Articoli di riviste sul tema "Zero-Frequency band gap"
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1
ALI, MUNAZZA ZULFIQAR, e TARIQ ABDULLAH. "APPEARANCE OF A ZERO-n AND A ZERO-ϕeff GAP IN DIFFERENT FREQUENCY RANGES IN A SINGLE 1D PHOTONIC BAND GAP STRUCTURE". International Journal of Modern Physics B 25, n. 22 (10 settembre 2011): 3027–34. http://dx.doi.org/10.1142/s0217979211100849.
Abstract (sommario):
We present a scheme to realize both the zero-n and the zero-ϕ eff gap in a one-dimensional photonic band gap structure containing metamaterials. The frequency dispersion of the effective electric permittivity and magnetic permeability of the metamaterials in the adjacent layers in one period are represented by the Drude model and the resonant model. The chosen structure is composed of alternate double-negative and double-positive layers which exhibit a zero-n gap in a certain frequency range whereas in a higher frequency range it behaves as alternate permittivity negative and permeability negative layers to exhibit a zero-ϕ eff gap. Some properties and benefits of having the zero-n and the zero-ϕ eff gap in the same physical system are discussed.
2
Zhou, Lei, Zhengyong Song, Xueqin Huang e C. T. Chan. "Physics of the zero- photonic gap: fundamentals and latest developments". Nanophotonics 1, n. 3-4 (1 dicembre 2012): 181–98. http://dx.doi.org/10.1515/nanoph-2012-0020.
Abstract (sommario):
AbstractA short overview is presented on the research works related to the zero- gap, which appears as the volume-averaged refraction index vanishes in photonic structures containing both positive and negative-index materials. After introducing the basic concept of the zero- gap based on both rigorous mathematics and numerical simulations, the unique properties of such a band gap are discussed, including its robustness against weak disorder, wide-incidence-angle operation and scaling invariance, which do not belong to a conventional Bragg gap. We then describe the simulation and experimental verifications on the zero- gap and its extraordinary properties in different frequency domains. After that, the unusual photonic and physical effects discovered based on the zero- gap and their potential applications are reviewed, including beam manipulations and nonlinear effects. Before concluding this review, several interesting ideas inspired from the zero- gap works will be introduced, including the zero-phase gaps, zero-permittivity and zero-permeability gaps, complete band gaps, and zero-refraction-index materials with Dirac-Cone dispersion.
3
Xu, Fei, e Yulin Chen. "Interesting Band Properties of One-Dimensional Photonic Crystals Containing Epsilon-Negative Layers". Zeitschrift für Naturforschung A 65, n. 4 (1 aprile 2010): 329–34. http://dx.doi.org/10.1515/zna-2010-0409.
Abstract (sommario):
The transmission properties of one-dimensional photonic crystals constituted by a periodic repetition of positive-index layers and epsilon-negative layers are studied theoretically. This structure shows some interesting properties including a wide gap in the low frequency range for small period number and a comb-like transmission band in the gap. The properties of the comb-like transmission band are sensitive to the period number of the structure. In contrast to the zero-ngap and the zero- φeff gap, the transmission properties are dependent on the structure parameters. A general method to decide the position of gap and transmission band in this kind of structure is also presented.
4
Lin, Qida, Jiaxi Zhou, Kai Wang, Daolin Xu, Guilin Wen, Qiang Wang e Changqi Cai. "Low-frequency locally resonant band gap of the two-dimensional quasi-zero-stiffness metamaterials". International Journal of Mechanical Sciences 222 (maggio 2022): 107230. http://dx.doi.org/10.1016/j.ijmecsci.2022.107230.
5
Lin, Qida, Jiaxi Zhou, Kai Wang, Daolin Xu, Guilin Wen e Qiang Wang. "Three-dimensional quasi-zero-stiffness metamaterial for low-frequency and wide complete band gap". Composite Structures 307 (marzo 2023): 116656. http://dx.doi.org/10.1016/j.compstruct.2022.116656.
6
Movchan, N. V., R. C. McPhedran e A. B. Movchan. "Flexural waves in structured elastic plates: Mindlin versus bi-harmonic models". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, n. 2127 (22 settembre 2010): 869–80. http://dx.doi.org/10.1098/rspa.2010.0375.
Abstract (sommario):
The paper presents an analytical approach to modelling of Bloch–Floquet waves in structured Mindlin plates. The emphasis is given to a comparative analysis of two simplified plate models: the classical Kirchhoff theory and the Mindlin theory for dynamic response of periodic structures. It is shown that in the case of a doubly periodic array of cavities with clamped boundaries, the structure develops a low-frequency band gap in its dispersion diagram. In the framework of the Kirchhoff model, this band gap persists, even when the radius of the cavities tends to zero. A clear difference is found between the predictions of Kirchhoff and Mindlin theories. In Mindlin theory, the lowest band goes down to ω = 0 as the radius of the cavities tends to zero, which is linked with the contrasting behaviour of the corresponding Green functions.
7
Zhang, Li-Qin, Jin-Feng Zhang, Li-Ming e Shi-Tao Xu. "WSe2 Monolayer: A Stable Two-Dimensional Heterostructure Material from First-Principles of Simulation Calculations". Journal of Nanoelectronics and Optoelectronics 17, n. 10 (1 ottobre 2022): 1379–83. http://dx.doi.org/10.1166/jno.2022.3318.
Abstract (sommario):
P-N junctions or heterostructures are commonly used in the fabrication of self-driven photodetectors because they serve critical roles in influencing the electrical characteristics of two-dimensional (2D) materials. For stable 2D heterostructures, planar WSe2 monolayers have attracted a lot of interest. Using first-principles energetic and dynamic calculations, we find that the transition from the indirect band gap of WSe2 bulk phase to the direct band gap of a two-dimensional plane is caused by the formation of p-n hetero junctions. Furthermore, it affects the carrier concentration transport mode and results in a significant orbital spin coupling. There is no virtual frequency in the phonon dispersion curve across the Brillouin zone at zero pressure. The interaction of the nearest neighbour atoms causes the frequency of the two acoustic modes of the G-point to be zero, as well as the frequency of the two optical films to merge. The theoretical analysis can provide support for the transport of two-dimensional planar carriers in electronics and photonics.
8
Xiu, Chenxi, e Xihua Chu. "Study on dispersion and wave velocity in 2D elliptic granular crystals by a micromechanics-based micromorphic model". Advances in Mechanical Engineering 14, n. 8 (agosto 2022): 168781322211199. http://dx.doi.org/10.1177/16878132221119957.
Abstract (sommario):
This study considers two-dimensional elliptic granular crystals respectively with different aspect ratios. Using a micromechanics-based micromorphic model, macroscopic micromorphic constitutive modulus tensors of elliptic granular crystals are obtained. Two modes of Taylor expansion of relative displacements are used to establish contact relation between particles. This study obtains micromorphic transverse-rotational and longitudinal waves. Obvious dispersions of micromorphic waves are given in 2D elliptic granular crystals. With increase of aspect ratio, width of frequency band gap increases when wave propagates along [Formula: see text] direction but decreases when wave propagates along [Formula: see text] direction. Two modes of Taylor expansion of relative displacements only have influence on dispersions and frequency band gap of transverse-rotational waves. Velocities of longitudinal and transverse-rotational waves first decrease to zero, keep zero for a range of frequency and then increase to a larger wave velocity with increase of frequency for different aspect ratios. The situation with a larger aspect ratio leads to larger transverse-rotational and longitudinal velocities, and ratio between transverse-rotational and longitudinal velocities decreases from 0.7 to 0.59, when wave propagates along [Formula: see text] direction. However, it leads to smaller transverse-rotational and longitudinal velocities, and ratio between two velocities decreases from 0.88 to 0.56, when wave propagates along [Formula: see text] direction.
9
Alaa, Siti, Muhammad Fajrin, Eva Nurhaliza, Dian Wijaya Kurniawidi, Susi Rahayu e I. Wayan Sudiarta. "THE STUDY OF GRAPHENE BAND GAP USING HATREE FOCK METHOD IN MOLECULAR SCALE". Indonesian Physical Review 3, n. 1 (14 febbraio 2020): 24. http://dx.doi.org/10.29303/ipr.v3i1.35.
