Florence Sagnard

In situ characterization of building materials for propagation modeling: frequency and time responses

We propose original data processing methods for the dielectric characterization of frequency-dependent reflection coefficients of construction materials considering a very wide frequency band. Two types of approaches have been developed to obtain, from spectral measurements, estimates of the equivalent complex permittivity versus frequency or reconstruction of the impulse response. In particular, high-resolution (HR) algorithms based on the matrix pencil method have been used in an original way to identify wave multipath inside a sample. Both approaches have been used for the characterization of different types of building materials. A database of dielectric responses of materials is under construction in order to provide the deterministic propagation simulator with the characteristics of building materials.

In situ measurements of the complex permittivity of materials using reflection ellipsometry in the microwave band: experiments (Part II)

The aim of this series of two papers is to propose an original and low-cost tool dedicated to industrial applications and based on the reflection ellipsometry technique for in situ characterization of dielectric materials at microwave frequencies. In this first paper, different theoretical developments are presented that concern first a specific numerical method for calculating the complex permittivity of a single-layer sample from the measured parameters. Based on contour line charts, this method allows obtaining simultaneously the relative uncertainties on the real and imaginary parts of the complex permittivity. Secondly, for experimental comparisons with the classical Fresnel method, a numerical data processing method based on contour line charts has also been developed, which aims at the determination of the reflection coefficients in both parallel and perpendicular polarizations of the material.

Characterization and modeling of the MIMO propagation channel: an overview

This paper deals with several aspects relative to the multiple-input multiple-output (MIMO) propagation channel. Different approaches used to model the MIMO channel are first presented. Then, the different measurement techniques used in order to characterize the propagation channel are described. Measurement campaigns made in urban environments have been analyzed to obtain the relevant statistical parameters of the channel. These results make it possible to discuss the integration of MIMO techniques in practical wireless communication systems

Microwave measurements of the complex permittivity of construction materials using Fresnel reflection coefficients and reflection ellipsometry

We compare two free-space reflection methods dedicated to the determination of the complex permittivity of materials at microwave frequencies. Original numerical methods, based on constant value lines charts and nonlinear least squares optimization, have been developed for each approach. Results are given in the case of homogeneous, single layer building slabs of finite and infinite thicknesses.

Reflection ellipsometry for in-situ measurements of complex permittivity and thickness of a single-layer material at microwave frequencies : theory and experiments

For in-situ measurement of the complex permittivity of planar materials, we have developed a free-space experimental setup based on reflection ellipsometry and extended to microwave frequencies. Different angles of incidence were studied in the range [35 ; 50°]. Original numerical methods, derived from analytical relations based on contour line charts and least-square optimization, allow to highlight the influence of measurement uncertainties. Novel developments concerning the simultaneous determination of both complex permittivity and thickness of a single-layer sample are shown.

The microwave measurement of the conductivity of a small fiber with an open cavity

An original method of determining the electric conductivity of spheroidal inclusions of the order of a few microns is described. The measurements are made in an open cavity at microwave frequencies. In order to produce sufficient perturbations inside the cavity, a composite made up of dielectric and conductive media had to be designed. By combining the model of the dielectric properties of the composite with the model of the operating conditions of the open cavity, we show that it is possible to determine the conductivity of a unique inclusion by using an analytical expression. Measurements are presented which concern a type of carbon fiber with several micrometers diameter and a few millimeters length. The results obtained for different samples validate the method; they can be used as a reference in the microwave range.