Effective Dielectric Constant Research Articles

Iterative synthesis method for high‐directivity symmetrical stepped‐impedance microstrip parallel‐line coupler

AbstractTraditional quarter‐wavelength parallel‐line couplers (QWPLC) in microstrip form suffer heavily in low directivity because of unbalanced even‐mode and odd‐mode phase velocities. Related schemes to improve directivity lead to complex structures and large dimensions. This study derives and validates an iterative synthesis method to design a high‐directivity microstrip coupler adopting a symmetric stepped‐impedance microstrip coupled line (SSIMCL). Given that the even‐mode and odd‐mode effective dielectric constants (EDCs) vary with the characteristic impedances, the authors take the EDCs of traditional QWPLC as the initial values for an SSIMCL, and the characteristic impedances and EDCs can be computed and converged in several iterations, resulting in good phase delay balance and high coupler directivity. A 20‐dB microstrip coupler working at 1 GHz with high directivity is designed, fabricated, and measured. The obtained maximum directivity is 47 dB and approximately 1 GHz, while the relative bandwidth with a directivity higher than 20 dB and a return loss better than 20 dB is larger than 70%. The novel microstrip coupler also features a compact, simple structure shorter than λg/4.

Development of microfluidically reconfigurable antenna using additive manufacturing

This research presents a microfluidically reconfigurable additively manufactured antenna. The proposed configuration demonstrates the applicability of additive manufacturing (AM) for fabricating intricate and lightweight structures. Additionally, it established the feasibility of microfluidic technology for achieving continuous frequency reconfigurability. The proposed antenna utilizes the dielectric fluid for reconfiguration, facilitated by pumping it in and out of microfluidic structures using a syringe pump. The incorporation of dielectric fluid in the channels alters the effective dielectric constant of the substrate and causes perturbations in the electric field distributions around the metallic patch. To validate the proposed idea, a prototype of the microfluidically reconfigurable 3D-printed antenna is designed, fabricated, and tested. The operating frequency is reconfigured from 2.38 to 3.49 GHz with a tuning range of 1.11 GHz, and the radiation pattern remains stable across considered cases. It is observed that measured results are in good agreement with simulated values. The prototype of the antenna design is fabricated using a single machining process, eliminating the need for traditional machining. The proposed antenna’s configuration is advantageous for various applications such as IEEE802.11b/g/n, IEEE802.15.1, and IEEE802.16.

Real and damped modes for an interacting fermion–antifermion pair: exciton in monolayer medium

In this manuscript, we investigate the interaction between a fermion–antifermion pair in (2+1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(2+1)$$\\end{document}-dimensions, governed by a Coulomb-type inter-particle potential. We explore analytical solutions for a fully covariant two-body Dirac equation derived from quantum electrodynamics, focusing on a spinless composite system. We present a non-perturbative second-order wave equation and derive a solution using the generators of the sℓ2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$s\\ell _{2}$$\\end{document} algebra. Subsequently, we determine the relativistic frequency modes of the system and extend our findings to electron–hole pairs in a monolayer medium in the vicinity of substrate. We analyze the impact of the effective dielectric constant (ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon$$\\end{document}) of the surrounding medium on the real and damped modes of an exciton. Our results indicate that the ground state binding energy of the system can vary from the order of eV to a few meV, depending on changes in ε\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon$$\\end{document}. Additionally, we observe that the decay time for the ground state of such an exciton is on the order of ∼10-12\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 10^{-12}$$\\end{document} s. These findings suggest that the evolution of such a pair can be controlled by adjusting the effective dielectric constant of the surrounding medium.

Spatio-temporal electric field distributions in an atmospheric plasma jet impinging on a microchannel array surface

The electric field distribution in the ionization waves (IWs) propagating over a microchannel array dielectric surface, with the channels either empty or filled with distilled water, is measured by ps electric field induced second harmonic generation. The surface IW is initiated by the atmospheric pressure N2–Ar plasma jet impinging on the surface vertically and powered by ns pulse discharge bursts. The results show that the electric field inside the microchannels, specifically its horizontal component, is enhanced by up to a factor of 2. The field enhancement region is localized within the channels. The vertical electric field inside the channels lags in time compared to the field measured at the ridges, indicating the transient reversal of the IW propagation direction across the channels (toward the jet). This is consistent with the phase-locked plasma emission images and confirmed by the kinetic modeling predictions, which show that the IW ‘jumps’ over the empty channels and propagates into the channels only after the jump between the adjacent ridges. When the channels are filled with water, the wave speed increases by up to 50%, due to the higher effective dielectric constant of the surface. No evidence of a significant electric field enhancement near the dielectric surface (ceramic or water) has been detected, within the spatial resolution of the present diagnostic, ∼100 μm.

