Littérature scientifique sur le sujet « Perfect transmission resonances »

Abstract Existing resonant tunneling modes in the shape of line-type resonances can improve the transport properties of the junction. Motivated by the unique structural properties of monolayer WSe2 e.g. significant spin–orbitcoupling and large direct band gap, the transport properties of a normal/ferromagnetic/normal WSe2 junction with large incident angles in the presence of exchange field (h), off-resonance light ( Δ Ω ) and gate voltage (U) is studied. In a certain interval of U, the transmission shows a gap with optically controllable width, while outside it, the spin and valley resolved transmissions have an oscillatory behavior with respect to U. By applying Δ Ω (h), an optically (electrically) switchable perfect spin and valley polarizations at all angles of incidence have been found. For large incident angles, the transmission resonances change to spin-valley-dependent separated ideal line-type resonant peaks with respect to U, results in switchable perfect spin and valley polarizations, simultaneously. Furthermore, even in the absence of U, applying h or Δ Ω at large incident angles can give some spin-valley dependent ideal transmission peaks, making h or Δ Ω a transmission valve capable of giving a switchable fully spin-valley filtering effect. These findings suggest some alternate methods for providing high efficiency spin and valley filtering devices based on WSe2.

A broadband near-perfect absorber is analyzed by an amorphous silicon (a-Si) hook shaped nanostructure metasurface. The transmission and reflection coefficients of the metasurface are investigated in the point electric and magnetic dipole approximation. By combining square and semicircle nanostructures, the effective polarizabilities of the a-Si metasurface calculated based on discrete dipole approximation (DDA) exhibit broadened peaks of electric dipole (ED) and magnetic dipole (MD) Mie resonances. The optical spectra of the metasurface are simulated with different periods, in which suppressed transmission are shifted spectrally to overlap with each other, leading to broadened enhanced absorption induced by interference of ED and MD Mie resonances. The angle insensitive absorption of the metasurface arrives 95% in simulation and 85% in experiment in spectral range from 564 nm to 584 nm, which provides potential applicability in nano-photonic fields of energy harvesting and energy collection.

We study in this work, the occurrence of defects modes in the transmission spectrum and the band structure of a perfect photonic asymmetric serial loops structure (ASLS) utilized for narrow-band filtering. The perfect structure presents large photonic bandgaps that result from the modes of the loops resonances and the system periodicity. Besides that, the existence of defects within this perfect ASLS, whether at the segment or loop level, or both of them, causes the appearance of two, three, or four defect modes within gaps with good transmission rates and high-quality factors. These defects modes are extremely sensitive to changes in structural parameters. This system can be used to filter or guide the incoming electromagnetic waves. The interface response theory has been used to accomplish the analytical calculation. Green's function of the full system is determinated using this method. It allows us to calculate the dispersion relation and the transmission rate. Therefore, this paper can provide ideas for the design of multi-channel tunable filter using for frequency division multiplexing and microwave and signal processing.

In this paper, the design of a broadband multi-layer microstrip antenna is presented. The broadband characteristics are the results of coupled resonances of the patch and transmission line through the resonant aperture. For this purpose, a cross-shaped transmission line, a ring slot, and a shaped ring patch are used. The simulation and measurement results indicate that a wide impedance bandwidth of 70% for |S11| < −10 dB and a perfect impedance matching 35% for |S11| < −20 dB are achieved. The gain is stable over the impedance bandwidth. The maximum gain of the proposed antenna is 8.8 dBi at 5 GHz. The radiation pattern, radiation efficiency, and cross-polarization are also suitable throughout the impedance bandwidth.

Transmission metallic gratings having the shape of converging-diverging channel (CDC) give an extra degree of freedom to exhibit enhanced transmission resonances. By varying the gap size at the throat of CDC, the spectral locations of the transmission resonance bands can be shifted close to each other and have high transmittance in a very narrow energy band. Hence, the CDC shape metallic gratings can lead to almost perfect transmittance for any desired wavelength by carefully optimizing the metallic material, gap at the throat of CDC, and grating parameters. In addition, a cavity surrounded by the CDC shaped metallic grating and a one-dimensional (1D) photonic crystal (PhC) can lead to an enhanced emission with properties similar to a laser. The large coherence length of the emission is achieved by exploiting the coherence properties of the surface waves on the gratings and PhC. The new multilayer structure can attain the spectral and directional control of emission with onlyp-polarization. The resonance condition inside the cavity is extremely sensitive to the wavelength, which would then lead to high emission in a very narrow wavelength band. Such simple 1D multilayer structure should be easy to fabricate and have applications in photonic circuits, thermophotovoltaics, and potentially in energy efficient incandescent sources.