Abstract (sommario):
Graphene is known as an advanced material that has good electrical conductivity and heat conductivity. To understand the nature of graphene it is necessary to calculate the energy, band gap and vibrate frequency at the nanoscale. One method that can be used is the ab initio calculation using the Hatree-Fock method. In this research, we performed a computational study of the electronic properties of grapheme within RHF/STO-3G basis set in different cluster molecules. From this study we get band gap for graphene in ab initio level, have a consistant value around zero. Using ab initio method, we can obtain a deeper understanding about the graphene behaviour at the molecular scale.
10
Yuan, Bo, Yong Chen, Min Jiang, Shuai Tang, Miao He e Minglin Tu. "the Interaction of Resonance And Bragg Scattering Effects for the Locally Resonant Phononic Crystal with Alternating Elastic and Fluid Matrices". Archives of Acoustics 42, n. 4 (20 dicembre 2017): 725–33. http://dx.doi.org/10.1515/aoa-2017-0075.
Abstract (sommario):
Abstract Three-dimensional (3D) locally resonant phononic crystals (LRPCs) are studied with the aim of optimising the sub-wavelength band gaps of such composites. By analysing their effective acoustic properties, it has been found that the effective acoustic speed of the composite will drop to zero when local resonance arise, and will increase monotonically when Bragg scattering effects occur. Moreover, if the matrix is a low-shear-speed medium, local resonators can significantly reduce the effective acoustic speed of the composite and, therefore, lower the frequency where Bragg scattering effects occur. Hence, a specific LRPC with alternating elastic and fluid matrices is proposed, whose resonance and Bragg gaps are already close in frequency. The fluid matrix behaves as a wave filter, which prevents the shear waves from propagating in the composite. By using the layer-multiple-scattering theory, the coupling behaviour of local resonance and Bragg scattering band gaps has been investigated. Both gaps are enhanced when they move closer to each other. Finally, a gap-coupled case is obtained that displays a broad sub-wavelength band gap. Such proposal excels at the application of underwater acoustic materials since the arrangement of structure can be handily adjusted for tuning the frequency of coupled gap.
11
Dell, Alexander, Anton Krynkin, Kirill Horoshenkov e Gavin Sailor. "Low frequency attenuation of acoustic waves using sound-soft scatterers". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 265, n. 3 (1 febbraio 2023): 4941–49. http://dx.doi.org/10.3397/in_2022_0714.
Abstract (sommario):
The attenuation of acoustic waves by silencers is typically achieved through the employment of rigidly backed cavities, connected to a main waveguide by a perforated panel. This invokes a resonant response at frequencies determined by the dimensions of the perforation and the rigidly backed cavity. A limiting factor in this approach is that to achieve low frequency attenuation, either large cavity depths are required, which is often impractical, or narrow neck regions need to be used, where performance is limited due to the viscothermal losses. Within this paper, a non-rigidly backed perforated pipe is presented where the pressure release condition at each perforation creates an acoustic sound-soft boundary condition. By the introduction of sound-soft boundary conditions, a low frequency band gap is created as the first order mode is shifted to a non-zero value, the frequency of which is determined by the dimensions and separation of the perforations. Experimental results displaying this band gap are presented along with numerical models verifying the phenomenon and an ideal analytical model based upon the transfer matrix method.
12
Jafari, A., A. Rahmat e S. Bakkeshizadeh. "Band structure of one-dimensional doped photonic crystal with three level atoms using the Fresnel coefficients method". International Journal of Modern Physics B 32, n. 01 (8 gennaio 2018): 1750277. http://dx.doi.org/10.1142/s0217979217502770.
Abstract (sommario):
We consider a one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics. Electric permittivity and magnetic permeability of this crystal depends on the incident electromagnetic wave frequency. We suppose that three level atoms have been added to the second layer of each dielectric and this photonic crystal (PC) has been doped. These atoms can be added to the layer with different rates. In this paper, we have calculated and compared the band structure of the mentioned PC considering the effect of added atoms to the second layer with different rates through the Fresnel coefficients method. We find out that according to the effective medium theory, the electric permittivity of the second layer changes. Also the band structure of PC for both TE and TM polarizations changes, too. The width of bandgaps related to “zero averaged refractive index” and “Bragg” increases. Moreover, new gap branches appear in new frequencies at both TE and TM polarizations. In specific state, two branches of “zero permittivity” gap appear in the PC band structure related to TM polarization. With increasing the amount of the filling rate of total volume with three level atoms, we observe a lot of changes in the PC band structure.
13
Ding, Lan, Zhi Ye e Qiao-Yun Wu. "Flexural vibration band gaps in periodic Timoshenko beams with oscillators in series resting on flexible supports". Advances in Structural Engineering 23, n. 14 (16 giugno 2020): 3117–27. http://dx.doi.org/10.1177/1369433220928529.
Abstract (sommario):
The propagation properties of waves in Timoshenko beams resting on flexible supports and with periodically attached harmonic locally resonant oscillators are studied by the transfer matrix methodology. Through calculating the differential equations of the beam for the flexible vibration and the dynamic equations of the oscillators in series, the matrix of dynamic stiffness and the resulting transfer matrix are derived. Accordingly, the band gap in infinite system characterized by the propagation constant can be verified by comparing to the curve of transmission property, determined with the finite element method for the finite system. The mechanism of each band gap formation is further explored. Numerical results show that different from the single degree-of-freedom mass-spring model, one more locally resonant band gap is generated in the system of two oscillators in series. The introduction of flexible supports, allowing for variable internal coupling between the adjacent cells, produces an extra band gap with a minimum frequency of zero. It is also found that the starting frequencies of the locally resonant gaps are related to the spring stiffness and mass of the oscillator. Therefore, the positions and widths of the band gaps can be tuned by properly adjusting the four parameters of the oscillators and also the stiffness of the flexible supports.
14
Xu, Qiang-Rong, Yang Zhu, Kang Lin, Cheng Shen e Tian-Jian Lu. "Low-frequency sound insulation performance of novel membrane acoustic metamaterial with dynamic negative stiffness". Acta Physica Sinica 71, n. 21 (2022): 214301. http://dx.doi.org/10.7498/aps.71.20221058.
Abstract (sommario):
For improving the low-frequency sound insulation properties of membrane/plate structures, a new quasi-zero stiffness membrane acoustic metamaterial with dynamic magnetic negative stiffness is proposed. When the equivalent magnetic charge theory is used to investigate the dynamic magnetic negative stiffness, a theoretical model of proposed metamaterial with finite dimension is established based on the Galerkin method. Through a combination of theoretical analysis, numerical simulation and experimental measurement, the low-frequency (1–1000 Hz) sound insulation performance of the metamaterial is investigated from several perspectives, including structural modality, vibration mode, average velocity, phase curve, equivalent mass density, and equivalent spring-mass dynamics model. The results show that at a certain initial membrane tension, the decreasing of the magnetic gap or the increasing of the residual flux density can increase the dynamic magnetic negative stiffness. This in turn leads the peak frequency to decrease and the bandwidth of sound insulation to increase, thus achieving effective low-frequency sound insulation over a wide frequency band. Further, when the magnetic gap is larger than the second critical magnetic gap and smaller than the first critical magnetic gap, the first-order modal resonance of the metamaterial disappears, and the corresponding value of sound insulation valley increases significantly, thus demonstrating superior sound insulation effect in a wide frequency band. The proposed method of using dynamic magnetic negative stiffness to improve low-frequency sound insulation valleys due to modal resonance provides useful theoretical guidance for designing membrane/plate type low-frequency sound insulation metamaterials.
15
LINTON, C. M. "Water waves over arrays of horizontal cylinders: band gaps and Bragg resonance". Journal of Fluid Mechanics 670 (25 gennaio 2011): 504–26. http://dx.doi.org/10.1017/s0022112010005471.
