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Purpose The aim of this paper is to provide the theoretical conceptualization of a bandpass (BP) negative group delay (NGD) microstrip circuit. The main objective is to provide a theorization of the particular geometry of the microstrip circuit with experimental validation of the NGD effect. Design/methodology/approach The methodology followed in this work is organized in three steps. A theoretical model is established of equivalent S-parameters model using Y-matrix analysis. The GD analysis is also presented by showing that the circuit presents a possibility to generate NGD function around certain frequencies. To validate the theoretical model, as proof-of-concept (POC), a microstrip prototype is designed, fabricated and tested. Findings This work clearly highlighted the modelled (analytical design model), simulated (ADS simulation tool) and measured results are in good correlation. Relying on the proposed theoretical, numerical and experimental models, the BP NGD behaviour is validated successfully with GD responses specified by the NGD centre frequency: it is observed around 2.35 GHz, with an NGD value of about −2 ns. Research limitations/implications It is to be noticed the proposed GD analysis requires limitations of the theoretical NGD model. It is depicted and validated through a POC demonstrating that the circuit presents a possibility to generate NGD function around certain frequencies (assuming constraints around usable frequency and bandwidth). Practical implications The NGD O-shape topology developed in this work could be exploited in the future in the microwave and radiofrequency context. Thus, it is expected to develop GD equalization technique for radiofrequency and microwave filters, GD compensation of oscillators, filters and communication systems, design of broadband switch-less bi-directional amplifiers, efficient enhancement of feedforward amplifiers, design method of frequency independent phase shifters with negligible delay, synthesis method of arbitrary-angle beamforming antennas. The BP NGD behavior may also be successfully used for the reduction of resonance effect for the electronic compatibility (EMC) of electronic devices. Social implications The non-conventional NGD O-circuit theoretical development and validation through experimental POC could be exploited by academic and industrial developers in the area of wireless communications including, but not restricted to, 5-generation communication systems. The use of the remarkable NGD effect is also useful for the mitigation of electromagnetic interferences between electronic devices and more and more complex electromagnetic environment (current development of Internet of Things[ IoT]). Originality/value The originality of this work relies on the new NGD design proposed in this work including the extraction of S-matrix parameters of the microstrip novel structure designed. The validation process based upon an experimental POC showed very interesting levels of NGD O-circuit (nanosecond-GD duration).

In this paper, authors propose a study on microwave gas sensors and the influence of critical key parameters such as the sensitive material and the circuit conception process. This work aims to determine the influence of these parameters on the quality of the final response of the microwave gas sensor. The fixed geometry of the sensor is a microstrip interdigital capacitor coated with a sensitive layer excited with two 50 Ω SMA ports. The sensitive material has been chosen in order to interact with the target gas: ammonia. Indeed, this gas interacts with phthalocyanine and metal oxides like hematite, TiO2. To explore the effect of the circuit manufacturing process, three series of samples are prepared. The first series of sensors is produced by classical UV photolithography (process) in the laboratory. The second series of sensors is produced by a subcontractor specialized in rf circuits. The third series is obtained by the experimental platform of the FEMTO-ST laboratory with EVG620 Automated Mask Alignment System Nanoimprint lithography in a clean room. To examine the reliability of this gas sensor at room temperature, it was exposed to different ammonia gas concentrations from 100 to 500 ppm in an argon flow to eliminate coadsorption phenomena. According to the recorded frequency responses, the reflection and transmission coefficients show a change of resonance amplitude due to electrical characteristic modification. This can be correlated to the presence of gaseous ammonia. The chemical nature of the sensitive material layer has a major influence at the excited frequency range. The process of conception influences the sensor sensitivity. The analysis of the results shows a strong correlation between the injected ammonia concentration and its frequency response. The influence of the critical key parameters cited is discussed here.