Research and design of metasurface antennas based on composite dielectric materials

The metasurface has the ability to regulate electromagnetic waves, which is widely used for polarization state control, impedance bandwidth expansion, vortex beam generation, and high-directional antennas. Research shows that the substrate of the metasurface has a significant impact on the performance of the antenna. The equivalent dielectric constant of composite dielectric materials is investigated by using the characteristic mode analysis (CMA). A novel metasurface with composite dielectric substrate is proposed. The composite dielectric material consists of a substrate with a dielectric constant of 3.55 and an air gap. The calculation results of the effective dielectric constant of composite dielectric materials are basically consistent with the simulation results. Based on this composite dielectric material, a metasurface antenna is designed. S11 is less than-10 dB in the frequency range of 5.22–7.87 GHz. The peak boresight gain is 10.44 dBi at 6.5 GHz.

A novel methodology for designing Mono/Bi-slab X-band microwave absorbers of Carbon-Powder composites

This work introduces a methodology for the design of X-band microwave absorbers using carbon-graphite powder composites. The reflection loss (RL) is adjusted through variations in sample thickness, mono/bi-slab geometries, and effective dielectric constant. The impact of the particle size of the powders and the volume fraction (v.f.) of the composites on the effective dielectric permittivity has been systematically investigated. The Nicolson-Ross-Weir (NRW) conversion and the Birchak dielectric mixing model were employed. Optimal absorption conditions predicted by RL simulations were validated through experimental waveguide measurements for mono/bi-slab systems of paraffin-carbon composite samples. The mono-slabs with a particle size of 3.5 μm showed the best versatility for tailoring the RL in the X-band through v.f. variations while maintaining a fixed thickness of 2 mm. In addition, a bi-slab system (powder-paraffin/paraffin) for such powder size, at 18.0 % of v.f., showed an enhanced RL with a bandwidth of 2.6 GHz and a minimum of − 40 dB (at 11 GHz). Other dielectrics based on resin:paint mixtures were tested to replace the paraffin-matrix, revealing a strong powder-matrix interaction capable of modulating the effective dielectric permittivity. Finally, experimental antenna RL measurements conducted in free space were corroborated by theoretical simulations based on the waveguide characterizations.

Characterization of synthetic opals filled with copper

Photonic crystals based on synthetic opals filled with copper were produced by using the electrochemical deposition technique. Copper nanocrystal formation together with some quantity of their oxides inside opal pores was proved by the X-ray diffraction pattern. An angular behavior of reflectance maximum for opals with different copper content was satisfactorily described in the framework of theBragg light diffraction model. Effective dielectric constant of the opal-copper structures was determined.

Theoretical prediction of the effective dynamic dielectric constant of disordered hyperuniform anisotropic composites beyond the long-wavelength regime [Invited]

Torquato and Kim [Phys. Rev. X 11, 296 021002 (2021)10.1103/PhysRevX.11.021002] derived exact nonlocal strong-contrast expansions of the effective dynamic dielectric constant tensor ε e (k q ,ω) that treat general statistically anisoropic three-dimensional (3D) two-phase composite microstructures, which are valid well beyond the long-wavelength regime. Here, we demonstrate that truncating this general rapidly converging expansion at the two- and three-point levels is a powerful theoretical tool from which one can extract accurate approximations suited for various microstructural symmetries. Among other results, we show that such truncations yield closed-form formulas applicable to transverse polarization in layered media and transverse magnetic polarization in transversely isotropic media, respectively. We apply these formulas to estimate ε e (k q ,ω) for models of 3D disordered hyperuniform layered and transversely isotropic media: nonstealthy hyperuniform media and stealthy hyperuniform media. In particular, we show that stealthy hyperuniform layered and transversely isotropic media are perfectly transparent (trivially implying no Anderson localization, in principle) within finite wave number intervals through the third-order terms. For all models considered here, we validate that the second-order formulas, which depend on the spectral density, are already very accurate well beyond the long-wavelength regime by showing very good agreement with the finite-difference time-domain (FDTD) simulations. The high predictive power of the second-order formula is due to the fact that higher-order contributions are negligibly small, implying that it very accurately approximates multiple scattering through all orders. This implies that there can be no Anderson localization within the predicted perfect transparency interval in stealthy hyperuniform layered and transversely isotropic media in practice because the localization length (associated with only possibly negligibly small higher-order contributions) should be very large compared to any practically large sample size. Our predictive theory provides the foundation for the inverse design of novel effective wave characteristics of disordered and statistically anisotropic structures by engineering their spectral densities.

