Jérôme Sokoloff

Reconfigurable electromagnetic band gap device using plasma as a localized tunable defect

Electromagnetic band gap (EBG) structures have interesting properties in terms of electromagnetic wave propagation. Using a plasma discharge in an EBG structure may increase its reconfigurability. The use of microplasma arrays in the design of EBG structures is however complex and may cause energy losses. In this paper, we show through experiments and simulations that EBG effects can be obtained in structures where a single discharge plasma is used to create a defect in a periodic structure of metallic rods.

Plasma-based localized defect for switchable coupling applications

We report in this paper experimental measurements in order to validate the concept of switchable electromagnetic band gap filters based on plasma capillaries in the microwave regime. The plasma tube is embedded inside the structure to create a bistable (plasma on or off) punctual defect. We first investigate two kinds of discharge tubes: Ar–Hg and pure Ne, which we then use to experimentally achieve plasma-based reconfigurable applications, namely, a two-port coupler and a two-port demultiplexer.

Gaussian beam expansion for radiation analysis of metallic reflectors illuminated under oblique incidence

A flexible, rapid, and accurate method is presented for calculating the radiation of metallic reflectors illuminated under oblique incidence. The vectorial multimodal Gaussian beams are used to describe both co- and cross-polarization fields. Two cases are discussed for Gaussian or diverging feeds.

Electromagnetic Scattering of a Field Known on a Curved Interface Using Conformal Gaussian Beams

Asymptotic techniques have been successfully applied to compute electromagnetic wave radiation in various high-frequency engineering domains. Recent approaches based on Gaussian beams for tracking fields may overcome some problems inherent to the ray methods such as caustics. The efficiency of these methods is based on the ability to expand surface fields into a superposition of Gaussian beams. However, some difficulties may arise when the surface is curved. In this paper, we propose a new efficient way to expand fields on a curved surface into Gaussian beams. For this purpose, a new beam formulation called Conformal Gaussian Beam (CGB) is used. The CGBs have been developed to overcome the limitation of the expansion into paraxial Gaussian Beams. The analytical Plane-Wave Spectrum and far-field of a CGB are derived and compared with numerical calculations. A brief parameter analysis of the CGBs is realised.

UNIFORM ANALYTIC SCATTERED FIELDS OF A PEC PLATE ILLUMINATED BY A VECTOR PARAXIAL GAUSSIAN BEAM

Universit´edeToulouseUPS, INPT; LAPLACE118 route de Narbonne, F-31062 Toulouse cedex 9, FranceCNRS; LAPLACE; F-31062 Toulouse, FranceS. BolioliONERA Centre de ToulouseElectromagnetic and Radar Department31055 Toulouse, FranceAbstract—A uniform asymptotic expression is developed forcalculating the fields scattered by a perfect electrically conductingplate illuminated by a vectorial gaussian beam. This expressionhas been obtained under the physical optics approximation using thesaddle point method. Some numerical applications are presentedand compared with some reference methods such as a MoM. A briefparameter study of this solution is presented.1. INTRODUCTIONUniform asymptotic expression is developed in this paper forcalculating the fields scattered by a Perfect Electrically Conducting(PEC) plate illuminated by a Gaussian Beam (GB). This expressionhasbeenobtainedunderthePhysicalOpticsapproximation(PO).Thiswork is part of a general Gaussian Beams tracking method which isused for calculate interactions of electromagnetic waves with complex3D objects.Ray tracing and ray techniques have been widely used inelectromagnetics engineering for scattering problems. However, some

Reconfigurable modified surface layers using plasma capillaries around the neutral inclusion regime

We show both theoretically and experimentally reconfigurable properties achieved by plasma inclusions placed in modified surface layers generally used to tailor the transmission and beaming properties of electromagnetic bandgap based waveguiding structures. A proper parametrization of the plasma capillaries allows to reach the neutral inclusion regime, where the inclusions appear to be electromagnetically transparent, letting the surface mode characteristics unaltered. Varying the electron density of the plasma inclusions provoques small perturbations around this peculiar regime, and we observe significant modifications of the transmission/beaming properties. This offers a way to dynamically select the enhanced transmission frequency or to modify the radiation pattern of the structure, depending on whether the modified surface layer is placed at the entrance/exit of the waveguide.

One-dimensional electromagnetic band gap structures formed by discharge plasmas in a waveguide

We demonstrate the ability to develop one-dimensional electromagnetic band gap structure in X-band waveguide solely by using the positive columns of glow discharges in neon at the middle pressure. Plasma inhomogeneities are distributed uniformly along a typical X-band waveguide with cross section of 23 × 10 mm2. It is shown that electron densities larger than 1014 cm−3 are needed in order to create an effective one-dimensional electromagnetic band gap structure. Some applications for using the one-dimensional electromagnetic band gap structure in waveguide as a control of microwave (broadband filter and device for variation of pulse duration) are demonstrated.

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).

Scattering by an Array of Rods using the Gaussian Beam Formalism Coupled to the Scattering Matrix Method

An innovative method is proposed to compute the field scattered by an array of rods illuminated by a 3D regular field. The incident field is described as a sum of few Gaussian beams. The scattered field is derived with the Scattering Matrix Method introducing a paraxial approximation on each elementary incident Gaussian beam. Numerical and experimental tests reveal a good trade-off between the accuracy and the computational effort.

Physics-based expansion on 3D conformal Gaussian beams for the scattering from a curved interface

Gaussian beams techniques are high-frequency asymptotic methods that can be used to model the propagation/interaction of flelds in a variety of problems. In this article, an expansion is proposed to express the scattering of magnetic/electric currents from a curved interface in terms of a new kind of elementary beams, the conformal Gaussian beams. The expansion characteristics rely on the physical properties of the conflguration, which leads to represent the scattering with a small number of conformal Gaussian beams. An analytical formulation for the conformal Gaussian beams is developed, which expression is derived from an asymptotic evaluation of the radiation integrals valid at great distance from the interface. An example is presented to show that this analytical formulation is in good agreement with the reference result. Numerical tests are led on the expansion in order to show that the scattering can be represented with accuracy by adding the contribution of conformal Gaussian beams.