This work presents new developments in the microwave transduction and its application to gas sensors. Microwave measurements were extended to reflection/transmission coefficients through the use of a microstrip interdigital capacitor design. A sensitive layer composed of commercial TiO2 nanoparticles was deposited on the sensor surface, in order to detect the ammonia target gas. A complete analysis methodology is proposed. It allows to identify without ambiguity all the sensor frequencies of interest, as well as a full characterization of usual gas sensor parameters such as reproducibility, stability, response time, etc. Furthermore, it involves a new method of representation which significantly limits the amount of unexploited data collected during microwave measurements. The proposed sensor exhibits a strong correlation between response values and injected ammonia concentration between 100 and 500 ppm, with a good reversibility and stability of the measure.

Hematite α-Fe2O3 pseudocubes, rhombohedra, and spindlelike particles were prepared via a low cost and environmentally friendly microwave route. The structure and morphology were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Possible formation mechanisms of the particles are discussed. The design of the sensor includes a conductor-backed coplanar waveguide (CBCPW) on which a hematite sensitive layer is deposited. Hematite deposition was realized by doctor-blade on areas identified as the most responsive by near-field microwave microscopy (NFMM). A comparative microwave gas sensing study was conducted to evaluate the gas response of these morphologies upon ammonia exposure at room temperature. This paper represents a first look at the shape effect involved in microwave transduction, as each morphology presented a significant different behavior upon ammonia adsorption.

This work presents new microwave-based sensing measurements for the detection of NH 3 using metal-oxide sensitive layers, namely titanium dioxide nanoparticles (P25 Degussa). Several designs have been tested to assess the influence of the design on the microwave gas sensing response. The results for microstrip interdigital capacitor, rectangular spiral antenna and spiral resonator are presented over a wide range of frequencies (2-8GHz). All designs were firstly optimized by numerical simulation, then experimentally tested in presence of ammonia (from 100 to 500ppm in an argon flow).

We present here the development and the implementation of a technique of gas detection involving a microwave transduction method. The use of low-cost sensors based on microstrip or coplanar structures, adapted to the microwaves domain, allows the sensitive materials deposition under various forms. The purpose of the study is to assess the interest of microwave transduction for gas detection. The choice of the sensitive materials concerns materials widely used in the field of gas sensing: the metal oxides (SnO2 and TiO2) as well as molecular materials like cobalt phthalocyanine (CoPc). In this article we shall apply to explain the principles of the microwave transduction before approaching the conception of the sensors, the measurement protocols and the analysis obtained in various situations of measurement.

The gas sensing is an environmental topic representing a strong interest for this century. Whatever the purpose, industrial emissions control or indoor quality air supervision, the challenge remains to produce effective low costs detection systems adapted to the atmospheric conditions. This study focuses on the estimation of the microwaves transduction technique viability for the toluene detection. Sensors are based on zeolites powders, deposited on coplanar structures adapted to the microwave frequency range. We shall apply to explain the principles of the microwave transduction before approaching the conception of the sensors, the measurement protocol and the obtained results.

Monitoring burn depth in heart tissue during the ablation of atrial fibrillation will be a real challenge in coming years. Little is known about the influence of burning on the dielectric properties of tissue even though it will be of major interest in terms of characterization in medicine. In this study, the microwave characterization of biological tissues immersed in a liquid medium was carried out through an open-ended coaxial probe placed directly against each sample and a frequency range from 1 GHz to 6 GHz was used. The evolution of the relative variation of the reflection coefficient correlated with the depth of burned tissues. Bovine muscle and pig hearts were used for the experiments. The results were similar for both tissues. Monitoring the depth of burned tissue during ablation procedures could be a step forward to improve efficacy.

This work presents new elements of understanding for the microwave-based gas sensors behavior at room temperature. A TiO2-covered microstrip interdigital capacitor was submitted to various ethanol concentrations and showed a proportional response in the 1–10 GHz microwave range. For each concentration and right after ethanol injection, the sensor response presented a slight overshoot which is often found in gas sensors studies. Near ambient pressure photoemission experiments (NAP-XPS) were conducted to explore the physicochemical causes of this overshoot, and demonstrated the formation of an ethoxide during ethanol adsorption.

