Effective Dielectric Constant Research Articles

A novel S-shaped frequency and pattern reconfigurable patch antenna for 4G LTE, WLAN/Wi-Max application

PurposeIn wireless communication system, use of multiple antennas for different requirements of system will increase the system complexity. However, reconfigurable antenna is maximizing the connectivity to cover different wireless services that operate different frequency range. Pattern reconfigurable antenna can improve security, avoid noise and save energy. Due to their compactness and better performance at different applications, reconfigurable antennas are very popular among the researchers. The purpose of this work, is to propose a novel design of S-shaped antenna with frequency and pattern diversity. The pattern and frequency reconfiguration are controlled via ON/OFF states of the PIN diode.Design/methodology/approachThe geometrical structure of the proposed antenna dimension is 18 × 18 × 0.787 mm3 with εr = 2.2 dielectric constant. Three S-shaped patches are connected to a ring patch through PIN diodes. The approximate circumference of ring patch is 18.84 mm and length of patch is 5 mm, so approximate length of radiating patch is 14.42 mm and effective dielectric constant is 1.93. Conductor backed coplanar waveguide (CPW) is used for feeding. The proposed antenna is designed and simulated on CST microwave studio and fabricated using photolithography process. Measurements have been done in anechoic chamber.FindingsAntenna shows the dual band operation at 2.1 and 3.4 GHz frequency. The first band remains constant at 2.1 GHz resonant frequency and 200–400 MHz impedance bandwidth. Second band is switched at seven different resonant frequencies as 3.14, 3.45, 3.46, 3.68, 3.69, 3.83 and 3.86 GHz with switching of the diodes. The −10 dB bandwidth is more than 1.4 GHz.Research limitations/implicationsPattern reconfigurability can be achieved using mechanical movement of antenna easily but it is not a reliable approach for planar antennas. Electronic switching method is used in proposed antenna. Antenna size is very small so fabrication is very crucial task. Measured results are deviated from simulation results due to fabrication error and effect of leads of diodes, connecting wires and battery.Practical implicationsThe reconfiguration of the proposed antenna is controlled via ON/OFF states of the three PIN diodes. The lower band of 2.1 GHz is fixed, while second band is switched at five different resonant frequencies as 3.27, 3.41, 3.45, 3.55 and 3.88 GHz, with switching of the PIN diodes with all state of diodes and exhibit pattern reconfigurability at 2.1 GHz frequency. At second band center frequency is significantly changed with state of diodes and at 3.4 GHz pattern is also changed with state of diodes, hence antenna exhibits frequency and pattern reconfigurability.Originality/valueA novel design of pattern and frequency reconfigurable antenna is proposed. Here, work is divided into two parts: first is frequency reconfiguration and second is radiation pattern reconfiguration. PIN diodes as switch are used to select the frequency band and reconfigure the radiation pattern. This proposed antenna design is novel dual band frequency and pattern reconfigurable antenna. It resonates at two distinct frequencies, i.e. 2.1 and 3.4 GHz, and has a pattern tilt from 0° to 355°. The conductor backed CPW feed technique is used for impedance matching.

Electroreflectance spectroscopy of few-layer MoS2 : Issues related to A1s exciton subspecies, exciton binding energy, and inter-layer exciton

Optical spectra of few-layer transition metal dichalcogenide semiconductors reveal several transitions whose character and origins continue to be debated. We have studied hBN encapsulated few-layer MoS2 films using electroreflectance (ER) spectroscopy. Two strong features are seen in the reflectance spectrum of trilayer MoS2 around the ground state A–exciton transition. In ER, the corresponding features show opposite phase response to the applied voltage. Evidence from first principles ER line shape simulation and photoluminescence spectroscopy suggests that these two features are likely to be A1s exciton subspecies proposed earlier, whose energy depends on which layer the electron–hole pair is located in. The first excited state A2s exciton transition is also identifiable in ER. Through the two-dimensional hydrogenic exciton model, it enables an approximate estimation of the exciton binding energy Eb. The increase in Eb with decreasing film thickness, which originates from reduced dielectric screening, is phenomenologically analyzed through a film thickness and capping material dependent effective dielectric constant. Extending this idea, we show that the A1s exciton is mostly confined to a single S–Mo–S layer, as predicted by theory. An inter-layer (IL) exciton is expected in bilayer and thicker 2H-MoS2 films. However, we show that there can be bilayer films where the IL exciton is absent, which may be related to increased carrier concentration.

