Multilayer Dielectric Slab Research Articles

Development of an analytical method to determine the propagation characteristics of microstrip line on artificial perforated substrates

This paper presents an analytical method to investigate the propagation characteristics of a uniform microstrip line placed on porous substrates. The structure is periodic with a specified unit cell and the substrate is made of cascaded multi-layer dielectric slabs. The proposed method is started by solving wave equation by decomposing Helmholtz operator using appropriate eigen-functions and applying the associated boundary conditions of tangential electromagnetic fields of the unit cell. Then, using Floquet theorem, the equivalent propagation constant of a one-dimensional (1-D) periodic structure is obtained. In addition to, the proposed method is developed for two-dimensional (2-D) structures by a suitable transformation. Several practical structures are considered to verify the accuracy of the proposed method. The comparison of the proposed analytical model and measurement results and those obtained using simulation process provided by High Frequency Simulator Strctures (HFSS) are reported. It is shown that our method can be used for a wide variety of structures to quickly estimate the required parameters with a good accuracy.

A Review on Improved Design Techniques for High Performance Planar Waveguide Slot Arrays

Planar waveguide slot arrays (WSAs) have been used since 1940 and are currently used as performing antennas for high frequencies, especially in applications such as communication and RADAR systems. We present in this work a review of the most typical waveguide slot array configurations proposed in the literature, describing their main limitations and drawbacks along with possible effective countermeasures. Our attention has been focused mainly on the improved available design techniques to obtain high performance WSAs. In particular, the addressed topics have been reported in the following. Partially filled WSAs, or WSAs covered with single or multilayer dielectric slabs, are discussed. The most prominent second-order effects in the planar array feeding network are introduced and accurately modeled. The attention is focused on the T-junction feeding the array, on the effect of interaction between each slot coupler of the feeding network and the radiating slots nearest to this coupler, and on the waveguide bends. All these effects can critically increase the first sidelobes if compared to the ideal case, causing a sensible worsening in the performance of the array.

SCoBi Multilayer: A Signals of Opportunity Reflectometry Model for Multilayer Dielectric Reflections

A multilayer module is incorporated into the Signals of Opportunity (SoOp) Coherent Bistatic Scattering model (SCoBi) for determining the reflections and propagation of electric fields within a series of multilayer dielectric slabs. This module can be used in conjunction with other SCoBi components to simulate complex, bistatic simulation schemes that include features such as surface roughness, vegetation, antenna effects, and multilayer soil moisture interactions on reflected signals. This paper introduces the physics underlying the multilayer module and utilizes it to perform a simulation study of the response of SoOp-R measurements with respect to subsurface soil moisture parameters. For a frequency range of 100–2400 MHz, it is seen that the SoOp-R response to a single dielectric slab is mostly frequency insensitive; however, the SoOp-R response to multilayer dielectric slabs will vary between frequencies. The relationship between SoOp-R reflectivity and the contributing depth is visualized, and the results show that SoOp-R measurements can display sensitivity to soil moisture below the penetration depth. By simulation of simple soil moisture profiles with different wetting and drying gradients, the dielectric contrast between layers is shown to be the greatest contributing factor to subsurface soil moisture sensitivity. Overall, it is observed that different frequencies can sense different areas of a soil moisture profile, and this behavior can enable subsurface soil moisture data products from SoOp-R observations.

RETRACTED ARTICLE: Scattering coefficients and pathgain of a multilayer tissue structure using ABCD matrix method

Numerical modeling plays an important role in the prediction of received signal strength inside the human body, in case of on-body to in-body radio wave propagation in a body area network (BAN). Since the structure of a human body is heterogeneous in nature, the Fresnel scattering coefficients could not be used to incorporate the attenuation properties of the multilayer tissue structure of the human body. This paper proposes the use of ABCD matrix method, which has been used in the analysis of multilayer dielectric slab structure, to determine the attenuation of the electro magnetic (EM) signal due to various in-body structures. In addition, variation of reflection and transmission coefficients of a four-layer body tissue structure with respect to the incident angle is presented and recommends suitable operating frequency in ultra-wide band (UWB) for BAN applications. The authors conducted measurements in body mimicking liquid phantom in UWB and included in support of their research outcome.

