Gigantic Coaxial Line for Experimental Studies of the Interaction of Nanosecond Electromagnetic Pulses with an Ionized Gas Medium

A large-scale coaxial line filled with the plasma of RF discharge has been developed for laboratory modeling of the effects of the interaction of ultrashort electromagnetic pulses (EMPs) with the atmosphere and the ionosphere in the KROT facility. The oversized coaxial line ensures pulse transmission through an ionized medium in the TEM mode, which corresponds to the polarization of the transverse electromagnetic wave in free space, and in uniform isotropic plasma. The coaxial line has a length of 10 m and a diameter of 140 cm. The processes of propagation of the nanosecond and subnanosecond pulses in this line, in vacuum and with plasma, have been simulated numerically.

New coaxial low-pass filters with ultra-wide and spurious free stopband

Modern space communication systems often need high-power low-frequency (UHF, L-, S-, and C-band) low-pass filters (LPFs) with wide stopbands extending to Ka-band and beyond. Current design approaches frequently fail to meet these requirements completely. This paper proposes a new coaxial LPF concept and design methodology. The LPF consists of an array of cavity elements, which operate with transverse electromagnetic mode (TEM) and transverse magnetic (TM)-coupled resonances, and thus achieve a frequency response with a reflection zero at DC and transmission zeroes at targeted stopband locations. The design method is based on positioning the cavities in a quasi-periodic order, which efficiently spreads the transmission zeroes over the stopband, while keeping the characteristic impedance matched to the input/output interfaces over the passband. This design concept yields an ultra-wide, continuous and modal spurious-free stopband, while maintaining a low insertion loss, high peak power capacity, and low sensitivity to production tolerances.

Polarization insensitivity characterization of dual-band perfect metamaterial absorber for K band sensing applications

Polarization insensitive metamaterial absorbers (MA) are currently very attractive due to their unique absorption properties at different polarization angles. As a result, this type of absorber is widely used in sensing, imaging, energy harvesting, etc. This paper presents the design and characterization of a dual-band polarization-insensitive metamaterial absorber (MA) for K-band applications. The metamaterial absorber consists of two modified split ring resonators with an inner cross conductor to achieve a 90% absorption bandwidth of 400 MHz (21.4–21.8 GHz) and 760 MHz (23.84–24.24 GHz) at transverse electromagnetic (TEM), transverse electric (TE), and transverse magnetic (TM) mode. Polarization insensitivity of different incident angles for TE and TM mode is also investigated, which reveals a similar absorption behavior up to 90°. The metamaterial structure generates single negative (SNG) property at a lower frequency of 21.6 GHz and double negative property (DNG) at an upper frequency of 24.04 GHz. The permittivity and pressure sensor application are investigated for the proposed absorber, which shows its useability in these applications. Finally, a comparison with recent works is also performed to demonstrate the feasibility of the proposed structure for K band application, like sensor, filter, invasive clock, etc.

ON EFFECTIVE ACCELERATION OF CHARGED PARTICLES IN VACUUM

The results of studying the dynamics of particles in the fields of large-amplitude transverse electromagnetic waves are presented. The main attention is paid to the description of the found conditions, under which the effective transfer of wave energy to charged particles in vacuum is possible.

A Linear Microwave Plasma Source Using a Circular Waveguide Filled with a Relatively High-Permittivity Dielectric: Comparison with a Conventional Quasi-Coaxial Line Waveguide

For a conventional linear microwave plasma source (LMPS) with a quasi-coaxial line transverse electromagnetic (TEM) waveguide, a linearly extended plasma is sustained by the surface wave outside the tube. Due to the characteristics of the quasi-coaxial line MPS, it is easy to generate a uniform plasma with radially omnidirectional surfaces, but it is difficult to maximize the electron density in a curved selected region. For the purpose of concentrating the plasma density in the deposition area, a novel LMPS which is suitable for curved structure deposition has been developed and compared with the conventional LMPS. As the shape of a circular waveguide, it is filled with relatively high-permittivity dielectric instead of a quasi-coaxial line waveguide. Microwave power at 2.45 GHz is transferred to the plasma through the continuous cylindrical-slotted line antenna, and the radiated electric field in the radial direction is made almost parallel to the tangential plane of the window surface. This research includes the advanced 3D numerical analysis and compares the results with the experiment. It shows that the electron density in the deposition area is higher than that of the conventional quasi-coaxial line plasma MPS.

Collective modes of polarizable holographic media in magnetic fields

We consider a neutral holographic plasma with dynamical electromagnetic interactions in a finite external magnetic field. The Coulomb interactions are introduced via mixed boundary conditions for the Maxwell gauge field. The collective modes at finite wave-vector are analyzed in detail and compared to the magneto-hydrodynamics results valid only at small magnetic fields. Surprisingly, at large magnetic field, we observe the appearance of two plasmon-like modes whose corresponding effective plasma frequency grows with the magnetic field and is not supported by any background charge density. Finally, we identify a mode collision which allows us to study the radius of convergence of the linearized hydrodynamics expansion as a function of the external magnetic field. We find that the radius of convergence in momentum space, related to the diffusive transverse electromagnetic mode, increases quadratically with the strength of the magnetic field.

Modelling the Woven Structures with Inserted Conductive Yarns Coated with Magnetron Plasma and Testing Their Shielding Effectiveness

The paper proposes the analytic modelling of flexible textile shields made of fabrics with inserted conductive yarns and metallic plasma coating in order to calculate their electromagnetic shielding effectiveness (EMSE). This manufacturing process is highly innovative, since copper plasma coating improves EMSE on the fabrics with inserted conductive yarns of stainless steel and silver with 10–15 dB in the frequency range of 0.1–1000 MHz, as shown by the measured EMSE values determined according to the standard ASTM ES-07 via the Transverse Electromagnetic (TEM) cell. On the other hand, modelling of EMSE for such conductive flexible shields gives an insight on estimating EMSE in the design phase of manufacturing the shield, based on its geometric and electrical parameters. An analytic model was proposed based on the sum of EMSE of the fabric with inserted conductive yarns and EMSE of the copper coating. The measurement results show close values to the proposed analytic model, especially in case of fabric with conductive yarns having stainless steel content.