Abstract (sommario):
The existence of a band-gap structure associated with water waves propagating over infinite periodic arrays of submerged horizontal circular cylinders in deep water is established. Waves propagating at right angles to the cylinder axes and at an oblique angle are both considered. In each case an exact linear analysis is presented with numerical results obtained by solving truncated systems of equations. Calculations for large finite arrays are also presented, which show the effect of an incident wave having a frequency within a band gap – with the amount of energy transmitted across the array tending to zero as the size of the array is increased. The location of the band gaps is not as predicted by Bragg's law, but we show that an approximate determination of their position can be made very simply if the phase of the transmission coefficient for a single cylinder is known.
16
Wang, Kai, Jiaxi Zhou, Huajiang Ouyang, Li Cheng e Daolin Xu. "A semi-active metamaterial beam with electromagnetic quasi-zero-stiffness resonators for ultralow-frequency band gap tuning". International Journal of Mechanical Sciences 176 (giugno 2020): 105548. http://dx.doi.org/10.1016/j.ijmecsci.2020.105548.
17
Liu Li-Xiang, Dong Li-Juan, Liu Yan-Hong, Yang Chun-Hua, Yang Cheng-Quan e Shi Yun-Long. "Frequency properties of the defect mode inside a photonic crystal band-gap with zero average refractive index". Acta Physica Sinica 60, n. 8 (2011): 084218. http://dx.doi.org/10.7498/aps.60.084218.
18
Jafari, A., e A. Rahmat. "Band structure of one-dimensional photonic crystal with graphene layers using the Fresnel coefficients method". International Journal of Modern Physics B 32, n. 11 (16 aprile 2018): 1850132. http://dx.doi.org/10.1142/s0217979218501321.
Abstract (sommario):
In this paper, we have calculated the band structure of an instance of one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics via the Fresnel coefficients method. Then, we supposed the addition of a thin layer of graphene to each dielectric layer and the given photonic crystal (PC) composed of dielectric–graphene composites. The effects of graphene layers on the PC band structure were evaluated. We found out that according to the effective medium theory unlike the TE polarization, the electric permittivity of the dielectric layers changed at TM polarization. As such, the band structure of PC for TM polarization changed, too. Moreover, instead of bandgap related to “zero averaged refractive index” an approximately omnidirectional bandgap appeared and a related bandgap to “[Formula: see text] = 0” disappeared. In addition, a new angular gap branch appeared at a new frequency at TM polarization in which the width of gap increased as the angle increased.
19
CABUK, SULEYMAN. "FIRST-PRINCIPLES STUDY OF THE ELECTRONIC, LINEAR, AND NONLINEAR OPTICAL PROPERTIES OF Li(Nb, Ta)O3". International Journal of Modern Physics B 24, n. 32 (30 dicembre 2010): 6277–90. http://dx.doi.org/10.1142/s0217979210054415.
Abstract (sommario):
We investigate the energy band structure, total density of states, the linear, nonlinear optical (NLO) response, and the electron energy-loss spectrum for Li(Nb, Ta)O 3 using first principles calculations based on density functional theory in its local density approximation. Our calculation shows that these compounds have similar structures. The indirect band gaps of 3.39 eV (LiNbO3) and 3.84 eV (LiTaO3) at the Γ–Z direction in the Brillouin zone are found. A simple scissor approximation is applied to adjust the band energy gap from the calculations to match the experimental values. The optical spectra are analyzed and the origins of some of the peaks in the spectra are discussed in terms of calculated electronic structure. Calculations are reported for the frequency-dependent complex second-order NLO susceptibilities [Formula: see text] up to 10 eV and for zero-frequency limit [Formula: see text]. The results are compared with the theoretical calculations and the available experimental data.
20
Jawad, Huda M. "Quantum Mechanical Investigations into Thermochemistry Properties and Electronic, Structural of Nanocrystals". Al-Mustansiriyah Journal of Science 29, n. 3 (10 marzo 2019): 133. http://dx.doi.org/10.23851/mjs.v29i3.632.
Abstract (sommario):
This paper presents quantum mechanical investigations that is into electronic and thermochemistry properties of Gallium phosphide. It also investigates diamondoids and nanocrystals using the density functional theory. This is done at the generalized gradient approximation of Perdew et al basis set. This has been used to create Gaussian 09 program auxiliary by Gaussian view. In order to full investigate the ionization potential, affinity, valance bond, conduction bond, zero point energy and thermochemistry properties. The result GaP diamondoids. Electron affinity and conduction band, decreases as a function of the total number of Ga and P atoms in most of the investigated range. Ionization energies zero point and valance bands increased with the number of Ga and P atoms but there are fluctuations in tetramantane and hexamantane In fact, since the present diamondoids are built from nearly cubic cages. Thermochemistry entails calculation of frequency which also includes thermochemical analysis of actual system comprising of thermal energy correction, heat capacity and entropy.
21
Samy, Omnia, e Amine El Moutaouakil. "Comparing the plasmon dispersion in graphene and MoS2 nanoribbons array under Electromagnetic excitation". Journal of Physics: Conference Series 2751, n. 1 (1 aprile 2024): 012015. http://dx.doi.org/10.1088/1742-6596/2751/1/012015.
Abstract (sommario):
Abstract Terahertz properties of different materials have been recently studied due to their wide applications in optoelectronics, industry, product inspection, and spectroscopy. Terahertz frequency applications are promising for the medical field as they are considered safe frequencies. Previous terahertz plasma response focused on 2D materials like graphene and transition metal dichalcogenides (TMDs) due to their favourable electronic properties, high electric conductivity, and their band gap characteristics, so they can be used in electronic devices. Some of these materials showed good biocompatibility so they can be used in biomedical applications. Since graphene has zero band gap, researchers are continuously exploring methods to increase its band gap to be used in electronics. Graphene heterostructures or metamaterials are ways to enhance graphene characteristics for specific applications. This work investigates the possibility of using MoS2 with graphene in THz applications. The plasmon dispersion for graphene and MoS2 nanoribbon array structure is compared. Both graphene and MoS2 behave differently in response to terahertz radiation due to their different band gaps. The results showed that MoS2 exhibits a plasmonic response in the THz region at high carrier concentrations. This opens up opportunities for MoS2 to be employed in THz sensors, both independently and in conjunction with graphene within heterostructures or metamaterials for power sources and detectors. These advancements hold significant potential for the future THz imaging and communication technologies.
22
Devi, K. K. A., e C. H. Ng. "Analysis and Design of High Gain NRI Superstrate Based Antenna for RF Energy Harvesting System". Indonesian Journal of Electrical Engineering and Computer Science 2, n. 3 (7 maggio 2016): 647. http://dx.doi.org/10.11591/ijeecs.v2.i3.pp647-656.
Abstract (sommario):
<p>A high gain patch antenna inspired by 4 layers of negative refractive index (NRI) metamaterial superstrate is proposed to operate at downlink radio frequency (RF) band (935 MHz to 960 MHz of GSM 900). The metamaterial unit cell consists of a nested split ring resonator (SRR) and strip line laminated on other side of FR4 substrate. The effective permittivity and permeability of the proposed unit cell are designed synchronously to approach zero, which leads the NRI superstrate to have impedance match with zero and negative refractive index.The NRI superstrate is studied using Fabry-Perot (F-P) resonant cavity. The gain is improved by 82.48% at the air gap of 55 mm in the desired frequency band.Therefore, the gain of the antenna is effectively enhanced based on the negative refractive index metamaterial. The measured radiation pattern and S parameter results also showed that it has good agreement with the simulation results.</p>
23
Petrus, R. Yu, H. A. Ilchuk, A. I. Kashuba, I. V. Semkiv, E. O. Zmiiovska e R. M. Lys. "Optical Properties of Materials for Solar Energy Based on Cadmium Chalcogenides Thin Films". Фізика і хімія твердого тіла 20, n. 4 (15 dicembre 2019): 367–71. http://dx.doi.org/10.15330/pcss.20.4.367-371.
Abstract (sommario):
The optical constants and thickness of cadmium chalcogenides (CdX, X= S, Se and Te) thin films prepared by quasi close-space sublimation and high-frequency magnetron sputtering method are determined. The optical constants and the band gap of the films under study have been determined. Optical properties (refractive index n(λ), extinction coefficient k(λ) and dielectric functions ε(λ)) of thin films and thickness d can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. The material optical parameter such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio was also calculated.