Design of a Multi-Layered Reconfigurable Frequency Selective Surface Using Water Channels

In this study, we propose a multi-layered reconfigurable frequency selective surface (FSS) using water channels, which can be switched between the bandpass and bandstop states. Variation ratio in transmission between the bandpass and bandstop states is drastically improved by multi-layer dielectric slabs with water channels. We then fabricate the design, and the measured results in the X-band shows a good agreement with the simulation. The variation in transmission coefficients between the two states increases from 0.34 to 0.71 using the 5-layered dielectric slabs with water channels, which verifies the reconfigurability of the proposed FSS.

Broadband circularly polarized Fabry‐Perot antenna utilizing Archimedean spiral radiator and multi‐layer partially reflecting surface

This article presents a method to design broadband circularly polarized (CP) Fabry-Perot Resonator (FPR) antenna. The proposed antenna is based on multi-layer thin dielectric slabs arranged in close proximity as a partially reflecting surface (PRS) and an Archimedean spiral as a CP radiating source. Experimental results show a broadband operation from 6 to 13 GHz, in which the reflection coefficient is less than −10 dB and the axial ratio (AR) is lower than 3 dB. In addition, good radiation patterns and high broadside gain of better than 10.8 dBic are achieved over the operating bandwidth. The proposed antenna can be used for C- and X-band satellite communications.

Subwavelength Target Detection Using Ultrawideband Time-Reversal Techniques With a Multilayered Dielectric Slab

We employed a multilayered dielectric slab to implement subwavelength target detection by utilizing ultrawideband (UWB) time-reversal (TR) techniques. Simulation results with/without the multilayered dielectric slab are presented to show the benefit of the multilayered dielectric slab structure using finite-difference time-domain (FDTD) method.

A periodic FMM for Maxwell’s equations in 3D and its applications to problems related to photonic crystals

This paper presents an FMM (Fast Multipole Method) for periodic boundary value problems for Maxwell’s equations in 3D. The effect of periodicity is taken into account with the help of the periodised moment to local expansion (M2L) transformation formula, which includes lattice sums. We verify the proposed method by comparing the obtained numerical results with analytic solutions for models of the multi-layered dielectric slab. We then apply the proposed method to scattering problems for periodic two-dimensional arrays of dielectric spheres and compare the obtained energy transmittances with those from the previous studies. We also consider scattering problems for woodpile crystals, where we find a passband related to a localised mode. Through these numerical tests we conclude that the proposed method is efficient and accurate.

Generalized Transmission Line Method to Study the Far-zone Radiation of Antennas under a Multilayer Structure

This book gives a step-by-step presentation of a generalized transmission line method to study the far-zone radiation of antennas under a multilayer structure. Normally, a radiation problem requires a full wave analysis which may be time consuming. The beauty of the generalized transmission line method is that it transforms the radiation problem for a specific type of structure, say the multilayer structure excited by an antenna, into a circuit problem that can be efficiently analyzed. Using the Reciprocity Theorem and far-field approximation, the method computes the far-zone radiation due to a Hertzian dipole within a multilayer structure by solving an equivalent transmission line circuit. Since an antenna can be modeled as a set of Hertzian dipoles, the method could be used to predict the far-zone radiation of an antenna under a multilayer structure. The analytical expression for the far-zone field is derived for a structure with or without a polarizer. The procedure of obtaining th Hertzian dipole model that is required by the generalized transmission line method is also described. Several examples are given to demonstrate the capabilities, accuracy, and efficiency of this method. Table of Contents: Antennas Under a Multilayer Dielectric Slab / Antennas Under a Polarized Multilayer Structure / Hertzian Dipole Model for an Antenna / Bibliography / Biography

３次元Ｍａｘｗｅｌｌ方程式の周期境界値問題における高速多重極境界要素法

This paper presents an FMM for periodic boundary value problems for Maxwell's equations in 3D. The periodic Green function and its derivatives, which are essential to the present method, are derived with Fourier analysis. We verify the proposed method by comparing the obtained numerical results with analytic solutions for models of the multi-layered dielectric slab. We then apply the proposed method to scattering problems for periodic two dimensional arrays of dielectric spheres and compare the obtained energy transmittances with those in the previous studies. We observe good agreements.

