Artificial Dielectric Research Articles

Magneto-plasmonic scattering by a disk-shaped particle made of an artificial dielectric

The main features of artificial dielectrics are high anisotropy and controllable heterogeneity, as well as adjustable values of their synthesized material parameters. In this work, we numerically study the scattering features of a disk-shaped particle made of an artificial dielectric (finely stratified structure, FSS) that is composed of magnetic and semiconductor constituents influenced by an external static magnetic field. The tensor-valued permittivity and permeability of the FSS are derived involving the effective medium theory. Due to a specific composition of the FSS, the material properties of the disk simultaneously acquire electric and magnetic gyrotropy, which depends on the proportion of the semiconductor and magnetic components included in the FSS. It is supposed that the ferromagnetic and plasma resonances of the constitutive materials are closely spaced. In particular, we examine the electric and magnetic dipole contributions to the scattering and absorption cross-sections obtained in the framework of the multipole decomposition method while accounting for the polarizability and magnetization induced in the particle by the field of incoming radiation. By varying the proportion of components of the artificial dielectric, we demonstrate the magneto-plasmonic functionality of the particle. Our presentation generalizes and complements several known solutions obtained separately for either magnetic or dielectric anisotropic particles. This approach can be used to study magneto-optical effects in metamaterials and metasurfaces composed of an ensemble of gyroelectric and gyromagnetic particles that is important for both plasmonic and photonic applications.

Laser assisted direct ink writing of multi‐material bismuth molybdate—silver artificial dielectrics for radio frequency applications

AbstractAdditive manufacturing of co‐fired low temperature ceramics offers a unique route for the fabrication of novel 3D radiofrequency (RF) and microwave components, embedded electronics and sensors. This study demonstrates the fabrication, materials analysis, and RF characterization of a multi‐material bismuth molybdate—silver (Bi2Mo2O9—Ag) artificial dielectric fabricated by laser assisted direct ink writing. The proposed fabrication technique enables 3D printing of dissimilar materials while minimizing inter‐material diffusion through the liquid phases. The permittivity of the artificial dielectrics increased up to 99% over the investigated frequency range (8–12 GHz) compared to the fabricated pure ceramic sample.

Phased Array With Pattern Shaping and Scan Loss Reduction for Millimeter Waves

In this work, we investigate antenna architectures to implement dual-mode operation in phased array designs. Planar slot antenna elements are used in array configuration, in combination with artificial dielectrics layers (ADLs) located in the close proximity of the array, to achieve pattern shaping. The artificial dielectric superstrate supports the propagation of leaky waves that can be optimized to enhance the gain in a specific angular region or to enlarge the array field of view. By controlling the amplitude and phase of the antenna elements, the radiation patterns can be combined to realize either wide or narrow beams. This concept present advantages for both millimeter-wave (mm-wave) communication and radar applications. A design of a four-element array fabricated in standard printed circuit board (PCB) technology validates the feasibility of the dual-mode operation. The measured results also show good agreement with simulations.

Моделирование магнитоэлектрического материала для антенн

The paper is devoted to the modeling of magnetoelectric material for antennas. The effect observed in magnetoelectric gradient structures is discussed. Gradient magnetoelectric structures are a new type of composite structures consisting of a magnetoelectric material and an artificial dielectric. A new principle of controlling the antenna wave properties based on the geometric displacement of the excitation point due to the application of an external electric field is being considered. The use of an artificial dielectric in a multiferroid structure will make it possible to more flexibly control the areas of conversion of a magnetostatic surface wave into an electromagnetic wave, which in practical terms will give new opportunities for controlling the characteristics of antennas. The conclusion about the possibility of controlled conversion of a magnetostatic surface wave into an electromagnetic wave was obtained as a result of calculations based on the developed model by selecting the values of stationary magnetic and electric fields, and the values of the permittivity of the artificial dielectric layer

Analysis of Nonsquare Artificial Dielectric Layers and Application to the Design of Anisotropic Slabs

We present a general analysis to describe non-square artificial dielectric layers (ADLs). Closed-form expressions for the equivalent layer impedance are given for generic plane-wave incidence, assuming that the ADLs have different geometrical parameters in the x- and y-directions. The analytical expressions account for the interaction between layers due to higher-order Floquet modes, thus remain valid for arbitrarily small electrical distance between layers. Such non-square geometries allow the design of artificial anisotropic slabs with azimuth-dependent effective refractive index. As an example for an application, the equivalent model is used to design the superstrate of a double slot antenna, with independent pattern shaping in the two main planes.

