Bidirectional Beams Research Articles

Advanced Crack Detection in Bidirectional Gradient Material FGM Beams: A Neural Network Approach with Adam Optimization

Advanced Crack Detection in Bidirectional Gradient Material FGM Beams: A Neural Network Approach with Adam Optimization

Dynamic behaviors of general composite beams using mixed finite elements

A novel mixed finite element method is developed and implemented for analyzing the vibration and buckling behavior of general composite beams which consists both transversely layered and axially jointed materials. The governing state-space equations are derived using the Hamilton's principle, where both displacements and stresses are treated as fundamental variables. This semi-analytical method uses transfer relations in the transverse direction and finite element meshing in the longitudinal direction, overcoming the difficulties for general composite beams analysis and providing computational efficiency and analyzing flexibilities. The developed mixed finite element model ensures continuity of both displacements and stresses across the material interface, thereby resolving interfacial stress singularity issues and offering more reliable simulations of boundary conditions at both ends. The proposed method is formulated and validated for the free vibration and buckling analysis of general composite beams. Additionally, it is observed that material properties such as Young's modulus and density, as well as the stiffness of the interface connecting layers, have significant effects on the free vibration and buckling responses of the composite beams. Analysis of periodically distributed and bi-directional composite beams demonstrates the versatility of this method in handling two types of combination forms. The proposed method serves as a valuable reference for obtaining accurate vibration and buckling results while ensuring stress-compatibility for composite beams in practical applications.

A Low-Profile and High-Gain Antenna With Bidirectional Beams Enabled by Integrating Folded Transmitarray and Fabry–Perot Cavity

A Low-Profile and High-Gain Antenna With Bidirectional Beams Enabled by Integrating Folded Transmitarray and Fabry–Perot Cavity

Bidirectional multi-beam with multi-polarizations tensor holographic metasurface using bilayer anisotropic elements.

In this paper, we present and design a tensor holographic metasurface (THMS) capable of radiating multiple beams with different polarizations in both forward and backward directions. The proposed THMS manipulates the fundamental TE mode surface waves (SWs) to produce bidirectional leaky-wave radiation using bilayer anisotropic metal patches. To achieve the independent control of the direction and polarization of bidirectional beams, the nature of the capacitive impedance element supporting TE mode SWs is exploited. A dual-feed scheme exciting orthogonal TE SWs is proposed for THMS generating circularly polarized beams with good performance. As a proof of concept, a bidirectional THMS integrated with two WR-28 waveguide sources based on the orthogonal-feeds scheme, which simultaneously radiate linear- and circular-polarized four beams, is designed, fabricated, and measured at 35 GHz. The experiment results are in good agreement with the simulated ones, achieving a peak gain of 19.2 (19.6) dBi, a -3 dB gain bandwidth of 9.14% (4.3%), for circularly-polarized (linearly-polarized) beams and a 3 dB axial ratio bandwidth of 13% for circularly-polarized beams. The sidelobe levels and cross polarization levels of all beams are below -15 dB and -22 dB, respectively.

Bidirectional vortex beam and reflective polarization conversion terahertz metasurfaces

We design a terahertz metasurface with the functions of bidirectional vortex beams and reflection polarization conversion. The unit cell of the proposed metasurface consists of a vanadium dioxide metal mixed layer, a dielectric layer, a vanadium dioxide thin film, a dielectric layer, and a metal open ring. At room temperature, when a left-handed circularly polarized wave is incident, the metasurface generates a reflected mode vortex beam with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.34 THz. Simultaneously, the metasurface produces transmitted mode vortex beams with topological charges of l=−1 and l=−2 at frequencies of 0.33 and 0.36 THz. When the temperature changes to 68°C and y-polarized waves are incident, the metasurface generates a reflected left-handed circularly polarized wave in the frequency bands of 0.6–0.65 THz and 1.75–1.93 THz, and a right-handed circularly polarized wave in the frequency band of 0.86–0.9 THz, achieving the function of converting linearly polarized waves into circularly polarized waves. This metasurface provides a new method for designing a single metasurface structure to achieve bidirectional multifunctional terahertz devices for transmission and reflection modes. In addition, the designed metasurface achieves a perfect polarization conversion function that can convert linearly polarized waves into circularly polarized waves.

