Dielectric Plate Research Articles

Controlling Properties of Interfaces in Nonlinear Sandwich-Type Structures with a Defocusing Internal Layer

A model of a three-dimensional optical structure in which the plane-parallel boundaries have intrinsic nonlinear properties is considered. The internal layer with a finite thickness is an optically transparent medium with defocusing Kerr nonlinearity; on the outside, it is in contact with dielectric linear half-spaces. The mathematical formulation of the model reduces to the nonlinear Schrodinger equation with a positive coefficient of cubic nonlinearity and with a nonlinear self-consistent potential. It is shown analytically that the system contains a nonlinear light wave propagating along the optical layer and localized in dielectric plates. The frequencies of light-field localization in this structure are obtained and the conditions for their existence are determined for different characteristics of the media and the interfaces between them. It is shown that the light field can be localized along the layers for different signs of the nonlinear response of the interfaces between layers of the three-layer structure in the case where one of them is characterized by a focusing nonlinearity; and the other, by a defocusing one.

Evaluation of the Laguerre-Gaussian mode purity produced by three-dimensional-printed microwave spiral phase plates.

Computer-aided design software and additive manufacturing provide flexibility for the direct fabrication of multi-material devices. This design and fabrication versatility has been investigated for the manufacture of dielectric spiral phase plates (SPP) that generate electromagnetic waves with helical wavefronts. Three types of SPPs designed to produce an orbital angular momentum (OAM) mode number l = |1| were additively manufactured using material extrusion and polyjet fabrication methods. The OAM mode characteristics of the transformed helical microwaves as a function of the SPP geometrical features were investigated experimentally in the 12–18 GHz frequency range. The SPPs were further combined with an additively manufactured dielectric lens that provided a marked improvement in OAM mode purity. Finally, multiplexing and de-multiplexing of two OAM modes were demonstrated successfully using an optimum SPP geometry and arrangement.

Wideband Windows for Millimeter- and Submillimeter-Wave Vacuum Devices

We present the results of a theoretical calculation and an experimental study of double-sided antireflective processing of a dielectric plate by creating a specially profiled corrugated structure on its surface. Such a structure allows one to minimize the reflection coefficient of an electromagnetic wave to a level of about −30 dB within a range of at least one octave. This antireflective effect can be used in energy output windows of frequency-tunable generators operated in the millimeter- and submillimeter-wave bands. It can also be applied in windows of wideband spectroscopy devices used to diagnose a broad range of materials including both gases and condensed media, as well as in medical devices, in which the studied sample/object is placed in a vacuum-tight box. Theoretical calculations are based on solving numerically the complete equations of the electromagnetic field. Reflections from double-sided corrugated plates were studied experimentally using a Michelson interferometer. It is shown that the reflection coefficient is equal to no more than −23 dB in the 50–220 GHz frequency range. The antireflective profile was manufactured using a plate of radiation-processed fluorine F-4 (Raflon). This new material allowed us to manufacture an antireflective structure with a required accuracy.

Рупорна антена на основі заграничного прямокутного хвилеводу із частковим діелектричним заповненням та петлею зв’язку

The characteristics of the horn antenna based on the foreign rectangular waveguide with partial dielectric filling (PDF) and the communication loop are considered. The mirror method was chosen for the experimental measurement of the antenna gain. Accordingly, it is proposed to use a resonance model (rectangular resonator) for the analysis of such antennas. The formula for calculating the input resistance of the communication loop, which excites the resonator, is obtained. The formula takes into account the additional resistance in the loop circuit, which appears due to the excitation of the electromagnetic field in the resonator. This allows us to calculate the standing wave ratio (SWR) and the gain of the antenna in particular. Experimental measurements of the dependences of SWR on the change in the length, thickness of dielectric plates with relative dielectric constant and the diameter of the communication loop wire in a rectangular waveguide with dimensions of mm for a type wave were performed. Optimal dielectric plate sizes and communication loop positions are proposed to improve antenna alignment. The results of experimental measurement of the antenna gain are given, which do not have significant differences with the calculations. The considered dependences of the antenna gain have a resonant character, which indicates the correctness of the application of the resonant model for the analysis of such emitters.

