Miloš Beković

Determination of the Heating Effect of Magnetic Fluid in Alternating Magnetic Field

In this paper, we have investigated the heating power of magnetic fluid, when exposed to a high-frequency magnetic field. Commercially available sample of magnetic fluid has been used and some basic investigation revealed maghemite ¿-Fe2O3 particles with 10.9-nm mean diameter and 10.57% volume concentration. We present an improved experimental system, capable of generating homogeneous magnetic field of amplitudes up to 4 kA/m and frequencies from 10 kHz to 1 MHz. In this paper, none of the heating generation mechanisms (NE¿el or Brownian relaxation or eddy current losses) have been determined solemnly, therefore, the outcome of their activity has been examined by two methods. In case of calorimetric measurements method key parameter is temperature rise while in case of magnetic measurement method key parameters are time-dependent magnetic field strength H and appurtenant magnetic flux density B. Calorimetric measurements are performed and used to determine specific absorption rate curve. Alternatively, this curve has been obtained with the measurement of B(t) and H(t), when a sample is exposed to the same magnetic conditions. Integration of the hysteresis loops has resulted in loss power of the fluid. Proposed magnetic measurement methods proved to be a decent alternative in the process of determining losses.

Spark Breakdown in Gas-Discharge-Tube Surge Arrester at Voltage Pulse

The sparkover voltage of gas discharge tubes for surge voltage protection has been found to be dependent on the rate of voltage rise. At slow voltage increase, it is close to stationary voltage conditions and is assumed to be the breakdown voltage at a given pd regarding Paschen law. The deviation of stationary sparkover voltage measured on test samples is assigned to the variation of electrode conditions and illustrated as the effect of the Townsend coefficient γ. The increase of impulse sparkover voltage at fast voltage rise depends on the time lag of the spark breakdown where the effect of statistical and formative time lag is assessed. As an origin of ion avalanche and streamer formation, the cold-field electron emission process is considered where the Poisson probability function for rare stochastic events is concerned for the evaluation of emitted electron current. Due to the absence of applicable values for relevant system parameters, the relationship between the impulse sparkover voltage and the rate of voltage rise obtained by simulation have more or less qualitative character. Values taken for the coefficients of simulation are chosen by fitting the simulated results to the measured ones. Their relevance is verified by comparing it with the typical values of discharge quantities found in the literature.

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.

Experimental System for Determining the Magnetic Losses of Super Paramagnetic Materials; Planning, Realization and Testing

In recent decades we have witnessed the development of nanotechnology throughout all fields of science including the field of magnetic materials. When it comes to nanotechnology is usual for at least one of the dimensions to be in nm scale and therefore the nano-materials or nano-equipment exhibit certain unique characteristics. The area of magnetic materials also followed the developments within this field, with the focus on magnetic nanoparticles, which are typically super-paramagnetic. Within the context of nanotechnology, it is necessary to observe particles in comparison with solid magnetic materials because the unique characteristics enable some completely new applications.

Finding a crack's position and its parameters on the basis of non-destructive testing, using eddy currents

Purpose – The purpose of this paper is to find the geometry of a crack within a conductive plate and its parameters, on the basis of non-destructive testing, using eddy currents. The input data represents the measured values of magnetic flux density within the centre of the excitation coil. Design/methodology/approach – The position of a crack can be determined by taking into consideration any change in the magnetic flux density between the measured points. The depth and width are determined through the use of a finite element model. Findings – These calculations are the basis for determining a function that explains how magnetic flux density changes if the depth or width has changed. Jacobis matrix is calculated using the determined functions’ analytical derivatives. Originality/value – After wards, through the Newton-Raphson iterative procedure using the finite element method calculation results, the crack-depth and width can be obtained, this being one of the objectives in this paper. The suitability ...

FEM thermal analysis of magnetic fluid heating power

In this paper we will present analysis of magnetic fluid heating power. For this purpose we will first determine the specific heating power (SHP) of the magnetic fluid sample when exposed to ac magnetic field of known frequency and amplitude using commercial FEM program. These results will be used in the same FEM model for thermal analysis where results of calculated temperature increase in the sample will be compared with actual measurements. This method will allow determination of temperature increase only from permeability measurement.