An Area-Averaged Conformal Technique for the Electromagnetic Simulations of Debye Medium

A novel area-averaged dielectric conformal technique combined with the finite-difference time-domain (FDTD) method has been investigated in accuracy and efficiency for modeling curved dispersive medium objects in this article. The proposed method utilizes an effective average dielectric constant, which is derived by area averages of different dielectric regions in irregular cells cut by curved surfaces, to modify the magnetic field updating equations in auxiliary differential equation FDTD method. The accuracy and efficiency of the method are verified by comparing the radar cross section results produced by the method of moments and the FDTD method with very fine meshes, respectively. Numerical results show that good agreements can be achieved by using coarse mesh size (12 cells per wavelength). Further, the proposed method is devoted to analyzing the bio-electromagnetic effects of a dispersive human body in a vehicle platform to show its good ability in solving such complex problems.

IPD Millimeter-Wave Bandpass Filter Chip Based on Stepped-Impedance Coupled-Line Dual-Mode Resonator for 5G Application

A novel stepped-impedance coupled-line dual-mode resonator (SICLDMR) is presented and analyzed in this brief. The resonator is a closed ring structure, constructed by two coupled lines with different impedances. The even- and odd-mode resonance frequencies of this SICLDMR are created due to the different effective dielectric constants of the two modes. Based on the proposed resonator, a simple bandpass filter (BPF) is designed by adding two symmetric open-stub feeding structures. For demonstration, a narrowband BPF operating at 35 GHz is simulated, fabricated by using the 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> -thick-GaAs integrated passive device (IPD) technology. And the measured results show that the BPF with a good fractional bandwidth of 13% realizes a low insertion loss of 0.74 dB, sharp roll-off skirt of passband, and wide stopband rejection. The advantages of the proposed IPD BPF indicate that it has a promising application prospect in 5G millimeter-wave systems.

Reduced graphene oxide loaded with rich defects CoO/Co3O4 for broadband microwave absorption

Graphene-based microwave absorbing (MA) materials have been extensively studied due to their excellent physical properties. However, very few research has successfully achieved broader frequency MA materials while ensuring good wave absorption properties. In this work, we obtained reduced graphene oxide (RGO) modified with magnetic CoxOy nanoparticles by assembling Co nanoparticles onto graphene with a simple hydrothermal method followed by pyrolysis at different temperatures, possessing wideband broad bandwidth microwave absorbing capability. The electromagnetic parameters, attenuation constants, and impedance matching of the CoxOy/RGO composites pyrolyzed at different temperatures were analyzed to determine the optimum pyrolysis temperature for the CoxOy/RGO composites. After heat treatment at 500 °C, a large number of CoO/Co3O4 interfaces appeared. The minimum reflection loss of the sample reaches −67.2 dB and the effective absorbing bandwidth (EAB) (RL < −10 dB) is 9.1 GHz, covering the whole X, Ku, and K bands. It is worth noting that such a good microwave absorption performance is attributed to the fact that the structure of cobalt nanospheres can adjust the effective dielectric constant of the material, and the existence of CoO can promote dipole polarization and interfacial polarization process to improve impedance matching, so as to obtain a wider absorption effect.

Metal oxide nanocomposite based flexible nanogenerator: synergic effect of light and pressure

Here, we report the fabrication of nanocomposite comprising of CuO and poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) for application in flexible piezoelectric nanogenerators (PENG). The chemically grown CuO nanostructures have been characterized through electron microscopy, x-ray diffraction, and spectroscopic techniques. It has been found that the incorporation of optimal CuO nanostructures in PVDF-HFP can increase the output voltage of the PENG by 22 times and is assigned to the increment in the effective dielectric constant of host PVDF-HFP. Further, the nanogenerator exhibits a maximum power of ∼20 μW cm−2 at 3 MΩ load and can charge a capacitor under continuous bio-mechanical impart. Further, upon slight alteration of the device configuration, the output of the nanocomposite-based nanogenerator can be enhanced under illumination condition. The increment in overall piezopotential through photoexcitation in optically active CuO nanostructures can be assigned to the increment in output voltage. The wavelength dependent output variation reveal the maximum output of the PENG under blue light. Further, under white light illumination, the nanogenerator exhibits a maximum power which is 3 times higher than in dark condition and can charge a capacitor 52 times faster. The development of such superior flexible and optically active nanogenerators are quite promising for futuristic self-powered devices operated under mechanical and solar energies.

