Search

International audience

International audience; In this paper, a contactless microwave transition is described and characterized. In our "ElectroMagnetic Drive" (EMDrive) measuring setup, it will be dedicated to transmit high Radio Frequency (RF) powers without any mechanical effort. It exhibits very good matching and transmission performances. It is found to transmit 100 W microwave power range at 2.45 GHz without any visible mechanical effect on a 10 mg precision balance, contrary to a previous coaxial cable. This device appears useful to every EMDrive setup and can be easily implemented.

International audience; The demonstration of enhanced spatial control of nanosecond microwave plasmas generated by the time reversal plasma source is presented in this paper. This new microwave plasma source relies on the spatio-temporal control of the electric field inside an all-metal plasma reactor by modifying the waveform of a high power microwave signal. More specifically, it originally used the spatio-temporal focusing capabilities of the time reversal method to focus a high electric field in a small location. However, a parasitic microwave breakdown can still occur at sharp corners or wedges inside the cavity due to the local enhancement of the residual electric field during time reversal focusing. Thus, it is proposed to use the linear combination of configuration field method to improve field control inside the reactor. Its transient electric field shaping capabilities turn out to be a good candidate for the development of a low pressure microwave "plasma brush".

Touroult, Julien, Pascal, Olivier, Barnier, Florian, Pollet, Marc (2021): The "Our Planet Reviewed" Mitaraka 2015 expedition: a full account of its research outputs after six years and recommendations for future surveys. Zoosystema 43 (32): 811-833, DOI: 10.5252/zoosystema2021v43a32

Recently, space-time plasma-steering source has been proposed as an innovative microwave plasma source to meet the challenge of controlling plasmas in overmoded cavities. This concept has been successfully demonstrated experimentally, allowing the space-time control of nanosecond microwave plasmas on initiators. This paper gives insights into the path that shall be taken to reach full space-time control of plasmas in overmoded cavities. To that end, a key criterion, namely the “plasma-steering criterion,” is introduced and verified with a numerical model. This criterion must be respected for an accurate space-time control of plasmas in overmoded cavities. The usefulness of the plasma density (depending on its value with respect to the critical plasma density) on the plasma-control capabilities is also highlighted.

We present an experimental realization of virtual critical coupling in microwave, i.e., virtual perfect absorption of an incident wave by a resonant cavity, through transient time modulation of its amplitude. The design of a waveform matched to the ignition process of a plasma, characterized in a simplified way by two operating modes over time (plasma off/plasma on), motivates this first step in practical realization of virtual critical coupling in microwaves. We propose a time domain method for extracting necessary parameters for realization of virtual critical coupling, especially the complex frequency called zero of the S-matrix. To this end, we start from the experimental characterization of a single-mode and single-access microwave cavity including metal protrusions for future plasma ignition. Then, the method relies on the analysis of harmonic response of the overcoupled cavity during three time periods: the transient under excitation, the steady state under excitation, and the transient after excitation cutoff. Finally, an experimental demonstration of virtual critical coupling is performed.

International audience; The high demand for an alternative ignition system for air breathing engines has motivated lot of innovative studies in the last decades. The present paper discusses the results of kerosene droplet ignition with a waveguide based resonant cavity. We show that with this kind of setup, the needed power (injected in the cavity) required to ignite kerosene droplets (with diameter 130 µm) is as low as 4.5 W, depending on the gap size.

International audience; The aim of this paper is to present the promising outlooks that lies ahead for the innovative plasma source we introduced recently. The idea of this source is to dynamically control the plasma location by changing the waveform of the transmitted signal to an overmoded cavity. It is then the behavior of the waves inside the cavity that dynamically control the plasma location, hence the name of Space-Time Plasma Steering Source. Since its introduction in 2019, we have produced three main papers, aimed at different scientific communities: applied physics, physics of plasma, signal processing and mathematical and numerical methods. An overview of these works is first presented in this paper. Then, the promising outlooks for this unusual plasma source are identified and classified into four domains, among which the most important and essential one being the unhooking of the plasmas from the initiators in order to control their location anywhere in the cavity. Several solutions for this “unhooking issue” are then proposed, the most straightforward one being the use of non-intrusive probes.

