Low-loss Dielectric Material Research Articles

Broadband terahertz metamaterial absorber enabled by using high-loss dielectric materials

Metamaterial absorbers consisted of two metallic layers separated by low-loss dielectric materials have been extensively presented and studied. However, these absorbers using low-loss dielectric materials usually exhibit narrow bandwidth, which are not conductive to the practical applications. Here, we demonstrate a novel terahertz meta-device that can obviously widen the absorption bandwidth of metamaterial absorber. This meta-device is composed of a high-loss dielectric material sandwiched by a metallic strip and an opaque metallic mirror. Absorption of greater than 80% of the meta-device can cover a continuous frequency range of 2.43 THz, and its relative absorption bandwidth can reach 89.17%. These two indexes are both much larger than those of previous absorption devices using low-loss dielectric materials. Physical mechanism of the meta-device originates from the superposition of two different resonant modes. More importantly, the variation of meta-device parameters can provide considerable degree of freedom to regulate the absorption bandwidth and relative absorption bandwidth of the device

Measurement of Dielectrics From 20 to 50 GHz With a Fabry–Pérot Open Resonator

A novel approach to the measurement of complex permittivity of low-loss dielectric materials with the aid of an open Fabry–Perot resonator with concave Gaussian mirrors is presented in this paper. For that purpose, a new scalar 1-D layered electromagnetic (EM) model of the resonator is proposed. The model takes the advantage of Cartesian-to-Gaussian coordinate transformation and axisymmetrical properties of the TEM modes of interest. There are several advantages of the proposed approach. The first is the use of Gaussian mirrors instead of spherical ones, which better fit to the shape of Gaussian wavefronts. Second, the model more accurately accounts for oblique incidence of the wave onto the surface of the sample, which is one of the major challenges in case of alternative models based on a characteristic equation. An automated measurement setup operating in the 20–50-GHz range has been designed and manufactured to experimentally validate the proposed measurement method. A real part of permittivity of a few well-known materials, such as silicon, quartz, polystyrene, or polyethylene terephthalate (PET) foil, has been measured with the accuracy better than 0.5%, which means a significant improvement as compared to the state of the art in this area.

Applications of Microwave Materials: A Review

The performance of microwave devices mainly depends on the properties of materials used in the fabrication. Knowledge of material properties at microwave frequencies is a prerequisite to select suitable materials for various microwave applications and vice versa. In this review, seven categories of materials and their applications in a microwave regime are elaborately discussed. The categories include magnetic materials, carbon-based materials, flexible or stretchable materials, biomaterials, phantoms, tunable materials and metamaterials. A brief overview of other important microwave materials such as low-loss ceramic dielectric materials, low-loss polymer ceramic composites, glass ceramics and multilayer ceramics is also given. The objective of this review is to expose the world of materials for wide microwave applications and thereby properly assisting the material selection for specific applications. Moreover, this review has dual significance. It helps material scientists to develop new materials and modify the properties of the available materials with respect to the application requirements. It also assists microwave engineers to select and use appropriate materials for different microwave applications.

Structural and electrical properties of CuLayFe2-yO4 ferrites


 
 
 
 Ferrite with the general formula CuLayFe2-yO4 (where y=0.02, 0.04, 0.06, 0.08 and 0.1), were prepared by standard ceramic technique. The main cubic spinel structure phase for all samples was confirmed by x-ray diffraction patterns with the appearance of small amount of secondary phases. The lattice parameter results were 8.285-8.348 Å. X-ray density increased with La addition and showed values between 5.5826 – 5.7461gm/cm3. The Atomic Force Microscopy (AFM) showed that the average grain size was decreasing with the increase in La concentration. The Hall coefficient was found to be positive. It demonstrates that the majority of charge carriers of p-type, suggesting that the mechanism of conduction is predominantly caused by hopping of holes. The resistivity was noticed to increase with the increase in La substitution. The activation energy Eav decreased with the frequency increase. The AC conductivity was found to increase with the frequency and La addition. Dielectric constant was noticed to decrease with frequency and La addition. The dielectric loss factor decreased with La content because rare earths are known as low dielectric loss materials.
 