The Principle of Creating Quasiperiodic Surfaces under the Action of a Vibrating Dielectric Matrix

A method for creating metasurfaces using a standing wave, formed in a dielectric, is proposed. Such metasurfaces are formed from metal suspensions, are deposited on a dielectric plate, is placed in a metal frame-screen. A method of creating standing waves is presented. The Chladni`s principle is used for creating acoustic figures was taken as the basis. Mathematical description of this model is proposed, as well as the main research methods.

Complex Effective Dielectric Permittivity and Characteristic Impedance of Tunable Coplanar Line

An analysis of complex dielectric permittivity and characteristic impedance of micromechanically tunable coplanar line is presented. The coplanar line parameters tuning is achieved by signal line electrode movement above the substrate or the dielectric plate above the surface of line electrodes. A reconfiguration of electromagnetic field with complex nature occurs as a result of such movement in the line. It is described in terms of effective permittivity and characteristic impedance. We studied an influence of physical and geometrical parameters of the line on characteristics of effective permittivity tuning and change in characteristic impedance and line loss. It is found that proposed method for line tuning parameters allows us to obtain a high sensitivity to movement for effective parameters, wherein the level of losses in the line is not deteriorated, and under certain conditions are reduced. These results make it possible to design high-quality tunable resonant elements and phase shifters based on micromechanically controlled coplanar line.

Self-amplification of radiation from an electron bunch inside a waveguide filled with periodic medium

We investigate the radiation from a bunch of relativistic electrons moving along the cylindrical waveguide axis, assuming that the waveguide is partially loaded by a medium with periodic dielectric permittivity and magnetic permeability. The spectral distribution of the radiation energy flux through the cross section of the waveguide is studied at large distances from the medium. The analysis is based on the corresponding exact solution of Maxwell equations for the case of a single electron moving along the waveguide axis. The results of numerical calculations are presented in the special case of layered medium consisting of a finite number of dielectric plates separated by vacuum gaps. We show that under certain conditions on the problem parameters the quasi-coherent Cherenkov radiation generated by the electron bunch inside the plates is self-amplified at certain waveguide modes. A visual explanation of this phenomenon is provided that reproduces the main features to rather good accuracy.

Discharge propagation on a dielectric surface in a single-filament arrangement

Discharge development and streamer propagation on a dielectric surface were investigated in nitrogen-oxygen gas mixtures at atmospheric pressure. A coaxial pin-to-pin arrangement was used to generate single surface discharges driven by positive unipolar square wave high voltages of between 7 and 9 kV at 4.3 kHz. The development of surface discharges was recorded by ICCD and streak cameras. The discharges developed on the surface using pin electrodes attached directly to the dielectric plate. The accumulation over several discharge events showed a propagation front evolving from the electrode tip, while images of single discharges showed a non-uniform and branched structure of discharge channels. The electrode polarity influenced the discharge expansion and propagation velocity. Positive polarity of the metallic electrode (rising slope of HV pulses) led to a cathode-directed streamer with higher propagation velocities (5 × 105 m/s) than for negative polarity (relative to surface charges; falling slope). The increase in the O2 content in N2 from 0.1 to 20 vol% resulted in a decrease in discharge duration and an increase in streamer velocities.

Phase-controlled, second-harmonic-optimized terahertz pulse generation in nitrogen by infrared two-color laser pulses

