Waves In Frequency Range Research Articles

Hydroelastic analysis of interaction between water waves and a floating laminated disk

This paper studies the interaction between water waves and a very large floating laminated disk in water of finite depth. The disk is a composite structure consisting of two surface sheets and a middle low-density elastic core layer. Based on the linear potential flow theory, an analytical solution of the hydroelastic problem is developed using the eigenfunction expansion method for the velocity potential of fluid motion. In the solution procedure, the laminated disk is regarded as double circular Euler sheets connected by a series of closely spaced and mutually independent vertical springs, and then an eighth-order differential equation of motion of the laminated disk is derived as the elastic boundary condition of the hydroelastic problem. An approximated model is then developed for the hydroelastic problem in shallow water. The deflection and bending moment of the disk and the free surface elevation near the disk are calculated, and it is found that the series solution for the velocity potential converges rapidly. Typical examples are presented to show the effects of different parameters, including wave frequency, the edge conditions of the disk, and the elastic coefficient of the core layer, on wave force, structural hydroelastic response, and wave field. Moreover, viscoelastic damping is introduced in the core layer, and its effect on the hydroelastic response is evaluated by adopting the complex stiffness method. The results indicate that the wave force on the laminated disk is larger than that on a corresponding rigid one over a very wide range of wave frequencies, and the local deformation of the lower sheet can be suppressed by designing a core layer with viscoelastic damping.

Design of Phononic Bandgap Metamaterials Based on Gaussian Mixture Beta Variational Autoencoder and Iterative Model Updating

AbstractPhononic bandgap metamaterials, which consist of periodic cellular structures, are capable of absorbing energy within a certain frequency range. Designing metamaterials that trap waves across a wide wave frequency range is still a challenging task. In this paper, we present a deep feature learning-based design framework for both unsupervised generative design and supervised learning-based exploitative optimization. The Gaussian mixture beta variational autoencoder (GM-βVAE) is used to extract latent features as design variables. Gaussian process (GP) regression models are trained to predict the relationship between latent features and properties for property-driven optimization. The optimal structural designs are reconstructed by mapping the optimized latent feature values to the original image space. Compared with the regular variational autoencoder (VAE), we demonstrate that GM-βVAE has a better learning capability and is able to generate a more diversified design set in unsupervised generative design. Furthermore, we propose an iterative GM-βVAE model updating-based design framework. In each iteration, the optimal designs found property-driven optimization is used to update the training dataset. The GM-βVAE model is re-trained with the updated dataset for the optimization search in the next iteration. The effectiveness of the iterative design framework is demonstrated by comparing the proposed designs with the designs found by the traditional single-loop design method and the topologically optimized designs reported in literatures. The caveats to designing phonic bandgap metamaterials are summarized.

Wave energy converter optimization based on differential evolution algorithm

A parameter optimization method for an oscillating buoy-type wave energy converter (WEC) is presented from the perspective of submerged buoy volume; which affects both the power production and cost investment. The effects of submerged buoy volume on the optimal power capture are studied using the differential evolution algorithm and linear potential flow theory. The cost indictor V/P (V and P representing submerged buoy volume and power capture, respectively) is introduced to measure the cost-effectiveness of the WECs. The power capture and cost performance of the optimized WECs in regular and irregular waves are discussed. The results show that the WEC with the large power take-off (PTO) damping has good adaptability to a range of wave frequencies; however, the optimal submerged buoy volume is not cost-efficient due to the consequent relatively large cost indicators. The best choice of WEC in terms of cost-effectiveness is one designed with a large PTO damping and a buoy of slightly small non-optimal submerged volume.

Study of the free surface Green function at zero forward speed in finite water depth using Newman’s method

This study details the computation of the finite depth Green function at zero forward speed based on Newman’s method. The Green function is evaluated using either a series expression or an integral expression. An asymptotic analysis of the integral expression is performed and enables an accurate power series approximation over the whole range of wave frequencies. The zero and infinite-frequency limits of the Green function are studied and match their expected values leading to a consistent behaviour with the last results of the literature.The computation of the finite depth Green function is then checked with two verification cases.

