Academic literature on the topic 'Zero-Frequency band gap'
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Journal articles on the topic "Zero-Frequency band gap":
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ALI, MUNAZZA ZULFIQAR, and 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, no. 22 (September 10, 2011): 3027–34. http://dx.doi.org/10.1142/s0217979211100849.
Abstract:
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, and C. T. Chan. "Physics of the zero- photonic gap: fundamentals and latest developments." Nanophotonics 1, no. 3-4 (December 1, 2012): 181–98. http://dx.doi.org/10.1515/nanoph-2012-0020.
Abstract:
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.
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Xu, Fei, and Yulin Chen. "Interesting Band Properties of One-Dimensional Photonic Crystals Containing Epsilon-Negative Layers." Zeitschrift für Naturforschung A 65, no. 4 (April 1, 2010): 329–34. http://dx.doi.org/10.1515/zna-2010-0409.
Abstract:
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.
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Lin, Qida, Jiaxi Zhou, Kai Wang, Daolin Xu, Guilin Wen, Qiang Wang, and Changqi Cai. "Low-frequency locally resonant band gap of the two-dimensional quasi-zero-stiffness metamaterials." International Journal of Mechanical Sciences 222 (May 2022): 107230. http://dx.doi.org/10.1016/j.ijmecsci.2022.107230.
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Lin, Qida, Jiaxi Zhou, Kai Wang, Daolin Xu, Guilin Wen, and Qiang Wang. "Three-dimensional quasi-zero-stiffness metamaterial for low-frequency and wide complete band gap." Composite Structures 307 (March 2023): 116656. http://dx.doi.org/10.1016/j.compstruct.2022.116656.
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Movchan, N. V., R. C. McPhedran, and 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, no. 2127 (September 22, 2010): 869–80. http://dx.doi.org/10.1098/rspa.2010.0375.
Abstract:
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.
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Zhang, Li-Qin, Jin-Feng Zhang, Li-Ming, and Shi-Tao Xu. "WSe2 Monolayer: A Stable Two-Dimensional Heterostructure Material from First-Principles of Simulation Calculations." Journal of Nanoelectronics and Optoelectronics 17, no. 10 (October 1, 2022): 1379–83. http://dx.doi.org/10.1166/jno.2022.3318.
Abstract:
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.
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Xiu, Chenxi, and Xihua Chu. "Study on dispersion and wave velocity in 2D elliptic granular crystals by a micromechanics-based micromorphic model." Advances in Mechanical Engineering 14, no. 8 (August 2022): 168781322211199. http://dx.doi.org/10.1177/16878132221119957.
Abstract:
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.
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Alaa, Siti, Muhammad Fajrin, Eva Nurhaliza, Dian Wijaya Kurniawidi, Susi Rahayu, and I. Wayan Sudiarta. "THE STUDY OF GRAPHENE BAND GAP USING HATREE FOCK METHOD IN MOLECULAR SCALE." Indonesian Physical Review 3, no. 1 (February 14, 2020): 24. http://dx.doi.org/10.29303/ipr.v3i1.35.
Abstract:
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.
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Yuan, Bo, Yong Chen, Min Jiang, Shuai Tang, Miao He, and 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, no. 4 (December 20, 2017): 725–33. http://dx.doi.org/10.1515/aoa-2017-0075.
Abstract:
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.
Dissertations / Theses on the topic "Zero-Frequency band gap":
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Zeng, Yi. "On the Design and Realization of Broadband Seismic Metamaterials." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0036.
Abstract:
Les métamatériaux sismiques (SMs) permettent de protéger les bâtiments en atténuant et en contrôlant efficacement les ondes sismiques. Les SM peuvent atténuer les ondes sismiques qui se propagent vers les bâtiments, protégeant ainsi la vie et les biens des personnes. Compte tenu des risques multiples et élevés des tremblements de terre, ainsi que de certains inconvénients qui ne peuvent être ignorés dans les isolations sismiques, les SM ont montré des perspectives d'application. Plusieurs métamatériaux sismiques ont été conçus dans cette thèse pour isoler les ondes sismiques de Rayleigh. Ces métamatériaux peuvent atténuer les ondes sismiques de Rayleigh dans la gamme des basses fréquences et des ultra-basses fréquences, afin de protéger les bâtiments construits par l'homme et de réduire les dommages causés par les tremblements de terre. Ce travail fournit non seulement de nouvelles approaches pour contrôler les ondes sismiques de surface à ultra-basse fréquence, mais aussi de nouvelles idées de conception pour la direction des ondes de surfaceThe seismic metamaterials (SMs) make it possible to protect buildings in a way of efficiently attenuating and effectively controlling seismic waves. The SMs can attenuate seismic waves on the way of propagating to buildings, thereby protecting people's lives and property. Considering the multiple and high hazard of earthquakes, as well as some disadvantages that cannot be ignored in the seismic isolations, SMs have shown the application prospects. Several SMs are design in this thesis for isolating seismic Rayleigh waves. These SMs can attenuate seismic Rayleigh waves in the wide-low-frequency range and ultra-low frequency range, to protect man-made buildings and reduce the damage of earthquakes. This work not only provides new approaches for controlling seismic surface waves at ultra-low frequency, but also provides new design ideas for steering surface wave
Conference papers on the topic "Zero-Frequency band gap":
1
Shepherd, T. J. "Photonic Band Gaps." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.tut1.