Broadband terahertz radiation can be efficiently produced by mixing laser pulses of different colors in the mid-infrared (MIR) and longwave-infrared (LWIR) spectral region. In this paper, we report on a numerical investigation of ultrashort terahertz pulse generation from plasmas created in nitrogen gas by two-color laser pulses with the fundamental laser pulse wavelength between 2.15 and 15.15 µm, in order to explore the efficiency of the terahertz pulse generation process. The results show that the electron acceleration efficiency increases monotonically with the fundamental laser pulse wavelength. The most intense terahertz pulse generation is observed at 12.30 µm with four optical-cycle laser pulses with 2.5 GW peak power. The results show that the terahertz pulse generation with a MIR laser is one order of magnitude and with a LWIR laser is two orders of magnitude more efficient than the terahertz pulse generation with Ti:Sapphire lasers using the exact same pulse parameters. The terahertz pulse generation efficiency is also known to be very sensitive to the relative phase between the components of the two-color laser pulses. One of the most useful tools to control the relative phase and optimize the terahertz pulse intensity is thin dielectric plates. It has been shown that alkaline halides and alkaline earth halides have suitable optical properties for the relative phase control for efficient terahertz pulse generation in the MIR spectral range.

The effect of electrodynamic parameters of a composite material on the characteristics of the wave reflected from a dielectric layer

Variable electrodynamic parameters of composite materials are determined using the methods providing simultaneous measuring of the free- space permittivity and magnetic permeability within a broad band. Thus, the problems regarding reflection of an electromagnetic wave from the boundary of a dielectric layer and modeling of the phase shift of the wave reflected from a dielectric plate become rather relevant. We report the results of studying the effect of the electrodynamic parameters of composite materials on the characteristics of the wave reflected from a dielectric plate. Analytical expressions are derived for the phase of the reflected wave when an incident plane wave is oriented at an angle to the composite plate with variable electrodynamic parameters. The matrix method is used to obtain the equations for calculating the phase shift of the reflected wave. It is shown that for incident waves with a vector of electric field lying in the plane of incidence (TM waves) and normal to it (TE waves), a jump in the phase shift by π is observed for the electric thickness of the plate multiple of the half-wavelength. A similar phase jump is observed in the case of an incident TM wave near the Brewster angle. An analysis of the frequency dependences of the phase shift, including the phase shift and amplitude drop at a corresponding frequency, as well as data on the effect of losses in the plate material on the phase shift of the reflected wave are presented. The results of studying the angular dependence of the phase shift of the reflected wave in the region of the Brewster angle can be used in solving applied problems of electrodynamics (e.g., when developing a broadband broad-band direction finding device).

Electro-elastic Lamb waves in dielectric plates

We study the propagation of Lamb waves in soft dielectric plates subject to mechanical and electrical loadings and find the explicit expressions for the dispersion equations in the cases of neo-Hookean and Gent dielectrics. We elucidate the effects of the electric field, of the thickness-to-wavelength ratio, of pre-stress and of strain-stiffening on the wave characteristics.

Stability of an anisotropic dielectric elastomer plate

A variety of methods have been proposed to improve the performance of dielectric elastomer transducers, which lead to the anisotropic electromechanical behavior of the material. This paper theoretically analyzes the effect of material anisotropy on the diffuse modes of instability in dielectric elastomer plates. As a first step, a transversely isotropic material is considered in the present study. The linearized incremental theory is used and the plate thickness is considered in the stability analysis. The bifurcation equations are solved with Wolfram Mathematica (Wolfram Research, Inc., 2019) [1] to obtain the critical stretches under different electric field. It is found that, compared to the isotropic material, material anisotropy results in larger unstable regions and higher critical stretches above which the plate is stable. It is also shown that material anisotropy has a stronger influence on a thinner plate. As the plate thickness increases, the influence decreases.

A compact circularly polarized isosceles triangular microstrip patch antenna with parasitic elements for multiband application