International audience; A harmonic oscillator model is proposed to study the intensification of microwave radiation of an electrically small antenna when surrounded by a subwavelength plasma discharge. This model describes the oscillations of free electrons in a spherical plasma when it is excited by an incident electromagnetic wave. It shows that at resonance, these charge oscillations lead to a significant volume current, and thus to an enhancement of the radiation. Depending on the electron density of the plasma, this radiation enhancement may occur in the microwave range. The proposed model is compared with the Mie scattering theory with perfect agreement when the electrical size ka of the spherical plasma remains smaller than 0.1. Despite its apparent simplicity, this model unveils the main mechanism that stands behind the intensification of microwave radiation by a subwavelength plasma discharge.

In the present paper, a detailed investigation of the spatio-temporal dynamics of the recently developed time reversal microwave plasma source is presented. This novel source allows to ignite a plasma at a desired location in a reverberant cavity by focusing the electromagnetic energy in time and space. An important feature is the possibility to control the plasma position only by changing the input microwave waveform. The source is operated in a repetitive pulsed mode with very low duty cycle (typically 5 × 10−2%). Nanosecond pulses have rise time lower than 1 ns. The generated plasmas have typical sizes in the millimeter range and are observed using imaging for dozens of nanoseconds. The plasma behavior is investigated for different pressures and repetition frequencies. A strong dependence is observed between each discharge pulse suggesting the existence of an important memory effect. The latter is probably due to argon metastable atoms and/or residual charges remaining in the post-discharge and allowing the next breakdown to occur at a moderate electric field.

International audience; This paper proposes an improved algorithm, based upon an explicit finite difference scheme, in order to simulate the plasma breakdown induced by a monochromatic High Power Micro-Wave (HPM). The 3D coupled Maxwell–plasma equations are to be solved. We want to study with this model the geometry of the discharge and plasma formation at high pressure which may contribute to shield microwave sensors or circuits. Generally, the simulation of this kind of problem is very time-consuming, but by using the fact that the plasma evolution in time is slow relatively to the monochromatic source period, we can drastically reduce the simulation time. By considering this assumption, we describe in the paper a process which allows to obtain this important reduction. Finally, an example where we show the gain obtained in terms of computation time with our process is given to validate and illustrate the global work.

A preliminary study of the design of an electrically small plasma-based resonator using a localized surface plasmon resonance (LSPR) above 1 GHz is presented. Such a resonator is intended to be used to develop an electrically small antenna with frequency agility. This resonator consists of a plasma discharge confined in a hemispherical glass shell 3 cm in diameter on a ground plane. From 1 to 1.5 GHz, the plasma electron density required to achieve the LSPR must be between 0. $5\times 10^{11}$ and $1.4\times 10^{11}\mathrm{c}\mathrm{m}^{-3}$. Plasma losses are taken into account in this study and provide information on the required gas pressure. Typically for neon gas, the working pressure must be around 50 mTorr. A practical implementation using a miniature inductively coupled plasma (mICP) source is finally discussed.

International audience; This paper details the work of the LAPLACE Electromagnetism Research Group to develop an original measuring setup dedicated to the detection of an EMDrive like force. Recent peer-reviewed experimental results [1, 2] were obtained using similar setups based on a torsion pendulum combined with an optical sensor. These very accurate measurement setups are appropriate for measuring such an extremely weak force. They also appear costly, which may discourage other research teams from working on this topic. Our main goal is then to provide an alternative configuration, based on a commercial precision balance, in order to build a measuring setup more affordable, handy, and accurate enough to measure an EMDrive like force. Our experimental system is capable of feeding a truncated cone shaped 2.45 GHz resonant cavity with power up to 140 W. To calibrate the EMDrive force and avoid false positive thrusts, an original setup has been proposed and evaluated. It allows us to really consider that the parasitic effects do not alter the hypothetical force measurement by the use of force direction switching during the measurement.