International audience; A new microwave sensor coupled with molecularly imprinted silica is described here for the first time in order to detect iprodione fungicide in hydroalcoholic medium. A Molecularly Imprinted Silica (MIS) and its control (Non-imprinted silica, NIS) were synthesized and characterized by infrared spectroscopy and scanning electron microscopy. The capacity of the MIS was determined by batch binding studies. MIS showed aggregates on micrometric scale and had a good capacity of sorption towards iprodione of 25 mg/g, whereas the NIS adsorption of iprodione was insignificant. MIS and NIS were deposited on the surface of the sensor by spin coating. The MIS and NIS microwave sensors were then tested in hydroalcoholic medium containing iprodione. The sensor response was stable over 10 min. The response of the MIS microwave senor was dependent on iprodione concentration whereas, the response of the NIS microwave sensor was not. The lowest detected iprodione concentration was 10−9 mol/L or 0.33 ng/L of iprodione.

In literature, many papers describe the applications of semiconductor as sensitive material in sensor field. The gas sensor using tin oxide requires a strictly controlled high operating temperature in order to detect both reducing and oxidizing gases. The semiconductor nanoparticles, with their high specific surface area, increase the gas sensing performance. The originality of this work is to valorize the nanoparticle of metal oxide like SnO2, TiO2 obtained by microwave thermohydrolysis synthesis, using a gas sensing microwave transduction. The present synthesis is to prepare metal oxide nanocrystalline powder with a high surface area by microwave-induced thermohydrolysis. We propose to study the influence of the metal oxide nanoparticle, as a sensitive layer, in gas sensing measurement. The pollutant is added into an argon flow (dynamic regim). This work highlights a specific sensor response to each ammonia concentration at room temperature. It shows a quasi-linear relationship between the set of points of the real part of the response and the ammonia concentration. The authors are currently working on these issues as well as the interaction mechanism between adsorbed gas molecules and metal oxide films.

This work presents the development of a microwave gas sensor at room temperature. The design of the sensor includes a coplanar grounded wave guide where is deposited a molecular gas sensing material. In this study, the sensitive material is a thin layer of cobalt phthalocyanine (CoPc), sensitive to ammonia and toluene. Submitted to an electromagnetic incident wave in the microwave range, the sensor response is a reflected wave. In the presence of pollutant, the reflected wave shape is specific to the species concentrations. The results interpretation is led at each frequency by the evaluation of the reflected coefficient, which traduces the ratio between the reflected wave over the incident wave. This study deals with the influence of molecular sensitive materials on the sensor response in the presence of ammonia (or toluene) in an argon flow. All the measurements are carried out at room temperature.

The adsorption of a target gas on a material induces a change in several physical characteristics, such as the dielectric constant, the work function or the conductivity. The use of different transducers sensitive to the variation of these parameters appears to be a relevant methodology worthy of investigation. In the field of sensors, molecular materials present interesting and potentially valuable features as sensing elements for real gas sensor applications. In this article, we review the different types of conductimetric transducers and also show how a molecular material-based microwave transducer can be used for gas sensing. Among conductimetric transducers, resistors have been historically the most commonly exploited way for the detection and quantification of gas pollutants. Herein, we focus on new transducers, either based on the well-known OFETs, or on transducers combining two molecular materials, namely the p–n junctions and the brand new molecular semiconductor–doped insulator (MSDI) heterojunctions. The sensitivity of the devices is demonstrated through the detection of ammonia and ozone in the range of ppm and ppb, respectively.

International audience; Since 2005, the microwave transduction coupled with a sensitive material is devoted to gas detection. In this work, we demonstrate the possibility to detect liquid pollutant (pesticide, fungicide) for food-processing industry. The principle is based on the interaction of the pollutant with a sensitive material within a microwave structure. The sensor is submitted to an electromagnetic excitation in wideband frequencies (GHz) and presents a quantitative response to liquid pollutant expositions at low concentration. The retained sensitive material is a molecularly imprinted polymer (MIP) specific to the pesticide targeted in a model wine. The coupling with this material selectivity and the in situ microwave transduction presents a threshold of detection in the ng/l range.