Design and performance analysis of 3-D braided piezoelectric composite vibration energy harvester

In this article, an innovative three-dimensional (3-D) braided piezoelectric composite vibration energy harvester (BPCVEH) is designed. The geometry and representative volume unit (RVU) models of the 3-D braided piezoelectric composites (BPCs) are established based on the braided process. The effective elastic, piezoelectric, and dielectric constants of the 3-D BPCs are also predicted. The electro-mechanical coupling vibration equation of the 3-D BPCVEH under forced vibration is derived, and its output response and vibration mode are analyzed. The effects of environment frequency, load resistance, and external excitation acceleration on the voltage and power response of 3-D BPCVEH with different volume fractions are studied.

Annealing modulated microstructural and electrical properties of plasma-enhanced atomic layer deposition-derived HfO2/SiO2 nanolaminates on AlGaN/GaN

In current work, HfO2/SiO2 nanolaminates and HfO2 films were grown on AlGaN/GaN substrates via plasma-enhanced atomic layer deposition. A comparative study of how rapid thermal annealing modulates the microstructural and electrical properties of both films has been presented. It is found that the HfO2/SiO2 nanolaminate keeps an amorphous structure when thermally treated below 600 °C, whereas crystal grains appear within the 800 °C annealed sample. High-temperature annealing facilitates the transformation from Hf–O and Si–O to Hf–O–Si in the HfO2/SiO2 nanolaminates, forming an HfSiO4 composite structure simultaneously. The 800 °C annealed HfO2/SiO2 shows a low k value and large leakage current density. While the 600 °C annealed HfO2/SiO2 possesses an effective dielectric constant of 18.3, a turn-on potential of 9.0 V, as well as a leakage density of 10−2 μA/cm2 at gate biases of both −10 and 2 V, revealing good potential in fabricating high electron mobility transistors.

Оптические свойства сверхтонких пленок Pd и Pt на кварцевой подложке и на пленках триоксида вольфрама

Based on ellipsometry and transmission spectra, optical parameters of palladium and platinum films were determined. The Pd and Pt films had a thickness of 5 – 7 nm and were studied both on a SiO2 and WO3 substrates. Despite the extremely small thicknesses, the parameters of most films were well described by isotropic dielectric constant. An interesting feature was that films deposited directly on a SiO2 substrate had a positive (rather than negative, characteristic of a metal) real part of the effective dielectric constant, while the films deposited on WO3 exhibited metallic properties for unannealed films and properties characteristic of metal-dielectric composites for films that have been annealed (some of the films annealed at 300°C in argon retained their metallic properties).

Frequency self-compensating technique for mitigating detuning effects due to bending for wearable patch antennas

This paper presents the design analysis and measurement of a linearly polarized microstrip patch antenna resonating in the X-band regime with a self-compensating mechanism to mitigate the detuning effects due to bending. The antenna is studied for its variation in the resonant frequency for bending radii up to 20 mm and a compensation of ≈50% is achieved as compared to its counterpart. The compensation technique is realized by altering the effective dielectric constant of the substrate by injecting dielectric fluids into the grooves incorporated in the substrate, supplemented by a shape variation of the grooves due to bending. The antennas demonstrated in the current work exhibits a gain of more than 7 dBi throughout along with a consistent −10 dB impedance bandwidth.

Exciton–Polaritons in CsPbBr3 Crystals Revealed by Optical Reflectivity in High Magnetic Fields and Two‐Photon Spectroscopy

Cesium lead bromide (CsPbBr3) is a representative material of the emerging class of lead halide perovskite semiconductors that possess remarkable optoelectronic properties. Its optical properties in the vicinity of the bandgap energy are greatly contributed by excitons, which form exciton polaritons due to strong light–matter interactions. Exciton–polaritons in solution‐grown CsPbBr3 crystals are examined by means of circularly polarized reflection spectroscopy measured in high magnetic fields up to 60 T. The excited 2P exciton state is measured by two‐photon absorption. Comprehensive modeling and analysis provides detailed quantitative information about the exciton–polariton parameters: exciton binding energy of 32.5 meV, oscillator strength characterized by longitudinal–transverse splitting of 5.3 meV, damping of 6.7 meV, reduced exciton mass of 0.18m0, exciton diamagnetic shift of 1.6 μeV T−2, and exciton Landé factor . It is shown that the exciton states can be described within a hydrogen‐like model with an effective dielectric constant of 8.7. From the measured exciton longitudinal–transverse splitting, Kane energy of Ep = 15 eV is evaluated, which is in reasonable agreement with values of 11.8–12.5 eV derived from the carrier effective masses.

