Permittivity Of Dielectric Substrate Research Articles

Simulation of Wave Propagation in Plasma-Metamaterial Composites Based on Plasma Parameters and Metamaterial Structures

Metamaterial is a left-handed medium used in antenna design to overcome the typical design's larger size and untunable nature. Because of its design with a high permittivity dielectric substrate and some deformation, the wireless sector may be able to solve this difficulty. Metamaterial antennas have a five-fold reduction in size, a higher bandwidth, a wider scanning angle, good beam performance, and electronically controlled targeting. Metamaterials antennas also improve antenna parameters such as frequency generation, gain, and bandwidth. This research aims to suggest the best metamaterials structure for improving antenna performance using plasma as a base. This study used 12 types of plasma with varying plasma frequencies and collision frequencies with four metamaterials structures: 1D-split ring structure, Symmetrical structure, Omega structure, and S structure. Computer Simulation Technology (CST) Studio Suite was used to design and simulate each structure with a sequence of plasma. At frequencies ranging from 1 GHz to 20 GHz, parameters including return loss, gain, radiation pattern, and Voltage Standing Wave Ratio (VSWR) are used to assess an antenna's performance. Due to its electromagnetic qualities, the 1D-split ring construction has a better omnidirectional figure and VSWR value of 1.0039 dB. When all criteria were considered, the best results were obtained when using a 1D-split ring structure of the Plasma 9 (plasma frequency of 3.58528 x1011 rad/s and collision frequency of 1.3349 x109 1/s) produces an efficient return loss, high gain, better VSWR and a better omnidirectional figure among the four structures evaluated.

A Dielectric Loaded Resonator for the Measurement of the Complex Permittivity of Dielectric Substrates

A new configuration of dielectric-loaded resonator (DR), particularly versatile for the complex permittivity measurement of substrates for microwave circuits, even in the presence of back metal plates, is shown here. To test this technique in a wide interval of the values of the complex permittivity, the versatility of 3-D printing is exploited to print samples with different densities, thus artificially changing the effective permittivity in the interval (1.7–3.1) for the real part and (0.02–0.06) for the imaginary part. The designed resonator, tuned at ~12 GHz, is experimentally validated by the comparison of measurements obtained on these samples with a split ring resonator (SRR) and standard transmission/reflection waveguide methods. Then, the versatility of the designed resonator is shown in the characterization of FR4-fiberglass and Kapton polyimide samples.

Mm-Wave Complex Permittivity Extraction of LTCC Substrate Under the Influence of Surface Roughness

As many emerging technologies require the use of high-speed signals, the understanding of dielectric properties of materials used in manufacturing printed circuit boards (PCBs) is an essential aspect for accurate high-speed circuit designs, especially at millimeter-wave (mm-wave) frequencies. This work demonstrates a methodology for extracting complex relative permittivity of dielectric substrates covering mm-wave frequencies. For this purpose, low-temperature cofired ceramic (LTCC) substrate was measured up to 85 GHz and its complex relative permittivity was extracted. The approach used in this work is based on multiline thru–reflect–line (TRL) calibration for measuring the propagation constant and electromagnetic (EM) simulations to estimate the losses contributed by the conductor while accounting for surface roughness. An estimate of complex relative effective permittivity is obtained, from which the actual relative dielectric constant and the loss tangent of LTCC substrate are extracted. The estimated values for the relative dielectric constant and the loss tangent show an excellent agreement compared with the results obtained via split cavity resonator measurements.

METAMATERIALS: NEW ASPECTS IN ANTENNA DESIGN

The recent developments of the telecommunication systemstipulate miniaturization and integrating multiple functions is of extreme importance. Particularly devices which are generally used in day to day life like smartphones, tablets, smart TVs, wireless internet devices,mobile communication system, etc. To fulfill this constraint, the handheld devices component should be of more compact, equipped with multiple functions, and operates for a different band of frequencies. Antenna having distinctive features like compact size, conformal to planar and non-planar structures, proficient in operating one or more band of frequencies, etc., is a keyelement in enhancing the performance of wireless communication systems. Currently, there are numerous techniques to address these issues such as high permittivity dielectric substrate,fractal geometry,altering ground plane, and so on. But these techniques have low gain, narrow bandwidth demerits. A novel technique that is of superior attention to antenna researchers is designing antenna by incorporating electromagnetic metamaterial. It consents to change electromagnetic wave propagation resulting in a negative refraction index (NRI). The metamaterials with NRI property performs as filters, radiating element, decoupling network,etc. Hence metamaterial stimulated antennas reduces size as well as enhances antenna parameters. So, in this paper, an effort is made to highlight the implications of metamaterials on antenna design to improve performance and achieve multiband,reconfigurable,miniaturization, isolation enhancement characteristics.