International audience; Based on the skin effect, our recent developments using scanning microwave microscopy lead to propose a non-destructive method to detect located buried defect in metal samples like stainless steel. A 3D tomography is possible by taking advantage of microwave measurement, using a vector network analyzer in bandwidth frequencies, and the nanometer resolution positioning capabilities with atomic force microscopy. At each used frequency, an incident electromagnetic wave is sent to the sample and the reflected wave gives information on a specific depth layer in the material. With diagnostic tools of nanotechnologies (SEM. AFM, etc.), different stainless steel samples (from Areva NP) presenting local buried defects are studied. The materials used in this study are conventional stainless steels like a 304 stainless steel which is the most versatile and widely used stainless steel. The results of the tomography applied on these samples are in accordance with the skin effect equation.

This study focuses on the determination of a protocol for the production of a hybrid material composed of a polymer and a macrocyclic complex, namely polystyrene and a tetra-tert-butyl-copper phthalocyanine (Cu[(tBu)4Pc]), in order to obtain a layer thickness of about 100 nm and a controlled porosity in a highly reproducible way. Several methods were implemented and their reproducibility was evaluated through elements of characterization such as optical microscopy, atomic force microscopy and scanning electron microscopy. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers

The conductivity of CoPc (cobalt phthalocyanine) and Co[(SO3Na)2,3Pc] was measured under a flow of two different gases (NH3 and O3), during exposure/recovery cycles. It appears that the relative responses are linearly related to the concentration, in the 20–200 ppb range for O3 and in the 20–200 ppm range for NH3. Observed during time, the sensing parameters allow a qualitative understanding of the kinetics. The comparative study of those products under both different gases gave interesting results for sensor applications. Whereas CoPc is sensitive to both gases, its sulfonated counterpart is only sensitive to NH3.

This work presents a novel approach in gas detection by an original method of microwave transduction. The design of the sensor includes a coplanar grounded wave guide with a gas sensing material to study its sensitivity to ammonia in argon flux. The sensing material can play the role of the substrate or can be deposited as a thin layer on a microstrip structure used in electronics. Submitted to an electromagnetic excitation in microwave energies, the sensor response in the presence of a gas results in a specific modification of the reflected wave (real and imaginary parts). The goals of this study include an examination of the form of the sensitive material and its influence on the response of the microwave gas sensor. Two cases are considered: bulk or thin layer. In bulk case, the material plays the role of the substrate of the microstrip structure. In the second case, a thin layer is deposited on the sensor. We showed how, in the presence of ammonia, the reflected wave is related to its concentration. The response to the material–gas interaction depends on the excitation frequency. The parameter used as the sensor response is the ratio of the reflected wave on the incident wave at each frequency. The study deals with the influence of molecular sensing materials (CoPc) on the response of the sensor in the presence of ammonia. All the measurement were carried out at room temperature.

A series of new molecular semiconductor-doped insulator (MSDI) heterojunctions as conductimetric transducers to NH3 sensing were fabricated based on a novel semiconducting molecular material, an amphiphilic tris(phthalocyaninato) rare earth triple-decker complex, Eu2[Pc(15C5)4]2[Pc(OC10H21)8], quasi-Langmuir–Shafer (QLS) film, as a top-layer, and vacuum-deposited and cast film of CuPc as well as copper tetra-tert-butyl phthalocyanine (CuTTBPc) QLS film as a sub-layer, named as MSDIs 1, 2 and 3, respectively. MSDIs 1–3 and respective sub-layers prepared from three different methods were characterized by X-ray diffraction, electronic absorption spectra and current–voltage (I–V) measurements. Depending on the sub-layer film-forming method used, α-phase CuPc film structure, β-phase CuPc crystallites and H-type aggregates of CuTTBPc have been obtained, respectively. An increasing sensitivity to NH3 at varied concentrations in the range of 15–800 ppm, follows the order MSDI 2