AbstractIn this research paper, a isosceles triangular radiating patch with two triangular coplanar parasitic elements has been used to design a compact circularly polarized (CP) microstrip patch antenna that can be used for (2.320‐2.345 GHz) satellite digital audio radio systems (SDARS), (2.30‐2.39 GHz) wireless broadband (WiBro), LTE 2300 (2.3‐2.4 GHz), and WIMAX (2.50‐2.69 GHz) application band. Corners of the two parasitic element along with a portion of driver patch has been cut and optimize to obtain CP characteristics of the antenna with broadside radiation pattern. A slot is also introduced and optimized on the radiating patch to improve the impedance matching. Frequency band generated by the antenna is (2.09‐2.64 GHz) having impedance bandwidth of (S11 ≤ −10 dB) 550 MHz 23.25% and two 3‐dB axial ratio (AR) bandwidth of 5.1% (2.29‐2.41GHz) and 1.54% (2.58‐2.62 GHz). The size of proposed antenna is 56 × 52 × 3.2 mm3 in which, FR4 material has been used as dielectric substrate and thin copper plate as radiating patch and ground. Before physical fabrication, HFSS ver13 software has been used to design and analyzed the proposed antenna. It has been found that the measured results of fabricated antenna and simulated results are closely matching.

Spatially resolved absolute densities of reactive species and positive ion flux in He-O2 RF-driven atmospheric pressure plasma jet: touching and non-touching with dielectric substrate

Atmospheric pressure plasma jets (APPJs) are operating in direct contact with dielectric substrates for many applications. Nonetheless, many studies have been focusing on free jets. In this letter, we report spatially resolved measurements of reactive species including neutral and ionic species in an He + 1% O2 RF-driven APPJ by molecular beam mass spectrometry equipped with a dielectric sampling plate, enabling to detect species densities for APPJ operating remotely or in direct contact with a substrate. The spatially resolved distribution of O, O2(a1Δg) and O3 is dominated by convection and, remarkably, shows minimum differences between touching and non-touching conditions.

High Refractive Index Electromagnetic Devices in Printed Technology Based on Glide-Symmetric Periodic Structures

We demonstrate the beneficial effects of introducing glide symmetry in a two-dimensional periodic structure. Specifically, we investigate dielectric parallel plate waveguides periodically loaded with Jerusalem cross slots in three configurations: conventional, mirror- and glide-symmetric. Out of these three configurations, it is demonstrated that the glide-symmetric structure is the least dispersive and has the most isotropic response. Furthermore, the glide-symmetric structure provides the highest effective refractive index, which enables the realization of a broader range of electromagnetic devices. To illustrate the potential of this glide-symmetric unit cell, a Maxwell fish-eye lens is designed to operate at 5 GHz. The lens is manufactured in printed circuit board technology. Simulations and measurements are in good agreement and a measured peak transmission coefficient of −0.5 dB is achieved.

3-D-Printed High Data-Density Electromagnetic Encoders Based on Permittivity Contrast for Motion Control and Chipless-RFID

The 3-D-printed electromagnetic encoders based on permittivity contrast are presented and discussed in this article. The encoders, implemented using exclusively dielectric materials, are based on linear chains of dielectric inclusions. Two types of encoders are considered: 1) those where the inclusions are simple apertures made on a 3-D-printed dielectric plate (or substrate) and 2) those with inclusions made of high dielectric constant material 3-D-printed on a dielectric substrate (also 3-D-printed). In both cases, encoding is achieved by varying the dielectric constant of the substrate at predefined positions by means of the inclusions. For encoder reading, a microstrip line loaded with a slot resonator (etched in the ground plane) and a series gap is proposed. Such structure is very sensitive to short range dielectric constant variations, being able to detect the presence or absence of closely spaced inclusions when the encoder is displaced on top of the sensitive part of the reader, the slot resonator. For that purpose, the reader line is fed by a harmonic signal conveniently tuned, so that an amplitude-modulated (AM) signal containing the identification (ID) code is generated at the output port of the line. The proposed reader/encoder system is useful for motion control applications (linear displacement and velocity sensors) and for near-field chipless-radio frequency ID (RFID). Lower cost and major robustness against mechanical wearing are potential advantages of these encoders over other electromagnetic encoders based on a similar principle but based on metallic inclusions.