24
Movchan, A. B., N. V. Movchan e R. C. McPhedran. "Bloch–Floquet bending waves in perforated thin plates". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 463, n. 2086 (17 luglio 2007): 2505–18. http://dx.doi.org/10.1098/rspa.2007.1886.
Abstract (sommario):
This paper presents a mathematical model describing propagation of bending waves in a perforated thin plate. It is assumed that the holes are circular and form a doubly periodic square array. A spectral problem for the biharmonic operator is formulated in a unit cell containing a single defect, and its analytical solution is constructed using a multipole method. The overall system for the coefficients in the multipole expansion is then solved numerically. We generate dispersion diagrams for the two cases where the boundaries of holes are either clamped or free. We show that in the clamped case, there is a total low-frequency band gap in the limit of inclusions of zero radius, and give a simple formula describing the corresponding band diagram in this limit. We show that in the free-edge case, the band diagram of the vibrating plate is much closer to that of plane waves in a uniform plate than for the clamped case.
25
Chen, Jia-Xin, Xiao-Ge Zhao, Xing-Xing Dong, Zhen-Long Lv e Hong-Ling Cui. "Density Functional Study of the Electronic, Elastic and Optical Properties of Bi2O2Te". Zeitschrift für Naturforschung A 75, n. 1 (18 dicembre 2019): 73–80. http://dx.doi.org/10.1515/zna-2019-0185.
Abstract (sommario):
AbstractLayered crystal Bi2O2Te has recently been found to have high electron mobility and excellent thermoelectric properties for technical applications; however, its other properties are not well studied yet. In this work, the electronic, elastic and optical properties of Bi2O2Te are systematically studied using the density functional method. The results indicate that Bi2O2Te is a narrow band gap semiconductor. The gap is formed by the Te 5p orbital at the top of the valence band and the Bi 6p orbital at the bottom of the conduction band. There are both ionic and covalent interactions within the Bi–O layers, and these layers are linked by the ionic Bi–Te bonds forming the crystal. Bi2O2Te is mechanically stable but anisotropic. It is easy to fracture along the c axis under shear stress. Its shear modulus is far smaller than its bulk modulus, so shape deformation is easier to occur than pure volume change. Its melting point is predicted to be 1284.0 K based on an empirical formula. The calculated refractive index at zero frequency reveals that Bi2O2Te is a negative uniaxial crystal with a birefringence of 0.51, making it a potential tuning material for optical application. The characteristics and origins of other optical properties are also discussed.
26
Liu, Jianlong, Xin Li, Ruirui Jiang, Kaiqiang Yang, Jing Zhao, Sayed Ali Khan, Jiancheng He, Peizhong Liu, Jinfeng Zhu e Baoqing Zeng. "Recent Progress in the Development of Graphene Detector for Terahertz Detection". Sensors 21, n. 15 (22 luglio 2021): 4987. http://dx.doi.org/10.3390/s21154987.
Abstract (sommario):
Terahertz waves are expected to be used in next-generation communications, detection, and other fields due to their unique characteristics. As a basic part of the terahertz application system, the terahertz detector plays a key role in terahertz technology. Due to the two-dimensional structure, graphene has unique characteristics features, such as exceptionally high electron mobility, zero band-gap, and frequency-independent spectral absorption, particularly in the terahertz region, making it a suitable material for terahertz detectors. In this review, the recent progress of graphene terahertz detectors related to photovoltaic effect (PV), photothermoelectric effect (PTE), bolometric effect, and plasma wave resonance are introduced and discussed.
27
Lu, Wei-Bing, Hui Chen e Zhen-Guo Liu. "A review of microwave devices based on CVD-grown graphene with experimental demonstration". EPJ Applied Metamaterials 6 (2019): 8. http://dx.doi.org/10.1051/epjam/2019001.
Abstract (sommario):
As a two-dimension planar material with zero-gap structure, graphene has a lot of outstanding properties in microwave frequency band, and the chemical vapor deposition (CVD) method can produce the large-scale graphene sheets with high quality for applications. Thus, the study about the microwave devices based on CVD-grown graphene has been aroused wide interests in the past few years. In this paper, mainly concentrating on the research by Chinese scientific groups, we review the development of microwave devices based on the CVD-grown graphene which are all validated by experiments, including attenuators, absorbers, antennas, electromagnetic interference (EMI) shielding and beam reconfiguration.
28
Poulin, Mathieu, Steven Giannacopoulos e Maksim Skorobogatiy. "Surface Wave Enhanced Sensing in the Terahertz Spectral Range: Modalities, Materials, and Perspectives". Sensors 19, n. 24 (13 dicembre 2019): 5505. http://dx.doi.org/10.3390/s19245505.
Abstract (sommario):
The terahertz spectral range (frequencies of 0.1–10 THz) has recently emerged as the next frontier in non-destructive imaging and sensing. Here, we review amplitude-based and phase-based sensing modalities in the context of the surface wave enhanced sensing in the terahertz frequency band. A variety of surface waves are considered including surface plasmon polaritons on metals, semiconductors, and zero gap materials, surface phonon polaritons on polaritonic materials, Zenneck waves on high-k dielectrics, as well as spoof surface plasmons and spoof Zenneck waves on structured interfaces. Special attention is paid to the trade-off between surface wave localization and sensor sensitivity. Furthermore, a detailed theoretical analysis of the surface wave optical properties as well as the sensitivity of sensors based on such waves is supplemented with many examples related to naturally occurring and artificial materials. We believe our review can be of interest to scientists pursuing research in novel high-performance sensor designs operating at frequencies beyond the visible/IR band.
29
Huang e Yuan. "A Compact Wideband SIW Bandpass Filter with Wide Stopband and High Selectivity". Electronics 8, n. 4 (17 aprile 2019): 440. http://dx.doi.org/10.3390/electronics8040440.
Abstract (sommario):
A novel method to design a wideband substrate integrated waveguide (SIW) bandpass filter (BPF) with compact size, wide stopband and high selectivity is presented. In this method some unique electromagnetic band-gap (EBG) cells are periodically etched on the top layer of SIW to realize a wide passband propagating below the equivalent waveguide cutoff frequency. By changing the configuration of EBG cells, undesired harmonics in upper stopband can be suppressed and a wideband BPF with wide stopband can be obtained. By symmetrically loading two complementary split ring resonators (CSRRs) on the tapered gradient lines of the input/output ports, a transmission zero near the passband can be introduced, and it makes the frequency selectivity of upper sideband improve significantly. As a verification, a wideband SIW BPF with a 3.02 GHz absolute bandwidth (ABW) and a 64.7% fractional bandwidth (FBW) centered at 4.67 GHz is designed, simulated, manufactured, and measured. The results of the experiment and simulation are in good agreement.
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Tuluhong, Ayiguzhali, Weiqing Wang, Yongdong Li, Haiyun Wang e Lie Xu. "Research on Modelling and Stability Characteristics of Electric Traffic Energy System Based on ZVS-DAB Converter". Journal of Electrical and Computer Engineering 2020 (28 maggio 2020): 1–10. http://dx.doi.org/10.1155/2020/5450628.
Abstract (sommario):
We study and describe mostly used traditional simplified circuits for full-bridge Zero Voltage Switching-Dual Active Bridge (ZVS-DAB) converter and deduce their mathematical model. On this basis, we propose a high-frequency (HF) mathematical model, which takes into account conduction loss and HF characteristics of the ZVS-DAB converter model. We compare the static and dynamic stabilities of the traditional and the proposed HF mathematical model by simulation. Finally, the high-frequency planar transformer (HFPT) with good heat dissipation and the wide band gap (WBG) semiconductor SiC switches with fast switching speed are employed to build a 4.4 kw, 40 KHz experimental prototype to verify the effectiveness of the improved HF circuit of ZVS-DAB converter. The results show that the proposed HF mathematical model is superior to the traditional one, and it fully considers the HF characteristics of the circuit and effectively improves the HF oscillation, DC bias, and waveform distortion of the ZVS-DAB converter.