Plasma-based microwave power limitation in a suspended microstrip transmission line integrating a micro hollow cathode discharge (MHCD) in its centre is experimentally and numerically studied. Transient and steady state microwave power measurements exhibit a limitation threshold of 28 dBm and time responses of 25 microseconds. Intensified charge-coupled device imaging shows that microwave breakdown occurs at the top of the MHCD. The plasma then extends towards the microwave source within the suspended microstrip transmission line. Besides, a self-consistent model is proposed to simulate the non-linear interaction between microwave and plasma. It gives numerical results in agreement with the measurements, and show that the plasma expansion during the transient response is related to a shift between the ionization source term and the electron density maximum. The propagation speed, under the tested conditions, depends mainly on the stepwise ionization from the excited states.

An original electrically small antenna concept relying on plasma discharges is presented in this paper. It consists of a small coaxial probe placed above a ground plane and surrounded by a hemispherical inductively coupled plasma discharge. This plasma discharge behaves as a subwavelength epsilon-negative resonator exhibiting a localized surface plasmon resonance at microwave frequencies with significant radiation efficiency. Measurements show that the plasma allows impedance matching of the radiating element and frequency agility from 310 to 390 MHz by controlling the power delivered to the discharge. Meanwhile, significant radiation enhancement up to 20 dB at 300 MHz is measured. The existence of the localized surface plasmon resonance is finally confirmed by a Mie analysis considering the measured plasma characteristics.

We report the experimental demonstration of plasma generation by time-reversal focusing. After a learning phase, the amplified time reversed signal built at a central frequency of 2.45 GHz injected in a low loss metallic cavity allows us to ignite and maintain a localized centimeter-sized plasma in argon at 133 Pa. The plasma spatial position is totally controlled by the signal waveform.

International audience; Motivated by the high demand for an alternative, more reliable, high energy ignition source to facilitate the re-ignition of lean-burn combustion chambers which are necessary to reduce pollutant emissions, a new set-up has been designed to study plasma/microwave sources. The use of a waveguide-based resonant cavity leads to very low power plasma ignition. An example in this paper shows that a plasma at atmospheric pressure can be maintained with less than 2 W input power. Such a performance is possible using the large variety of possible adjustments (resonance frequency, different kind of initiators, etc.) that this versatile set-up offers. To illustrate the wide range of possible studies, another example is given and discussed : minimum ignition energy for an ethanol droplet stream with aluminum and stainless steel initiators. The results show that the initiator material and its surface quality have an influence on the minimum ignition energy, especially for large gaps. Depending on the gap size we can get down to under 10 W entering the cavity to ignite the droplet stream.

During the “Our Planet Reviewed” French Guiana 2014-2015 expedition, Diptera were collected in seven habitat types over an approximately 1 km2 area in the Mitaraka Mountains of southwestern French Guiana. Sixteen collecting methods were used, seven of which yielded multiple samples containing Dolichopodidae. The survey produced a total of 4918 specimens of Dolichopodidae, belonging to 244 morphospecies, 31 genera including four new ones, and 10 recognized subfamilies. This is the highest dolichopodid species richness thus far recorded from a single location anywhere in the world. Three taxa could be identified to species level and all represent first records for French Guiana. Paraclius Loew, 1864, Chrysotus Meigen, 1824 and Medetera Fischer von Waldheim, 1819 were the most speciose genera. Paraclius represented by 50 species, exhibited an unprecedented species richness, mainly in the palm swamps. The three most productive methods in terms of numbers of specimens collected (68% of all specimens obtained using the three methods combined), SLAM traps, sweep nets, and a 6 m long Malaise trap, each yielded between 78 and 90 species, with approximately half of the species from each trap type unique to that method. Both blue, white or yellow pan traps, on the contrary, captured less than 20 species, and overall yellow traps were clearly the least efficient. Pan trap yields, however, were severely affected by repeated heavy rainfall. The highest species richness was recorded around the drop zone and in the base camp, on river banks and in river bank forests, with 40 to 60% of species unique to one of these habitat types. Forty-five species were collected on ‘savanes roches’, and 14 species on inselbergs, with four species shared by both types of rocky outcrops and uniquely found on them.

