Wave Beam Research Articles

UAV-Enabled Integrated Sensing, Computing, and Communication: A Fundamental Trade-Off

We propose an unmanned aerial vehicle (UAV) enabled integrated sensing, computing, and communication (U-ISCC) framework, where a treble-functional UAV performs local computation and also delivers its computational tasks to ground access points. Meanwhile, this UAV is employed to sense a target by using the unified beam waves. Our goal is to characterize the Pareto boundary between the computation capacity and the sensing beampattern gain, by which the fundamental trade-off of them is unveiled. To solve the challenging problem, we propose a joint optimization algorithm by applying the semidefinite programming method and the concave-convex procedure technique, which ensures the rank-1 constraint with a low complexity. Numerical results finally verify that the proposed algorithm explicitly depicts the performance region, and demonstrate that the UAV boosts the ability of sensing, computing, and communication to strike a balance by fully exploring its functions.

Investigation on Self-Excited Oscillation for Nonuniform Periodic Sheet Beam Traveling-Wave Tubes

The utilization of phase velocity tapering or jumping techniques in the design of traveling wave tubes (TWTs) has become a widely accepted practice for enhancing the efficiency of beam–wave interaction. However, these approaches are not without their challenges, as they can lead to a series of self-excited oscillation (SEO) issues that restrict further improvement in power. In this article, a nonlinear numerical method is explored for fast prediction of SEO in nonuniform periodic sheet beam TWTs (NP-SBTWTs). The oscillation thresholds at the upper and lower band edges are analyzed and discussed under different voltage and current conditions to determine the stable operating conditions for NP-SBTWT. In addition, the concept of “sideband absolute self-excited state” is proposed to be avoided in dispersion design, and the impact of actual reflection characteristics on stability is quantified by defining the eigenvalues of the feedback gain of the interaction structure based on the real reflection parameter. The results demonstrate that this approach distinguishes itself from conventional time-domain particle-in-cell (PIC) simulation techniques by its capacity to integrate authentic reflection parameters into the computation process to achieve a fast prediction of SEO in NP-SBTWT.

Kappa-Distributed Electrons in Solar Outflows: Beam-Plasma Instabilities and Radio Emissions

Electrostatic (ES) wave instabilities are assumed to be at the origin of radio emissions from interplanetary shocks, and solar coronal sources are most likely induced by electron beams, more energetic but less dense than electron strahls in the solar wind. In this paper, we present the results of a new dispersion and stability analysis for electron populations with Kappa velocity distributions, as often indicated by in situ observations. We investigate, both theoretically and numerically, three electron plasma beam configurations with different implications in the generation of radio emissions. The same three cases, but for Maxwellian distributed electrons, were considered in numerical simulations by Thurgood and Tsiklauri (Astronomy and Astrophysics 584:A83, 2015). Our kinetic plasma approach clarifies the nature of the unstable mode as being an electron beam ES instability (and not a Langmuir instability) in all cases, and for both Kappa and Maxwellian approaches. Electron beam waves are Landau resonant and with frequencies of the fastest growing modes close to but below the plasma frequency (i.e., $\omega \lesssim \omega _{pe}$ ). Suprathermal Kappa tails tend to inhibit the instability by reducing the growth rates, but these effects become minor if the drift speed of the beam is sufficiently high compared to the thermal speed of the electrons. The frequency downshift, also revealed by the observations, clearly tends to increase in the presence of a Kappa-distributed beam. Particle-in-cell (PIC) simulations confirm the inhibiting effects of (initially) Kappa-distributed electrons, but these minor effects in the linear and quasi-linear phases unexpectedly lead to significant decreases in the wave energy levels of the (primary) ES fluctuations near the plasma frequency and higher harmonics. As a result, EM radio (secondary) emissions generated nonlinearly after saturation are even more drastically reduced and can even be completely suppressed. However, the EM emissions around the second harmonic ( $\omega \lesssim 2 \, \omega _{pe}$ ) are markedly powered by two symmetric countermoving beams, even in the presence of Kappa electrons. These results offer real promise for a realistic interpretation and modeling of radio emissions observed in heliosphere, arguing in favor of a rigorous spectral analysis of the wave instabilities at their origin.