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Sakib, Shihabun, Ahasanul Hoque, Sharul Kamal Bin Abdul Rahim, Mandeep Singh, Norsuzlin Mohd Sahar, Md Shabiul Islam, Mohamed S. Soliman e Mohammad Tariqul Islam. "A Central Spiral Split Rectangular-Shaped Metamaterial Absorber Surrounded by Polarization-Insensitive Ring Resonator for S-Band Applications". Materials 16, n. 3 (30 gennaio 2023): 1172. http://dx.doi.org/10.3390/ma16031172.
Abstract (sommario):
This paper reports a central spiral split-rectangular-shaped metamaterial absorber surrounded by a polarization-insensitive ring resonator for s-band applications. The rated absorption is 99.9% at 3.1 GHz when using a three-layer structure where the top and ground are made of copper and the center dielectric material is a commonly used FR-4 substrate. The central split gaps have an impact on the unit cell by increasing high absorption, and an adequate electric field is apparent in the outer split ring gap. At 3.1 GHz, the permittivity and permeability are negative and positive, respectively, so the proposed unit cell acts as an epsilon negative (ENG) metamaterial absorber. In a further analysis, Roger4450B was used as a substrate and obtained excellent absorption rates of 99.382%, 99.383%, 99.91%, and 95.17% at 1.44, 3.96, 4.205, and 5.025 GHz, respectively, in the S- and C-band regions. This unit cell acts as a single negative metamaterial (SNG) absorber at all resonance frequencies. The S11 and S21 parameters for FR-4 and Rogers4450B were simulated while keeping the polarization angle (θ and φ) at 15, 30, 45, 60, 75, and 90 degrees to measure, permittivity, permeability, reflective index, absorption, and reflection. The values of the reflective index are near zero. Near-zero reflective indexes (NZRI) are widely used in antenna gain propagation. The unit cell fabricated for the FR-4 substrate attained 99.9% absorption. S-band values in the range of (2–4) GHz can be applied for low-frequency radar detection.
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Berrada, K. "Entropy squeezing and coherence for a non-Markovian dissipative qubit system". Modern Physics Letters A 35, n. 08 (11 dicembre 2019): 2050046. http://dx.doi.org/10.1142/s0217732320500467.
Abstract (sommario):
We examine the impact of the non-Markovian environment on the dynamical behavior of the quantum coherence and entropy squeezing considering a two-level atomic system (qubit) immersed in a reservoir with zero-temperature for two types of non-Markovian environments. We consider a cavity little off-resonance with the transition frequency of the qubit and the case of a non-perfect photonic band gap (PBG). We show that the amount of coherence is dependent on the structure of the environment and influenced through the memory effects. We obtain that the delay and revival of the coherence loss might take place by controlling the detuning of the cavity-qubit system. Whereas, a partial coherence trapping occurs in non-ideal PBG and the decrease of the gap width will destroy the coherence. On the other hand, we show the situation for which the squeezing is occurring and enhanced with respect to the main parameters for the system. Finally, we display the monotonic dependence of the quantum coherence and squeezing on the main model parameters.
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Güllü, H. H., M. Terlemezoğlu, Ö. Bayraklı, D. E. Yıldız e M. Parlak. "Investigation of carrier transport mechanisms in the Cu–Zn–Se based hetero-structure grown by sputtering technique". Canadian Journal of Physics 96, n. 7 (luglio 2018): 816–25. http://dx.doi.org/10.1139/cjp-2017-0777.
Abstract (sommario):
In this paper, we present results of the electrical characterization of n-Si/p-Cu–Zn–Se hetero-structure. Sputtered film was found in Se-rich behavior with tetragonal polycrystalline nature along with (112) preferred orientation. The band gap energy for direct optical transitions was obtained as 2.65 eV. The results of the conductivity measurements indicated p-type behavior and carrier transport mechanism was modelled according to thermionic emission theory. Detailed electrical characterization of this structure was carried out with the help of temperature-dependent current–voltage measurements in the temperature range of 220–360 K, room temperature, and frequency-dependent capacitance–voltage and conductance-voltage measurements. The anomaly in current–voltage characteristics was related to barrier height inhomogeneity at the interface and modified by the assumption of Gaussian distribution of barrier height, in which mean barrier height and standard deviation at zero bias were found as 2.11 and 0.24 eV, respectively. Moreover, Richardson constant value was determined as 141.95 Acm−2K−2 by means of modified Richardson plot.
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Shuvaev, Alexey, Lei Pan, Peng Zhang, Kang L. Wang e Andrei Pimenov. "Faraday Rotation Due to Quantum Anomalous Hall Effect in Cr-Doped (Bi,Sb)2Te3". Crystals 11, n. 2 (3 febbraio 2021): 154. http://dx.doi.org/10.3390/cryst11020154.
Abstract (sommario):
Quantum anomalous Hall effect (QAHE) represents a quantized version of the classical anomalous Hall effect. In the latter case the magnetization takes over the role of magnetic field and induces nonzero off-diagonal elements in the conductivity matrix. In magnetic topological insulators with the band inversion the QAHE can be reached due to quantized conduction channel at the sample edge if the Fermi energy is tuned into the surface magnetic gap. In the static regime the QAHE is seen as a zero-field step in the Hall resistivity. At optical frequencies this step is transformed into a quantized value of the polarization rotation approaching the fine structure constant α=e2/2ε0hc≈1/137. However, due to material issues the steps reach the predicted values at millikelvin temperatures only. In this work we investigate the Faraday polarization rotation in thin films of Cr-doped topological insulator and in the sub-terahertz frequency range. Well defined polarization rotation steps can be observed in transmittance in Faraday geometry. At temperatures down to T=1.85 K the value of the rotation reached about 20% of the fine structure constant and disappeared completely for T>20 K.
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Kassam, Joumana, Manar Miri, Roberto Magueta, Daniel Castanheira, Pedro Pedrosa, Adão Silva, Rui Dinis e Atílio Gameiro. "Two-Step Multiuser Equalization for Hybrid mmWave Massive MIMO GFDM Systems". Electronics 9, n. 8 (29 luglio 2020): 1220. http://dx.doi.org/10.3390/electronics9081220.
Abstract (sommario):
Although millimeter-wave (mmWave) and massive multiple input multiple output (mMIMO) can be considered as promising technologies for future mobile communications (beyond 5G or 6G), some hardware limitations limit their applicability. The hybrid analog-digital architecture has been introduced as a possible solution to avoid such issues. In this paper, we propose a two-step hybrid multi-user (MU) equalizer combined with low complexity hybrid precoder for wideband mmWave mMIMO systems, as well as a semi-analytical approach to evaluate its performance. The new digital non-orthogonal multi carrier modulation scheme generalized frequency division multiplexing (GFDM) is considered owing to its efficient performance in terms of achieving higher spectral efficiency, better control of out-of-band (OOB) emissions, and lower peak to average power ratio (PAPR) when compared with the orthogonal frequency division multiplexing (OFDM) access technique. First, a low complexity analog precoder is applied on the transmitter side. Then, at the base station (BS), the analog coefficients of the hybrid equalizer are obtained by minimizing the mean square error (MSE) between the hybrid approach and the full digital counterpart. For the digital part, zero-forcing (ZF) is used to cancel the MU interference not mitigated by the analog part. The performance results show that the performance gap of the proposed hybrid scheme to the full digital counterpart reduces as the number of radio frequency (RF) chains increases. Moreover, the theoretical curves almost overlap with the simulated ones, which show that the semi-analytical approach is quite accurate.
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Demirbilek, Nihat, Fahrettin Yakuphanoğlu e Mehmet Kaya. "Structural and optical properties of pure ZnO and Al/Cu co-doped ZnO semiconductor thin films and electrical characterization of photodiodes". Materials Testing 63, n. 3 (1 marzo 2021): 279–85. http://dx.doi.org/10.1515/mt-2020-0042.
