G. Noyel

Influence of particle size distribution on the initial susceptibility of magnetic fluids in the Brown relaxation range

Abstract We present experimental results on magnetic liquids characterised by a size distribution of particles. The initial complex susceptibility has been studied in the Brown relaxation range using a polarimetric method. The position and the shape of the relaxation peak allow to determine apparent values of hydrodynamic mean diameter and its standard deviation. Theoretical calculations were made from the Debye model including the size distribution of particles and the experimental study shows its influence and the necessity to take it into account for a better results exploitation. In these conditions, the Debye model used gives excellent results in accordance with the experimental points.

Investigation of an inclination sensor using magnetic fluid for angle measurement up to 90 degrees

This paper describes an inclination transducer using magnetic fluid with a range of +or-90 degrees. This is a very simple device consisting of two identical coils wound around a torus, which is half-filled with a magnetic fluid.

A new broad-band method for magnetic thin-film characterization in the microwave range

A new method for magnetic thin-film characterization is presented. New microwave electronic technology challenges require integration of many passive components on chips. Among them, isolators and circulators are nonreciprocal passive devices which contain magnetic materials. The use of thin magnetic films in place of bulk materials seems to be a solution to integrate these components on chips. Hence, it is important to know the magnetic properties of thin films in the microwave range. An isolator is obtained by locating the thin magnetic film in a coplanar line; however, it is often difficult to measure the constitutive parameters of the film before the end of its production. The method described allows in situ measurement of two parameters of the film permeability tensor.

Electromagnetic study of a ferrite coplanar isolator suitable for integration

The transmission coefficient of a nonreciprocal coplanar waveguide (CPW) using ferrite rods is studied. A new approximate method is proposed to evaluate the propagation constant of such a perturbed waveguide, which is based on the use of numerical data referring to the nonperturbed waveguide. We have estimated the value of the nonreciprocity effect and settled the condition of the validity of our theory. Some experimental data of a CPW with ferrite inclusions are also presented.

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.

Longitudinal magneto-optical study of Brown relaxation in ferrofluids:: dynamic and transient methods. Application

We present a comparison between two magneto-optical methods (dynamic and transient) used to measure Browns relaxation time in a Faradays configuration. Results obtained from these two methods for several ferrofluids are in good agreement. An application to the estimation of the viscosity of a liquid by putting a drop of miscible ferrofluid in it is presented.

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.

Comparison between a magneto-optical method and Fannin's technique for the measurement of Brown's relaxation frequency of ferrofluids

A magneto-optical method, conceived in our laboratory to measure Browns relaxation frequency of ferrofluids, is compared with Fannins technique based on impedance measurements (slit toroid). We have developed a complete theory and an experimental setup of the first method and have briefly described the second one. We present a study of Browns relaxation of cobalt ferrite Fe/sub 2/CoO/sub 4/ in different carrier liquids (glycerol, diethylene glycol, dibutyl phthalate, and water). The two methods show very close results, proving the high sensitivity of both. The relation between the viscosity /spl eta/ and Browns relaxation frequency f/sub B/ has been verified. Moreover the analysis of relaxation and viscosity versus temperature has enabled us to estimate the hydrodynamic diameter of particles.

Dielectric properties of supercooled binary mixtures of water and N,N-dimethylacetamide: Determination and modeling in terms of ideal associated solution

Abstract Dielectric relaxation times and static permittivity of the aqueous mixtures of N,N-dimethylacetamide (CH 3 ) 2 NCOCH 3 (DMAA) are investigated in supercooled conditions down to 150 K. The evolution of these properties as a function of the composition can be well described using a model of ideal associated solution involving a trihydrate and a monohydrate for DMAA.

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.