Properties of Electrons Accelerated by the Ganymede‐Magnetosphere Interaction: Survey of Juno High‐Latitude Observations

AbstractThe encounter between the Jovian co‐rotating plasma and Ganymede gives rise to electromagnetic waves that propagate along the magnetic field lines and accelerate particles by resonant or non‐resonant wave‐particle interaction. They ultimately precipitate into Jupiter's atmosphere and trigger auroral emissions. In this study, we use Juno/JADE, Juno/UVS data, and magnetic field line tracing to characterize the properties of electrons accelerated by the Ganymede‐magnetosphere interaction in the far‐field region. We show that the precipitating energy flux exhibits an exponential decay as a function of downtail distance from the moon, with an e‐folding value of 29°, consistent with previous UV observations from the Hubble Space Telescope (HST). We characterize the electron energy distributions and show that two distributions exist. Electrons creating the Main Alfvén Wing (MAW) spot and the auroral tail always have broadband distribution and a mean characteristic energy of 2.2 keV while in the region connected to the Transhemispheric Electron Beam (TEB) spot the electrons are distributed non‐monotonically, with a higher characteristic energy above 10 keV. Based on the observation of bidirectional electron beams, we suggest that Juno was located within the acceleration region during the 11 observations reported. We thus estimate that the acceleration region is extended, at least, between an altitude of 0.5 and 1.3 Jupiter radius above the 1‐bar surface. Finally, we estimate the size of the interaction region in the Ganymede orbital plane using far‐field measurements. These observations provide important insights for the study of particle acceleration processes involved in moon‐magnetosphere interactions.

Bidirectional multi-mode multiple vortex beams generator based on terahertz metasurface

Herein, we propose a vortex beam generator based on vanadium dioxide (VO2), which can switch between two operating modes (reflection and transmission) to generate bidirectional multi-mode multi-vortex beams across a wide frequency band range of 0.8 THz to 1.6 THz. By leveraging the transition of VO2 from the insulating state to the metallic state with temperature changes, the switching between transmission and reflection modes is achieved. Furthermore, through the application of the convolution and superposition theorem, the multiplexing of orbital angular momentum (OAM) is realized. Our work introduces a new method for multi-channel, multiplexed communication and imaging systems, and offers a novel approach to achieve powerful and flexible regulation of terahertz communication systems.

Inclined crack identification in bidirectional FG beams on an elastic foundation using the h-version of the finite element method

This article examines the impact of inclined transverse cracking on the natural frequency of Euler-Bernoulli-model imperfect FG beams on an elastic foundation, taking into account the pinned-pinned and clamped-clamped boundary conditions. The equations are diffused using the classic finite element method (h-version). Material properties are considered to vary in both directions of the beam; width and thickness, using the power-law formula. The approximate porosity model is adopted with a uniform distribution. Cracked element stiffness is determined by reducing the cross-section of a bi-directional FG beam. The numerical results are compared with those of previous convergence studies for dimensionless fundamental frequencies. Case studies were carried out to evaluate the effect of the porosity values, the crack depth, the crack location, slope angle, and the Winkler-elastic foundation parameters on the first three natural frequencies of a beam with different support conditions and material gradient. In addition, the results demonstrated that the two-way distribution function plays an important role in the convergence of frequencies.

Flexural Behavior of Bidirectionally Graded Lattice

This study aims to investigate the flexural behavior of newly designed bidirectionally graded lattice beams with body‐centered cubic unit cells made of stainless steel 316 L. Uniform and unidirectionally graded lattice beams are also studied for comparison. All the lattice beams are fabricated by electron beam melting and tested under quasi‐static bending loads. The experimental results reveal that the flexural stiffness and strength of bidirectional lattice beams are higher than those of both the uniform and unidirectional counterparts. The unidirectional lattice beams display the lowest strength owing to the easier collapse of thinner lattice layers on the impact side with the indenter. Finite element models, developed and validated using the experimental results, are used to evaluate the effects of the density gradient and the loading velocity on the performance of bidirectional lattice beams. The parametric study shows that the flexural stress and the specific energy absorption capacity of bidirectional functionally graded lattice beams increase with increasing loading velocity and can be enhanced by manipulating the layer density gradient.

Nonlinear frequency analysis of porous Bi directional functionally graded beams utilizing reddy shear deformation theory

The nonlinear frequency response of bi-directional functionally graded porous beams experienced range of various end conditions is investigated in this work. The end conditions which are simply supported, clamped-simply supported, clamped-clamped, and clamped-free are taken by using the Von Karman geometric nonlinearity, Green's tensor and Reddy third-order shear deformation theory. A generalized differential quadrature technique (GDQM) accompanied by direct numerical iterance approach is proposed to solve equations. The findings are presented to aid in future research into the effects of various gradient indices, vibration amplitude ratios, porosity coefficients, shear and elastic substrate parameters, boundary conditions, and vibration frequencies on the bi-directional functionally graded beams. The outcomes of this research have practical applications and can be utilized to enhance the design of bi-directional beams. The results are also highly useful in anticipating and identifying potential causes of failure in these beams.