Abstract (sommario):
Abstract Nano-structured semiconductor thin films and p-type Si photodiodes were fabricated with the sol-gel spin coating technique using pure ZnO and co-doped ZnO:Alx:Cuy with x = 1 at.-%, y = 1, 2, 3, 5 at.-%. The structural and optical properties of thin films were examined using an XRD and a UV-spectrophotometer. The thin films have a hexagonal wurtzite crystal structure, and their optical band gap energies decrease with increasing Cu contribution. The electrical properties of photodiodes were assessed via I-V, C-V, (G/ω)-V and phototransient current (I-t, C-t) measurements. The Φ b(I-V), experimental zero-bias barrier height, rectification ratio, ideality factor and Ion/Ioff parameters of the diodes were calculated using thermoionic emission model. In addition, Φ b(C-V), barrier height, Vbi, built-in voltage, Vd, diffusion potential, Nd, donor concentration and Wd, depletion layer width of p-Si/ZnO:Alx:Cuy (x = 1 at.-%, y = 1 at.-%.) photodiodes were obtained using a C-2-V graph plotted at 1 MHz frequency. The photodiodes exhibit rectifying and photosensitive behaviors, and their reverse bias current increases with increasing light intensity. These results indicate that produced diodes can be employed as photodiodes or photosensors in optoelectronic circuits and electronic devices.
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Yuan, Yunyang, Zhishan Li e Zikai Wang. "A realistic assessment of the prospect of silicon be replaced by other materials for IC applications". Journal of Physics: Conference Series 2497, n. 1 (1 maggio 2023): 012014. http://dx.doi.org/10.1088/1742-6596/2497/1/012014.
Abstract (sommario):
Abstract Silicon is the most common material used in semi-conductor. It can be used to make single crystal silicon wafer. Though it has the widest usage, silicon has high calorific value. Also, the performance loss is high compared to silicon carbide and the operating temperature is relatively low compared to gallium oxide. Luckily, there are several materials that could possibly replace silicon. The first one is 2D semiconductor. The prospective evaluation of 2D semiconductors is high. But now the biggest problem is the low-resistance connections with them. The second one is gallium nitride. It has high hardness, melting point and stability. This makes it a good material for high temperature, high frequency and high power devices. However, excellent property brings high cost. This disadvantage prevents gallium nitride to be widely used. The last one is graphene. It has strong electrical conductivity, ultra-high strength, excellent electrical properties, and strong electron interaction. It has a higher carrier mobility than silicon. While every coin has two sides, producing graphene on a large scale is difficult and expensive. Besides, graphene is highly reactive with oxygen and heat. What’s more, zero band gap nearly makes it impossible to become a semi-conductor material. Even though there are many methods of opening the bandgap, these methods still bring inevitable drawbacks. All in all, there are still many problems to be solved when new materials replace silicon in integrated circuit applications.
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Szczepanek, Jan, Tomasz M. Kardas e Yuriy Stepanenko. "Group Delay measurements of ultrabroadband pulses generated in highly nonlinear fibers". Photonics Letters of Poland 8, n. 4 (31 dicembre 2016): 107. http://dx.doi.org/10.4302/plp.2016.4.06.
Abstract (sommario):
Ultra broadband supercontinuum pulses are commonly used as a source of different wavelengths from a wide spectral bandwidth or as a source of very short pulses. However the processes responsible for wide spectral broadening are still under investigation. In this paper we examine the temporal and spectral characteristics of the pulses broadened upon propagation in the highly nonlinear photonics crystal fibers with different dispersion profiles. Generated supercontinuum pulses were experimentally characterized using cross-correlation frequency resolved optical gating technique. Full Text: PDF ReferencesM. Bradler, P. Baum, and E. Riedle, "Femtosecond continuum generation in bulk laser host materials with sub-?J pump pulses", Appl. Phys. B 97, 561 (2009). CrossRef T. M. Kardas, B. Ratajska-Gadomska, W. Gadomski, A. Lapini, and R. Righini, "The role of stimulated Raman scattering in supercontinuum generation in bulk diamond", Opt. Express 21, 24201 (2013). CrossRef A. Brodeur and S. L. Chin, "Band-Gap Dependence of the Ultrafast White-Light Continuum", Phys. Rev. Lett. 80, 4406 (1998). CrossRef R. R. Alfano, ed., The Supercontinuum Laser Source: Fundamentals with Updated References, 2nd ed (Springer, 2006). DirectLink A. L. Gaeta, Phys. "Catastrophic Collapse of Ultrashort Pulses", Rev. Lett. 84, 3582 (2000). CrossRef J. M. Dudley, G. Genty, and S. Coen, "Supercontinuum generation in photonic crystal fiber", Rev. Mod. Phys. 78, 1135 (2006). CrossRef M. Klimczak, B. Siwicki, P. Skibinski, D. Pysz, R. Stepien, A. Heidt, C. Radzewicz, and R. Buczynski, "Coherent supercontinuum generation up to 2.3 ?m in all-solid soft-glass photonic crystal fibers with flat all-normal dispersion", Opt. Express 22, 18824 (2014). CrossRef D. J. Kane and R. Trebino, "Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating", IEEE J. Quantum Electron. 29, 571 (1993). CrossRef J. Dudley, X. Gu, L. Xu, M. Kimmel, E. Zeek, P. O'Shea, R. Trebino, S. Coen, and R. Windeler, "Cross-correlation frequency resolved optical gating analysis of broadband continuum generation in photonic crystal fiber: simulations and experiments", Opt. Express 10, 1215 (2002). CrossRef N. Nishizawa and T. Goto, "Experimental analysis of ultrashort pulse propagation in optical fibers around zero-dispersion region using cross-correlation frequency resolved optical gating", Opt. Express 8, 328 (2001). CrossRef X. Gu, L. Xu, M. Kimmel, E. Zeek, P. O'Shea, A. P. Shreenath, R. Trebino, and R. S. Windeler, "Frequency-resolved optical gating and single-shot spectral measurements reveal fine structure in microstructure-fiber continuum", Opt. Lett. 27, 1174 (2002). CrossRef S. Roy, S. K. Bhadra, and G. P. Agrawal, "Effects of higher-order dispersion on resonant dispersive waves emitted by solitons", Opt. Lett. 34, 2072?2074 (2009). CrossRef S. Bose, S. Roy, R. Chattopadhyay, M. Pal, and S. K. Bhadra, "Experimental and theoretical study of red-shifted solitonic resonant radiation in photonic crystal fibers and generation of radiation seeded Raman soliton", J. Opt. 17, 105506 (2015). CrossRef T. Roger, M. F. Saleh, S. Roy, F. Biancalana, C. Li, and D. Faccio, "High-energy, shock-front-assisted resonant radiation in the normal dispersion regime", Phys. Rev. A 88, (2013). CrossRef G. P. Agrawal, Nonlinear Fiber Optics, Fifth edition (Elsevier/Academic Press, 2013). DirectLink J. Szczepanek, T. Kardas, M. Nejbauer, C. Radzewicz, and Y. Stepanenko, "Simple all-PM-fiber laser system seeded by an all-normal-dispersion oscillator mode-locked with a nonlinear optical loop mirror", Proc. SPIE 9728, 972827 (2016). CrossRef C. Iaconis and I. A. Walmsley, "Self-referencing spectral interferometry for measuring ultrashort optical pulses", IEEE J. Quantum Electron. 35, 501 (1999). CrossRef L. E. Hooper, P. J. Mosley, A. C. Muir, W. J. Wadsworth, and J. C. Knight, "Coherent supercontinuum generation in photonic crystal fiber with all-normal group velocity dispersion", Opt. Express 19, 4902 (2011). CrossRef J. Szczepanek, T. M. Kardas, and Y. Stepanenko, "Sub-160-fs pulses dechriped to its Fourier transform limit generated from the all-normal dispersion fiber oscillator", Optical Society of America Frontiers in Optics conference, FTu3C?2 (2016). CrossRef G. Genty, M. Lehtonen, and H. Ludvigsen, "Effect of cross-phase modulation on supercontinuum generated in microstructured fibers with sub-30 fs pulses", Opt. Express 12, 4614 (2004). CrossRef S. Roy, S. K. Bhadra, K. Saitoh, M. Koshiba, and G. P. Agrawal, "Dynamics of Raman soliton during supercontinuum generation near the zero-dispersion wavelength of optical fibers", Opt. Express 19, 10443 (2011). CrossRef Y. Liu, Y. Zhao, J. Lyngso, S. You, W. L. Wilson, H. Tu, and S. A. Boppart, "Suppressing Short-Term Polarization Noise and Related Spectral Decoherence in All-Normal Dispersion Fiber Supercontinuum Generation", J. Light. Technol. 33, 1814 (2015). CrossRef
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Tsarev, V. A., A. Yu Miroshnichenko, A. V. Gnusarev e N. A. Akafyeva. "Investigation of the Two-Mode Regime of Two-Gap Photonic-Crystal Resonance Systems Produced on a Printed Circuit Board with Fractal Elements "Minkowski Island". Journal of the Russian Universities. Radioelectronics 24, n. 5 (29 novembre 2021): 80–88. http://dx.doi.org/10.32603/1993-8985-2021-24-5-80-88.
