On the measurement of the complex susceptibility and permittivity of magnetic fluids by means of two different measurement techniques

Two different transmission line techniques have been used to determine both? the complex magnetic susceptibility, chi(omega) = chi'(omega) - i chi "(omega), and complex permittivity epsilon(omega) = epsilon'(omega) - i epsilon "(omega), over the frequency range 100 MHz to 6 GHz, of two ferrofluid samples of ferrite particles in a hydrocarbon carrier. The susceptibility profiles are found to be remarkably similar with the fluids displaying a resonance effect indicated by the transition of the chi'(omega) components from a positive to a negative value. Both techniques give a resonant frequency, f(res), in the region of 1.7 GHz and a corresponding loss-peak frequency, f(max), of approximately 1.1 GHz. The corresponding epsilon'(omega) and epsilon "(omega) components are also found to be similar and approximately constant over the measured frequency range. In one case the onset of dimensional resonance is displayed. Automated measurements are obtained by the means of two different Hewlett Packard Network Analysers which operate over the frequency range concerned. (C) 1999 Elsevier Science B.V. All rights reserved.