Excitation of Ultraslow High‐q Surface Plasmon Polariton Modes in Dense Arrays of Double‐Walled Carbon Nanotubes

AbstractThis work explores the plasmonic properties of parallel double‐walled carbon nanotube arrays. It is shown that ultraslow surface plasmon polariton (SPP) modes possessing a phase velocity some orders of magnitude lower than the speed of light in vacuum and high Q‐factor can be generated in such arrays. It is demonstrated that nonrelativistic electron beams with the velocity less than 106 m s−1 can be used to excite SPPs in arrays of double‐walled carbon nanotubes. For the SPP modes excited by an electron beam, the frequency range of SPP waves and electron beam velocities corresponding to the phase matching within a wide frequency range are determined. It opens the way to design slow‐wave structures based on the dense arrays of multiwalled carbon nanotubes employing an efficient energy transfer from the pump to the SPPs.

Взаимодействие электромагнитной H-волны с полупроводниковым нанослоем

A theoretical model of the electromagnetic H-wave interaction with a semiconductor nanolayer, the thickness of which can be comparable to or less than charge carrier de Broglie wavelength is constructed. We assume the frequency range of the electromagnetic wave to be much less than the plasma frequency. Analytical expressions are derived for optical coefficients as the functions of the dimensionless thickness, electromagnetic wave frequency and incidence angle, chemical potential, and surface roughness parameters. The results derived for the limiting cases of degenerate and nondegenerate electron gas are analyzed.

Interaction of an electromagnetic H-wave with a semiconductor nanolayer

A theoretical model of the electromagnetic H-wave interaction with a semiconductor nanolayer, the thickness of which can be comparable to or less than charge carrier de Broglie wavelength is constructed. We assume the frequency range of the electromagnetic wave to be much less than the plasma frequency. Analytical expressions are derived for optical coefficients as the functions of the dimensionless thickness, electromagnetic wave frequency and incidence angle, chemical potential, and surface roughness parameters. The results derived for the limiting cases of degenerate and nondegenerate electron gas are analyzed. Keywords: nanolayer, Liouville equation, de Broglie wavelength, Soffer model, optical coefficients.

Investigation for conductor loss calculation including effect of adhesive layer of titanium in microwave, millimetre and terahertz frequency range

This paper presents the investigation of calculations for conductor loss including effect of adhesive layer of Ttitanium from frequency range 1 GHz to 1000 GHz. Here we present comparison between experimental conductor loss of the Thin Film Microstrip line with loss calculation from suggested model for the structures of TFML. It is found that the loss estimation in Millimeter wave and Terahertz frequency range is much more with adhesive layer than without adhesive layer in comparison to Microwave range for Thin Film Microstrip Line.

Towards Environmental RF-EMF Assessment of mmWave High-Node Density Complex Heterogeneous Environments.

The densification of multiple wireless communication systems that coexist nowadays, as well as the 5G new generation cellular systems advent towards the millimeter wave (mmWave) frequency range, give rise to complex context-aware scenarios with high-node density heterogeneous networks. In this work, a radiofrequency electromagnetic field (RF-EMF) exposure assessment from an empirical and modeling approach for a large, complex indoor setting with high node density and traffic is presented. For that purpose, an intensive and comprehensive in-depth RF-EMF E-field characterization study is provided in a public library study case, considering dense personal mobile communications (5G FR2 @28 GHz) and wireless 802.11ay (@60 GHz) data access services on the mmWave frequency range. By means of an enhanced in-house deterministic 3D ray launching (3D-RL) simulation tool for RF-EMF exposure assessment, different complex heterogenous scenarios of high complexity are assessed in realistic operation conditions, considering different user distributions and densities. The use of directive antennas and MIMO beamforming techniques, as well as all the corresponding features in terms of radio wave propagation, such as the body shielding effect, dispersive material properties of obstacles, the impact of the distribution of scatterers and the associated electromagnetic propagation phenomena, are considered for simulation. Discussion regarding the contribution and impact of the coexistence of multiple heterogeneous networks and services is presented, verifying compliance with the current established international regulation limits with exposure levels far below the aforementioned limits. Finally, the proposed simulation technique is validated with a complete empirical campaign of measurements, showing good agreement. In consequence, the obtained datasets and simulation estimations, along with the proposed RF-EMF simulation tool, could be a reference approach for the design, deployment and exposure assessment of the current and future wireless communication technologies on the mmWave spectrum, where massive high-node density heterogeneous networks are expected.