This article presents the experimental work performed as part of the use of the non linear plasma-wave interactions in planar circuits to design microwave power limiters. A first non-resonant plasma-based microwave power limiter composed of a pre-ionized plasma discharge integrated into a 50 Ohms microstrip line has been experimentally characterized with steady-state and transient measurements. These results have been then confronted at each step to a resonant one using the same plasma discharge. This study highlights the effect of the resonance on the non linear plasma-wave interactions and its consequences on the behaviour and the performances of a plasma-based microwave power limiter.

This article introduces the biodiversity survey “Our Planet Reviewed” in the south of French Guiana organized in February–March and August 2015. It has enabled more than 50 scientists to inventory the following groups: Actinopterygii, Amphibia, Annelida, Arachnida, Insecta, Mollusca and Squamata, with a particular effort on diverse and little-known orders, such as Coleoptera, Diptera, Hemiptera and Hymenoptera. The forested area under investigation presents a mosaic of hills and inselbergs, with a wide variety of ecosystems. The main objectives were to discover new species for science, report first records for French Guiana, and establish a baseline inventory for biogeographic studies. The organisation of the field trip and post-field phase are supported by coordinators of major taxonomic groups. Authorisations and associated commitments, including Access and Benefit Sharing (ABS) are specified. The sampling effort, in terms of number and diversity of methods, is certainly the largest ever made in French Guiana over a short period of time. Thirteen different trap types were used including four types of interception traps and nine types of attraction-based traps. Active research methods (13 techniques) and extraction from the substrate (five techniques, including Winkler sieves, emergence from dead wood, etc.) completed the sampling array. The sample processing procedure describes the difference between active collecting and the longer and more complex process of processing massive samples of traps such as window pane flight intercept traps, Malaise traps, colored pan traps and automatic light traps. After a sorting phase that lasted less than a year for most groups, a network of 165 taxonomic experts was mobilized by the coordinators to study the sorted specimens. The data are stored and managed in an observations database and in the database of the collections of the Museum national d'Histoire naturelle (Paris). Data are widely disseminated, notably in France via the Inventaire national du Patrimoine naturel (INPN) and internationally by the Global Biodiversity Information Facility (GBIF). This introductory article will be supplemented by a second paper, which will analyse research results three years after the survey and assess the effectiveness of the expedition in advancing taxonomic knowledge.

BPID5187151.45 GHz. Once characterized, it exhibits 100 MHz data rate modulation capability. The encoded orbital quantum (or index modulation) only uses three states (for Q-PSK) and four array elements. The received signals also suffer from conventional OAM line of sight links drawbacks, especially OAM “cross-talk” which comes from OAM states non ideal orthogonality in the realized setup.

This letter presents an analytical model to study the electrostatic scattering of subwavelength radially inhomogeneous spheres whose permittivity can be expressed as a general polynomial function of the radial distance r. This technique is particularly well suited to characterize the electrostatic resonance, also known as surface plasmon resonance, of radially inhomogeneous negative permittivity spheres.

Static and dynamic control of the limiting threshold in a very low-loss plasma-based microstrip power limiter is investigated in order to prevent receivers from being threatened by high-power microwave (HPM). An analytic model of the microstrip circuit is proposed to derive the influence of its design on the limiting threshold of the microwave power limiter. Experimental results are in good agreement with those expected. Finally, an original approach to allow discrete limiting threshold tunability is presented and validated experimentally.