Abstract (sommario):
Introduction. The development of new amplifiers and generators of the Ku- and K-bands (12…27 GHz) for use in onboard equipment is increasingly attracting research interest. Low-voltage multi-beam klystrons (LMBK) can be a promising element base for such devices. Serious problems are associated with the need to suppress parasitic modes of oscillations in NMLK operating in the centimeter and millimeter range. A possible solution is to use double-gap photonic-crystal resonators (DPCR) in LMBK. Another promising direction for improving the characteristics of such resonators is to use resonant segments of strip lines with fractal elements. In this case, the strip lines are placed on a dielectric substrate in the interaction space. Such resonators exhibit new properties that are useful for klystrons (an increase in characteristic impedance, suppression of the spectrum of unwanted frequencies, a reduction in mass and dimensions).Aim. Determination of an optimal set of electrodynamic and electronic parameters of double-gap photonic-crystal resonance systems with fractal elements "Minkowski Island" when operated as part of the LMBK resonator system, excited on π- and 2π-modes of oscillation.Materials and methods. To calculate the electrodynamic parameters of resonators, the method of finite differences in the time domain was used. The well-known Wessel-Berg method was used to calculate electronic parameters, such as the Ge / G0 electronic conductivity and the coupling coefficient M.Results. The main electrodynamic parameters of the resonator – Q-factor, resonant frequency and characteristic impedance – were investigated. The electronic parameters of the resonator, the coefficient of coupling with the electron beam, and the relative electronic conductivity for π- and 2π-modes of oscillations were calculated. In this case, three variants of the resonator with zero, first and second iterations of the fractal element were investigated. The amplitude-frequency characteristics of the resonator were investigated with a change in the pitch of the photonic crystal lattice. An estimation of the inhomogeneity of the high-frequency field in the interaction spaces of the resonator was carried out. Operational conditions were determined simultaneously for two types of oscillations without self-excitation.Conclusion. The results can find application in the development of resonator systems for klystron-type devices in the centimeter and millimeter ranges.
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Gupta, Sandhya, Gary Tuttle, Mihail Sigalas e Kai-Ming Ho. "Band-reject infrared metallic photonic band gap filters on flexible polyimide substrate". MRS Proceedings 484 (1997). http://dx.doi.org/10.1557/proc-484-183.
Abstract (sommario):
AbstractMetallic photonic band gap (MPBG) structures are multi-layer metallic meshes imbedded in a dielectric medium. We report the successful design, fabrication, and characterization of infrared band-reject filters using MPBG structures in a flexible polyimide substrate. The metal layers of the MPBG have square grid patterns with short perpendicular cross-arm defects added halfway between each intersection. The transmission characteristics of these filters show a higher order band-reject region in addition to a lower order band gap that extends from zero to particular cut off frequency. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and length of the cross-arm defects. Optical transmission measurements of the bandreject filters show lower edge cutoff frequency of about 2 THz and the higher order bandgap region centered around 4.5THz with attenuation of more than 35 dB in the bandgap region. This is in good agreement with the theoretical calculations. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure and have minimal dependence on angle of incidence.
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Chen, Qiunan, Zhixin Li, Xiaocheng Huang e Chen Zhang. "Study of Rheological-Mechanical Properties and Vibration Mechanics Bandgap of Row Pile Foundation". European Journal of Computational Mechanics, 30 giugno 2023. http://dx.doi.org/10.13052/ejcm2642-2085.3212.
Abstract (sommario):
To analyze the rheological and mechanical properties as well as the vibration-mechanical forbidden zone effect of row pile foundations, this paper employs time-dependent modulus to examine the rheological mechanics of soil. Drawing from viscoelastic theory, we derive the expression of deformation modulus in the frequency domain to analyze the frequency dependence of the shear modulus of rheological soils. We construct a continuous medium dynamics model of the pile-soil periodic structure, taking into account soil rheology, and derive the dispersion equation of shear waves in the periodic structure using the multiple scattering method. The band gap characteristics and parameters that influence the law of shear waves in rheological soil-row pile foundations are studied through the analysis of arithmetic cases. The results show that under the loading condition, the zero-frequency shear modulus of soil is larger than the initial modulus value, and the real part of the shear modulus decreases monotonically with the increase of frequency and finally converges to the initial modulus value; under the unloading condition, the zero-frequency shear modulus of soil is smaller than the initial modulus value, and the real part of the shear modulus increases monotonically with the increase of frequency and finally converges to the initial modulus value; the larger the relaxation time of soil, the faster the convergence rate; the imaginary part of the shear modulus of soil The imaginary part of the soil shear modulus is positive under loading condition and negative under unloading condition, the value of the imaginary part increases and then decreases with increasing frequency and finally converges to 0. The imaginary part reaches the peak at the critical frequency, the larger the relaxation time the smaller the critical frequency, and the peak of the imaginary part is independent of the relaxation time. This study analyzed the dispersion curve of shear waves in a pile-soil periodic structure and found that increasing low-frequency shear wave velocity in rheological soil pile foundation shifts the band gap position to a higher frequency band, resulting in a smaller band gap width than in linear elastic soil. The relaxation time of soil affects the frequency position and width of the band gap, with larger relaxation times resulting in higher frequency positions and smaller widths. Additionally, soil rheology widens the forbidden vibration band gap of the pile periodic structure when the filling rate of the pile foundation is larger.
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Cui, Jian-Guo, Tianzhi Yang, Mu-Qing Niu e Li-Qun Chen. "Tunable roton-like dispersion relation with parametric excitations". Journal of Applied Mechanics, 8 settembre 2022, 1–15. http://dx.doi.org/10.1115/1.4055545.
Abstract (sommario):
Abstract The band gap has been used to control the transmission features of acoustic/elastic waves. Roton-like dispersion relations show that the energy and momentum of acoustic waves are inverse proportional to each other. To modulate the band gap and obtain the unusual roton-like behavior, the Kapitza's pendulums and nonlocal connection stiffness are introduced into the linear mass-spring periodic system. The frequency range with the roton-like behavior is modulated via the parametric excitation. Moreover, the dispersion relations show some fascinating phenomena (i.e. the negative/zero group velocity) under special parameters, which indicate the potential application to control the transmission of acoustic/elastic waves and design a negative/zero-refraction or non-propagating-vibration structure.
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Taura, L. S., Isah Abdulmalik, A. S. Gidado e Abdullahi Lawal. "Structural, Electronic and Optical Properties of Stanene Doped Beryllium: A First Principle Study". Physical Science International Journal, 13 agosto 2021, 32–40. http://dx.doi.org/10.9734/psij/2021/v25i430251.
