Bidirectional Beam Research Articles

Vibration analysis of shear actuated bi-directional FGP beam using generalized differential quadrature method

The primary objective of this study is to exhibit the shear mode vibrations of a bidirectional functionally graded piezoelectric beam. All material properties are assumed to vary bidirectional in accordance with an exponential law. Using Timoshenko beam theory, the governing equations and boundary conditions are derived using the Hamilton principle. The equations of motion are then solved using the generalized differential quadrature method. Since no previous solutions existed for the current problem, the obtained results are compared with the findings from a simplified case in previous research. The effects of exponent parameters, slenderness ratios, and boundary conditions on natural frequencies of the bidirectional FGP beam are discussed in detail.

Bidirectional beam generation by metasurface for 6G communication

This paper presents a bidirectional metasurface that is polarization dependent and consists of 2-bit coding reflect-transmit (RT) elements. The proposed metasurface can transmit the vertical polarized (VP) incident wave and reflect the horizontal polarized (HP) wave with the same focal length. The 2-bit coding passive RT elements, named UC0 to UC3, have 0°, 90°, 180°, and 270° phase responses for both vertical and horizontal incidences. The array samples were fabricated using standard print circuit board (PCB) technology. The results of both numerical and experimental investigations demonstrate that the proposed metasurface is capable of beam control with an angular range of ±30° in the xoy, xoz, and diagonal planes. The reflected and transmitted beams have been found to exhibit peak gains of 22 dBi at 94.5 GHz with 7% 3-dB gain bandwidth and 22.1 dBi at 93 GHz with 14.8% 3-dB gain bandwidth, respectively. The proposed metasurface shows great potential for use in 6G wireless communication applications.

Impact of material distribution on the dynamic response of a bidirectional FG beam under general boundary conditions and supported by nonlinear substrate

Impact of material distribution on the dynamic response of a bidirectional FG beam under general boundary conditions and supported by nonlinear substrate

Context-aware code generation with synchronous bidirectional decoder

Code generation aims to map natural language descriptions to code snippets. Recent approaches using sequence-to-tree models have shown promising results. However, they generally adopt an autoregressive way to predict the next token based on previous ones and do not consider potential future tokens. To address this issue, we propose Contextor, a novel context-sensitive model employing a bidirectional decoder to generate tokens in two different orders synchronously and interactively. Specifically, we employ two decoders to generate two sequences of different traversals and share their context knowledge via the attention mechanism. As a result, our model can synthesize both previous and future information simultaneously. To alleviate the information leakage problem caused by the teacher-forcing training strategy and bidirectional decoding, we propose an adapted scheduled sampling technique to prevent the decoders from contacting the actual label. Furthermore, Contextor also features a bidirectional beam search algorithm to better interact with both decoders. Experimental results demonstrate that our approach outperforms the state-of-the-art baselines.

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.

Miniaturized low‐profile ultra‐wideband circularly polarized archimedes spiral antenna backed by an AMC reflector

AbstractA low‐profile ultra‐wideband (UWB) circularly polarized antenna is proposed in the form of a planar Archimedes spiral structure backed by an artificial magnetic conductor (AMC). To expand its bandwidth and minimize its size, the antenna is loaded with resistors and a metal ring near the end of the spiral arms. At the same time, the bidirectional beam is transformed into a unidirectional beam using the phase compensation mechanism by introducing an AMC reflector. The antenna achieves −10 dB impedance bandwidth and 3 dB AR bandwidth in 0.7 ~ 10.2 GHz (174.3%), with a height of only 0.035 wavelengths at 0.7 GHz, which shows advantages over most similar designs. Finally, the antenna is fabricated and measured to prove its effectiveness.