International audience; In the field of the transport, the increase of the security rule recommends to a periodic control of the structure to detect damage due to mechanical loadings. Now, current materials, used in the case of transport applications, are the composite materials. The methods, to control these materials or composite structures, need to be low cost, non-destructive, in-situ and swiftness as far as possible. The scientific literature reports many methods to control the damage in composite materials and structures. However the above requirements and the adaptation to composite materials reduce the number of methods that can be used. Currently, the adapted methods are based on infrared thermography, acoustical emission, EMIR (ElectroMagnetic InfraRed) or microwave imagery. We present an innovative non-destructive method of detecting damages in composite materials. The method is based on the observation and analysis of the modification in dielectric material resulting from damage. The originality of this method is that the diagnostic is obtained by using a microstrip resonator at microwave frequencies. The feasibility of the method is demonstrated by the detection of a fibre break into an unidirectional composite submitted to a flexural loading. The fibre break is the damage to detect. The perspective of this work is to develop a quantification and a localization of damages.

SPEIPMUB; Ancrée au cœur d’une région viticole historique, l’université de Bourgogne soutient de multiples projets de recherche viti-vinicoles et s’investit dans la formation des futurs professionnels du secteur. Elle est d’ailleurs la seule université française à disposer d’un domaine expérimental, situé à Marsannay-la-Côte. En activité depuis 1955, il apporte à la fois un support pédagogique aux étudiants de l’institut Jules Guyot, qui y effectuent différentes manipulations en conditions réelles, et répond à des demandes d’expérimentations émanant des viticulteurs et vignerons de la région. Dans ce cadre, il teste de nouveaux produits, matériaux ou micro-organismes susceptibles de mieux protéger les vignes et d’optimiser la vinification, notamment dans une optique de durabilité. Une préoccupation grandissante au sein de la filière viti-vinicole. Une action conjointe des chercheurs et des professionnels Permettre aux professionnels d’accéder à des méthodes et des outils favorables à une viticulture durable passe par une relation étroite entre professionnels du secteur et chercheurs. C’est dans ce but qu’a été créé, en juillet 2015, le pôle Bourgogne Vigne et Vin. Ce groupement d’intérêt public, porté à l'origine par l'université de Bourgogne, le conseil régional de Bourgogne et le Bureau Interprofessionnel des Vins de Bourgogne (BIVB) met en relation les besoins du monde professionnel et les recherches menées à l’uB. Et ce ne sont pas les initiatives qui manquent ! A l’université, une quinzaine de laboratoires sont impliqués dans la thématique Vigne et Vin à différentes échelles. Les recherches menées autour de la viticulture durable rassemblent des équipes issues de spécialités très variées, de la physico-chimie à la climatologie, en passant par les sciences humaines ou la santé.

Resume Nous presentons une methode originale de detection des gaz. Notre capteur se compose d'un materiau sensible introduit dans une structure coaxiale. Un champ electromagnetique (micro-ondes), emis a travers le capteur par un analyseur de reseaux vectoriel, sollicite le materiau sensible soumis a un gaz. La variation de la reponse du capteur observee est due aux variations des proprietes dielectriques du materiau sensible induite par l'adsorption du gaz. L'etude fait apparaitre que le capteur a base d'oxyde SrTiO3 est quantitatif et selectif pour trois gaz differents (eau, ethanol, toluene). Pour citer cet article : J. Jouhannaud et al., C. R. Physique 8 (2007).

The method of gas detection by a broadband microwave gas sensor is presented in this article. The principle of this method is to use a sensitive material as substrate of a transmission coaxial line. The sensor represents an open line with an extreme surface in contact with gas. The interaction with the gas and the surface induces a dielectric variation of the substrate. From experimental results, the interaction between the sensitive material and each tested gas present a specific frequency spectrum of the reflection coefficient at the input of the line. The proposed method has the advantage of a compact size, wide bandwidth, simple structure, and capable with all sensitive materials. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1739–1741, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25359

International audience; Contrarily to the widely-held opinion, the addition pattern issuing from the high temperature fluorination of single wall carbon nanotubes does not consist of a distribution of exo-addends on the outer surface of a tube. Instead, fluorotubes possess a varied bonding scheme consisting of graphite fluoride-like, fluorofullerene-like and internally 'addended' sections.