Design of a Low temperature cofired ceramic wideband WideScan antenna array for millimetre‐wave applications

The design, fabrication, and measurement of a 7 × 7 mm-wave array antenna have been presented for 5G communications. The substrate integrated waveguide (SIW)-fed antenna element is formed of four parts: a rectangular radiating patch, a coupling slot cut onto the broadwall of the SIW, a transition layer, and a feeding layer at the bottom. The bandwidth and radiation efficiency has been improved by embedding an air cavity below the radiating patch, as the effective dielectric constant of the substrate is reduced. Moreover, a prototype has been fabricated and measured to verify the design principles. The finite array operating over 23–28 GHz has achieved active voltage standing wave ratios of less than 2 and 2.5 in the E- and H-planes while scanning up to 45° respectively. Compared with the theoretical ideal gain, the average gain drop of the measured embedded element gain is 0.73dB.

Fabrication of On-Silicon Aperture Coupled Patch Antenna Through Micromachining and Cu-Cu Thermocompression Bonding

This paper, for the first time, reports the fabrication of an on-Silicon aperture-coupled 3D Patch antenna using micromachining and low-temperature, low-pressure Copper(Cu)-Copper(Cu) thermo-compression bonding. Micromachining technique was used to reduce the effective dielectric constant of Silicon (Si), thereby increasing the radiation efficiency. One of the main challenges in fabricating the aperture coupled patch antenna on Si is the realization of its 3D structure. The top and bottom substrates of the 3D antenna have to be bonded together without disturbing the micromachined thin membrane. This was achieved using thermo-compression bonding under optimized temperature and pressure conditions with a 3 nm Gold (Au) passivation layer, which prevents the oxidation of the Cu layer underneath and thereby reducing the inter-diffusion barrier across the interface. The proposed fabrication process flow introduces the novelty of using bonding/stacking metal inter-layer as the common ground of the antenna. The device was fabricated on high resistivity Si wafers to minimize the conduction losses. Herein, we have fabricated an aperture coupled 3D patch antenna with a cavity depth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200\pm ~10\mu \text{m}$ </tex-math></inline-formula> , and the device characteristics were compared with the HFSS simulation results. The reliability of the fabricated antenna was assessed by bond strength analysis, cross sectional FESEM and TEM imaging. The on-chip antenna yielded a resonance frequency of 13.4 GHz, with VSWR 1.16. The radiation pattern of the antenna was also analyzed experimentally. This technology is the way forward to fabricating miniaturized high performance on-chip antennas.

Using the Diamagnetic Coefficients to Estimate the Reduced Effective Mass in 2D Layered Perovskites: New Insight from High Magnetic Field Spectroscopy.

In this work, the current state of research concerning the determination of the effective mass in 2D layered perovskites is presented. The available experimental reports in which the reduced effective mass has been directly measured using magneto-absorption spectroscopy of interband Landau levels are reviewed. By comparing these results with DFT computational studies and various other methods, it is concluded that depending on the approach used, the found spans a broad range of values from as low as 0.05 up to 0.3 m. To facilitate quick and reliable estimation of , a model is proposed based solely on the available experimental data that bypass the complexity of interband Landau level spectroscopy. The model takes advantage of the value measured for (PEA)PbI and approximates the reduced effective mass of the given 2D layered perovskites based on only two experimental parameters—the diamagnetic coefficient and the effective dielectric constant. The proposed model is tested on a broad range of 2D layered perovskites and captures well the main experimental and theoretical trends.

Effect of spin-polarization on filamentation in magnetized quantum plasma

A theoretical study analysing the effects of spin- polarization resulting from the difference in concentration of the oppositely spinning electrons on the filamentation instability of an intense laser beam propagating in magnetized quantum plasma. The ponderomotive force has been evaluated taking into account the electron’s Fermi pressure, quantum Bohm potential and electron’s spin. The effective dielectric constant has been calculated. For the filamentaton instability, the dispersion relation has been established and the growth rate has been studied analytically. The spin-polarization is found to enhance the filamentation.

Electric Field Screening in Gate‐Tunable van der Waals 2D‐Metal/InSe Junctions

AbstractThe prediction of the dielectric response in 2D metal–semiconductor junctions (MSJs) is challenging since the screening is inhomogeneous. Herein, a generalized model is proposed to uncover the relationship between interfacial electrostatic screening and the modulation of Schottky barrier height (ΦSB) in 2D MSJs. This model is developed based on the effective dielectric constant, interfacial distance, and van der Waals gap that sheds light on the profound difference between dielectric screening in 2D and conventional MSJs. This model can predict the variation of ΦSB for a series of 2D MSJs. Combining thermionic field emission theory with the model, several compatible 2D metals are provided for low‐dimensional electronics, among which the α‐graphyne‐based junction exhibits the largest on/off ratio.