Exciton routing in the heterostructure of a transition metal dichalcogenide monolayer on a paraelectric substrate

We propose a scheme for the spatial exciton energy control and exciton routing in a transition metal dichalcogenide (TMD) monolayer which lies on a quantum paraelectric substrate. It relies on the ultrasensitive response of the substrate dielectric permittivity to temperature changes, allowing for spatially inhomogeneous screening of Coulomb interaction in a monolayer. As an example, we consider the heterostructure of TMD and strontium titanate oxide SrTiO$_3$, where large dielectric screening can be attained. We study the impact of substrate temperature on the characteristic electronic features of TMD monolayers such as the particle bandgap and exciton binding energy, Bohr radius and nonlinearity (an exciton-exciton interaction). The combination of particle bandgap and exciton binding energy modulation results in the shift of the exciton resonance energy. Applying local heating, we create spatial patterns with varying exciton resonant energy and an exciton flow towards the energetically lower region of the sample.

Dielectrics for Terahertz Metasurfaces: Material Selection and Fabrication Techniques

AbstractManipulation of terahertz radiation opens new opportunities that underpin application areas in communication, security, material sensing, and characterization. Metasurfaces employed for terahertz manipulation of phase, amplitude, or polarization of terahertz waves have limitations in radiation efficiency which is attributed to losses in the materials constituting the devices. Metallic resonators‐based terahertz devices suffer from high ohmic losses, while dielectric substrates and spacers with high relative permittivity and loss tangent also reduce bandwidth and efficiency. To overcome these issues, a proper choice of low loss and low relative permittivity dielectric layers and substrates can improve field confinement and reduce dissipation. Alternatively, replacing metallic resonators with a moderate relative permittivity dielectric material that supports cavity mode resonances also reduces dissipation due to the absence of conduction current. Herein, an overview of dielectric materials employed as spacers and dielectric resonators is provided, and the fabrication methods employed to realize these devices at the terahertz frequency range are also presented. Material selection guidelines, material‐specific and application‐specific fabrication quality metrics are outlined, and new techniques are proposed.

Controlled Out-of-Band Rejection of Filters Based on SIW With Alternating Dielectric Line Sections

A study for managing the out-of-band rejection in a new topology of filters based on substrate integrated waveguide with alternating dielectric line sections (ADLSs) is presented in this letter. ADLS is a filtering structure consisting on line sections of the same width but with alternating air and dielectric filling. The design of the lengths of each section provides the central frequency and the bandwidth of bandpass filter response. The proper selection of the structure substrate dielectric permittivity can increase the rejection band up to $2f_{o}$ . Moreover, the selection of the filter order (i.e., the number of sections with and without dielectric) can affect the depth of the rejection band. A study of the width and the depth of the rejection band is performed with different permittivities and orders for two different filters. Then, for validation purposes, the prototypes of both filters have been manufactured and measured.

Surface plasmon polaritons light radiation source with asymmetrical structure

An asymmetrical surface plasmon polaritons (SPPs) light radiation source with double metal films (SPLRD) is presented and studied. SPPs modes can be excited on the double metal films by a parallel traveling electron beam and then transformed into enhanced Cherenkov radiation in the substrate. Tunable dual-frequency radiation ranging from infrared to ultraviolet can be realized. In comparison with a single-metal-film structure, the efficiency, tunability, and output power density of the SPLRD are greatly increased, with up to eight times higher radiation power intensity being achievable. The radiation performance of a cylindrical SPLRD is enhanced to an even greater extent, with reductions in the required exciting electron-beam energy and the dielectric substrate permittivity. These novel properties due to the asymmetry of the structure and the SPPs excitation pattern are significant for furthering the understanding of electron beam–SPPs interaction and for the development of efficient wideband light radiation sources.

