Alain Celzard

Electromagnetic shielding efficiency in Ka-band: carbon foam versus epoxy/carbon nanotube composites

Abstract. The wide application of microwaves stimulates searching for new materials with high electrical conductivity and electromagnetic (EM) interference shielding effectiveness (SE). We conducted a comparative study of EM SE in Ka-band demonstrated by ultra-light micro-structural porous carbon solids (carbon foams) of different bulk densities, 0.042 to 0.150u2009u2009g/cm3, and conventional flexible epoxy resin filled with carbon nanotubes (CNTs) in small concentrations, 1.5 wt.%. Microwave probing of carbon foams showed that the transmission through a 2 mm-thick layer strongly decreases with decreasing the pore size up to the level of 0.6%, due to a rise of reflectance ability. At the same time, 1 mm thick epoxy/CNT composites showed EM attenuation on the level of only 66% to 37%. Calculating the high-frequency axial CNTs’ polarizability on the basis of the idea of using CNT as transmission lines, we devised a strategy to improve the EM SE of CNT-based composites: because of the high EM screening of inner shells of multi-walled CNTs in the GHz range, it is effective to use either single-walled CNT or multi-walled CNTs with a relatively small number of walls (up to 15, i.e., those taking part in the EM interaction, if the CNT length is 20 μm).

Measuring and understanding radon adsorption in microporous materials

The background from the radon decay chain is the strongest constraint for many experiments working at low energy and very low counting rate. A facility for studying the optimum radon capture by very selective porous materials was developed at CPPM in the context of the SuperNEM O project. In collaboration with Institut Jean Lamour, studies were carried out for better understanding radon adsorption in carbon adsorbents.

6.4.4 Development of a gas micro-preconcentrator for the analysis of explosive traces: study and characterization of various adsorbing materials

Actually, the rapid detection of explosive agents in air has become a real need. In this context, the aim of this research work is to develop a micro-fluidic platform integrated on a silicon substrate for the monitoring of explosive traces in air. This platform is composed by a micro-preconcentrator followed by a chromatographic micro-column and a tin oxide- based sensor. The target molecule studied is the orthonitrotoluene (ONT) known as a simili vapor of trinitrotoluene (TNT). The present study is focused on the gas micro-preconcentrator performances, and in particular on the choice of the adsorbent. Various adsorbents such as activated carbons, polymer and hydrophobic zeolite were then studied in order to identify the best material to be used in the gas preconcentrator.