 
 

Characterization of additively manufactured cellular alumina dielectric structures

Additive manufacturing (AM, also known as 3D printing) can produce novel three-dimensional structures using low-loss dielectric materials. This enables the construction of dielectrics with complex shapes that enable innovative microwave applications such as resonators, filters, and metamaterial lenses. This paper addresses the production and characterization of cellular structures of various designed densities created with a low loss ceramic material, alumina (aluminum oxide), via vat photopolymerization. The permittivity of these printed structures is variable over roughly an octave, with a range of relative permittivites from 1.78 to 3.60, controlled via part geometry.

Lattice Resonances and Local Field Enhancement in Array of Dielectric Dimers for Surface Enhanced Raman Spectroscopy

In this paper, we propose the use of high refractive index dimers for the realization of a surface enhanced Raman spectroscopy substrate, with an average enhancement factor comparable to plasmonic structures. The use of low loss dielectric materials is favorable to metallic ones, because of their lower light absorption and consequently a much lower heating effect of the substrate. We combined two different mechanisms of field enhancement to overcome the main weakness of dielectric dimers: a low enhancement factor compared to the plasmonic ones. A first mechanisms is associated to surface lattice resonances. This generates a narrow-band high enhancement, which is exploited to enhance the excitation light. A second mechanism exploits the local field enhancement between the dimers’ resonators, for the band where the molecule Raman emission spectrum is located. The fact that both field enhancements can be tuned by acting on separate geometric parameters, makes possible to optimize the design for many different molecules. The optimized structure and its performance is presented together with a discussion of the different enhancement mechanisms.

Photosensitive Polyimide having low loss tangent for RF application

Abstract Progress of 5G telecommunication and mm radar for autopilot, high frequency operation is required. Insulator materials having low loss at high frequency is desired for the applications. We designed the low dielectric constant, and low dielectric loss materials examined molecular structure of the polyimide and found that permittivity 2.6 at 20GHz, dielectric loss 0.002. Furthermore, in consideration of mechanical properties such as the toughness and adhesion to copper from a point of practical use. Dielectric properties largely turned worse when giving photosensitivity. To overcome the poor dielectric properties, we designed the photosensitive system. After all, we successfully obtained 3.5 of dielectric constant and 0.004 of dielectric loss, and 100% of elongation at break. In addition, we offered a B stage sheet as well as varnish. These materials are applicable to re-distribution layer of FO-WLP, Interposer and other RF applications for microelectronics.

Polyvinyl Alcohol/EuBa2Ca2Cu3O9−x Composites: Dielectric and Mechanical Properties

In the present work, the influence of EuBa2Ca2Cu3O9−x (coded as Eu-1223) ceramic additive on the mechanical and dielectric properties of poly(vinyl alcohol) (PVA) polymer were investigated for the first time. PVA/Eu-1223 polymer-ceramic thick film composites were prepared by solution casting method with different ceramic contents varying from 1 to 5%. The surface morphology of the samples were studied with scanning electron microscope revealed that adding higher concentration of Eu-1223 increases the roughness of the surface as well as the fragility of the PVA. Thermogravimetric analyses results revealed that the increasing Eu-1223 additive enhances slightly both the thermal and oxidative stability of the PVA. Furthermore, FTIR analysis of the composite displayed new FTIR transmittance peaks that can be attributed to the formation of a reaction between the PVA polymer chain and the ceramic additive. The mechanical properties in the context of stress–strain curves of the samples unveiled that increasing ceramic doping improves the Young’s modulus of PVA films. The impedance and dielectric properties of the samples recorded at room temperature indicated a space charge polarization regardless of the doping concentration. The complex electrical modulus analysis also pointed out a pure conduction process. The Nyquist and phase angle plots defined the grain and grain boundary properties along with the ideal capacitor ability of the composites. Especially, the lower e′ and e″ values were achieved for the 5% Eu-1223 additive level concentration. This work brings out that 5% Eu-1223 added PVA thick film may be suggested as a low dielectric loss dielectric material for supercapacitor applications.