Abstract:
Photonic band gaps are ranges of frequency within which electromagnetic propagation is completely forbidden. They are present in certain materials which possess a periodicity of permittivity at the wavelength scale. Materials with these extreme properties are not known to occur naturally, and. at the optical wavelength scale, require fabrication methods at the current limits of technological feasibility. Such a photonic crystal provides a lossless barrier to propagation, and can suppress the emission of a photon by a decaying atom if the frequency of the emitted photon lies within the gap. A preferred propagation route, or mode, can be specified by designed defects within the photonic crystal; thus it is expected that I photonic crystals can provide a means whereby spontaneous emission is controlled in active media, and that all the spontaneously emitted light enters a single mode, resulting in an ideal zero-threshold laser. More generally, the photonic density of states is altered in these materials, and spontaneous emission can be enhanced or suppressed, as required. Other applications include novel all-angle reflectors, narrow-band filters, resonators, waveguides, and delay lines. When the fabrication problems for optical photonic crystals have been conquered, wavelength-scale periodic media will form an essential functions in a large range of optoelectronic systems.
2
Yablonovitch, Eli. "Photonic band structure." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.me1.
Abstract:
By analogy to electron waves in a crystal, electromagnetic waves in a 3-D periodic dielectric structure should be described by band theory. The idea of photonic band structure1 is rapidly2–5 gaining acceptance. The concepts of reciprocal space, Brillouin zones, dispersion relations, Bloch wave functions, Van Hove singularities, etc., are now being applied to optical waves. If the depth of refraction index modulation is sufficient, a photonic band gap can exist. This is a frequency band in which electromagnetic modes, spontaneous emission, and zero point fluctuations are all absent. Indeed, a photonic band gap cam be essentially ideal provided the dielectric response is real and dissipationless. In addition to the obvious uses in atomic and laser physics, photonic band structure can now begin to play a role in microwave and millimeter wave electronics. Defects can be introduced into the otherwise perfect 3-D structures, creating electromagnetic donor modes and acceptor modes. Effectively, these defects are purely dielectric single-mode high-Q cavities suitable for a range of frequencies from microwaves to the visible. At the outset it was realized1 that a face-centered-cubic (FCC) array in real space would produce the most spherelike Brillouin zone in reciprocal space. This spherelike geometry increased the likelihood that a forbidden gap would overlap all the way around the surface of the Brillouin zone. But is was unclear what should be the shape in real space of the atoms in this FCC array. The history of this field has been a search for that optimal 3-D dielectric geometry, favored by nature and by Maxwell’s equations. During this same period, electronic band theorists began calculating photonic band structure. It rapidly became apparent that the familiar scalar wave band theory, so frequently used for electrons in solids, was in utter disagreement with experiment on photons.7–10 Recently3–5 a full vector-wave band theory became available, which not only agreed with experiment, it successfully highlighted some discrepancies in the experiment.
3
Tehrani, M. M., and G. J. Olson. "Optical switching effect in HgCdTe at room temperature." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/oam.1985.fu6.
Abstract:
Transmission of intense, nonresonant, optical pulses at 10.6-μm wavelength through bulk HgCdTe at room temperature is investigated experimentally and theoretically. The incident photon energy is slightly less than twice the energy band gap in our sample. Our experimental results indicate that for incident intensities up to 1 MW/cm2 no significant optical nonlinearity takes place. However, at ~1 MW/cm2 and higher intensities the transmission drops to zero in ~1 ns. We describe this effect in terms of the absorption of the incident light by the electron plasma in the sample, the plasma being created as a result of the two-photon absorption process of the leading edge of the incident pulse. The theory predicts that, at a threshold of 0.9-MW/cm2 incident intensity, the plasma density is sufficiently high for the plasma frequency to be at the incident light frequency which is in good agreement with our experimental results.
4
Zhang, Ming, Jia Li, Xu Dong, Dakun Sun, and Xiaofeng Sun. "Experimental Study on Different Tip Clearance of Low-Speed Axial Fan." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59899.