Quasi-fractal axial-symmetric structure feeded by segment of nongrounded coplanar line

Background. Developments in telecommunication technologies and global implementation of wireless systems calls far new types of antenna systems. Microstrip antennas look the most promising in this field since they possess multiband operation capability with small dimensions and low weight, high degree of integration with other microstrip circuits and can be used as elements of phased antenna arrays. Objectives. The goal of this paper was to simulate electrodynamic characteristics of quasi-fractal radiating structure with complex composition based on a microstrip monopole, to optimize parameters of the excitation element in the form of unshielded coplanar waveguide segment. Matherials and methods. Quasi-fractal radiating structure with complex composition based on a microstrip monopole consists of dielectric substrate, microstrip monopole with quasy-fractal aperture, an unshielded coplanar waveguide segment. The analysis was based on the Finite Elements Method with Integral Equation Method used to account for electromagnetic fields at infinity. Results. Within scope of numerical simulation spectral characteristics of the antenna were analyzed. Comparative analysis of spectral characteristics of canonical disk resonator excited with a microstrip line segment and canonical disk resonator excited with a segment of a coplanar line with eigenmode spectrum of a quasi-fractal excited with a segment of a coplanar waveguide was performed. Influence of dielectric substrate permittivity value on frequency and power characteristics of the radiating structure was studied. It was shown that variations in dielectric permittivity value lead to significant changes of frequency response in the higher frequency band only, wherein increase of dielectric permittivity value leads to a shift of frequency response minima towards lower frequencies of the given frequency band. It was determined that radiating structure is dualband and bandwidth of operating bands was different. Lower frequency bandwidth on dB was , and higher frequency bandwidth was . Numerical simulation of power characteristics was performed with the radiation patterns presented as elevation patterns with fixed azimuthal angle at various frequencies. Possible methods of radiating structure parameters correction with the goal of improving power characteristics and external circuits matching were given. Conclusions. Within scope of numerical simulation was determined that the given quasi-fractal radiating structure with complex composition based on a microstrip monopole can provide effective radiation with acceptable parasitic loss rate. The structure can provide acceptable level of external circuits matching in wide enough frequency band. The ability to form radiated fields with given characteristics in two operating bands.

Broadband angle- and permittivity-insensitive nondispersive optical activity based on planar chiral metamaterials

Because of the strong inherent resonances, the giant optical activity obtained via chiral metamaterials generally suffers from high dispersion, which has been a big stumbling block to broadband applications. In this paper, we propose a type of planar chiral metamaterial consisting of interconnected metal helix slat structures with four-fold symmetry, which exhibits nonresonant Drude-like response and can therefore avoid the highly dispersive optical activity resulting from resonances. It shows that the well-designed chiral metamaterial can achieve nondispersive and pure optical activity with high transmittance in a broadband frequency range. And the optical activity of multi-layer chiral metamaterials is proportional to the layer numbers of single-layer chiral metamaterial. Most remarkably, the broadband behaviors of nondispersive optical activity and high transmission are insensitive to the incident angles of electromagnetic waves and permittivity of dielectric substrate, thereby enabling more flexibility in polarization manipulation.

Substrate effects on piezoresponse force microscopy electromechanical responses of piezoelectric thin films

To explore substrate influences on piezoresponse force microscopy (PFM) responses, the coupled theory is extended to investigate the electromechanical responses of PFM on piezoelectric films bonded to rigid and dielectric, rigid and insulating, elastic and conducting and elastic and dielectric substrates. It is found that all responses transit to the half space results when the normalized thickness (film thickness to tip curvature radius t/R0) is larger than about 0.08 for PZT4, and degenerate to the dielectric half space solutions as expected for rigid and dielectric substrate case, when the normalized thickness approaches zero verifying the calculations. PFM responses are greatly reduced by substrate dielectric permittivity thus a conducting substrate is recommended to eliminate the dielectric constant influences and the dielectric “dead layer” should be avoided or carefully dealt with. For elastic substrates, the tip induced surface displacement for a relatively thick film, image charge and image charge distance are slightly affected by the change of the substrate Young's modulus and Poisson's ratio. And the effective piezoelectric coefficient is remarkably decreased when t/R0 < 0.001. However as t/R0 > 0.001 in which region a practical PFM experiment would fall, so long as the substrate is matched or harder, the substrate could be deemed as a rigid one and the investigation of PFM responses would be greatly facilitated. Then effective piezoelectric coefficients from the decoupled and coupled theories of films on elastically matched, conducting or dielectric substrates are compared indicating that the decoupled theory tends to overestimate effective piezoelectric coefficient for thin films, the same as that for half space case. The obtained influences of substrate properties may serve as a primary experimental guidance for the choosing a proper substrate and supply useful information for the quantitative interpretation of the PFM signals.