A Twofold Approach in Loss Reduction of KTa0.5Nb0.5O3 Ferroelectric Layers for Low-Loss Tunable Devices at Microwaves.

Ferroelectric oxide films are attractive to design and fabricate reconfigurable and miniaturized planar devices operating at microwaves due to the large electric field dependence of their dielectric permittivity. In particular, KTa1-xNbxO3 (KTN) ferroelectric material presents a high tunability under moderate dc bias electric field. However, its intrinsic dielectric loss strongly contributes to the global loss of the related devices and limits their application areas at microwaves. In this paper, a twofold approach is investigated to reduce the device loss. The intrinsic loss of KTN is first reduced by doping the ferroelectric material with a low-loss dielectric material, namely, MgO. Second, the doped ferroelectric films are confined using an original laser microetching process. Both routes have been implemented here to provide a synergic effect on the total insertion loss of the microwave test device, namely, a coplanar waveguide stub resonator. The experimental data demonstrate a decrease of the intrinsic loss by a factor of ~2 and a decrease of the global loss by a factor of ~4 with a frequency tunability close to 10% at ~10 GHz under a moderate biasing (80 kV/cm).

High breakdown strength and low loss binary polymer blends of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) and poly(methyl methacrylate)

Dielectric materials with high breakdown strength and low loss are of crucial importance in capacitive energy storage electronics. Herein, a kind of polymer blend composed of poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) ferroelectric terpolymer and linear dielectric poly(methyl methacrylate) (PMMA) is presented. The polymer blend shows a breakdown strength of 733 MV/m and a charge‐discharge efficiency over 90% at 200 MV/m with optimized PMMA content, which are 101% and 28% higher than that of neat terpolymer. Moreover, microsecond discharge time of 2.26 μs, along with a power density that is 3.6 times that of the current commercially available biaxially oriented polypropylene, as well as great cyclic performance, has been achieved under an electric field of 200 MV/m. The findings of this research demonstrate that the incorporation of linear dielectric PMMA into poly(vinylidene fluoride)‐based ferroelectric polymer provides a new strategy in designing high breakdown strength low loss dielectric materials for reliable compact flexible film capacitors.

Harnessing magnetic dipole resonance in novel dielectric nanomaterials.

Photonic manipulation with plasmonic materials is typically associated with high ohmic losses, which has triggered interest in alternative strategies based on low loss dielectric materials. Here we describe a novel dielectric nanomaterial capable of supporting strong Mie resonances from the visible to IR regimes. The fundamental block of this metamaterial is based on nanopillars in a core-shell configuration, with a large refractive index (RI) contrast between the (low RI) core and the (high RI) shell. The material showed strongly tunable optical resonances that varied from visible to near and mid IR as a function of shell thickness, core diameter and inter-pillar spacing. The numerical simulations, which are in good agreement with the experimental results, suggest the optical response to be dominated by magnetic dipole resonances. This versatile material platform is CMOS compatible, can be fabricated in a scalable manner as thin films, can act as strong scatterers in colloidal suspensions and thereby can provide several promising technological opportunities in nanophotonics.

Analysis of a thin, penetrable, and non‐uniformly loaded cylindrical reflector illuminated by a complex line source

A thin, penetrable, and cylindrical reflector is illuminated by the incident field of a complex source point. The scattered field inside the reflector is not considered and its effect is modelled through a thin layer generalised boundary condition (GBC). The authors formulate the structure as an electromagnetic boundary value problem and two resultant coupled singular integral equation system of equations are solved by using regularisation techniques. The GBC provides us to simulate the thin layer better than the resistive model which is applicable only for very thin sheets. Hence, the more reliable data can be obtained for high-contrast and low-loss dielectric material. The scattering and absorption characteristics of the front-fed and offset reflectors are obtained depending on system parameters. Also, the effects of the edge loading are examined for both E- and H-polarisations. The convergence and the accuracy of the formulation are verified in reasonable computational running time.

Directional Emission from Dielectric Leaky-Wave Nanoantennas.