Multiband terahertz metamaterial perfect absorber for microorganisms detection

We report a multi-resonant terahertz (THz) metamaterial perfect absorber (MPA)-based biosensor in the working frequency range of 0 - 3.8 THz for sensing of microorganisms (such as fungi, yeast) and wheat pesticides. Nearly 100% absorption is realized at f_1= 1.7THz, f_2= 2.8THz, f_3=3.2THz, and f_4=3.5THz. We designed our THz MPA sensor making resonators’ gap area compatible with the microorganisms’ size. To obtain optimum performance of the MPA, a mapping of amplitudes and shifts in the absorption resonance peaks with different structural parameters of the resonators is carried out. A very high-frequency shift is obtained for microorganisms such as Penicillium chrysogenum (fungi), yeast, and pesticides (Imidacloprid, N, N-Diethyldithiocarbamate sodium salt trihydrate, Daminozide, N, N-Diethyldithiocarbamate sodium salt hydrate, and Dicofol). An equivalent circuit model using Advance Design System (ADS) software is developed. The calculated results through the model show similar trends as obtained in the simulations using CST. Investigations of the effect of incidence angle of THz wave on the absorption spectra of the MPA are also carried out. It is found that incidence angle does not impact the stability of the lower resonance absorption peak (1.79THz). Due to the wide working frequency range, the proposed sensor is extremely suitable for the detection of all range of pesticides because their specific absorption fingerprint lies in the frequency range of 0–3.8THz. We believe that our sensor could be a potential detection tool for detecting pesticide residues in agriculture and food products. The THz MPA-based biosensor is capable of detecting a very small change in the effective dielectric constant of the MPA environment. Therefore, it can also offer huge opportunities in label-free biosensing for future biomedical applications.

Modeling of hysteretic response of porous piezo/ferroelectric ceramics

The hysteretic character of the electromechanic coupling in porous piezoeceramics is a fundamental issue to be investigated in order to design porous materials with enhanced functional responses and increased figure of merit. In the present work, the porosity-dependent evolution of polarization-field PE and strain-field sE hysteretic responses of porous ferro/piezoceramics are simulated by using the Jiles-Atherton model for switching, combined with Finite Element Analysis in order to determine the local electrical and mechanical responses and the effective dielectric and piezoelectric constants. By considering 2D arrays of porous structures, the local electric field, potential and strain–stress local distributions are firstly evaluated in discrete elements. The macroscopic polarization and deformation responses vs. the applied field are determined by computing the response of each dense region subjected to its corresponding local field. The obtained nonlinear decrease of polarization and deformation vs. porosity are comparatively discussed for square, hexagonal regular pore arrays and for randomly distributed porosity. Further, the effective permittivity and piezoelectric constant d33 and conversion figure of merit vs. porosity computed in different polarization states are estimated and discussed. The present approach may offer a support for the design of porous structures with enhanced piezoelectric response.

Thermodynamic property of one-dimensional hydrogenic impurity in Nitride semiconductor quantum well

ABSTRACT The thermodynamic properties of one-dimensional (1-D) hydrogenic impurity in Nitride semiconductor quantum well have been investigated. Firstly, using a combination of the linear variational approach and the effective mass approximation, we obtain the eigen-energy of hydrogenic impurity states in AlN, GaN and InN quantum wells. Subsequently, we explore the quantum size effect on the thermodynamic properties of these low-dimensional semiconductor structures, revealing some novel and intriguing phenomena. It is found as the width of the quantum well is increased, the energy of hydrogenic impurity gets decreased, however, the thermodynamic parameters, such as the average energy, entropy and heat capacity of the hydrogenic impurity become increased. The physical origins of these peculiar phenomena are attributed to the competitive mechanism between the quantum confinement effect and Coulombic interaction between the electron and impurity. Finally, by conducting a comprehensive comparison of the thermodynamic parameters among GaN, InN, and AlN quantum wells, we propose an innovative strategy for modulating the thermodynamic properties of these low-dimensional semiconductor structures. This manipulation can be achieved not only through external factors such as temperature and quantum well size, but also by altering internal variables like the effective mass and relative dielectric constant of the semiconductor material. This study not only advances our understanding of the thermodynamic properties of hydrogenic impurities in semiconductor quantum wells, but also provides some theoretical guidance for practical applications in fields such as semiconductor physics, condensed matter physics, chemical physics, etc.