Research on bidirectional beam tracking and performance analysis of optical communication system with microvibrations

AbstractThe impact of tracking errors over the vibration interference is investigated. A novel expression is presented for the bidirectional laser tracking mechanism which takes in account both periscope communication terminal and beam acquisition process with beaconless technology. In this paper, platform microvibrations are measured and compensated to improve the tracking characteristics of the optical communication terminal. An experiment was conducted to verify the high precision tracking system with the combination of coarse and fine tracking technologies, which represents that the fine tracking error is suppressed to 2.1 μrad. This high precision implementation demonstrates the effectiveness of the tracking control loop, and will contribute to the space laser communication.

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.

Linear phased meta-material incorporated patch antenna array at sub-6 GHz for 5G base stations

ABSTRACT This article presented a four-element dual-band linear phased antenna array operating at sub-6 GHz. The single-element antenna was designed by mounting a double-negative single- layered Complementary Split Ring Resonator (SL-CSRR) on the patch and grounding with a rectangular slot and four SL-CSRR’s array; it was resonated at dual bands 3.43–3.56 GHz and 4.93–5.75 GHz and got size shrinkage of 80.45% with dimensions 0.35λx0.35λx0.028λ mm3. The proposed phased array antenna was resonated in 3.42–3.57 GHz and 4.86–5.74 GHz with central frequencies 3.49 GHz and 5.18 GHz, respectively, with respect to −10 dB impedance bandwidth. It was dimensioned with 0.35λx2.42λx0.028λ mm3. The isolation of > 16 dB, ECC < 0.1, DG ~ 10 dB, CCL < 0.15bits/s/Hz and MEG<-6 dB were achieved. The maximum gain of 8.4dBi and 10.4dBi and maximum efficiency of 81.14%, and 99.12% were achieved over the two resonated bands, respectively. The array antenna excited initially with 0° phase difference was radiated bi-directional beam focused to 0° and 180° in the pattern like a broadside array and with the change of phase difference, the structure capable to focus the beam to ± 90° like end-fire array at 3.49 GHz and it was capable to steer the beam to ± 48.6° at 5.18 GHz. These results demonstrated that the proposed phased array antenna is a good candidate to provide services at base stations for 5 G sub-6 GHz applications. The prototypes of the single-element antenna and four-element phased array antennae were fabricated and tested. The matching of simulation results with measurement one has a good commitment to similarity.

A Pattern-Reconfigurable Endfire Antenna Based on Compact Folded Slot With Vertical Polarization

A pattern reconfigurable antenna with vertical polarization is proposed based on two folded near-coupled slot antennas. To achieve two end-fire beams and a bidirectional beam respectively, a central feeding structure and a reconfigurable feeding strip are designed based on the current reverse principle with the help of PIN diodes. A prototype has been fabricated and measured to validate this design. Three high-quality radiation beams have been obtained. In the two end-fire states, the measured peak gain can reach 7.15 dBi and the front-to-back (F/B) ratio is more than 22 dB at 5.7 GHz. In the bidirectional state, the measured peak gain can reach 3.94 dBi and the F/B ratio is less than 0.3 dB.

Sideband power control in Time-Modulated antenna arrays for bidirectional harmonic beamforming and beam scanning

Beamforming and beam scanning in a specific angular region for establishing a secure communication channel has become the dire need of modern wireless communication system. This paper aims to propose an unconventional yet cost effective solution for beamforming and scanning by controlling the inherent sideband patterns of time-modulated antenna arrays. First of all, beam scanning with different scan angles is targeted by proposing asymmetric sequential time schemes. To achieve that, the phase center of the array is unidirectionally shifted by controlling a cluster of array elements. The idea is to model suitable pulse-shifted time schemes so that a good scanning coverage can be achieved without affecting the shapes of the radiation beam patterns. In this way, simultaneous bidirectional sideband patterns can be controlled for beam scanning. Furthermore, beamforming with enhanced efficiency for single channel secure communication is also addressed in this work by reducing the sideband levels (SBLs) of the array. The same concept of shifting the phase center unidirectionally is used for reducing the SBL, but with a higher number of clusters of array elements. The mathematical validation behind the proposed idea is thoroughly discussed and the closed-form sideband power expression is derived after investigating all possible combinations of pulse-shifted time schemes. 16-element linear timed arrays have been chosen to investigate the proposed idea and the supportive outcomes are presented in detail with comparisons.