BBU instability in rectangular dielectric resonator

Studies were made into the arise and an evolution of the beam breakup (BBU) instability in a rectangular dielectric resonator under excitation by a sequence of relativistic electron bunches. The dielectric resonator is a section of a rectangular waveguide loaded by the two dielectric slabs (located along the wide side) and closed by the metal grids. A material of the slabs is teflon. A thickness of the slabs is 8.2 mm, a wide size and a length of the slabs are equal to the resonator wide size and length respectively. The metal grids are transparent for the charged particles and nontransparent for the excited electromagnetic fields. The wavelength of the LSM2,1,12 (Longitudinal Section Magnetic) operating mode is 53.2 mm. The electron energy of bunches is 4.5 MeV , the charge of each bunch is 6.4 nC, the bunch repetition period is equal to twice the wavelength of the LSM2,1,12 mode. By the use of numerical PIC simulations, the charge losses of electron bunches on the dielectric plates were investigated as the bunches were displaced relative to the cavity axis. It is found that the charge losses on the dielectric slabs due to the BBU instability do not exceed 5%. When the bunch repetition period is changed to a multiple of another eigenfrequency (e.g., the LSM1,1,12 mode), the charge losses of drive bunches do not change appreciably.

The dynamic evolution and interaction with dielectric material of the discharge in packed bed reactor

In this paper, dielectric columns with different dielectric constants are employed as dielectric materials in the packed bed reactor to investigate the dynamic behaviors of plasma interaction processes. The effects of the dielectric constants (zirconia: ε = 25 and PTFE: ε = 2.5) on the production of reactive species are studied for plasma catalysis applications. Comparison studies of discharge images, electrical characteristics, discharge dynamic evolution and spatial-temporal resolved optical emission spectroscopy are carried on when zirconia and PTFE columns are employed. The results show that there are four discharge processes existing in the packed bed reactor: surface streamer on the dielectric column, local discharge at the contact point, surface discharge on the grounded dielectric plate, and the volume discharge. The production of reactive species such as N2(C3Пu), N2+(B2Σu+) and O(3p5P) depend on the discharge processes to a great extent. The production of the N2+(B2Σu+) always accompanies the formation of the streamer by electrons direct impact process to excite the ground state nitrogen molecules to N2+(B2Σu+). The O(3p5P) is generated in two different ways, which plays a major role during the voltage pulse raising and falling time, respectively. The first way is the direct and fast one-step ionization and excitation by high energy electrons with O2. The second way is the energy transfer from the nitrogen metastable N2(A3Σu+) and energetic electrons, in which the O is first ionized from O2 and then excited to O(3p5P). Furthermore, compared with a zirconia column, a PTFE column is more conductive to the generation of reactive species.

INFLUENCE OF EXCITATION PERIOD ON THERMAL TRANSFER OF TOW-PLASTER THERMAL INSULATION PLATE ATTACHED TO WALL: APPLICATION TO COLD ROOM

06Apr 2020 INFLUENCE OF EXCITATION PERIOD ON THERMAL TRANSFER OF TOW-PLASTER THERMAL INSULATION PLATE ATTACHED TO WALL: APPLICATION TO COLD ROOM Baba Mbengue , Issa Diagne , Mamadou Babacar Ndiaye , Youssou Traore , Seydou Faye , Pape Touty Traore , Cheikh Thiam , Ablaye Fame , Sokhna Khadidiatou Ben Thiam and Gregoire Sissoko Polytechnic School of Thies, BP A10, Thies, Senegal. Laboratory of Semiconductors and Solar Energy, Physics Department, Faculty of Science and Technology, University Cheikh Anta Diop, Dakar, Senegal. University Institute of Technology, University of Thies, Thies, Senegal.

Mechanics of reversible wrinkling in a soft dielectric elastomer.

A parallel array of wrinkles can be generated in a simple parallel plate capacitor arrangement with a soft dielectric elastomer plate constrained all around its periphery and coated with flexible electrodes. The direction of the wrinkles is predetermined and the phenomenon is reversible in a range of applied potentials. A model of the wrinkled plate as a prestretched neo-Hookean membrane with superposed small out-of-plane bending displacements yields good estimates of the potential range for wrinkling as well as the number of parallel wrinkles. The mechanics is controlled by the thickness and aspect ratios, prestretch, and a nondimensional electric potential.