Porosities-dependent wave propagation in bi-directional functionally graded cantilever beam with higher-order shear model

The contribution provided in this paper is to investigate the dynamic response of bidirectional graded material beams with porosities. Higher order shear deformation beam theory for wave propagation in porous functionally graded cantilevered beam are developed, taking into account the bidirectional distribution, which is mainly represented in the density and the Young’s modulus. The material properties of the porous FG beam are graded through the thickness and width using a power law distribution. The governing equations of the wave propagation in the porous FG beam are derived by employing the Hamilton’s principle. The analytic dispersion relation of the bidirectional porous FG beam is obtained by solving an eigenvalue problem. Two porosities models approximating the even and uneven distributions of porosity are considered. The results obtained for bidirectional FG beam were compared with those reported in the literature, and the results were very agreement. The effects of the volume fraction distributions, the number of wave propagation, various parameters and the porosity type on dynamic of functionally graded beam are discussed in details. The numerical results show that the power law index, number of wave, wave velocity, and porosity distribution model affect the dynamic behavior of the beam significantly. The results show that the uneven porosity predicts higher natural frequencies than the even porosity.

Ion-Scale Magnetic Flux Rope Generated From Electron-Scale Magnetopause Current Sheet: Magnetospheric Multiscale Observations.

We present in-depth analysis of three southward-moving meso-scale (ion-to magnetohydrodynamic-scale) flux transfer events (FTEs) and subsequent crossing of a reconnecting magnetopause current sheet (MPCS), which were observed on 8 December 2015 by the Magnetospheric Multiscale spacecraft in the subsolar region under southward and duskward magnetosheath magnetic field conditions. We aim to understand the generation mechanism of ion-scale magnetic flux ropes (ISFRs) and to reveal causal relationship among magnetic field structures, electromagnetic energy conversion, and kinetic processes in magnetic reconnection layers. Results from magnetic field reconstruction methods are consistent with a flux rope with a length of about one ion inertial length growing from an electron-scale current sheet (ECS) in the MPCS, supporting the idea that ISFRs can be generated through secondary reconnection in an ECS. Grad-Shafranov reconstruction applied to the three FTEs shows that the FTEs had axial orientations similar to that of the ISFR. This suggests that these FTEs also formed through the same secondary reconnection process, rather than multiple X-line reconnection at spatially separated locations. Four-spacecraft observations of electron pitch-angle distributions and energy conversion rate suggest that the ISFR had three-dimensional magnetic topology and secondary reconnection was patchy or bursty. Previously reported positive and negative values of , with magnitudes much larger than expected for typical MP reconnection, were seen in both magnetosheath and magnetospheric separatrix regions of the ISFR. Many of them coexisted with bi-directional electron beams and intense electric field fluctuations around the electron gyrofrequency, consistent with their origin in separatrix activities.

Assessing the impact of different foundations on the thermodynamic response of bidirectional FG porous beams

Assessing the impact of different foundations on the thermodynamic response of bidirectional FG porous beams

Investigation on static stability of bidirectional FG porous beams exposed to variable axial load

Investigation on static stability of bidirectional FG porous beams exposed to variable axial load

Effect of two-dimensional material distribution on dynamic and buckling responses of graded ceramic-metal higher order beams with stretch effect

The contribution provided in this article is to examine free vibration and stability response of bidirectional graded material beams (BDFB) considering different boundary conditions. The stretch effect by means of a normal deformation in conjunction with the shear deformation influence are integrated for accurate results. The beam materials features are expected to depend on gradation pattern over the length and transverse directions via power law form. Lagrange’s principle is employed in order to extract the governing equations of motion. A novel approach namely differential quadrature-based Galerkin method (DQGM) is used as an effective and accurate semi-analytical tool to compute the critical stability loads and natural frequencies of (BD-FG) beam for the first time. The approach takes features from simplicity and reduced computational cost of the DQ in combination with the efficacy of the Galerkin method for its analytical aspect and easy dealing with mixed boundary conditions resulting in more accurate results. The correctness of the results obtained from the present approach for two-directional functionally graded materials (FGMs) beams have been verified. Finally, the impacts of design parameters such as material grading exponent distributions, length to thickness ratios, porosity amount, and end support types on the natural frequencies and maximum of stability loads related to the present 2D-FGM beams are examined.