Editorial Special Issue on Microwave Photonics

The papers in this special issue focus on lightwave technology on mirowave photonics. An important portion of the papers published in this special issue are an expanded version of those presented at the International Topical Meeting on Microwave Photonics 2020 (MWP2020) held in Matsue, Japan, from November 22-25, 2020. The field of Microwave Photonics keeps continuously growing and expanding. By exploiting the inherent ultrawide fractional frequency range of optical waves, the frequency reach of the field has exceeded the microwave range to include the millimeter and Terahertz wave bands. Photonic integration technology is having a disruptive effect in the field, enabling reduction of the the size and the weight of microwave photonic systems to unprecedented levels. The number of technology platforms used for microwave photonic implementations is also greatly expanding, from indium phosphide to silicon and silicon nitride, enabling important performance improvements of critical functions as well as unlocking the potential of novel structures (photonic crystal structures and graphene metasurfaces, among others).

Quasilinear Model of Jovian Whistler Mode Emission

AbstractThe whistler mode chorus emissions are pervasively detected by the Juno satellite in Jupiter’s magnetospheric environment. This article pays particular attention to a sample observation made by the Juno on 3 November 2019, where typical whistler mode chorus waves are measured. The emission is characterized by a broad range of wave frequencies from below fce/2, where fce denotes the local electron cyclotron frequency, down to the lower‐hybrid frequency, with a gradually downshifting frequency over time. The excitation appears to coincide with the detection of a “butterfly” pitch‐angle distribution and the expected loss‐cone feature associated with the energetic electrons. These anisotropic features, especially the butterfly pitch‐angle distribution, gradually disappear as the waves are excited and the electron phase space distribution becomes isotropic. The aim of this article is to model the characteristics by means of quasilinear kinetic theory of the whistler instability driven by a loss‐cone electron distribution function with a narrow loss‐cone angle, which is to be expected from low‐latitude regions of the Jovian magnetosphere. It is shown that the theoretically constructed dynamic wave spectrum is consistent with the observation made on 3 November 2019. The present finding demonstrates that the quasilinear theory can be a powerful theoretical tool for interpreting various Jovian plasma wave emissions, which includes the whistler waves, but also other wave modes.

Evidence of wave–wave coupling between frequency harmonic bands of magnetosonic waves

Previous studies demonstrated that frequency harmonic structures of fast magnetosonic (MS) waves are usually excited by the hot proton instability. Here, we present an unusual event of MS waves with more than six harmonics wavebands (n = 1–6) in which their high harmonic bands are highly phase-coupled with their fundamental waveband. While calculations of the wave growth rates indicate that the local instability of the hot protons can excite the fundamental waveband (n = 1) as well as only a part of wave branches in the second and third wavebands (n = 2, 3), the bicoherence index adopted to analyze the phase coupling between different wavebands provides evidence that the wave–wave coupling between the low-frequency parts of MS waves can contribute to the generation of their higher harmonics (n > 1). Such wave–wave coupling processes have the potential to additionally redistribute the energy of MS waves and then broaden the frequency range of wave–particle interactions, which has important implications for a better understanding of the generation, distribution, and consequence of space plasma waves.

Estimation of the optimal frequency range of EM waves for the implementation of a wireless channel of charge activation during drilling and blasting operations

The article analyzes the methods of wireless detonation of underground charges during drilling and blasting operations. The technologies considered are intended mainly for disrupting the integrity of rocks during tunneling and extraction of mineral resources in mines and quarries, as well as for the controlled demolition of buildings. The methods presented in the scientific press do not provide sufficient accuracy of time synchronization between the moment of the explosion and the command to launch the operator of the explosive machine, which is a necessary requirement for seismic exploration, and are also based on the use of magnetic antennas for wireless activation of detonators located at a depth of 30 m. The article, by the authors, on the basis of the analytical solution of equations and computational modeling, considers the physical processes of propagation of electromagnetic fields and currents induced by a grounded electric dipole, which is an alternative method of transmitting radio signals to a linear group of detonators. The most favorable operating frequency range of the channel is also analyzed based on the absorbing properties of the medium.

