Thierry Callegari

New Insights in the Physics of DBD Plasma Actuators for Flow Control

*We have shown in previous publications that the ElectroHydroDynamic (EHD) force in a surface dielectric barrier discharge takes place in the ion clouds that form and extend above the dielectric surface during the corona phase of the discharge (i.e. before the formation of a quasi-neutral plasma, and between successive current pulses). During the positive phase of the sinusoidal voltage (i.e. when the anode is above the dielectric layer), a positive ion cloud forms and spreads above the surface, as in a transient corona discharge, until breakdown (filamentary glow discharge or streamer breakdown) occurs. During the negative part of the cycle (when the electrode above the dielectric surface plays the role of a cathode), the current is composed of higher frequency lower amplitude pulses. In air, a negative ion cloud forms above the surface and continuously grows as the voltage drop between the electrodes increases. The EHD force during the negative phase of the sinusoidal voltage is in the same direction as during the positive phase, and can be as large as in the positive phase. In this paper we study in detail the surface DBD and the generated EHD force in air. We perform a parametric study (voltage amplitude and frequency) of the EHD force and dissipated power, and compare the model results with available experimental results.

Widely tunable high-Q SIW filter using plasma material

This paper presents a novel concept to tune the resonant frequency of an evanescent-mode substrate integrated waveguide resonator while maintaining a high-Q in the tuned frequency range. The tunability is based on the insertion of vertical switchable capacitive post within SIW cavity. The filter is tuned from 18GHz to 7.5GHz, with insertion losses ranging from 0.8 to 2 dB in the frequency range for 1.4% bandwidth filter. The main interest of this work is the use of the argon material under high pressure and DC voltage to generate a dense plasma media.

Non-Self-Sustained Atmospheric Pressure Glow Discharges Maintained by the DC Helium Glow Discharge

The possibilities of obtaining large-volume non-self-sustained atmospheric pressure glow discharge with the help of the self-sustained normal dc glow discharge in helium are demonstrated. The latter plays the role of ldquoplasma electroderdquo for the main discharge in a neighboring chamber in the three-electrode configuration. Electrical parameters of the non-self-sustained discharge for different voltage sign combinations of electrodes are presented. Conditions of discharge transfer from one chamber section to another are under investigations. The spatial profiles of potential at different discharge currents are determined. It is shown that larger volumetric plasma can be generated in the anode-cathode-anode configuration.

Atmospheric-Pressure Air Glow Discharge in a Three-Electrode Configuration

Nonthermal non-self-sustained dc glow discharge in atmospheric-pressure air was developed in a three-electrode configuration. A self-sustained normal dc atmospheric-pressure glow discharge in helium served as a ldquoplasma cathoderdquo for the main discharge in ambient air. Conditions of discharge transfer from helium volume to atmospheric air are under investigation. It is shown that a smooth transfer between the discharges in both volumes takes place only at small gaps between the ldquoplasma cathoderdquo and the third electrode (less than 5 mm) as the voltage applied to the air gap is increased. For larger gaps, this transfer is accompanied by discontinuous changes in both the voltage and current. After the jump, the discharge is contracted. But if the interelectrode gap is increased (more than 10 mm), then two forms of the discharge exist in one discharge space: diffuse and contracted.

Experimental protocol and critical assessment of the Pockels method for the measurement of surface charging in a dielectric barrier discharge

The behaviour of dielectric barrier discharges (DBDs) is controlled by the successive charging and discharging of the dielectric surface. Measuring the space and time evolution of the charges on the dielectric layers is of great interest to optimize these discharges and better understand the transition from homogeneous to filamentary regimes and the formation of patterns. Such measurements can be performed using a diagnostic technique based on the Pockels effect, where an electro-optic crystal is used as the dielectric layer of a DBD and as a probe of the electric field across the layer. The surface charge density is related to this field and can, in some limited conditions, be simply deduced from it. The principle of this technique is relatively simple but the necessary care that must be taken in its application to DBDs has not been described in detail in the literature. The aim of this paper is to provide a critical assessment of the method and to illustrate its application in the case of a low pressure dielectric barrier glow discharge.

A Tunable Electromagnetic Bandgap Structure Using Plasma

A tunable electromagnetic-bangap (EBG) structure based on a double layer slotline using plasma is proposed. The plasma permittivity can be tuned by the electron density. The idea of integrating periodical plasma elements inside the slot to tune the stopband is investigated. An electron density and an electron collision frequency equal to 1:7510 13 cm i3 and 10 10 s i1 respectively, are the plasma parameters selected in this study. The simulations reveal a shift rate of the second stopband equal to 6%. A new conflguration of the structure is also proposed to adapt it better to the experimental requirements. Based on the simulation results, adding the plasma elements to the modifled conflguration shifts the stopband 4% and reduces its bandwidth by 43% (at i20dB).

Improvement of PDP discharge efficiency based on macro-cell studies

In this paper we explain how macro-cells (real PDP cells scaled-up a hundred times) with external and removable electrodes have been validated by comparison with real panels and modeling and used to optimize the luminous efficacy of real PDPs. We illustrate the application of the macroscopic PDP tool to optimize the electrode configuration of short-gap discharges towards higher luminous efficacy, as well as its use in conjunction with 2D and 3D modeling to lower the operating voltages of high-efficacy long-gap discharges triggered by auxiliary electrodes.

Static and dynamic control of limiting threshold in plasma-based microstrip microwave power limiter

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.

Modeling and experimental measurements of a tunable microstrip resonator using plasma discharges

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.

Antena impresa invertida reconfigurable en frecuencia a base de una microdescarga de plasma

espanolEn este articulo se propone el estudio de una antena impresa invertida reconfigurable en frecuencia a base de una microdescarga de plasma. La idea es generar una microdescarga controlada en corriente al interior de una cavidad situada entre el plano tierra de la antena y su conductor principal, cuyo objetivo final es de modificar la frecuencia de resonancia de la antena. El interes en la utilizacion del plasma como elemento reconfigurable es su tiempo de conmutacion y, sobre todo, su capacidad de manejo de altas potencias. Se demostro de manera teorica que la reconfiguracion en frecuencia de una antena tipo parche, con una microdescarga en su cavidad, es dependiente de la densidad electronica del plasma. Ademas, se implemento un prototipo de antena impresa invertida reconfigurable en banda X integrando una microdescarga, la que tuvo excursion en frecuencia medida de 180 MHz. EnglishThis paper proposes the study of an inverted microstrip plasma-based reconfigurable antenna. The scope is to generate controlled microplasma inside the cavity between the antenna ground plane and its main conductor. This plasma will modify the resonant frequency of the antenna. The interest of using a plasma discharge as an active reconfigurable element is its switching time and mainly its capability of handling high microwave power. It was demonstrated, theoretically, that the reconfiguration frequency of a microstrip patch antenna with a microdischarge in its cavity, depends on the electron density of the plasma. Furthermore, a prototype of an X-Band inverted microstrip patch antenna, which integrates a microdischarge, was implemented. The measured frequency excursion for this prototype was 180 MHz