L. Jorat

Improvement of the transmission/reflection method for dielectric and magnetic measurements on liquids between 0.1 and 20 GHz

We propose an appropriate calculation method, giving both the complex permittivity epsilon * and permeability mu * of a liquid sample, from transmission/reflection measurements obtained from a network analyser working on a coaxial line between 0.1 and 20 GHz. A 20 mm long specific coaxial cell has been constructed using two polytetrafluoroethylene joints to ensure air tightness. Its small length allows rejection towards the upper frequencies of the measurement anomalies given by the Nicolson-Ross equations. Positions and thickness of the joints are taken into account by the calculus. The whole system has been tested with the empty cell and then on several alcohols and ferrofluids. The results on alcohols are in excellent agreement with all previous results; measurement on one of the magnetic fluids (Fe2MnO4 in CCl4) has shown a Neel relaxation and also a gyromagnetic resonance.

Gravitational electrical generator on magnetic fluid cushion

The paper describes the possibility to capture the energy of the vertical movement of the ocean waves, using a gravitational electrical generator on magnetic fluid cushion. This is constructed from a permanent magnet in a magnetic fluid shell, which, under the ocean waves action, is moving by translation inside a hermetically sealed tube.

Influence of the magnetic permeability of materials used for the construction of inductive transducers with magnetic fluid

Abstract The paper presents the influence of relative magnetic permeability of the magnetic fluid ( μ r L ) on the sensitivity of the inductive transducers and the influence of relative magnetic permeability of the magnetic shell ( μ r E ) on its performances.

Magneto dielectric response of a ferrofluid at low temperature

Abstract This paper presents a dielectric study of a ferrofluid Fe2CoO4 in dibutyl phthalate at different concentrations from room temperature down to low temperature less than -100°C. With results from our spectrometer we discuss, for a large interval of temperature, the homogeneity of the ferrofluid solutions when a continuous magnetic field is applied perpendicularly to the electric field.

Aspects concerning the dimensioning of the inductive transducers with magnetic fluids

Abstract Using numerical simulation methods, the paper presents the influence of some geometrical dimensions (radius of the coil, radius and thickness of magnetic shell) on the performances of the inductive transducers with magnetic fluids. The conclusions of the paper allow the calculation of some geometrical tolerances of the transducer so that the assembly will be placed in a desired precision class.

Magneto dielectric behavior of the magnetic fluid manganese ferrite in carbon tetrachloride

Abstract This work concerns the research on ferrofluids or magnetic liquids. Fast changes of their dielectric properties, which may be induced by phase transitions of the carrier liquid or by aggregates or multi-layers forming, require the whole automation of the measurement process. Therefore, we have used a high impedance programmable adaptor working on shunt mode in the frequency range 1 mHz-10 kHz. It allowed us to characterize, between +50° C and −200° C , an ionic ferrofluid made from nanometric particles of manganese ferrite (Fe 2 MnO 4 ) diluted at different concentrations in carbon tetrachloride (CC1 4 ) used as carrier liquid. We have pointed out the different phases of pure CCI 4 (liquid, plastic and solid). In our experimental conditions, we have shown the lack of the ferrofluid stability at low temperature and high concentration. In addition, a magneto dielectric anisotropy is observed when a continuous magnetic field (parallel or perpendicular to the electric field) is applied.

Dielectric study of a ferrofluid Fe2CoO4 in dibutyl phthalate or diethylene glycol in the frequency range 1 mHz–10 MHz

Abstract We present a dielectric study on ferrofluid solutions of Fe 2 CoO 4 in diethylene glycol or dibutyl phthalate, from 50 mHz to 10 MHz, in the temperature range -160–+40°C. When a transversal magnetic field is applied, a magnetodielectric anisotropy is in evidence. Above a concentration limit the colloidal suspensions do not remain well dispersed at low temperature. Moreover it seems that the melting point of a solution could be affected.

A magneto-optical method for viscosimetric measurements

We present a magneto-optical method using Browns relaxation in ferrofluids. This method permits one to make some viscosimetric measurements by putting a drop of miscible ferrofluid into a test liquid, glycerol or diethylene glycol (DEG). To test this method we have compared our results obtained for glycerol with those obtained from a more conventional method and we observed good agreement. After this validation, we were able to study the viscosity of DEG between -20 and +90 °C by using our magneto-optical method. The comparison of these results with those obtained in standard ways (in the temperature range from -10 to +20 °C) revealed very slight deviations.

Gyromagnetic resonance in ferrofluids made from manganese ferrite or magnetite particles: influence of a constant axial magnetic field

Abstract We have measured the susceptibility of two ferrofluids in the frequency range 0.1–20 GHz. We confine the liquid under test in a coaxial line cell and we use the reflection/transmission method to obtain χ ∗ . If we add a constant axial magnetic field to the microwave field we evidence an increase of the gyromagnetic resonance phenomenon appearing as a consequence of the artificial increase of anisotropy.

Shear viscosity and dielectric relaxanon time of dibutyl phthalate down to glass transition temperature.

Abstract We studied the shear viscosity and the main dielectric relaxation time of dibutyl phthalate from 97°C down to −96°C (near its glass transition temperature Tg). A visco penetrometer and a dielectric spectrometer built in our laboratories allowed us to obtain experimental data in the ranges 10-109 Pa.s for viscosity and 1 mHz–2 MHz for dielectric relaxation time. All these data and those of different authors give viscosity and dielectric relaxation time versus temperature on twelve decades; they are well fitted by the Cohen and Grest relation. These fits obtained on a large temperature range show that there is a strong correlation between viscosity and dielectric relaxation time. Furthermore it appears that the dielectric relaxation time distribution is broadening in the vicinity of Tg.