An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry. A promising way to circumvent these problems is the use of broadband nanoantennas made from low-loss dielectric materials. Here, we report on highly directional emission from hybrid dielectric leaky-wave nanoantennas made of Hafnium dioxide nanostructures deposited on a glass substrate. Colloidal semiconductor quantum dots deposited in the nanoantenna feed gap serve as a local light source. The emission patterns of hybrid nanoantennas with different sizes are measured by Fourier imaging. We find for all antenna sizes a highly directional emission, underlining the broadband operation of our design.

All-dielectric integration of dielectric resonator antenna and photonic crystal waveguide.

Two-dimensional photonic crystal waveguides can support guided modes with low loss. Interfacing such a guided mode with free-space propagation modes is crucial for photonic integrated circuits. Here we propose a dielectric resonator antenna (DRA) fully integrated with a photonic crystal waveguide for endfire radiation. High radiation efficiency can be achieved from the DRA that relies on oscillating displacement currents in a low-loss dielectric material. The antenna is designed to operate at a high-order resonance for high gain. The reflection loss at the interface between the two components is minimized via a matching air hole, the mechanism of which is qualitatively described via temporal coupled-mode theory. As a proof of concept, the all-dielectric integrated structure is realized on a single intrinsic silicon wafer to operate at terahertz frequencies. The antenna footprint is only about one square operational wavelength. The experimental validation confirms the maximum gain of over 10.6 dBi with 3-dB angular beam widths of 29.0 degrees and 45.7 degrees in orthogonal dimensions. The impedance bandwidth obtained from simulation is 6%, spanning 311 to 331 GHz. Given a suitable low-loss dielectric material, this all-dielectric structure holds potential for scaling to infrared and visible light frequencies.

Structural, optical, dielectric and magnetic properties of CaFe2O4 nanocrystals prepared by solvothermal reflux method

Single crystalline CaFe2O4 nanospheres were synthesized by solvothermal reflux method using high boiling point organic solvents mixture. Both X-ray diffraction and electron diffraction profiles were confirmed single phase nature of the compound. The sample shown spherical morphology with average particle size of 10 nm which is same as crystallite size determined from the XRD. A thin layer of surfactant oleic acid was adsorbed on the surface of the nanoparticles. The optical excitation spectra reveals that the compound has direct allowed energy bandgap of 1.26 eV. The temperature dependent dielectric constant (εr′) and dielectric loss (εr″) measurements show low values at room temperature and were nominally changes with enhance of temperature upto 650 K. Above which both εr′ and εr″ were steeply increased with small variation of temperature which could be assigned to enhanced electrical conductivity due to surface charge conduction and, partially, to on-set of decomposition of oleic acid present on the surface of the sample. The samples show variable electron hopping conductivity in the temperature range studied and was supported by both Arrhenius plots and electric modulus studies at different frequencies. The CaFe2O4 nanoparticles show superparamagnetic nature at room temperature with high saturation magnetization (48.54 emu/g). The magnetization is much higher than ferrimagnetic bulk magnetization. Langevin function fit to magnetization data give 8 nm magnetic domain diameter and 1 nm magnetically disordered thin shell on the surface of the nanoparticles. As CaFe2O4 nanoparticles were electrically resistive and low dielectric loss materials, they may find applications in microwave engineering. In addition, the CaFe2O4 superparamagnetic nanoparticles were biocompatible and have high saturation magnetization, they could be used in biomedical applications such as magnetic hyperthermia and directed drug delivery applications.

A novel temperature-stable and low-loss microwave dielectric using Ca0.8Sr0.2TiO3- modified Li2Mg3TiO6 ceramics