Magnetoelectric gradient structures

This work is a comprehensive theoretical study of a new class of structures – magnetoelectric gradient structures, which are a product of the integration of magnetoelectric mutliferroic layered structures and an artificial dielectric. In this paper, a mathematical model of the behaviour of a layered multiferroic structure in inhomogeneous electric and magnetic fields is built on the basis of solving Maxwell’s equations, taken in the magnetostatic approximation, and the equation of motion of the magnetization. Based on the constructed mathematical model, the influence on the spectrum of eigenwaves of stationary magnetic and electric fields, as well as the values of the dielectric constant of an artificial dielectric layer, are analysed. The results of the study confirm the possibility of designing a new class of electronically controlled microwave devices with a triple control mechanism: magnetic field – electric field – artificial distribution of dielectric constant.

Design of compact and broad-bandwidth rectangular patch antenna using cylindrical rods artificial dielectric

This paper presents novel compact and high performance microstrip patch antenna by using artificial dielectric. Cylindrical rods artificial dielectric is embedded in substrate of reference patch antenna, this makes the antenna compact, reflection coefficient improves and enhancement in impedance bandwidth is achieved. Technique of designing the cylindrical rods artificial dielectric in given frequency range is also presented in this paper. Practical swarm optimization technique (PSO) is used to design and optimize the proposed antenna. Finally, RMPA with cylindrical rods embedded substrate is proposed that provides 47.2% compactness, improved return loss and bandwidth. Mathematical analysis of proposed antenna is also done to verify the simulated results of proposed antenna. The effect of rods parameters (height, radius, and distance between rods) on the performance of patch antenna is also analysed.

Super-capacitive patches and their use in low-pass filters and artificial dielectrics

The use of capacitive metal meshes consisting of square patches is well established in the design of millimeter-wave optical devices such as filters, half-wave plates, and graded-index lenses. The main property of these meshes, the capacitance, is controlled by the size of the square patch in the mesh’s unit cell up to a limit imposed by the minimum feature size of the manufacturing process. We report the results of a study into the feasibility of increasing the capacitance beyond this limit by extending fingers into the adjacent unit cell. This is shown to increase the range of admittance characteristics available with the meshes and how this might be useful for the implementation of low-pass filters and artificial dielectrics is demonstrated.

Comparative analysis of Luneberg spherical lens designs

Formulation of the problem. The development of modern mobile satellite communication systems dictates the need for the development of multipath antennas having: high values of the directional coefficient, low level of side lobes, a large number of scanning beams in a wide viewing sector without distortion in the azimuthal and angular planes. Multipath antenna systems based on spherical Luneberg lenses have these advantages. Despite their advantages, the spherical lenses of Luneberg did not find wide practical use due to the complexity of the design, the high cost of production, and the large mass (in some cases). Thanks to the progress in the field of artificial media, the emergence of new production methods, various designs of spherical Luneberg lenses have been developed. The use of artificial dielectrics allows you to create inexpensive, lightweight spherical Luneberg lenses. One widely used method of creating an artificial environment is to use partial air filling dielectrics. Luneberg lenses based on such media can have various designs: based on a dielectric ball with radial holes of variable diameter, from electrically small dielectric cubes of variable size, from a set of perforated dielectric disks, etc. For the manufacture of such lenses, various manufacturing technologies can be used, for example, three-dimensional printing, CNC machine. Purpose. Comparative analysis of the characteristics of two structures of the spherical Luneberg lens with the aim of working at frequencies above 9 GHz: from a set of perforated dielectric disks, from dielectric cubes of different sizes. Results. The results of comparative analysis of two designs of the spherical Luneberg lens are presented. The procedure of synthesis of each structure is considered. Design dependencies of effective dielectric constant used in development of investigated spherical lenses of Luneberg are given. Possible methods of technical implementation for each lens are considered, as well as important features that should be taken into account when designing and technical implementation. The weight of each structure was estimated. Conclusions about mechanical strength were made. Based on numerical modeling using the Weyland method, a comparison of directional properties in a wide frequency band was made. Conclusions have been drawn about the similarity and difference in directional characteristics. Practical importance. The scientific and technical results obtained in the article will be useful in choosing the design of the Luneberg lens from artificial dielectrics, depending on the specified technical requirements, and production conditions.

Optically and radio frequency (RF) transparent meta-glass

Abstract We propose a radio frequency (RF) and visibly transparent composite metasurface design comprising newly developed transparent multilayer conductive coatings. Detailed experimental and theoretical analysis of the RF/visible transparency of the proposed meta-glass is provided. The proposed nature-inspired symmetrical honeycomb-shaped meta-glass design, alters the electromagnetic properties of the glass substrate in the RF spectrum by utilizing visibly transparent Ag-based conductive coatings on each side. Furthermore, the competing effect of the Ag thickness on optical and RF transparency is discussed. We show that using multilayer dielectric-metal coatings, specifically 5-layered spectrally selective coatings, RF transparency of the meta-glass can be enhanced while preserving visible transparency. Herein we demonstrate high transparency meta-glass with 83% and 78% peak RF and optical transmission at 28 GHz and 550 nm, respectively. The meta-glass yields enhanced RF transmission by 80% and 10% when compared to low-emissivity glass and bare glass, respectively. The meta-glass design presented here is amenable to a variety of 5G applications including automobile radar systems. This work provides a superior alternative to the standard indium-tin-oxide (ITO) transparent material which is becoming scarce. Moreover, this study paves the way for the design of new visibly transparent metamaterials and artificial dielectrics.