Buckling and Post-Buckling of Bidirectional Porous Beam Under Bidirectional Hygrothermal Environment

In this paper, buckling and nonlinear post-buckling behaviors of a bidirectional porous (BDP) beam are investigated under bidirectional hygrothermal environment. Euler–Bernoulli beam theory with the von Kármán nonlinearity is employed to derive the nonlinear variable coefficient governing differential equations based on Rayleigh quotient method. Analytical solutions of critical buckling load and load–deflection equilibrium path in post-buckling are deduced for the single directional varying (SDV) porous beam. The general numerical solutions for bidirectional varying (BDV) porous beam are obtained by differential quadrature finite element method (DQFEM) with Newton–Raphson iteration method based on the variation principle. The high accuracy of the present numerical method with higher computing efficiency is verified by comparison with published reports and the analytical results in this work. Parametric analysis on effects of the porosity bidirectional distributions, porosity coefficients, distributions of hygrothermal environment and boundary conditions on buckling load and post-buckling response is carried out to enhance the buckling and deformation resistances in design, manufacture and usage of porous structures. The results show that the bidirectional porosity pattern, linear and nonlinear hygrothermal distribution and boundary conditions play a significant role on buckling critical external load and critical hygrothermal increments, buckling form and post-buckling path.

Compact, Wideband, Dual-Band Polarization and Pattern Diversity Antenna for Vehicle Communications

A new design approach of dual-band polarization and pattern diversity antenna for vehicle communications is presented. This antenna consists of three essential parts: Monopole array, swastika-shaped gap-coupled patch, and customized L-shaped driven dipole. Firstly, the monopole array composed of four monopoles beneath the patch, is excited by dipole-induced patch mode of the swastika-shaped gap-coupled patch so as to realize bidirectional beam in the upper band. Secondly, the swastika-shaped gap-coupled patch is reused as the main radiator of the lower band to achieve wideband broadside right-handed circular polarization (RHCP) radiation, which is excited by a pair of customized parallel-lines-fed L-shaped driven dipoles. Finally, two short-circuited branches are etched in the long arm of the L-shaped driven dipole, bringing in the out-of-band suppression improvement between the lower and upper bands. In order to verify the developed design method, a dual-band antenna with different polarization and radiation properties over two bands was designed, fabricated, and tested. Measured results indicate that the developed antenna with a compact transversal size of 0.36λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> *0.36λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> radiates broadside RHCP electromagnetic wave in 3.55-4.25GHz and bidirectional vertical polarization (VP) in 5.62-6.38GHz, which covers C-band and DSRC-band, and especially serves as a promising candidate for applications in both vehicle-to-satellite (V2S) and vehicle-to-everything (V2X) communications.

Bidirectional coherent beam combining and turbulence mitigating by phased fiber laser array in a 2 km atmospheric link

We first demonstrated bidirectional coherent beam combining and aberrations mitigating with a 6-aperture phased fiber laser array in urban atmospheric turbulence over 2 km, simultaneously realizing the receiving by optical coherent combining, and efficiently achieving the coherent beam combining at the target. The power of the received combining beam increased about 5.8 times and the combining efficiency was promoted up to about 81.1 %. Based on the optical reciprocity, the control delay induced by double propagations of the target-in-the-loop was reduced and a clear interference pattern with obvious fringe visibility was obtained. These results show great worth to the transceiving of free-space optical communication.

Effect of material distribution on bending and buckling response of a bidirectional FG beam exposed to a combined transverses and variable axially loads

This article considers a bidirectional functionally graded (BDFG) beam with various distributions of volume fraction. The impact of these distributions on the buckling and bending response of BDFG beam with general boundary conditions is investigated via a quasi-3D solution. It is assumed that the beam is exposed to a set of in-plane varying compressive loads and there mechanical characteristics change in both directions. Also, the BDFG beam is considered to be exposed different external mechanical loads. Hamilton’s principle is employed to derive the governing equations, which are then solved using analytical solution to obtain buckling and bending characteristics. The precision of the current formulation is investigated via a comparison with available data in literature. Some numerical results are presented and discussed to assess the effect of different parameters such type of volume fraction, boundary condition, varying load, and beam geometry on the buckling and bending of BDFG beam.