Caustic spin wave beams in soft thin films: Properties and classification

In the context of wave propagation, caustics are usually defined as the envelope of a finite-extent wavefront; folds and cusps in a caustic result in enhanced wave amplitudes. Here, we tackle a related phenomenon, namely, the existence of well-defined beams originating solely from the geometric properties of the corresponding dispersion relation. This directional emission, termed caustic beam, is enabled by a stationary group velocity direction, and has been observed first in the case of phonons. We propose an overview of this ``focusing'' effect in the context of spin waves excited in soft, thin ferromagnetic films. Based on an analytical dispersion relation, we provide tools for a systematic survey of caustic spin wave beams. Our theoretical approach is validated by time-resolved microscopy experiments using the magneto-optical Kerr effect. Then, we identify two cases of particular interest both from fundamental and applicative perspectives. Indeed, both of them enable broadband excitations (in terms of wave vectors) to result in narrow-band beams of low divergence.

Wave propagation analysis in laminated composite periodic frame structures using spectral finite element method

In this article, wave propagation in a one-dimensional (1-D) composite periodic frame structure is analyzed using spectral finite elements (SFE) method together with Bloch’s theorem. Each element in the periodic frame structure is modeled as a first-order shear deformation theory (FSDT) beam element and wave equations for the beam elements are derived using FSDT considering axial, flexural, and shear deformations. Next, these equations are solved using the frequency domain SFE method to obtain an elemental dynamic stiffness matrix which on assembly gives the dynamic stiffness matrix for the unit cell of the periodic structure. A polynomial eigenvalue problem is formulated thereafter using Bloch’s theorem to evaluate the dispersion coefficients and wave amplitude ratios. Finally, the entire periodic frame is modeled as homogenized two-noded elements capturing the wave response of the PS with a drastic reduction in computational cost. The results obtained using the present method are validated with finite element simulation using ANSYS mechanical Ansys Parametric Design Language (APDL). The frequency band gaps observed in the frequency domain responses are investigated and corroborated with those predicted by the dispersion relations. This is followed by a detailed parametric study on the influence of different parameters on the band gap characteristics. The present method provides a scheme of wave propagation analysis of composite periodic frames with substantial computational efficiency.

Ultrathin and Ultra‐Broadband Terahertz Single‐Layer Metasurface Based on Double‐Arrow‐Shaped Resonator Structure for Full‐Space Wavefront Manipulation

AbstractIn this paper, a simple design of an ultrathin and ultra‐broadband single‐layer MS based on double‐arrow‐shaped resonator (DASR) structure for both transmission and reflection modes in terahertz (THz) region is presented. The single‐layer MS is composed of a periodic array of the combination of the metal DASR and complementary circular patch (CCP) adhered on an ultrathin dielectric substrate. Numerical results show that the MS structure can convert CP wave to its orthogonal component after reflection and transmission simultaneously, and the corresponding amplitudes are ≈0.45 on average from 0.45 to 1.75 THz with a relative bandwidth of 118.2%, in which the CP conversion efficiency is closing to theoretical limit (25%) of the single‐layer structure. Furthermore, the 0–2π phase shifts for the reflected and transmitted orthogonal CP wave can be achieved simultaneously by adjusting the oriented angle (α) of the DASR structure along the wave propagation direction. For the concept proofs, wave beams deflection, vortex beam generation, and focusing effect for both reflection and transmission modes are demonstrated numerically. The design can provide new possibilities and potential to develop multifunctional full‐space devices.