Broadband graded index Gutman lens with a wide field of view utilizing artificial dielectrics: a design methodology

A novel all-metal graded index Gutman lens is proposed. It exploits an interleaved metasurface unit-cell with glide symmetry that can provide high values of equivalent refractive index with low frequency dispersion. The result is a compact lens with broadband performance and a wide field of view up to ±70°. The proposed lens exhibits low loss, directive beams and is an appealing candidate for space applications. The design approach introduced can be applied to other graded index lenses with circular symmetry using rectangular or circular periodic structures.

A Linear Array of Skewed Dipoles With Asymmetric Radiation Pattern for Angular Filtering

In this letter, we present a design of a linear array of tilted dipoles to achieve radiation patterns with asymmetric angular filtering characteristics. To realize the asymmetric radiation, the dipole elements are spaced by a distance larger than half a wavelength, thus allowing for grating lobes to occur in the visible region. Moreover, the dipoles are loaded with artificial dielectrics to increase the front-to-back ratio and consequently to enable higher gain in certain desired angular regions. Based on the design, a linear array with ten elements is manufactured and tested. The measured results show the ability of such an array to achieve stable gain from broadside up to 90° scanning while implementing a stopband angular filter for negative scanning angles.

On the fabrication of thin-film artificial metal grid resonator antenna arrays using deep x-ray Lithography

In this paper, a unique microfabrication approach for designing high permittivity, high gain and wideband thin-film artificial metal grid dielectric resonator antenna (GDRA) arrays for mm-wave applications is presented. Fabrication of the GDRAs with a strip template frame is based on deep-x-ray lithography (DXRL) using a 500 µm thick polymethylmethacrylate (PMMA) layer as the photoresist. The simple low-cost fabricated DXRL mask for exposure consisted of gold absorbers patterned by direct-write ultraviolet (UV) laser lithography on a carbon substrate. To avoid the trapping of gas bubbles in the dense, high aspect ratio (HAR) deep grid structures, a novel development approach was introduced utilizing in-vacuum, room temperature dip development to facilitate the collapse of forming gas bubbles. The developed voids were subsequently electroplated to a nickel thickness of 300 µm to obtain high permittivity artificial dielectrics. The paper describes the entire fabrication sequence. Also, the x-ray mask and DXRL structures are examined for dimensional accuracy and structural quality. This strip template frame approach has superior performance in terms of impedance bandwidth, gain and radiation efficiency as compared to the previously published solid template frame approach. For the purpose of the demonstration, a four-element GDRA array sample was fabricated and tested. A wide measured impedance bandwidth of 5 GHz from 58 GHz to 63 GHz and measured broadside radiation pattern with a peak gain of 10.9 dBi was achieved.

Wide-band effective medium theory for a cubic array of metallic spherical particles

Based on the multi-scattering Mie theory, the effective relative permittivity and permeability of metal-dielectric non-resonant artificial dielectric are derived in a closed form in this study for a quite broad frequency range. The artificial dielectric is a 3-D infinite isotropic homogenous dielectric medium with periodically imbedded non-magnetic metallic inclusions of spherical shape.The obtained effective medium theory is shown that belonging to a general class of non-resonant metamaterials, the considered composite medium exhibits an effective “ultra-low index behavior” at the THz frequencies. The results obtained for the case of non-magnetic metallic inclusions are compared with the Lewin’s theory. The comparisons of results of the proposed theory with the experimental results of the authors are presented in the study from deep UV to visible region.

Marked effects of lateral displacement on the optical transmission properties of stacked artificial dielectric systems composed of metallic sub-wavelength slit arrays

Metallic sub-wavelength slit-array slabs act just like dielectrics when the incident wavelength is longer than the slit interval. However, their stacked structures do not always exhibit optical properties equivalent to conventional dielectric multilayers, which should be due to the lateral periodicity. This work investigated in detail the lateral displacement dependence on the characteristics of the Fabry–Perot-like waveguide resonance modes of two-tier systems. Simulation studies clarified the behavior of the resonance modes and the physical mechanism underpinning the transmission disappearance by the lateral displacement. Furthermore, we determined that the critical frequency, above which the even-order modes exhibit blue-shifts with increases in the air gap spacing, can be predicted very accurately using a simple equation including the lateral displacement. Additionally, the transmission characteristics assessed experimentally were compared with the simulation results. The geometrically-tunable unique optical characteristics are expected to promote the future applications of artificial dielectrics operating in low-frequency optical regions.