P163 Slow wave transcranial electrical stimulation during wake to investigate the consolidation of new learning

Abstract Introduction Slow, oscillatory, transcranial electrical stimulation (so-tES) applies a current over the scalp that oscillates in intensity at a frequency associated with slow wave sleep (SWS; 0.75Hz). When applied during SWS, so-tES can enhance SWS EEG power compared to sham stimulation, as well as overnight declarative memory consolidation. When applied during wake, so-tES can enhance local EEG power in the slow wave frequency range (0.5–4.5Hz) compared to sham. Therefore, this study will investigate whether so-tES can enhance the early consolidation of new learning compared to sham, when applied during wake. A preliminary analysis of data will be presented. Methods Healthy, young, right-handed adults (18–35 years) practiced a motor sequence learning task for 30 minutes, before receiving 15 minutes of active or sham so-tES (0.75Hz) during quiet wakefulness. Task performance was assessed by recording the total number of correct sequences performed in 30 seconds before practice, after practice, and after stimulation. Performance improvements will be compared between stimulation conditions. Non-invasive, electrophysiological corticospinal excitability measurements (i.e., motor-evoked potentials) were also recorded at six timepoints throughout each session, to investigate whether active so-tES can modulate corticospinal excitability differently to sham. Progress to date Data collection is ongoing, and completion is expected by late 2021. Intended outcome and impact We expect so-tES to enhance early skill consolidation during wake, and that enhanced consolidation will be associated with less variable measurements of corticospinal excitability, when compared with sham stimulation.

Millimeter Wave Absorption Properties of Teflon at Frequency Range from 50 GHz to 67 GHz

In this paper, teflon material with dimensions 3.76 mm×1.88 mm×1.6 mm was prepared from the Indonesia materials market for the millimeter wave characteristics. The permeability, permittivity, and millimeter wave absorption properties were studied using a vector network analyzer in the frequency range of 50−67 GHz. The results indicated that teflon material have a good reflection loss and broadband absorption and a appropriate absorber in the millimeter wave frequency range.

Higher-order harmonic induced wave resonance for two side-by-side boxes in close proximity

Wave resonance in a narrow gap formed by two boxes in the side-by-side arrangement is investigated by employing a numerical wave flume based on the OpenFOAM® package. In the present study, the main focus lies in the exploration of the nonlinear resonant behavior induced by the second- and third-order harmonic components which occur around half and one third of the resonant frequencies. A wide range of incident wave frequencies is considered, by which the higher-order harmonic induced wave resonance at lower wave frequencies is discussed. By the harmonic analysis, it is revealed that at the resonant frequency the first-order harmonic component dominates the wave resonance and the second-order effect is minor, which coincides with the conclusion drawn in the previous study. However, around half or one third of the resonant frequencies, the first-order harmonic component is in good agreement with the linear potential flow solutions, but the second- or third-order harmonic component is significant, causing the corresponding higher-order harmonic induced wave resonance. In addition, the numerical results show that the second- and third-order harmonic induced wave resonances only influence the wave properties inside the narrow gap, such as the wave response in the narrow gap and the horizontal wave forces on the boxes. The wave responses around the two-box system, the vertical wave forces on the boxes and the reflection and transmission coefficients are hardly affected by the wave resonance around the corresponding half and one third of the resonant frequencies. The higher-order harmonic induced normalized wave elevation in the narrow gap increases with the increase in incident wave height, implying the increased influence of the free surface nonlinearity.

Boundary integrals for oscillating bodies in stratified fluids

The theoretical foundations of the boundary integral method are considered for inviscid monochromatic internal waves, and an analytical approach is presented for the solution of the boundary integral equation for oscillating bodies of simple shape: an elliptic cylinder in two dimensions, and a spheroid in three dimensions. The method combines the coordinate stretching introduced by Bryan and Hurley in the frequency range of evanescent waves, with analytic continuation to the range of propagating waves by Lighthill's radiation condition. Not only are the waves obtained for arbitrary oscillations of the body, with application to radial pulsations and rigid vibrations, but also the distribution of singularities equivalent to the body, allowing later inclusion of viscosity in the theory. Both a direct representation of the body as a Kirchhoff–Helmholtz integral involving single and double layers together, and an indirect representation involving a single layer alone, are considered. The indirect representation is seen to require a certain degree of symmetry of the body with respect to the horizontal and the vertical. As the surface of the body is approached the single- and double-layer potentials exhibit the same discontinuities as in classical potential theory.