Numerical study of energy capture equipment using tanker rolling motion for different wave heights and encounter angles

ABSTRACT An energy capture equipment is proposed, which can harvest the mechanical energy generated by the rolling motion of a tanker, and the structure of the equipment is designed. The mass-spring-damping mathematical model of the slider is established. Then, a numerical wave tank is created by Fluent to simulate the rolling motion of a typical ship equipped with equipment. According to the data of ship rolling motion and the mathematical model solved by the Newmark-β method in MATLAB, the equipment's power is obtained. Specifically, when the encounter angle is beam wave condition (90 degree), the rolling motion is violent and the equipment power reached the maximum value (187.16 W). Besides, the power generation with the quartering wave is better by comparing the equipment's power under the conditions of the bow and quartering wave. Finally, the wave height becomes bigger, the ship's rolling angular displacement and the equipment's power become larger.

Developing coexisting traveling and standing waves in Euler-Bernoulli beams using a single-point excitation and a spring-damper system

In the inner ear, the Basilar Membrane (BM) and inner hair cells work to transduce acoustic waves into electrical signals; of these, the BM is the structural membrane that carries the acoustic information as traveling structural waves. These waves propagate from the base of the cochlea towards its apex. The helicotrema is the main component of the cochlea's apex, which prevents the waves from traveling back from the apex to the base. Due to this unique characteristic of the BM, humans are able to hear continuous acoustic signals without any reflection and overlap of acoustics. The work herein is inspired by this biological behavior and seeks to understand and replicate such behavior in a passive manner in basic structures.This feature of the inner ear leads us to study the dynamics of a uniform beam connected to a spring-damper system as a passive absorber, in order to understand some of the observed phenomenological behaviors of the basilar membrane. The location of the spring-damper system divides the beam into two dynamic regions: one which exhibits non-reflecting traveling waves and the other with standing waves. In this paper, traveling waves co-existing with standing waves in the two distinct regions of the structure and are realized analytically, numerically, and experimentally. The results of this work can be used in various applications such as vibration energy harvesting, particle transportation, vibration suppression and control, and in exploring possible explanations of the functionality of the helicotrema in the cochlea.

Superconducting radio frequency photoinjectors for CW-XFEL

A dependable and consistent electron source is a crucial requirement for the achievement of high-power free electron lasers (FELs). Over the past two decades, it has been demonstrated that photoinjectors based on SRF technology (SRF guns) are suitable for continuous wave (CW) beam generation. SRF guns possess both the high accelerating field gradients of normal conducting RF photoinjectors and the low power dissipation thanks to mature SRF cavity technology, and therefore have the potential to provide the high-brightness, high-current beams required for CW-XFELs. After the demonstration of the first SRF gun in Dresden-Rossendorf, several SRF gun programs based on different approaches have achieved promising progress and even succeeded in routine operation. SRF guns are expected to play an important role in XFEL facilities in the near future. In this paper, we give an overview of design concepts, important parameters and development status of the worldwide SRF gun projects.

Algorithm design of a Rubik metamaterial for sextuple orbital angular momentums

AbstractThis letter presents a Rubik metamaterial with sextuple orbital angular momentum (OAM) capabilities. The design is based on a comprehensive algorithm that draws inspiration from the Rubik's cube. This metamaterial can generate multiple phased vortex waves using only one model and is easily constructed from metallic blocks with varying heights. The performance of the metamaterial is verified at 18 GHz with a gain of over 30 dB. A faster verification process is achieved using an automated program based on macroscript for height‐adjusted Rubik metamaterials, which is more efficient than manual operations. By calculating the purity of the sextuple OAMs, it can be determined that the Rubik model is capable of generating multiple phased vortex wave beams as effectively as possible. This Rubik metamaterial has potential applications in experimental and educational settings, particularly with the growing trend in three‐dimensional printing.