The electric conductance of the graphite ribbon with locally applied gate voltage has been studied in terms of the Landauer approach. In the low-energy region, nano-graphite ribbon with zigzag boundaries exhibits the single electronic transport channel due to the edge states. The chemical potential dependence of the electric conductance shows qualitatively different behavior, depending on whether the magnitude of the potential barrier (gate voltage bias) Vg is larger than the energy gap Δ of the single channel region of the zigzag ribbon. For positive Vg with Vg < Δ, the zero-conductance resonances appear for 0 ≤ E ≤ Vg, and average transmission probability is quite small in this region. However the transmission probability is almost one, i.e. perfect transmission, for E > Vg. This step-function-like behavior of the conductance shows that it is possible to fabricate a nano-graphite-based switching device by the application of weak gate voltage bias.

Lizards have highly directional ears, owing to strong acoustical coupling of the eardrums and almost perfect sound transmission from the contralateral ear. To investigate the neural processing of this remarkable tympanic directionality, we combined biophysical measurements of eardrum motion in the Tokay gecko with neurophysiological recordings from the auditory nerve. Laser vibrometry shows that their ear is a two-input system with approximately unity interaural transmission gain at the peak frequency (∼1.6 kHz). Median interaural delays are 260 μs, almost three times larger than predicted from gecko head size, suggesting interaural transmission may be boosted by resonances in the large, open mouth cavity ( Vossen et al. 2010 ). Auditory nerve recordings are sensitive to both interaural time differences (ITD) and interaural level differences (ILD), reflecting the acoustical interactions of direct and indirect sound components at the eardrum. Best ITD and click delays match interaural transmission delays, with a range of 200–500 μs. Inserting a mold in the mouth cavity blocks ITD and ILD sensitivity. Thus the neural response accurately reflects tympanic directionality, and most neurons in the auditory pathway should be directional.

We develop a theoretical approach to calculate the scattering and localization properties in the inhomogeneous hexagonal nanostructure system with adsorbed chain. Our numerical results are presented for three different positions of the defect, Top, Hollow and Bridge. The breakdown of translation symmetry induced by the inhomogeneity, gives rise to localized elastic wave modes at its neighborhood. The Landauer and Buttiker method is used to analyze the elastic wave scattering phenomena for atomic sites that constitute a minimum representation set in the neighborhood of the defect. The transmission and reflection probabilities as well as the phonons average transmittance across and the vibration density of states are determined for a large band of incident scattering energies. The coherent coupling between the localized elastic wave and the propagating modes of the perfect hexagonal structure leads to Fano resonances in the phononic conductance spectra of the studied structure. This is directly related to the measurable physical thermal conductivity of the perturbed domain.

As is well known, Fano resonance originates from the interference between a continuum energy band and an embedded discrete energy level. We study transmission properties of the discrete chain-structure of additional defects with an isolated ring composed of N defect states, and obtain the analytical transmission coefficient of similar Fano formula. Using the formula, we reveal conditions for perfect reflections and transmissions due to either destructive or constructive interferences. It is found that a nonlinear Kerr-like response leads to bistable transmission, and for either linear cases or nonlinear ones, the defects in main arrays have a major impact on perfect reflections, but has no effect on perfect transmission.

