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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.

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.

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.

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; 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.

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

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

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.

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.

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.

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.