Basic Concept of the Beam Wave based Element for Mid and High Frequency Analysis

This paper describes a Hermite beam wave based element of the steady-state dynamic response of a 1D structure system. This study focuses on the development of beam wave based elements. Compared with standard piecewise polynomial approximation, the wave basis is shown to give a considerable reduction in computational degrees of freedom. In practical terms, it is concluded that the degrees of freedom for which accurate results can be obtained, using these new techniques, can be up to half of that of the conventional finite-element method.

Coupled FPSO roll motion response and tank sloshing in a pair of two row cargo tanks

The advantages offered by Floating Production Storage and Offloading Units (FPSOs) continue to make them high in demand and widely used. Continuous loading and offloading of FPSOs means the presence of slack cargo tanks is inevitable and can impact the seakeeping performance of FPSOs. Published experimental data on this impact is limited. This paper experimentally studies liquid cargo and its effect on roll motion in a pair of two-row cargo tanks of a FPSO model in regular beam waves. The results show that the liquid cargo motion effect on floating vessels cannot be studied using solid cargo. The results also show that varying the liquid cargo loading affects floating vessels’ Response Amplitude Operators (RAOs).

Inertial wave attractors in rapidly rotating tilted cuboids

Flows in rapidly rotating fluid-filled containers are strongly constrained by the restorative Coriolis force. Their responses to small amplitude perturbations may result in the excitation of regular modes of the container for some very selective geometries, but in general the response is a network of inertial wave beams. Due to the peculiar laws governing how these beams reflect, the network of reflected beams may focus onto highly localized regions of the container, where the beam energy and wavenumber become unbounded in the absence of viscous and nonlinear processes. Here, we explore in detail this focusing of wave beams in cuboids, enabling a comprehensive analysis of this intriguing process.

Nonparaxial Tilted Waveobjects

Simple closed-form analytical expressions for tilted astigmatic wave beams and wavepackets that are exact solutions of the wave equation are constructed. They are obtained through two different but equivalent derivations, one is based on a complex shift in the Bateman-type solutions, the other employs their Lorentz transformation. Analytic expressions for the propagation invariants: energy, momentum and orbital angular momentum of tilted waveobjects with general astigmatism are presented.

Spatiotemporal theory of the sectioned gyro-BWO with the zigzag quasi-optical system

We present the quasi-analytical spatiotemporal theory, which describes the process of establishing generation in a backward-wave gyro-oscillator based on the use of a sectioned quasi-optical system with the zigzag path of the operating wave beam. This theory explains peculiarities (namely, a piecewise character) of changing the operating frequency and power of the output signal in the process of the broadband frequency tuning provided by changing the operating magnetic field. This theory also describes competition of different modes of the system in the process of excitation of auto-oscillators and predicts the possibility for realization of the regime of automodulations of the output power, as well as the regime of formation of a short powerful super-radiant pulse.

Guided wave propagation and skew effects in anisotropic carbon fiber reinforced laminates

Guided ultrasonic waves provide a promising structural health monitoring (SHM) solution for composite structures as they are able to propagate relatively long distances with low attenuation. However, the material anisotropy results in directionally dependent phase and group velocities, in addition to energy focusing, wave skewing, and beam spreading phenomena. These effects could lead to inaccurate damage localization if not accounted for. In this contribution, the guided wave propagation behavior (A0 mode) for a highly anisotropic, unidirectional carbon fiber reinforced polymer laminate is systematically investigated through both finite element analysis and non-contact laser measurements and compared to theoretical predictions. The directional dependency of phase and group velocity measured for a point and line source shows good agreement with theoretical predictions, once a correction for wave skew effects is applied. Wave skew angles were evaluated from the experimental and numerical wave propagation in multiple directions and matched theoretical predictions based on the phase slowness curve. Significant guided wave beam spreading from a line source was observed and quantified from both experiments and simulations and compared with theoretical predictions using the anisotropy factor. The impact of anisotropic guided wave propagation behavior on SHM is discussed.