International audience; This work presents a new transduction mode for gas sensing using a passive microwave circuit at room temperature. The design of the sensor includes a microstrip line where is deposited a thin molecular layer of cobalt phthalocyanine (CoPc). The material is sensitive to ammonia and toluene. Submitted to an electromagnetic incident wave in the microwave range, the sensor response is a reflected wave. In the presence of ammonia, the reflected wave is specific to the species concentration. The sensor response is the reflected wave over the incident wave ratio at each frequency traduced by the reflected coefficient. The study deals with the influence of molecular sensitive materials on the sensor response in the presence of ammonia (or toluene) in an argon flow. (C) 2012 Elsevier Ltd .... Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.

International audience; On compare dans cette étude deux méthodes de détection d'endommagement dans les composites : une basée sur la technologie des structures propagatives électromagnétiques dans la gamme des micro-ondes et l'autre basée sur la mesure de champs thermiques dans la gamme des infrarouges. Toutes deux sont appliquées à la détection des ruptures de fibres et du délaminage dans des composites fibres/résine de type verre/époxy et carbone/époxy.

This paper reports the local detection of buried calibrated metal defects in metal samples by a new experimental technique, scanning microwave microscopy. This technique combines the electromagnetic measurement capabilities of a microwave vector network analyzer with the subnanometer-resolution capabilities of an atomic force microscope. The network analyzer authorizes the use of several frequencies in the range 1--6 GHz, allowing three-dimensional tomographical investigation, which is useful for the detection of bulk defects in metal materials.

National audience; On présente dans cette étude deux méthodes de détection d'endommagement dans les composites : une basée sur la technologie des structures propagatives électromagnétiques dans la gamme des micro-ondes et l'autre basée sur la mesure de champs thermiques dans la gamme des infrarouges. Toutes deux sont appliquées à la détection des ruptures de fibres et du délaminage dans des composites fibres/résine de type verre/époxy et carbone/époxy. La méthode par micro-onde est fondée sur les modifications des propriétés diélectriques d'un milieu lors d'un endommagement. Elle analyse les modifications de l'onde réfléchie d'une onde transmise dans le matériau vue comme une structure propagative et dont les propriétés se dégradent par la présence d'endommagement. La méthode par thermographie infrarouge repose sur les modifications des propriétés thermiques d'un milieu lors d'un endommagement. La propagation des ondes thermiques transmises dans le matériau est analysée. Lorsque ces ondes rencontrent un défaut, elles sont perturbées et la différence de température entre les différents milieux est alors mesurée. Des essais de flexion 3 points provoquant des endommagements (ruptures de fibre et délaminage) ont été menés. Pour conclure sur la pertinence de la détection, on corrèle les mesures électromagnétiques avec la perte de rupture de pente de la courbe force/flèche et avec la détection par thermographie infrarouge.

International audience

National audience; On présente dans cet article la détection de ruptures de fibre et du délaminage dans les composites unidirectionnels verre/époxy et carbone/époxy en utilisant des structures propagatives électromagnétiques dans la gamme des micro-ondes.

During their setting off, circuit breakers and vacuum switch devices are accompanied by an electric arc whose physical and chemical properties are governed by emissive current sites at the cathode surface called cathode spots. Assuming the continuity of the current on the cathode surfaces, the cathode spots contribute to supply the electrical arc by electron emission and material ejection. Thus they cause erosion on the contact electrodes inducing a dysfunction of contactors. The apparition of these cathode spots is due essentially to dust particles and surface irregularities at different scales. This experimental work represents a contribution to the understanding of the electrical arc behaviour by an investigation at submicronic scale on the influences of nanostructured carbon tips on the electric arc initiation and the cathode spots birth.