Nonlinear vibration analysis of bidirectional porous beams

Nonlinear vibration analysis of bidirectional porous beams

Characteristics of Suprathermal Electrons in Small-Scale Magnetic Flux Ropes and Their Implications on the Magnetic Connection to the Sun

Small-scale magnetic flux ropes (SMFRs) are observed more frequently than larger-scale magnetic flux ropes (e.g., magnetic clouds) in interplanetary space. We selected 235 SMFRs by applying cylindrical linear force-free fitting to 20-year observations of the Wind satellite, which meets the criteria of low beta, low temperature, an enhanced magnetic field, and a rotation feature. By examining the pitch angle distribution of suprathermal electrons for these events, we found that approximately 45.1% of the SMFRs were accompanied by unidirectional beams (strahl). A much smaller percentage of SMFRs (∼10.7%) were associated with bidirectional beams. We also found a small percentage (∼7.2%) of (sunward) conic distributions during SMFR events. Last, the remaining ∼37.0% of SMFRs were associated with complex electron distributions. The unidirectional beams and most of the conics (together corresponding to ∼50% of the total 235 SMFRs) imply open-field SMFRs with only one end connected to the Sun. For ∼37.7% of the unidirectional beam SMFRs, the local IMF field polarity was orthogonal or inverted (possibly due to interchange reconnection). Based on the solar wind conditions around the bidirectional beams, we suggest that more than half of the bidirectional beams were not necessarily closed-field-line SMFRs.

An inverted relativistic magnetron with virtual cathode based on bidirectional electron beams

An improved L-band inverted relativistic magnetron powered by a virtual cathode is presented. An extra emitter is introduced at the end of a slow-wave structure to reduce the desired π mode start-oscillation time, which is critical when short radiation pulses are required. Electrons produced by both upstream and downstream emitters are injected into the interacting space simultaneously, and the rapid increase in electron density in this region accelerates the establishment of a virtual cathode. Furthermore, the additional emitter provides more charged particles for beam–wave interaction, so that the amplitude of output power can be improved. The particle-in-cell simulation demonstrates that a power conversion efficiency of 76.5% could be obtained for a diode voltage of 500 kV and guiding magnetic field of 0.165 T. Compared with the same slow-wave structure powered by a single beam, the output microwave power is increased from 1.1 to 3.1 GW and the startup time is shortened from 53 to 29 ns.

Generation of a High-Gain Bidirectional Transmit–Reflect-Array Antenna With Asymmetric Beams Using Sparse-Array Method

A high-gain transmit-reflect-array (TRA) antenna with asymmetric bidirectional beams using sparse-array method is presented in this communication. The proposed element consists of three-layer hexagonal-ring-patch (HRP) structure, able to achieve both amplitude (0 or 1) and phase modulation. Based on this kind of element structure, a 125 mm × 125 mm square-shaped TRA is designed and fabricated. A 45.3% of the radiation units operate in transmission mode while others in reflection mode. Spatially fed by a conical horn antenna, two well-defined beams are obtained on both sides of the TRA, pointing to the direction of θ = 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> and 170° ( φ = 0 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> ), respectively. The measured results show a maximum gain of 21.4 dBi with a 1 dB gain bandwidth of 6.7% for the transmitted beam, and a maximum gain of 24.4 dBi with a 1 dB gain bandwidth of 9.3% for the reflected beam. To the authors' best knowledge, it is the first time that the sparse-array method is employed in spatially fed antenna design. The proposed method can conveniently manipulate the pointing directions and beampattern characteristics of the bidirectional beams, providing a promising candidate for bidirectional wireless communication applications.

Planar Dual-Polarization Bidirectional Multibeam Array Antenna for Millimeter-Wave Applications

A millimeter-wave (mm-wave) dual-polarization bidirectional multibeam array antenna based on substrate integrated waveguide (SIW) technology is presented in this article, which can generate 16 bidirectional radiation beams with two orthogonal linear polarizations. The proposed dual-polarization bidirectional multibeam array antenna, based on a new configuration, consists of two transverse slot array antennas (TSAAs), two longitudinal slot array antennas (LSAAs), and two dual-layer <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> Butler matrices (BMs). To realize dual polarizations, a new type of TSAA is designed and combined with a conventional LSAA. For the purpose of bidirectional radiation, two types of dual-polarization array antenna (DPAA), which are realized by combining different arrangements of the TSAA and the LSAA, is composited. In addition, a dual-layer <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula> BM is developed, which can excite both the TSAA and the LSAA and generate dual-polarization bidirectional multibeam. Finally, the prototype of the planar dual-polarization bidirectional multibeam array antenna is fabricated, measured, and discussed. The measured results satisfactorily validate the simulated results.