Miniaturized suspended strip-line bandpass filter based on spoof surface plasmon polaritons

In this letter, we propose the design of miniaturized suspended strip-line (SSL) filters based on spoof surface plasmon polariton (SSPP), a sub-wavelength mode confined tightly around artificial structures. To avoid using high-density lossy dielectric fillings, we place a periodic corrugated metallic strips (PCMS) structure in a rectangular metallic cavity. Two probes are positioned near the two ends of PCMS structure. Since PCMS structure support SSPP with shorter wavelength, it can be treated as low-loss artificial dielectrics with high permittivity εr equivalently. The cut-off frequency f lower of waveguide modes in the cavity will be reduced, which, plus the cut-off frequency f upper of SSPP, will produce a pass band between f lower and f upper. Due to high εr, low insertion loss and light weight of the PCMS structure, miniaturized band-pass filters can be implemented using such a configuration. We demonstrated a prototype operating a bandpass filter in 2.7–4.6 GHz. The cross-section of cavity is reduced by more than 75%. The filter is with quite low insertion loss only 0.1–0.3 dB. Both simulation and measurement results verify this design. This work provides an alternative to miniaturized, light-weight, high-efficiency SSL filters.

Dissipation Losses in Artificial Dielectric Layers

Closed-form expressions to describe artificial dielectric layers with finite conductivity are presented. The propagation of a generic plane wave within the artificial material is described by means of transmission line models, where each layer is represented as an equivalent shunt impedance. The given analytical formulas for the shunt impedance are derived assuming finite conductivity of the metal, and thus, also an accurate estimation of the losses within the artificial dielectric is obtained from the equivalent circuit. The expressions account for the reactive coupling between the layers due to higher order Floquet modes, thus remain valid even for extremely small electrical distance between layers.

Insertion effects of natural dielectric between artificial dielectrics formed by metallic sub-wavelength slit arrays

We investigated the optical transmission properties of a metamaterial system in which a natural dielectric is inserted between metallic sub-wavelength slit arrays that behave as an artificial dielectric when the incident light wavelength is longer than the slit periodicity. Transmission spectra were measured using terahertz time-domain spectroscopy, and the experimental results were analyzed by simulations based on the finite-difference time-domain method. We revealed that the resonance characteristics are defined by the two diffraction-limit frequencies for the inner and outer openings of the slits, which are different for the insertion of the dielectric. We also determined further details on the blue-shift behavior specific to the even-order resonance modes by accounting for the refractive index of the inserted intermediate dielectric. In addition, we experimentally demonstrated that insertion of a dielectric having a high refraction index enhances the frequency repulsion at the anticrossing, i.e., the coupling strength, between the symmetric and antisymmetric optical modes. These experimental and theoretical results will be essential for understanding and developing applications for hybrid systems composed of dielectrics with both fixed and widely tunable refractive indices.

Artificial dielectric stepped-refractive-index lens for the terahertz region.

In this paper we theoretically and experimentally demonstrate a stepped-refractive-index convergent lens made of a parallel stack of metallic plates for terahertz frequencies based on artificial dielectrics. The lens consist of a non-uniformly spaced stack of metallic plates, forming a mirror-symmetric array of parallel-plate waveguides (PPWGs). The operation of the device is based on the TE1 mode of the PPWG. The effective refractive index of the TE1 mode is a function of the frequency of operation and the spacing between the plates of the PPWG. By varying the spacing between the plates, we can modify the local refractive index of the structure in every individual PPWG that constitutes the lens producing a stepped refractive index profile across the multi stack structure. The theoretical and experimental results show that this structure is capable of focusing a 1 cm diameter beam to a line focus of less than 4 mm for the design frequency of 0.18 THz. This structure shows that this artificial-dielectric concept is an important technology for the fabrication of next generation terahertz devices.

Analytical Formulas for Artificial Dielectrics With Nonaligned Layers

In this paper, we present analytical models to describe artificial dielectric layers (ADLs), when a lateral shift between layers is present. The alternate lateral displacement between layers is an important parameter to engineer the desired effective electromagnetic properties of the equivalent homogeneous material realized with the ADLs. More specifically, the equivalent dielectric constants that can be realized by alternatively shifting the layers are higher compared with the aligned case. Closed-form expressions are derived for the equivalent layer reactance that includes the higher order interaction between shifted layers. The given analytical formulas can be used to derive an equivalent circuit model that describes the scattering parameters of a plane wave impinging on a slab composed by an arbitrary finite number of metal layers. To aid the design of artificial dielectric slabs, the effective permittivity and permeability tensors are also retrieved from the scattering parameters.