Field-angle-dependent multi-frequency electron spin resonance spectroscopy in submillimeter wave range based on thermal detection.

We report the thermally detected electron spin resonance (ESR) spectroscopy in the frequency range of millimeter and submillimeter waves. Under high vacuum conditions, a cantilever-shaped device detects ESR absorption of a mounted sample as a temperature difference in its beam direction. Despite the simple experimental setup, the spin sensitivity of the order of 1012 spins/G was achieved at 10K. The developed sample stage is small enough to be used in a 10T split-pair superconducting magnet with a bore of 25mm, enabling precise field-angle-dependent ESR measurements at multi-frequencies above 500GHz. We demonstrate its usefulness by studying the field-angle dependence of the excitation energy of the dimer triplet state in the Shastry-Sutherland magnet SrCu2(BO3)2.

Low Frequency ULF Waves in the Earth's Inner Magnetosphere: Statistics During Coronal Mass Ejections and Seeding of EMIC Waves

AbstractHere we perform a statistical analysis of low frequency ultra‐low‐frequency (ULF) waves ( mHz ‐ Hz) in the Earth's inner magnetosphere excluding electromagnetic ion cyclotron waves concurrently observed. We use the magnetic field data from the two Van Allen Probes during their first magnetic local time (MLT) revolution that cover the periods of coronal mass ejections. The major results of our analysis are as follows. (a) Spectra of both the transverse and compressional ULF waves are well approximated by the power‐laws in the mHz ‐ Hz frequency range. (b) There are two sources of the low frequency ULF waves: an internal magnetospheric source and an external source outside of the magnetosphere. (c) The average transverse power in the 6–24 h MLT sector dominates that in the 0–6 h sector, whereas the compressional power in the 12–24 h sector dominates that in the 0–12 h sector. (d) The average powers of transverse and compressional ULF waves in the plasmasphere dominate the average powers in the high L shell region of , and there is a deep power minimum in the intermediary region of . (e) The compressional ULF wave power has a maximum in the near equatorial region, whereas the transverse power has a minimum there. (f) A wave energy cascade from low frequency ULF waves into the higher frequency range of EMIC waves ( Hz) supplies the nonthermal seed fluctuations from which EMIC waves can then grow due to instabilities of the energetic magnetospheric ions.

Non-linear dynamic simulations of two-body wave energy converters via identification of viscous drag coefficients of different shapes of the submerged body based on numerical wave tank CFD simulation

Two-body point absorbers are useful for wave energy conversion in high energetic and high wave period sea locations. Analysis and simulation show that the two-body point absorbers have high efficiencies which makes them a potential candidate to promote wave energy harvesting technology towards commercialization and implementation. The submerged body of the two-body point absorbers has a large effect on their performance, hence the question arises: which geometric shape of the submerged body will lead to the best performance of the two-body wave energy harvesters? This paper presents a comprehensive study that analyses the different shapes of the submerged bodies based on the numerical wave tank simulated viscous drag coefficient and hydrodynamic property parameters of the oscillating device. A set of transient and three-dimensional computational fluid dynamic simulations of a numerical wave tank were carried out in Ansys Fluent to determine the viscous drag coefficients of the different submerged body shapes. And then the boundary element hydrodynamic simulation and linear dynamic frequency-domain modeling have been applied to identify the optimized PTO damping. Finally, non-linear time-domain modeling has been applied with the identified viscous damping drag coefficient and PTO damping coefficients to predict and compare the power output performance of different large-scale devices with different shapes of submerged bodies. It is found that each submerged body shape is suitable for a different range of wave frequencies, as one must establish a balance between the hydrodynamic properties and the viscous drag of the submerged body based on the sea location. It is also found that the typical viscous drag coefficient values used in the past studies underestimate the drag coefficient, and the linearized model widely adopted in frequency domain models is non-accurate for the devices with large viscous drag forces.