Abstract:
Abstract Tip clearance flow is not only the source of undesirable noise but also a potential indicator for critical operating conditions with rotating stall or surge. It can induce blade vibration, which would cause premature blade failure when the vibration is strong enough. The paper presents experimental studies on the effects of tip clearance on the stall inception process in a low-speed high-load single stage fan with different tip clearance. From the point of view of flow range, it has been proved by computations that there is an optimal gap value, and an explanation is given according to different stall mechanisms of large and small tip clearance. However, the experiment of no tip clearance is not easy to achieve. In this experiment, a wearable soft wall casing was used to achieve “zero clearance”, and an explicit conclusion was obtained. The pressure rise and efficiency are improved at small tip clearance. Instantaneous Casing Pressure Field Measurement was carried out: instantaneous casing pressure fields were measured by 9 high response pressure transducers mounted on the casing wall. At the near stall point with large tip clearance, a narrow band increase of the amplitudes in the frequency spectrum at roughly half of the blade passing frequency can be observed according to the spectrum of static pressure at points on the endwall near the leading-edge and above the rotor. This phenomenon was explained from two aspects: tip clearance flow structure and pressure signal spectrum.
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Yan, Yucong, Yueyang Liu, Jun Qin, Longjiang Deng, Yang Li, and Lei Bi. "A magnetic field tunable Zero-Index-Metamaterial." In CLEO: Applications and Technology. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/cleo_at.2022.jw3b.61.
Abstract:
We report a magnetic tunable structure consists of YIG nanorods. Applied magnetic field leading to a tunable band gap from 0 to 0.67 GHz, effective refractive index from 0 to 0+0.09i at 9 GHz frequency.
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Wright, Terry, and William E. Simmons. "Blade Sweep for Low-Speed Axial Fans." In ASME 1989 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1989. http://dx.doi.org/10.1115/89-gt-53.
Abstract:
The available literature on aerodynamic and acoustic properties of axial fans with swept blades is presented and discussed with particular emphasis on noise mechanisms and the influence of high-intensity inlet turbulence on “excess” noise. The acoustic theory of Kerschen and Envia for swept cascades is applied to the problem of axial fan design. These results are compared to available data and a provisional model for specifying sweep angles is presented. The aerodynamic performance theory for swept-bladed rotors of Smith and Yeh is adapted for use in designing low speed axial fans. Three prototype fans were designed using the resultant computer codes. One is a baseline fan with blade stacking lines radially oriented, and two are fans having swept blades of increasingly greater forward sweep. Aerodynamic testing shows that performance of the fans lie within a band width of about ± two percent of volume flow rate and pressure rise predictions in the region of design performance, effectively validating the design procedure for selection of the blading parameters. Noise testing of the fans was carried out and the results show an average noise reduction for the swept-bladed fans of about 7 dBA overall, and a reduction of pure tone noise at blade-pass frequency of about 10 dB compared to the zero-sweep baseline model in close agreement with the theory of Kerschen and Envia.
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Huang, Paul Xiubao, and JianAn Yin. "From Rotating Stall to Surge: A Shock Tube Mechanism." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-94128.
Abstract:
Compressor surge is a complete breakdown in compression resulting in an abrupt momentary reversal of gas flow and the violent pressure fluctuation with relatively low frequency and high amplitude. It commonly exists in dynamic type turbo compressors, particularly axial compressor and jet engine, or turbo charger for reciprocating engines. It is generally accepted that surge is preceded by a rotating stall, a situation of a few stalled blades rotating around compressor annulus (cascade) with much higher frequency. In jet engine, violent surge event typically produces a frightening loud bang, lots of vibrations and could cause catastrophic structural failures if not timely managed. Naturally, as important matters as rotating stall and surge, there have been tremendous R/D efforts from academia, government and industry devoted to this area, especially since jet engines became the prime powerhouses for modern airplanes. Despite of all the efforts, there still seems to be a more urgent need to understand the physical characteristics of the transition from a rotating stall to surge that has mystified researchers due to its transient nature. Fundamental questions remain unanswered even today, such as: What exactly triggers the surge to take place from a rotating stall? What is the physical nature of a compressor system or a local incipient surge: is it a movement of wave or fluid particles or both? How to estimate the quantitative destructive forces of a severe surge, that is, the maximum possible surge strength? This paper attempts to answer these questions by applying the classical Shock Tube Theory to the transient process from rotating stall to surge. The Shock Tube analogy is established with the hypothesis (implied from experimental observations) that an instant zero through flow condition exists inside a stalled cascade cell or dynamic compressor that triggers surge. It is revealed that surge event consists of a pair of non-linear compression and expansion waves (CW & EW) that instantly reverse gas flow (IRFF) by the pushing force of upstream propagating CW and the pulling force from downstream travelling EW. The surge strength is shown to be proportional to the square root of the pressure ratio of the involved cascade or compressor. Surge Rules are deduced to predict the location of surge initiation, the minimum and maximum surge strengths, travelling directions and speed. Moreover, a pro-active control strategy called SEWI (Surge Early Warning Initiative) is proposed using the unique characteristics of CW-IRFF-EW formation of a cascade cell induced surge as precursors for subsequent warning and controls before the destructive compressor surge takes place.