Composition, Roughness, and Topography from Radar Backscatter at Selk Crater, the Dragonfly Landing Site

The Selk crater region is the future landing site of NASA’s Dragonfly mission to Titan. The region was imaged by the Cassini RADAR at incidence angles from 5° to 72° and at various polarization angles. Using this data set, we mapped six terrain units and assembled a backscatter curve for each, providing normalized backscatter cross section (σ 0) as a function of incidence angle. By fitting these backscatter curves with a sum of a quasi-specular and diffuse terms and evaluating three alternative formulations of the first and two for the second, we extracted the best-fit surface effective dielectric constant, rms slope, and scattering albedo. Although the parameters’ absolute values are model dependent, relative values between terrains indicate real variations in surface properties. The results are consistent with the impact exposing and fracturing a low-loss tangent material such as the water-ice bedrock, which is likely also present in the hummocky terrains and to a lesser degree in the plains and interdune regions. The dunes and dark terrains are composed of smooth, uniform material with low dielectric constant (1.5–2.3 median values for all models) compatible with organic sand. A diffuse single-scattering model enabled independent derivation of the dielectric constant from high-incidence observations, leading to low values (<2) over all terrains, indicating a depolarizing (sub)surface. Finally, radarclinometry revealed lateral variations in rim height, which remains below 300 m along the SARTopo profile but reaches up to 600 m at other locations, hinting at a rim less eroded than previously thought.

Simple and High-Sensitivity Dielectric Constant Measurement Using a High-Directivity Microstrip Coupled-Line Directional Coupler

Simple methods using a microstrip coupled-line directional coupler (CLDC) are presented for dielectric constant measurements. The material under test (MUT) is placed on the coupled-line section of the coupler, and either the coupler’s coupling ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{31} \lvert $ </tex-math></inline-formula> ) or its isolation level ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{41} \lvert $ </tex-math></inline-formula> ) is considered as the sensor’s response. Putting different MUTs on the microstrip line leads to a change in the effective dielectric constant of the structure and consequently causing a change in the coupling coefficient. In addition, since the isolation level of a microstrip coupled-line coupler depends on the phase velocity difference between the substrate and the medium above the signal strips, putting different MUTs on the line significantly changes the isolation level. This change is significantly greater than the change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lvert S_{21} \lvert $ </tex-math></inline-formula> level of a microstrip line when loaded with different MUTs. Validation of the method is presented through measurements for both solid and liquid MUTs.

Determining dielectric properties of nematic liquid crystals at microwave frequencies using inverted microstrip lines

ABSTRACT In this paper, we have investigated the dielectric properties of nematic liquid crystals (NLCs) by measuring the resonant frequencies of inverted microstrip lines (IMSLs) of NLC being the substrate material at the microwave frequency band. The designed IMSL devices consist of a cavity for NLC mixture between the inverted microstrip line and the ground plane. The anisotropy values of the NLCs were determined by observing the change of the resonant frequency when the strength of external electric fields applied on the NLCs varied. The experiments demonstrated that the effective dielectric constant of the NLC can be manipulated by the proposed devices via external bias voltage for tuning. The accuracy of the method for determining the dielectric constants of JC-M-LC-E7 (JC-E7) and QYPD-036 LCs was analysed with several prototypes based on two separate designs. The high accuracy of 91% in permittivity determination was demonstrated, and the design and fabrication techniques are beneficial for making microwave components of high tunability.

One-dimensional excitons in long phosphorene atomic chains

The electronic structure of phosphorene atomic chains (PACs) embedded in various dielectric environments is studied theoretically by using a configuration interaction approach beyond the conventional double-excitation scheme. While the nominal single-particle gap of the PACs is shown to roughly obey an expected scaling law of ${L}^{\ensuremath{-}2}$, where $L$ measures the length of PACs, the quasiparticle shift is found to gradually converge to a value that is insensitive to the dielectric environment as $L$ increases. In the meantime, exciton binding energies are revealed to obey a simple scaling law of $0.96/(\ensuremath{\kappa}L)\ensuremath{-}0.02$, with $\ensuremath{\kappa}$ being the effective dielectric constant. As $L$ goes to infinity, the quasiparticle and excitonic effect are both found to be greatly suppressed as if the long-range electron-electron interactions are quenched in long PACs.

