimi vrednostmi, ki so dostopne v literaturi, saj zadovoljivih meritev ni bilo možno izvesti. Eksperimentalno in numerično je bila ovrednotena razporeditev magnetnega polja v ravnini nad konicami magnetne tekočine, s čimer je bilo potrjeno teoretično predvidevanje, da je razporeditev magnetnega polja nad tekočino podobna razporeditvi konic na prosti površini.The thesis deals with the computation of a magnetic liquid free surface deformation under the influence of a homogeneous magnetostatic field. When a magnetic liquid, which is a stable colloidal suspension of magnetic nanoparticles, is exposed to an external magnetic field exceeding a certain critical value, spike-like shapes appear on the surface of the liquid. The distribution and the height of the spikes depend on the magnetic field strength, as well as the properties of the magnetic liquid. Two case studies of free surface deformation are covered theoretically and numerically in the thesis. The first case study is devoted to a single spike, where the free surface is described as a polynomial function in cylindrical coordinates with applied cylindrical symmetry. To obtain the shape deformation, a system of nonlinear magnetic augmented Young-Laplace equations is solved iteratively. In the second case study, the research effort is focused on the free surface deformation of a central spike in a periodical hexagonal pattern placed in three-dimensional space (3D). Due to the periodical nature of the problem, the free surface is approximated by three planar waves, whose two-dimensional wave-vectors are mutually displaced by 2/3 in the x-y plane. The surface deformation is achieved through the energy function, with the combination of Differential Evolution and the Ritz method. The computational strategy is divided into two stages. At the first stage, the magnetic field is computed by the Finite Element Method (FEM), while a free surface profile is obtained in the second stage. The numerical results of the magnetic liquid free surface deformation obtained by the proposed methods are compared by the numerical and experimental results published in the References. To support the theoretical predictions as well as numerically obtained results, measurements of the magnetic field were performed at a close distance above the spikes of the magnetic liquid, which show that the magnetic field is distributed in a similar way as a free surface

Energy Based Calculation of the Second-Order Levitation in Magnetic Fluid

A permanent magnet immersed in magnetic fluid experiences magnetic levitation force which is of the buoyant type. This phenomenon commonly refers to self-levitation or second-order buoyancy. The stable levitation height of the permanent magnet can be attained by numerical evaluation of the force. Various authors have proposed different computational methods, but all of them rely on force formulation. This paper presents an alternative energy approach in the equilibrium height calculation, which was settled on the minimum energy principle. The problem, involving a cylindrical magnet suspended in a closed cylindrical container full of magnetic fluid, was considered in the study. The results accomplished by the proposed method were compared with those of the well-established surface integral method already verified by experiments. The difference in the results gained by both methods appears to be under 2.5%

Contactless Determination of a Permanent Magnet’s Stable Position within Ferrofluid

The paper deals with the contactless detection of a rod permanent magnet’s position within a ferrofluid. The working principle of the proposed approach is grounded on the solenoidal nature of the field lines. For the line detection technique analyzed in this article, where the magnetic field is scanned along the line parallel to the magnet’s axial direction, the center of the magnet corresponds to the point on the line where the radial component of the magnetic field vanished. The concept introduced here was evaluated numerically, where the results showed a promising perspective for the technique to be employed in practice. In contrast to the X-ray or Vernier-caliper-based technique, the one proposed here is somewhat more suitable for employment in applications where simplicity and robustness are of vital importance

Numerical Model for Determining the Magnetic Loss of Magnetic Fluids

Magnetic fluid hyperthermia (MFH) is a medical treatment where the temperature in the tissue is increased locally by means of heated magnetic fluid in an alternating magnetic field. In recent years, it has been the subject of a lot of research in the field of Materials, as well as in the field of clinical testing on mice and rats. Magnetic fluid manufacturers aim to achieve three objectives; high heating capacity, biocompatibility and self-regulatory temperature effect. High heating power presents the conversion of magnetic field energy into temperature increase where it is challenging to achieve the desired therapeutic effects in terms of elevated temperature with the smallest possible amount of used material. In order to carry out the therapy, it is primarily necessary to create a fluid and perform calorimetric measurement for determining the Specific Absorption Rate (SAR) or heating power for given parameters of the magnetic field. The article presents a model based on a linear response theory for the calculation of magnetic losses and, consequently, the SAR parameters are based on the physical parameters of the liquid. The calculation model is also validated by calorimetric measurements for various amplitudes, frequencies and shapes of the magnetic field. Such a model can serve to help magnetic fluid developers in the development phase for an approximate assessment of the heating power