In this paper, we suggest the use of a cold plasma as tunable material inside a microstrip resonant cavity. Plasma dielectric constant can indeed be moved to values below 1 to tune its resonant frequency. DC plasma analysis were conducted and integrated into classic electromagnetic solvers to investigate tuning abilities. Numerical simulations are consistent with experimental results and make this original tuning techniques viable for high power applications.

An original and integrated solution to provide frequency agility to microstrip circuits using plasma is proposed. A volume DC plasma discharge is implemented inside a microstrip circular resonator to change its dielectric permittivity in order to tune its frequency. Plasma relative permittivity indeed exhibits positive values lower than 1. Experimental measurements confirm the tuning abilities and performances of such a solution for different pressures and types of gas.

The use of microplasma discharges as power-induced limiter elements in microstrip devices is proposed to protect receivers against high-power microwave threats. A microstrip bandpass filter integrating such a microplasma-based active microwave power limiter has been designed and measured. Power limitation is observed when the input power exceeds 19 dBm with a leakage power of 14 dBm. Due to the gaseous properties of the active medium, the proposed structure exhibits a very low additional insertion loss of 0.06 dB.

The use of low pressure non-equilibrium plasma as epsilon negative medium for a zero-order spherical antenna resonator is considered. Static behaviour of the resonance for a non-homogeneous plasma is investigated under quasi-static assumption and discrete radial description of the plasma. Analytical and numerical results are consistent and show that the implementation of such a plasma-based antenna is possible.

At radio frequencies, previous works by Mohammadi et al. derived from quantum mechanics state that the spin angular momentum (SAM), orbital angular momentum (OAM), and their sum [the total angular momentum (TAM)] can be estimated locally without ambiguity. In this letter, we highlight an inconsistency in this method when adding an SAM with an OAM. The latter cannot be estimated for a nonzero SAM. From optical currents, we propose a more general method. It is based on the Poynting expansion into spin and orbital components to estimate the OAM regardless of the SAM value.

The radiation of a series gap in a coplanar waveguide (CPW) line has been studied for Ku band applications. While theoretical models usually describe accurately the capacitance of the gap, they fail to include the radiation loss. This paper shows that it is a relevant phenomenon in Ku Band when the width of the line is close to 1mm and low precision etching is employed (low cost printing technology). Additionally, a technique for the reduction of such losses is presented and evaluated.

International audience; The modelling of plasma formation during microwave breakdown is a difficult task because of the strong non-linear coupling between Maxwell's equations and plasma equations, and of the large plasma density gradients that form during breakdown. An original Finite Volume Time Domain (FVTD) method has been developed to solve Maxwell's equations coupled with a simplified fluid plasma model and is described in this paper. This method is illustrated with the study of the shielding of a metallic aperture by the plasma generated by an incident high power electromagnetic wave. Typical results obtained with the FVTD method for this shielding problem are shown.

En 2006, une grande expédition naturaliste se déroule au Vanuatu, sur l’île de Santo. Organisée par le Muséum National d’Histoire Naturelle de Paris, Pro-Natura International et l’Institut de Recherches pour le Développement, financée par des mécènes privés, elle va connaître un succès médiatique sans précédent pour ce genre d’opérations. Elle inaugure un nouveau type d’expéditions scientifiques caractérisées par des stratégies de communication efficace, condition nécessaire pour bénéficier d’une bonne couverture médiatique recherchée par les mécènes. Dans ce contexte de professionnalisation du journalisme environnemental, nous nous intéressons ici à la chaîne de production de l’information depuis les sources jusqu’à leur traitement médiatique. Nous verrons ainsi que les sources elles-mêmes – les institutions et acteurs organisateurs des expéditions- diffusent les ingrédients nécessaires pour donner de la grandeur, historique, scientifique et politique à ces expéditions. In 2006, the National Museum of Natural History of Paris, Pro-Natura International and the Research Institute for Development, organized a broad naturalistic expedition in Santo’s island, in Vanuatu. Supported by private foundations, this expedition had an unprecedented media success. It marks the start of a new kind of scientific operations with an efficient strategy of communication, which leads to a good media coverage researched by the sponsors. In this context of the professionalization of environmental journalism, this paper is focused on the production of information, from sources to medias. It shows that ingredients in the sources themselves give historical, scientific, and political greatness to those expeditions.