Compact half H‐shaped dielectric resonator antenna for wideband applications

AbstractIn this study, the authors present the design of a half H‐shaped dielectric resonator antenna (DRA) for compact size and wide bandwidth. The trapezoidal patch feed is used to excite the DRA, which results in TE113Y and TE115Y resonant modes of the rectangular DRA (RDRA). It is found that the broad‐side higher‐order TE113Y with the TE115Ymode is used in the proposed design to make it wideband. The effective dielectric constant of the proposed DRA is reduced by the slots and then the structure is made half to make it compact. Finally, for further improvement in bandwidth, the size of the ground plane is reduced, which increases the parallel capacitive reactance and decreases the Q‐factor. The proposed structure achieves measured impedance bandwidth S11 ≤ −10 dB of 75% (4.30–9.50 GHz) with a maximum gain of 7.20 dB. The proposed DRA is applicable for WLAN (5.15–5.72 GHz) and orthogonal frequency‐division multiplexing 802.11a (5.72–5.85 GHz).

Screening of Excitons by Organic Cations in Quasi-Two-Dimensional Organic-Inorganic Lead-Halide Perovskites.

Interlayer organic cations in quasi-two-dimensional halide perovskites are a versatile tuning vehicle for the optoelectronic properties of these complex systems, but chemical intuition for this design route is yet to be established. Here, we use density functional theory, the GW approximation, and the Bethe-Salpeter equation approach to understand the contribution of the organic cation to the quasiparticle band gap and exciton binding energy of layered perovskites. We show that organic cations in quasi-two-dimensional perovskites contribute significantly to the dielectric screening in these systems, countering quantum confinement effects on the quasiparticle band gap and the exciton binding energy. Using a simple electrostatics model inspired by parallel-plate capacitors, we decouple the organic cation and inorganic layer contributions to the effective dielectric constants and show that dielectric properties of layered perovskites are broadly tunable via the interlayer cation, providing a direct means of tuning photophysical properties for a variety of applications.

Wideband Balanced Filters With Intrinsic Common-Mode Suppression on Coplanar Stripline-Based Multimode Resonators

In this paper, two types of coplanar stripline (CPS)-based multimode stepped-impedance resonators are proposed for exploration of wideband balanced filters with intrinsic common-mode (CM) suppression. Such CPS multimode resonators (MMRs) can be readily terminated with either a pair of open- or short-circuited ends with no need of via holes. With resorting to a proper impedance ratio, the first three modes of each MMR are assembled to construct a wide differential-mode (DM) passband. Afterwards, two distinctive broadside-coupled sections are further investigated based on their open- and short-ended circuit models, respectively. Characteristic impedances and effective dielectric constants can be adequately obtained by virtue of an efficient quasi-static approach under the odd- and the even-mode operations. As such, two types of CPS-MMR-based bandpass filters each with five transmission poles are synthetically designed. For experimental validation, the proposed balanced filters are finally fabricated and measured with the help of two identical pairs of balanced-to-balanced microstrip-to-CPS transitions. Theoretical, simulated, and measured results are found in reasonable agreement with each other with/without the transitions, thus demonstrating that the proposed CPS-based MMRs are well characterized with the wideband DM transmission and intrinsic CM suppression.

Rotating structure of the Euler-Heisenberg black hole

In this work, we deal with the QED interpretation of the Euler-Heisenberg nonlinear electrodynamics as the effective theory after a one-loop of nonperturbative quantization. It endows the vacuum with an effective dielectric constant, the polarizability and magnetizability of which are determined by clouds of virtual charges surrounding the real currents and charges. Therefore, we study the Euler-Heisenberg nonlinear electrodynamics as a screened Maxwell theory. We generate a rotating electrically charged Einstein-Euler-Heisenberg black hole solution and interpret it as a Kerr-Newman-like one with screened electric charge, as it happens for the static electrically charged black hole Einstein-Euler-Heisenberg solution, which is considered as a Reissner-Nordstr\"om-like solution with screened electric charge.

Novel Compact and Wideband Tuning Fork Shaped DRA

In this paper, a novel compact and wideband tuning fork shaped DRA is presented. The augmented design resonates at 1.75 and 2.24 GHz and results in wide impedance bandwidth of 95% at 2.8 GHz. The effective dielectric constant is altered using three rectangular-shaped slots which leads to wide impedance bandwidth and the edge grounding technique is used to make geometry compact. The fundamental mode TE111x is preserved in the modified geometry. Further, the surface area to volume ratio is enhanced by 0.51 which leads to improvement in bandwidth. The proposed design achieves a gain of more than 5.5 dBi and greater than 90% of radiation efficiency for the complete bandwidth of operation, making it useful for WLAN (2.4/3.6 GHz), WiMAX (2.3/2.5/3.4 GHz), most L-band and entire S-band applications.