L'interaction des ondes avec des milieux possédant des fluctuations spatiales et/ou temporelles conduit à une phénoménologie intéressante. Dans ce cadre, dans la présente thèse quatre phénomènes ondulatoires sont étudiés: deux se produisant dans des milieux variant dans l’espace et deux dans des milieux variant dans le temps. Nous commençons par explorer la diffusion des ondes par une configuration spatialement périodique finie sujette à des perturbations. Nous nous concentrons sur les résonances de transmission parfaite (PTR) et nous développons une méthode pour les préserver sous des perturbations asymétriques. L'analyse effectuée révèle une connexion par paire entre les PTR d'une configuration de diffusion spatialement périodique avec des cellules à symétrie miroir. Dans le même contexte de milieux variant spatialement, nous calculons la longueur de localisation des modes de bord topologiques qui sont supportés dans une chaîne mécanique masse-ressort possédant des fluctuations aléatoires de ses paramètres de rigidité. En présence d'un fort désordre chiral, la longueur de localisation diverge, ce qui implique une transition de phase topologique induite uniquement par le désordre. Dans une prochaine étape, nous considérons le cas où les couplages de la chaîne masse-ressort mécanique varient avec le temps de manière déterministe. Ce système variable dans le temps peut alors servir de plate-forme pour transférer un mode de bord topologique. Au-delà de la limite adiabatique, nous concevons un protocole pour les couplages variables dans le temps qui aboutit à un transfert rapide et robuste et conduit encore plus à une amplification du mode de bord transféré. Pour éclairer le phénomène d'amplification dans une plateforme variable dans le temps, nous explorons la propagation d'une onde dans un milieu à indice de réfraction périodique et dont la dynamique des ondes est régie par l'équation de Mathieu. L'onde présente une amplification transitoire en raison de la nature non normale de la matrice de propagation et nous fournissons la preuve numérique que les caractéristiques d'amplification globales sont fournies simplement par la matrice de monodromie
The interaction of waves with media possessing spatial or/and temporal fluctuations leads tointeresting phenomenology. Within this framework, in the present thesis four wave phenomena arestudied: two occurring in spatially-varying media and two in time-varying media. We begin byexploring wave scattering by a finite spatially-periodic setup that is subject to perturbation. Ourfocus is on perfect transmission resonances (PTRs) and we develop a method for preserving themunder asymmetric perturbations. The performed analysis reveals a pairwise connection betweenPTRs of a spatially-periodic scattering setup with mirror symmetric cells. In the same contextof spatially varying media, we compute the localization length of the topological edge modes thatare supported in a mechanical mass-spring chain possessing random fluctuations of its stiffnessparameters. In the presence of strong chiral disorder the localization length diverges, implying atopological phase transition that is induced purely by disorder. As a next step we consider thecase where the couplings of the mechanical mass-spring chain vary with time in a deterministicway. Then this time-varying system can serve as a platform for transferring a topological edgemode. Going beyond the adiabatic limit, we design a protocol for the time-varying couplingsthat results in a fast and robust transfer and even more leads to amplification of the transferrededge mode. To shed light into the phenomenon of amplification in a time-varying platform, weexplore the propagation of a wave in a medium with time-periodic refractive index and with wavedynamics governed by the Mathieu equation. The wave exhibits transient amplification due to thenon normal nature of the propagator matrix and we provide numerical evidence that the globalamplifying features are provided merely by the monodromy matrix

Chapter 2 explores the conceptual implications of the myth of perfect fidelity by further analyzing the two case studies introduced in chapter 1. While analog noise reduction and the addition of “dither”-noise in the digital domain at first seem diametrically opposed (reducing and adding noise, respectively), closer analysis shows that they both serve to conceal the physical influence of the medium on the reproduced sound. Following a conceptual logic of noise reduction, they strive to achieve the most accurate copy of the “original” sound. Information theory has shown, however, that this influence of media technological transmission channels on the output signal is inevitable, because the physical limitations of the medium cannot be fully overcome. The chapter therefore suggests replacing the myth of perfect fidelity with the competing concept of a noise resonance of sound media, to account for the fact that noise, distortion, and randomness unavoidably shape all reproduced sound.

For the requirement of NB-IOT applications, rectangular micro strip slot antennas have been developed with sufficient bandwidth of 112.5 MHz. The above 50% size of the antennas has been reduced by making multiple rectangular slots on the patch surface. Fr4 material has been utilized as a dielectric substrate. The position of the transmission line has been varied to match the perfect impedance matching. The proposed antenna model has been simulated on HFSS software. To check the practical behavior of the designed antenna, it has been fabricated and tested by using vector network analyzer. The proposed antenna has resonance frequency band from 1718.75 MHz – 1831.25 MHz with minimum return loss performance as below -20 dB.