Novel 0.22-THz Extended Interaction Oscillator Based on the Four-Sheet-Beam Orthogonal Interconnection Structure

Numerous terahertz vacuum electronic devices (TVEDs) have been proposed. Among these devices, extended interaction oscillators (EIOs) exhibit small-volume, lightweight, low-working-voltage, stable-working frequency, and high-power characteristics. The ladder-line slow wave structure exhibits strong coupling and can interact with the sheet beam to considerably improve the efficiency of beam–wave interaction. In this study, a novel high-frequency structure was proposed. Four conventional ladder-line slow wave structures were placed vertically to form a four-sheet-beam orthogonal interconnection structure (OIS) that considerably increased the coupling efficiency between the cavities, improved output power and efficiency, and interacted perfectly with the TM81 mode. In this study, the dispersion characteristics and field distribution were studied through numerical and simulation calculations, and the optimal working parameters and output structure were analyzed using particle-in-cell (PIC) software. Next, a 0.22-THz extended interaction oscillator based on four-sheet-beam OSI was designed. Simulation results have shown the achievement of the output power of 0.22-THz wave over 500 W with four sheet beams at 16.6 kV and each current of 0.8 A. Finally, preliminary processing and cold tests of the structure were performed. This novel structure provided an alternative for the development of terahertz EIOs.

An Angular Radial Extended Interaction Amplifier at the W Band

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam-wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (-2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the -2° EIA can be improved by nearly 30% compared to the 0° EIA, and the -2° EIA has a greatly improved beam-wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed.

Seismic metamaterials based on coupling mechanism of inertial amplification and local resonance

Inertial amplification mechanisms could be used to control the propagation of elastic waves in beams and slabs, but it was a difficult problem to apply inertial amplification mechanisms to seismic metamaterials to design low-frequency broadband. This paper presents a inertially amplified locally resonant seismic metamaterial (IALR-SM) using the coupling mechanism of inertial amplification and local resonance. In contrast to the locally resonant seismic metamaterial (LRSM), the large-mass columns as local resonators of IALR-SM are attached to the connector and small-mass columns to form the inertia amplification structures. The finite element method calculates the eigenmodes’ band structure and displacement vector field. Numerical results indicated that the bandwidth of the IALR-SM increases by 194% compared to LRSM for seismic surface waves below 20 Hz. The formation mechanism of the yield in large band gaps is attributed to the coupling mechanism of local resonance and inertial amplification. In addition, the numerical effects of geometric parameters on the band gaps are investigated. The findings showed that the side length of the small-mass columns plays a vital role in determining which coupling mechanism is dominant. Finally, field experiments demonstrated that the IALR-SM generates low-frequency broadband.

Photon’s Spin Mechanism and Wave-Particle Hybrid Structure. It Exhibits both Wave Property and Particle Property at the Same Time in all Experiments.

The interpretation of single photon double slits Wheeler's delayed choice experiment leads to a weird inference: "what the observer does now can change what happened in the past". It subverts our cognitions. Other interpretations are also in dispute. Is there another possible way that can better explain experiments? For this purpose, we try to reacquaint what is a photon? What structure does it have? How does the structure influence the photon behavior? In 1905 Einstein supposed that the photon is a quantum of EM radiation; according to the quantum interpretation, the probability density of a coherent state undergoes a sinusoidal vibration with time. It will also excite a quantized EM wave. So, our research object must be an EM wave beams. We discover and prove that under the Quantification Law of Charge, there is a kind of axial symmetric EM-wave beam it is a quantum of circularly polarized light. Its energy is concentrated in a very small packet; this energy packet will be proved having the photon properties, like , , spin , obeying B-E statistics and so on; On the other hand, the width of the sodium spectral lines identifies that the energy packet carries a long EM wave beam. They form a wave-particle hybrid structure. It exhibits both wave property and particle property at the time in all experiments. Its interpretation for the single photon double slits Wheeler's delayed choice experiment does not lead to the above strange inference.