Abstract (sommario):
Stanene is a 2D hexagonal layer of tin with exceptional electronic and optical properties. However, the semiconductor applications of stanene are limited due to its zero band-gap. However, doping stanene could lead to a band gap opening, which could be a promising material for electronic and optical applications. In this work, optimized structure, electronic band structure, real and imaginary parts of the frequency-dependent dielectric function, electron loss function, and refractive index of stanene substitutionally doped with alkaline earth metal (beryllium) were analyzed using density functional theory (DFT) calculations as implemented in the quantum espresso and yambo suites. A pure stanene has a zero band gap energy, but with the inclusion of spin-orbit coupling in the electronic calculation of pure stanene, the band-gap is observed to open up by 0.1eV. Doping stanene with beryllium opens the band-gap and shifts the Dirac cone from the Fermi level, the band gap opens by 0.25eV, 0.55eV, and 0.8eV when the concentration of Beryllium is 12.5%, 25%, and 37.5% respectively. The Dirac cone vanished when the concentration of the dopant was increased to 50%. The Fermi level is shifted towards the valence band edge indicating a p-type material. The material absorption shows that SnBe absorption ranges in the visible to the ultraviolet region, The refractive index in stanene doped beryllium (SnBe) was found to be higher than that of pristine stanene, the highest refractive index was 9.2 at SnBe25%. In a nutshell, the results indicate that stanene can be a good material for electronic and optical applications if doped with beryllium.
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Cai, Changqi, Jiaxi Zhou, Kai Wang, Daolin Xu e Guilin Wen. "Metamaterial plate with compliant quasi-zero-stiffness resonators for ultra-low-frequency band gap". Journal of Sound and Vibration, settembre 2022, 117297. http://dx.doi.org/10.1016/j.jsv.2022.117297.
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Xie, Buliang, e Meiping Sheng. "Ultralow-frequency band gap in a quasi-zero-stiffness multi-resonator periodic hybrid structure". Wave Motion, settembre 2021, 102825. http://dx.doi.org/10.1016/j.wavemoti.2021.102825.
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Woźny, Mariusz, Wojciech Szuszkiewicz, Mateusz Dyksik, Marcin Motyka, Andrzej Szczerbakow, Witold Bardyszewski, Tomasz Story e Józef Cebulski. "Electron-phonon coupling and a resonant-like optical observation of a band inversion in topological crystal insulator Pb1-xSnxSe". New Journal of Physics, 23 maggio 2024. http://dx.doi.org/10.1088/1367-2630/ad4fba.
Abstract (sommario):
Abstract The optical reflectivity of n-type Pb0.865Sn0.135Se and Pb0.75Sn0.25Se solid solutions was measured in the THz spectral region energetically corresponding to optical phonon excitations and in the temperature range from 40 K to 280 K. The first solid solution exhibits an open energy gap with trivial band ordering at all temperatures, while for the second one the transition from trivial insulator to topological crystal insulator phase is expected. The analysis of Pb0.75Sn0.25Se data performed within the dynamic dielectric function formalism revealed an anomaly of resonance-like character in the temperature dependence of LO phonon frequency. The formula for LO phonon energy renormalization reproduced observed anomaly for energy gap equal to zero, the phase transition occurred at T0 = (172 ± 2) K. This effect was absent for Pb0.865Sn0.135Se. Present results show that reflectivity measurements in the THz range in the vicinity of LO phonon frequency can be valuable experimental method for precise determining of band inversion temperature in narrow-gap topological materials.
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Xiaoxia Zhou, Ying Chen e Li Cai. "A ultra-narrow-band optical filter based on zero refractive index metamaterial". Acta Physica Sinica, 2023, 0. http://dx.doi.org/10.7498/aps.72.20230394.
Abstract (sommario):
Due to the photonic band gap effect and defect state effect, Photonic metamaterials have received strong attention in the design of narrow bandpass filters, which are the key devices of optical communication equipment such as wavelength division multiplexing devices. In this paper, based on zero-index metamaterials (ZIM), a compact filter with both high peak transmission coefficient and ultra-narrow bandwidth is proposed. Photonic metamaterial with conical dispersions and Dirac-like point is achieved by optimizing structure and material component parameters of dielectric rods with square lattice in air. It has been demonstrated that a triply degenerate state can be realized at the Dirac-like point, which relate this metamaterial to a zero-index media with effective permittivity and permeability equal to zero simultaneously. Electromagnetic (EM) wave can propagate without any phase delay at this frequency, and strong dispersion occurs in the adjacent frequency cone, leading to dramatic changes in optical properties. We explore introducing ZIM into photonic metamaterial defect filter to compress the bandwidth to realization of ultra-narrow bandpass filter. The ZIM is embedded into the resonant cavity of line defect filter, which is also composed of dielectric rods with square lattice in air. In order to increase the sensitivity of the phase change with frequency, the Dirac-like frequency is adjusted to match the resonant frequency of the filter. We study the transmission spectrum of the structure by the COMSOL Multiphysics simulation software, it has been found that the peak width at half-maximum of the filter decreases as the thickness of ZIM increase, and the peak transmittance is still high as well when bandwidth is greatly compressed. zero phase delay inside the slab can be observed. Through field distribution analysis, the zero-phase delay and strong coupling characteristics of electromagnetic field are observed at peak frequency. As well as the comparison with conventional photonic metamaterials filter is discussed. We believe that this work is helpful in investigating the realization of ultra-narrow bandpass filters.
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Gong, Tao, Iñigo Liberal, Miguel Camacho, Benjamin Spreng, Nader Engheta e Jeremy N. Munday. "Radiative energy band gap of nanostructures coupled with quantum emitters around the epsilon-near-zero frequency". Physical Review B 106, n. 8 (25 agosto 2022). http://dx.doi.org/10.1103/physrevb.106.085422.
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Xu Qiang-rong, Zhu Yang, Lin Kang, Shen Cheng e Lu Tian-jian. "Low-frequency sound insulation performance of novel membrane acoustic metamaterial with dynamic negative stiffness". Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.7120221058.
Abstract (sommario):
For improving the low-frequency sound insulation properties of membrane/plate structures, a new quasi-zero stiffness membrane acoustic metamaterial with dynamic magnetic negative stiffness is proposed. Upon applying the equivalent magnetic charge theory to derive the dynamic magnetic negative stiffness, a theoretical model of proposed metamaterial with finite dimensions is established based on the Galerkin method. Through a combination of theoretical analysis, numerical simulation and experimental measurement, the low-frequency (1—1000 Hz) sound insulation performance of the metamaterial is investigated from several perspectives, including structural modality, vibration mode, average velocity, phase curve, equivalent mass density, and equivalent spring-mass dynamics model. Results show that, at a certain initial membrane tension, decreasing the magnetic gap or increasing the residual flux density can increase the dynamic magnetic negative stiffness. This in turn leads to decreased peak frequency and enlarged bandwidth of sound insulation, thus achieving effective low-frequency sound insulation over a wide frequency band. Further, when the magnetic gap is larger than the second critical magnetic gap and smaller than the first critical magnetic gap, the first-order modal resonance of the metamaterial disappears, and the corresponding value of sound insulation valley increases significantly, thus demonstrating superior sound insulation effect with wide frequency band. The proposed method of using dynamic magnetic negative stiffness to improve low-frequency sound insulation valleys due to modal resonance provides useful theoretical guidance for designing membrane/plate type low-frequency sound insulation metamaterials.
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Salehian, Kamran, e Majid Tayarani. "A novel SIGGW dual post band-pass filter for 5G millimeter-wave band applications with a transmission zero". Scientific Reports 13, n. 1 (25 novembre 2023). http://dx.doi.org/10.1038/s41598-023-47490-1.
Abstract (sommario):
AbstractIntegration of planar circuits been considered a credible technique for low-cost mass production of microwave and millimeter-wave circuits and systems. For the first time, in this research a dual-post band-pass filter is designed and simulated in a three-layer substrate integrated gap groove waveguide (SIGGW) for 5G millimeter-wave frequency band applications. The filter includes 12 posts ($$6 \times 2$$ 6 × 2 ). Also, the structure facilitates to use resonant posts and so we can design the posts to add a transmission zero in lower rejection band. The design theory algorithm and its limitations are investigated based on the circuit model of filter. The results shows that FBW of 5% and a lower band transmission zero for the proposed 12 posts filter. Also, the results are verified by simulation using CST. According to the results, the proposed filter is a good option for Ka-band applications and can be used as the building block for suppressing the LO leakage that is commonly used for up-converting the 5G signal to Ka band.