International audience

International audience

The aim of this paper is to improve our knowledge concerning the power balance at the electrode surfaces in the case of an electric arc of short duration with a small electrode gap burning in air at atmospheric pressure.With this aim in view, we propose a simple method using the experimental results obtained through the observation of the tracks left by the arc and a numerical simulation of the thermal phenomena occurring in the electrode during the arc heating.This method, based on the analysis of the compatibility between experimental results and modelling results, allows us to assess a zone of possible values for the main parameters of the arc root (power and surface power density brought by the arc to the electrodes). A simple usual volt equivalent approach of the power balance is proposed. Calculations and experiments have been conducted for several copper anodes and cathodes. The values for the volt equivalent at the anode are found in the range 9?12.6?V, for the cathode 5.4?9?V. The values for the surface power density are found to be near 6.5 ? 109?W?m?2 at the cathode and 6 ? 109?W?m?2 for the anode.

6-8 juin 2007; National audience

International audience

The interaction between electrical arc and cathode represents a crucial problem in the conception of arc jet thrusters, circuit breakers, and plasma torch or arc heaters. At the cathode surface, the current and energy transfers are controlled by the current emitting site (cathodic spot). Theories and experimental observations, at macroscopic and mesoscopic scale, deal with the erosion of the cathodic surface. Under micrometer range, theories refer to the arc root to describe the erosion of the surface. The works presented here propose an original method to evaluate the arc-cathode interaction at micrometric scale. A nanotechnology is used in order to control the roughness of the electrode surface and to deposit the microscopic tip. After discharge, the influence of the tip in the cathodic erosion process is studied. Scanning Electron Microscopy images show that a good reproducibility of the erosion zone is obtained by using this experimental method.

Resume On presente dans cet article une methode non destructive novatrice de detection d'endommagement dans les materiaux composites. Elle est fondee sur l'observation et l'analyse des modifications des proprietes dielectriques d'un milieu dues a un endommagement. Plus precisement, son originalite reside dans le fait que le diagnostic cherche est obtenu via un circuit resonant microbande soumis a un champ electromagnetique dans la gamme des micro-ondes. Dans cette Note, on montre la faisabilite de la methode en examinant sa capacite a detecter les ruptures de fibres au sein d'une eprouvette en composite unidirectionnel soumise a un effort de flexion. Pour citer cet article : J. Rossignol, A. Thionnet, C. R. Mecanique 334 (2006).

In this paper, we present a numerical simulation of three metal cathode (silver, copper and nickel) submitted to a constant flux power flux density ranging between and . The goal is to compare the interface evolution (vaporization and liquefaction rate, appearance time of liquid and vapour, energetic repartition) to predict the behaviour of the cathodes during an electric arc.

This paper presents a simple model of the fragment in the cathode electrical arc root taking into account the physical phenomena occuring on the cathode surface and the sheath. The goal is the obtainment of characteristics values of the heat flux, the electrons, and atoms density in the sheath. Computation is carried out on a one-dimensional model with a coupling between the equation obtained in the sheath and an enthalpy model of the cathode to describe the temperature evolution. In the modelling, we introduce a friction zone above the sheath edge to characterize the heavy particle interactions. Numerical simulation shows that the ionic friction phenomenon deriving from ion–atom collision regulates the heat flux lightening the surface, and the crucial necessity to obtain a good evaluation of the cross section of the charge exchange.

A numerical simulation of the ablation problem for the cathode spot that is based on the enthalpy formulation is presented and solved with a finite-element method using the Euler explicit scheme. Vaporization latent heat and ablation phenomena constitute the main difficulties of the cathodic surface erosion. We deduce characteristic information related to the cathode spot such as the energy repartition in three phases and the ablation length for different energy fluxes.

We outline the development of a gas sensor using microwave technology (0.3 MHz to 3 GHz). The sensor is a coaxial structure into which is introduced a sensitive material. An electromagnetic field (microwave), sent out through the sensor by a vectorial network analyzer, solicits the sensitive material exposed to a gas. The observed variation in the sensor response is due to the variation in the adsorption of this gas. SrTiO3, demonstrated to be the highly sensitive to water vapour, is exposed to differents gases (saturated vapour of water, ethanol and toluene). The response of the sensor is quantitative and typical for each gas. This method of measurement leads to the development of an alternative to the current gas sensor.