Microstructure and microwave dielectric properties of (1-x)Li2Mg3TiO6-xCa0.8Sr0.2TiO3 (x = 0.03, 0.06, 0.08, 0.09, 0.12) ceramics prepared by the conventional solid state route have been investigated. XRD and SEM-EDS analysis confirmed that ceramics contain Li2Mg3TiO6 and Ca0.8Sr0.2TiO3 phases. The microwave properties exhibited a significant dependence on the sintering temperature and Ca0.8Sr0.2TiO3 content. With increasing addition of Ca0.8Sr0.2TiO3, the dielectric constant $$({\varepsilon _r})$$ increased from 14.3 to 17.4 when samples sintered at 1410 °C for 4 h; the quality factor (Q × f) decreased from 133,905 to 101,000 GHz, and the temperature coefficient of resonant frequency ( $${\tau _f}$$ ) significantly increased from −39 to 6.35 ppm/°C when samples sintered at 1370 °C for 4 h. Sample with 0.91Li2Mg3TiO6-0.09Ca0.8Sr0.2TiO3 sintered at 1370 °C for 4 h possess excellent microwave properties with $${\varepsilon _r}$$ of 16.4, a Q × f of 113,000 GHz and $${\tau _f}$$ of −3.65 ppm/°C. It is proposed as low-loss and low-cost dielectric materials for microwave and millimeter wave application.

Electrical Insulation Characteristics and Mechanisms of Low Dielectric Loss Materials for High-Voltage HTS Cables

Toward the practical development of high-voltage high-temperature superconducting (HTS) cables, high electrical insulation characteristics, and low dielectric loss become important. Dielectric loss drastically increases with the increase of operation voltage of HTS cables. Therefore, it is highly expected to find a novel insulating material with low dielectric loss for the high-voltage HTS cables. We have focused on Tyvek ® , polyethylene (PE) nonwoven fabric, and Tyvek ® /PE, a syntactic paper bonding PE-sheet on Tyvek ® by heat, as low dielectric loss materials. In this paper, we investigated fundamental partial discharge inception characteristics and their mechanisms of Tyvek ® immersed in liquid nitrogen (LN 2 ).In addition, we compared the electrical insulation characteristics of Tyvek ® , Tyvek ® /PE, and polypropylene laminated paper (PPLP ® ), and discussed their mechanisms.

Anomalous reflection of visible light by all-dielectric gradient metasurfaces

Plane wave scattering by a planar metasurface composed of two periodically alternating rectangular dielectric rods is considered. A rigorous integral equation methodology is employed for the analysis and the accurate determination of the reflected and transmitted fields. Systematic optimizations with respect to the configuration’s parameters are performed, which reveal that it is possible to obtain significantly enhanced anomalous reflection (with simultaneously suppressed ordinary reflection predicted by Snell’s law) with power varying from 92% to almost 100% of the input one, depending on the color of the incident light. It is shown that these reflection properties are supported by metasurfaces easily realizable with specific low-loss dielectric materials. In this way, several all-dielectric optimal designs are reported that can be used in numerous applications demanding anomalous reflection in the visible range.

Terahertz near-field imaging of dielectric resonators.

As an alternative to metallic resonators, dielectric resonators can increase radiation efficiencies of metasurfaces at terahertz frequencies. Such subwavelength resonators made from low-loss dielectric materials operate on the basis of oscillating displacement currents. For full control of electromagnetic waves, it is essential that dielectric resonators operate around their resonant modes. Thus, understanding the nature of these resonances is crucial towards design implementation. To this end, an array of silicon resonators on a quartz substrate is designed to operate in transmission at terahertz frequencies. The resonator dimensions are tailored to observe their low-order modes of resonance at 0.58 THz and 0.61 THz respectively. We employ a terahertz near-field imaging technique to measure the complex near-fields of this dielectric resonator array. This unique method allows direct experimental observation of the first two fundamental resonances.

Measurement of Complex Permittivity of Materials Using a Double-Ridge Waveguide Resonator

A double-ridge waveguide resonator loaded with rod like dielectric material was analyzed based on the electromagnetic simulation software HFSS and microwave resonant cavity perturbation technique in this paper. The perturbation method is used to calculate the complex permittivity of the material due to the change of the resonator's tiny change. The calculation expression of complex permittivity was deduced and proper test system was built for the validation at several specific frequencies, the resonant parameters of the cavity were measured by the external Agilent vector network analyzer, according to the calibration of standard quartz sample, the complex permittivity of the quartz, sapphire and PTFE samples were calculated. Experimental result showed that the method has a good performance for measuring the complex permittivity of low dielectric loss dielectric materials.