Background and aims - The Coastal Forests of Eastern Africa, stretching along the Indian Ocean coastline from Somalia to Mozambique, are considered by Conservation International to be a global biodiversity hotspot - an area of high diversity and endemism under increasing threat. Although the largest remaining extent of these forests is reported to be found in Mozambique, very little is known on their extent, condition and composition here. In addition, the term 'coastal forest' has been used in different ways by different authors. This paper defines and characterises coastal dry forests found in northern Mozambique and assesses their present extent, botanical composition, conservation importance and the threats to these forests. Methods - The study area of 18,150 km2 lies in Cabo Delgado Province in north-east Mozambique, adjacent to Tanzania. Its limits are determined primarily by geological substrate and landform. Four smaller study sites were chosen covering a range of landforms. Manual interpretation of satellite imagery dating from 1999-2002 was used to calculate possible previous and present extent of 'dense vegetation'. Extensive field collecting was used in determining botanical composition and distribution patterns. IUCN Red List assessments were carried out on selected species using distributional criteria. Results - Dry forests similar to those in southern Tanzania are found widely scattered across coastal Cabo Delgado, sitting in a matrix of miombo woodland and other vegetation types. However, forest cover is not as extensive was believed. We calculate that the original extent of 'dense vegetation cover', which includes coastal dry forest, was 6087 km2. Owing to clearance over the last 150 years this is now only 1182 km2, of which perhaps only 400 km2 is moderately-intact dry forest. In this southern part of their range such forests are essentially dry, not moist and mesic, and dominated by a high proportion of deciduous or sclerophyllous evergreen trees. The plant species composition differs significantly from that of the surrounding woodlands. There is a marked change in species composition between forest patches along the coast, and they contain numerous species with restricted global distribution. Since 2003, 68 species new to Mozambique have been recorded from Cabo Delgado in addition to 36 possible new species. Many new records are of species previously only known from south-eastern Tanzania. Previously recorded patterns of restricted distribution and high species turnover between forest patches in Kenya and Tanzania are confirmed. Seven coastal forest species were assessed as Endangered. Regional context and conservation - Coastal dry forests are discussed in relation to the more widespread 'sand forests' of the continental interior of south-central Africa, and shown to have similarities in ecology, species composition, soils and ecology. Very little of the present extent of coastal forests in Mozambique lies within protected areas. The threats to their continued existence in the face of exploitation for timber, agriculture and oil exploration are outlined.

In this paper, the electromagnetic properties of two difier- ent High Impedance Surfaces (HIS) with or without Electromagnetic Band Gap (EBG) in difierent conflgurations are investigated for mutual coupling reduction in small antenna arrays. The resonant mechanisms of these structures are studied using transmission calculations in a par- allel plate waveguide. An optimum conflguration is then proposed. It is shown that a good isolation performance can be achieved without the need of metallic vias when the structure is embedded in a metal- lic cavity, which limits signiflcantly the number of HIS cells needed to perform a good isolation and the cost of manufacture.

International audience; An original and flexible pyramidal antenna for satellite or terrestrial application services is presented. The ground plane of the antenna is perforated and loaded with a cutoff open-ended waveguide: this original configuration leads to a good tradeoff between rear radiation and impedance matching. Trap-loads are used to achieve multiband operation while frequency agility may be simply obtained by loading the radiating element by radio-frequency switches. The antenna radiates linearly or circularly polarized electromagnetic fields with quasi-hemispheric radiation patterns at multiple operating frequencies. Several prototypes have been simulated, manufactured, and finally measured. A specific application is given in this paper for a triband GPS/Galileo/MicroSat Telemetry antenna to combine positioning and telemetry applications. The experimental results confirm the good performances observed with the electromagnetic simulations.