Template‐free Formation of Hybrid Dielectric for Flexible Capacitive Sensors with Wide‐Pressure‐Range Linear Detection

AbstractWearable and flexible capacitive pressure sensors have recently attracted significant attention in the fields of healthcare monitoring and intelligent human‐machine interaction. While considerable progress is made in achieving high‐pressure resolution over a wide linearity range, practical implementation still faces significant challenges due to complex manufacturing processes, as well as limited accuracy and stability for information transmission. To address these issues, inspiration is drawn from human skin and develop a new hybrid dielectric comprising a low‐permittivity (low‐k) micro‐cilia array and a high‐permittivity (high‐k) foam. Without assistance from an elaborate fabrication methodology, the template‐free method provides a cost‐effective and convenient way to realize the functional dielectric for flexible capacitive sensors. The hybrid dielectric exhibits a pressure‐induced series‐parallel conversion mechanism, enabling effective manipulation of the linear effective dielectric constant and controlled initial/resultant capacitance. Through systematic optimization, the sensor demonstrates a high sensitivity of 0.236 kPa−1 within an ultrabroad linearity range of up to 1100 kPa. Thanks to the unique characteristics of the hybrid dielectric, this device showcases potential applications in various domains including human joint motion analysis, healthcare monitoring, accurate message transmission, and convenient Morse code communication utilizing non‐overlapping capacitance signals.

Integrated Passive Sensing Chip for Highly Sensitive and Reusable Detection of Differential-Charged Nanoplastics Concentration.

In this work, a new type, highly sensitive, and reusable nanoplastics (NPs) microwave detection method is proposed, which can be used to rapidly analyze NPs with different surface charges and sizes. The effective dielectric constant of NPs varies according to the different concentrations, particle sizes, and surface charges of NPs in aqueous solution. The feasibility of the microwave method for differential-charged NPs detection is verified using a complementary split ring resonator sensor manufactured on a cost-effective printed circuit board, which shows a high sensitivity only for positively charged NPs (PS-NH2) detection. To achieve microwave detection of both positively and negatively charged NPs (PS-SO3H), a microscale spiral-coupled resonator sensing chip is manufactured through integrated passive technology, which demonstrates extremely low detection limits and high sensitivity for both PS-NH2 and PS-SO3H, with different concentrations, particle sizes, and charges. In addition, for NPs solution doped with methyl orange, the device can still perform stable measurements, overcoming the inability of traditional NPs molecular element determination and optical detection methods to detect NPs aqueous solution with organic matter doping and color presence. The proposed microwave detection method could also be extended to sensing detection for detecting other hazardous environmental substances.

Broadband co-polarized antenna using monolithic slotted dielectric patch for full-duplex system

This paper suggests a broadband co-polarized antenna utilizing monolithic slotted dielectric patch (DP) for the applications of in-band full-duplex (IBFD). Three slot pairs with different sizes in the center of the monolithic DP are constructed and reduce the effective dielectric constant at this region. As a result, the E-field distributions of the two employed modes (TM10 and TE12 modes) inside the DP are moved to the unetched part (apart from the center of the DP). In this way, a broadband co-polarized antenna using the TM10 and TE12 modes is constructed while the isolation between the two ports for transmitting (TX) and receiving (RX) can be enhanced significantly in a broadband. The measured results of the antenna prototype are quite consistent with the simulated results. The experimental results illustrate that within the operating bandwidth of about 18% (|S11|< −10 dB), an isolation measured greater than 28 dB is attained, with a maximum value of 49.8 dB. Overall, the proposed co-polarized antenna owns advantages of simple structure, broad bandwidth, high efficiency, and low profile.

Study of the electronic, elastic, piezoelectric and infrared properties of trigonal BPO4

Trigonal BPO4 is a crystal crystallizing in α-quartz structure, but most fundamental properties of it are still not well studied. In this work, first principles calculations are carried out to study its electronic, elastic, piezoelectric and infrared properties. Calculated electronic properties reveal that trigonal BPO4 is an indirect band gap insulator with a gap of 7.32 eV. The top of its valence band is mainly composed of the O 2p orbital while the bottom of the conduction band is chiefly formed by the p orbitals of the B and P atoms. Orbital hybridization exists between the B(P) and O atoms. Studies on its elastic properties indicate that trigonal BPO4 is mechanically stable but anisotropic. The two independent piezoelectric constants of trigonal BPO4 are predicted to be 0.13 C/m2 for e11 and 0.04 C/m2 for e14. Simulated infrared spectrum uncovers five peaks with a relative intensity larger than 0.1 although its has forty-three infrared-active modes. The vibrational manners of these modes are sketched and the origins of their intensities are unveiled. Besides, its bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Born effective charges and dielectric constants are also calculated and discussed.