Transition radiation from graphene plasmons by a bunch beam in the terahertz regime.

The terahertz band is an increasingly important spectrum in a wide range of applications from bioimaging and medical diagnostics to security and wireless communications. We propose a tunable terahertz coherent radiation source based on graphene plasmon-induced transition radiation. The transition radiation in terahertz regime arises from the graphene plasmons, which are excited by a normally incident bunched electron beam. We analyze the field-intensities and spectral-angular distributions of the transition radiation with respect to Fermi energy, substrate dielectric permittivity, and electron bunch energy for both the coherent and incoherent radiation. The effect of electron bunching on the radiation pattern is discussed. The mechanism of plasmon frequency-selective transition radiation is discovered.

Substrate and Fano Resonance Effects on the Reversal of Optical Binding Force between Plasmonic Cube Dimers

The behavior of Fano resonance and the reversal of near field optical binding force of dimers over different substrates have not been studied so far. Notably, for particle clustering and aggregation, controlling the near filed binding force can be a key factor. In this work, we observe that if the closely located plasmonic cube homodimers over glass or high permittivity dielectric substrate are illuminated with plane wave, no reversal of lateral optical binding force occurs. But if we apply the same set-up over a plasmonic substrate, stable Fano resonance occurs along with the reversal of near field lateral binding force. It is observed that during such Fano resonance, stronger coupling occurs between the dimers and plasmonic substrate along with the strong enhancement of the substrate current. Such binding force reversals of plasmonic cube dimers have been explained based on the observed unusual behavior of optical Lorentz force during the induced stronger Fano resonance and the dipole-dipole resonance. Although previously reported reversals of near field optical binding forces were highly sensitive to particle size/shape (i.e. for heterodimers) and inter-particle distance, our configuration provides much relaxation of those parameters and hence could be verified experimentally with simpler experimental set-ups.

Effects of two-step heat treatment on crystallization behavior, densification and microwave dielectric properties of MgO-Al2O3-SiO2-TiO2-Sb2O3 glass-ceramics

Glass-ceramics with a mass fraction composition (wt%) of 19MgO-23Al2O3-53SiO2-4TiO2-3Sb2O3 (M-A-S-T-S) were prepared by two-step (nucleation and crystallization) heat treatment of the parent glass at selected temperatures for 2h and/or 20h, respectively. A microwave dielectric characterization was performed in order to evaluate the suitability of M-A-S-T-S glass-ceramics as a lower permittivity (εr<4) dielectric substrate. X-ray diffraction analysis revealed that the addition of TiO2 and Sb2O3 into MgO-Al2O3-SiO2 glass could induce the coexistence of μ-cordietire and α-cordietire as the main phases, a small fraction of SiO2, MgSiO3 and Sb6O11 additionally crystallized as the second phases in this glass-ceramic system. Meanwhile, the prolonged heat treatment time~20h at selected nucleation and crystallization temperatures would cause the appearance of a small amount of MgTiO3 phase. The longer annealing time could not promote the densification and final dielectric properties, while a slightly increase in nucleation temperature~880°C of a short-time sintering (~2h) could reduce the dielectric loss. Wherein, after the two-step heat treatment (880°C/2h+930°C/2h), a better microwave dielectric properties of εr~3.65, Q×f~7900GHz (at 13.293GHz) and τf~−7.92ppm/°C can be obtained in this M-A-S-T-S glass-ceramic sample.

Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging

Developments in metamaterials and related structures such as metasurfaces have opened up new possibilities in designing materials and devices with unique properties. Here we report a new hybrid metasurface structure, comprising a two-dimensional metamaterial surface and a very high permittivity dielectric substrate, that has been designed to enhance the local performance of an ultra-high field MRI scanner. This new flexible and compact resonant structure is the first metasurface which can be integrated with multi-element close-fitting receive coil arrays that are used for all clinical MRI scans. We demonstrate the utility of the metasurface acquiring in-vivo human brain images and proton MR spectra with enhanced local sensitivity on a commercial 7 Tesla system.

Numerical simulations of graphene conductivity with realistic inter-electron potential

This paper provides results of numerical simulations of graphene conductivity. The numerical results were performed in tight-biding model with Coulomb potential screened by σ electron of carbon atoms. The dependence of the graphene conductivity on the dielectric permittivity of substrate was calculated. The results agreeds with experimental data.

Interaction of static charges in graphene

The study of the interaction potential between static charges within Monte-Carlo simulation of graphene is carried out. The numerical simulations are performed in the effective lattice field theory with noncompact 3 + 1-dimensional Abelian lattice gauge fields and 2 + 1-dimensional staggered lattice fermions. At low temperature the interaction can be described by the Coulomb potential reduced by some dielectric permittivity ϵR. The dependence of ϵR on the dielectric permittivity of substrate is determined. In addition, the renormalization of the quasiparticle charge is studied. At large temperatures the interaction potential can be described by the two-dimensional Debye screening. The dependence of Debye screening mass on the dielectric permittivity of substrate allows to determine the position of the insulator-semimetal phase transition. It is shown that graphene reveals in the semimetal phase the properties of the two-dimensional plasma of fermions excitations.

Compact Dual-Band Proximity-Fed Circularly Polarized Patch Antenna for BDS Applications

AbstractThis paper presents a compact dual-band proximity-fed circularly polarized (CP) patch antenna for BeiDou Navigation Satellite System (BDS) operation at B1 (1,561 MHz) and B3 (1,268 MHz) bands. The antenna aperture is minimized down to 26.6 mm (λ/9 at the B3 band) in diameter and 12 mm (λ/20 at the B3 band) in thickness using high permittivity dielectric substrate and meandered slots. The antenna design features that the resonant frequency in the higher band could be tuned independently by adjusting the branch length and breadth without affecting the lower band. To achieve right-handed CP (RHCP) radiation property, quadrature phase feeding is employed together with a broadband 0°–90° hybrid utilizing a small surface mount LTCC hybrid coupler chip. Experimental results show that the RHCP gain maintains larger than 1.5 dBic and the axial ratio (AR) stays below 3 dB within the B1 and B3 bands. This antenna design is a promising candidate for small BDS arrays as well as other dual-band BDS applications.

COMPACT FOUR-ELEMENT ANTENNA ARRAY DESIGN FOR BEIDOU NAVIGATION SATELLITE SYSTEM APPLICATIONS

In this letter, a compact four-element microstrip patch antenna array for BeiDou navigation satellite system (BDS) operation at the B3 (1268MHz) band is proposed. High permittivity dielectric substrate and slit-loaded microstrip patch are used to reduce the antenna element size down to 40mm × 40mm which implies an aperture size of only λ0/6 × λ0/6 at the B3 band. The right-handed circularly polarized (RHCP) radiation is achieved by connecting two coaxial probes to a 0◦–90◦ stripline hybrid. Four identical antenna elements are distributed with the same polarity and an inter-element separation of 80mm (λ0/3 at the B3 band). The overall size of the antenna array, including the stripline feeding network and supporting ground plane, is only 140mm × 140mm × 5.5mm. A prototype was fabricated and measured to verify the design concept. Simulated and measured results will be presented and discussed, showing that the proposed BDS antenna array is suitable for BDS applications.

Numerical simulation of graphene in an external magnetic field

In this paper the results of numerical simulation of monolayer graphene in external magnetic field are presented. The numerical simulation is performed in the effective lattice field theory with noncompact $3 + 1$-dimensional Abelian lattice gauge fields and $2 + 1$-dimensional staggered lattice fermions. The dependences of fermion condensate and graphene conductivity on the dielectric permittivity of substrate for different values of external magnetic field are calculated. It is found that magnetic field shifts insulator-semimetal phase transition to larger values of the dielectric permittivity of substrate. The phase diagram of graphene in external magnetic field is drawn.