The Focusing Waves Induced by Bragg Resonance with V-Shaped Undulating Bottom

Intensive wave reflection occurs when the wavelengths of the incident waves and bottom undulations are in a 2:1 ratio. Existing studies have included the Bragg resonance phenomenon of waves passing over a continuous undulating bottom parallel to and oblique to the shoreline. More generally, the Bragg resonance mechanism is used as a means of coastal protection, rather than wave power generation. To focus the wave energy in a specific area, here, we propose sinusoidal sandbars of a horizontal V-shaped pattern, which is formed by two continuous undulating bottoms inclined at an angle to each other and the center axis of the angle is perpendicular to the shoreline. Based on the high-order spectral (HOS) numerical model, both the characteristics of Bragg resonance induced by the regular waves and random waves are investigated. In the scenario of regular waves, it shows that the wave-focusing effect is related to the angle of the V-shaped undulating bottom, and the optimal angle of inclination for the V-shaped undulating bottom is 162.24°. On that basis, considering the interactions between the random waves and the V-shaped undulating bottom of 162.24°, the Bragg resonance characteristics of random waves are studied. The BFI factor combining wave steepness and spectrum width can evaluate the focusing intensity of the Bragg resonance of the random waves. For BFI, in the range of 0.15–1.0, the values of Hsmax/Hs0 linearly increase with the increase of BFI.

Латеральный спин-волновой транспорт в системе неидентичных магнонно-кристаллических микроволноводов

The control regimes of dipole coupling in the lateral system of non-identical magnonic crystals are investigated by the method of Mandelstam-Brillouin spectroscopy and by the method of micromagnetic modeling. The modes of spatial and frequency selection of the spin-wave signal near the frequency of the band gap zone of the magnonic crystal are revealed. The influence of changes in geometric parameters on the properties of waveguide modes near the frequency of the Bragg resonance is investigated. The results obtained can be used to create microwave signal processing devices, such as demultiplexers, power dividers, couplers.

Передача и преобразование электромагнитного излучения фотонно-кристаллическими металлодиэлектрическими системами на основе опалов

An experimental study of the optical properties of two types of metal-dielectric composites based on opal matrices was carried out: 1) layered structures obtained by successive deposition of metal and dielectric films on a monolayer of opal globules, where extraordinary transmission and extraordinary absorption of light were detected due to the excitation of surface plasmon polaritons of various types; 2) "massive" opal samples, which were infilled with metal by electrothermodiffusion, where an asymmetric form of Bragg resonance curves was observed, due to the Fano resonance.

Explosive instability due to flow over a rippled bottom

In this paper, we study Bragg resonance, i.e., the triad interaction between surface and/or interfacial waves with a bottom ripple, in the presence of background velocity. We show that when one of the constituent waves of the triad has negative energy, the amplitudes of all the waves grow exponentially. This is very different from classic Bragg resonance in which one wave decays to cause the growth of the other. The instabilities we observe are “explosive” and are different from normal mode shear instabilities since our velocity profiles are linearly stable. Our work may explain the existence of large-amplitude internal waves over periodic bottom ripples in the presence of tidal flow observed in oceans and estuaries.