Modeling and Analysis of a Multilayer Dielectric Slab Waveguide With Applications in Edge-Coupled Terahertz Photomixer Sources

The waveguiding properties of a multilayer dielectric slab waveguide structure with applications in edge-coupled terahertz photomixer sources are studied. The structure guides two interfering laser beams, which their central frequency difference falls into the terahertz spectrum. The top layer of the dielectric waveguide structure is made of an ultrafast photoabsorbing material, wherein the power of the guided modes are being absorbed and converted into a terahertz signal. The optical field and power distributions inside the waveguide structure are studied for different physical parameters of the dielectric layers. The absorbed optical intensity and the generated terahertz photocurrent and terahertz power inside the photoabsorbing layer are calculated

Directivity Enhancement of Printed Antennas Using a Class of Metamaterial Superstrates

In this paper, we present some applications of metamaterial superstrates for directivity enhancement of printed antennas. Three different types of superstrates, viz., multilayer dielectric slabs, electromagnetic band gap (EBG) materials, and frequency selective surfaces (FSSs) are discussed. We first present the design of a multilayer dielectric slab, consisting of high and low permittivity dielectric layers and air-gap tuners for suppressing the grating lobes of patch array antennas. Next, a dielectric-rod EBG-type superstrate with two defect frequencies is proposed for dual-band directivity enhancement of a patch antenna at a boresight. With this design we can increase the degrees of freedom that adjust the level of directivity enhancement and operating frequency location, relative to those of the multilayer dielectric slab type. Finally, an FSS superstrate consisting of two-layered FSS screens for dual-band directivity enhancement is introduced as an alternative to an EBG type of dielectric superstrate to reduce its height and facilitate the fabrication process.

Prism coupling into clad uniform optical waveguides

The theory of prism coupling into multilayered dielectric slab waveguides is presented. In addition to including the possibility of high index cladding, the present theory also extends the region of validity of previously reported work to cover the regime of ’’strong coupling’’. The limiting conditions for validity of the present theory are that both αm/k and αm±p/k be much smaller than either unity or ‖βm−βm±p‖, where m is the mode under consideration, αm is the leakage of that mode, and ‖βm−βm±p‖ is the separation of the effective indices of adjacent modes. A numerical example is presented in which the coupling efficiency into a uniform or slab waveguide with Δn=0.002 is calculated for various cladding thicknesses with a cladding index of 2.5. The introduction of cladding is found to reduce coupling efficiency in this example due to increased phase mismatch between the incident and ’’ideal’’ beams.

Optical Transmission through Multi-Dielectric Slab

This paper deals with the study of light transmission through multi-layered dielectric slab. It is Seen that W type structure is quite suitable. Some important computations for such a structure are presented.

Ray optical analysis of waveguide transformers with dielectric inserts

The behaviour of TEmo mode wave propagation, in dielectric filled parallel-plate waveguides with axial step change in the dielectric constant, is analysed using laws of geometrical optics. The resulting expressions are the same as those obtained by the mode matching technique. As a result, reflection, transmission and cut-off conditions at the dielectric discontinuity are determined simply from Snell's law and the laws of reflection and refraction of plane waves at dielectric interfaces. The study also includes an extension of the theory of small reflections used in transmission line analysis to apply in the case of a plane wave obliquely incident on a multilayered dielectric slab with parallel interfaces. As an application, the length and permittivity of matching sections of a waveguide transformer with maximally flat pass-band characteristic connecting two guides filled with different dielectrics are determined using geometrical optics and the extended form of the theory of small reflections. The result...

Dielectric Properties of Mixed Barium and Strontium Titanates at 10,000 Mc./s

MEASUREMENTS have been made of the complex permittivity (χ'—jχ) of a series of mixed barium and strontium titanates at 9,450 Mc.—s. and 20° C. by a technique, already described1,2, which employs a wave-guide containing a multilayer dielectric slab.