Measurement of Complex Permittivity of Oil-Based Ferrofluid in Magnetic Field

Abstract

The changes of dielectric parameters in oil-based ferrofluid have been measured in an external magnetic field. The frequency dependent real permittivity and the dissipation factor were measured within the frequency ranges from 1 mHz to 2 MHz by a capacitance method. These parameters have been studied in combined electric and magnetic field, when fields were parallel and perpendicular. The Cole-Cole model has been used to analyze measured data. When a magnetic field was applied, the interaction between the magnetic field and magnetic moments of nanoparticles led to the aggregation of magnetic nanoparticles to new structures -thick chains which had influence on the value of dielectric permittivity. At constant magnetic field the dependence of real permittivity and tan δ on angle between the electric and magnetic field (anisotropy) were measured, too. The various influences of magnetic field development on the investigated liquid are discussed. IntroductionFerrofluids have specific properties and various technical and biomedical fields of their applications already exist. The study of their dielectric parameters by dielectric spectroscopy can lead to better understand polarization phenomena and improve their properties. The measurements for various concentrations and temperatures showed two main relaxation processes [1,2], the first for high frequencies -the Maxwell-Wagner effect and the second for low frequencies -the Schwarz model [3]. The dielectric behavior of ferrofluid changes with the application of an external magnetic field and with the relative orientation of the electric and magnetic fields. This effect is known as magneto-dielectric anisotropy effect [2,4]. The acoustic spectroscopy is also very useful tool for the study of structure changes of ferrofluids in the magnetic fields [5,6].The complex relative permittivity is one of important dielectric parameter, which is a measure of how much energy from an external electric field is stored in a material and how dissipative a material is to an external field. It can be modeled by the Cole-Cole model plus the addition of dc losses [7] in the form

Influence of Temperature on the Magneto-Dielectrics Effect of Oil-Based Ferrofluid

“…The dissipation factor decreases under application of magnetic field. The magnetic field changes the structure of ferrofluid by rearranging the magnetic nanoparticles to forms like oligomers, thin or thick chains [7][8][9]. For the parallel orientation of the magnetic and electric fields the decrease is bigger than for a perpendicular orientation.…”

“…1). This fact causes the increase of dissipation factor at higher frequency [9] and its increase at lower frequency with temperature. The analysis of the development of tan δ at given frequency and temperature depends on whether the frequency is lower or higher than the eigenfrequency.…”

Frequency Diagnostics of Insulating System of Power Transformers

“…These goals will be achieved on the basis of complex analysis of the measured values using the measurements implied by the established and new diagnostic methods and techniques, simulated and experimental analysis and electronic equipment [26], [27].…”