Single-Row Coding Metasurface for Bi-directional Beam Multiplexing in Mid-infrared Regime

Single-Row Coding Metasurface for Bi-directional Beam Multiplexing in Mid-infrared Regime

Reconfigurable Bidirectional Beam-Steering Aperture With Transmitarray, Reflectarray, and Transmit-Reflect-Array Modes Switching

The design and experiment of an electronically reconfigurable bidirectional spatially-fed array are presented, which combines the functionalities of reconfigurable transmitarray (TA), reflectarray (RA), and transmit-reflect array (TRA). First, we demonstrate a novel bidirectional unit cell composed of a tunable resonant layer between a pair of orthogonally oriented metal gratings. Two positive-intrinsic-negative (PIN) diodes are integrated into the tunable resonant layer to achieve the 1-bit phase resolution in either transmission or reflection mode. Based on the proposed unit cell, a 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times16$ </tex-math></inline-formula> -element array arranged in a square grid, which can be controlled independently by a field programmable gate array (FPGA)-based digital control circuit, is excited by a linearly-polarized horn to show the beam steering ability of reconfigurable TA and RA. To realize TRA function integration with the bidirectional beam independent steering simultaneously, the method based on superposition of the aperture fields (SAF) on the aperture is used. In SAF design, the entire aperture is divided into transmission and reflection modes co-existing, and the arrangement and phase distribution are optimized by particle swarm optimization (PSO) algorithm to achieve minimum sidelobe levels (SLLs) and peak gain of bidirectional beam. The measured results of the prototype demonstrate that the antenna can steer bidirectional beam both in simultaneous and time division operating modes, which is not reported to the best of the authors’ knowledge. Our proposed method opens a new avenue for the design of high-performance multifunctional reconfigurable antenna systems.

Full-Vectorial Bidirectional Beam Propagation Method for Nonradiative Dielectric Waveguides

Full-Vectorial Bidirectional Beam Propagation Method for Nonradiative Dielectric Waveguides

Study of crack’s effect on the natural frequencies of bi-directional functionally graded beam

In this article, we analyze the effect of transverse cracks on the natural frequencies of Euler–Bernoulli functionally graded beam, the studied beam was Discretized into finite elements and the global matrices of the governing equation of motion are determined applying the Lagrange's equation on the kinetic and strain energies of the beam. The material properties are considered vary in the both; thickness and width; directions of the beam, the gradation is described by the power–law distribution, the stiffness of the cracked element is determined based on the reduction of the cross section of the beam. The numerical results obtained are compared with those available in previous study. Finally, case studies were conducted to analyze the influence of power law index, depth, and crack location on the natural frequencies of the beam for different boundary conditions; these studies demonstrate the advantage of the bidirectional FG beam over to the pure metallic and unidirectional FG beams.

High-performance dielectric nano-cavities for near- and mid-infrared frequency applications

We present a judicious design approach for optimizing semiconductor nanocavities, starting from single photonic atoms to build photonic molecules functioning as high-performance nanocavities. This design approach is based on exact analytical solutions to the Maxwell equations for collective Mie resonances. Conceptually, we distinguish different concepts of cavity modes including Mie mode, collective Mie mode, photonic-crystal (PC) band-edge mode, and Feshbach-type bound states in the continuum (BIC) mode. Using the design approach, we present a unique structure of nanocavity supporting the Feshbach-type BIC mode, capable of enhancing the emission rate of a dipolar emitter by orders of magnitude. This high-performance nanocavity suppresses radiative loss channels strongly via destructive interference and consequently channels the emission light efficiently into an in-plane bi-directional beam with a divergence angle of 10°. Engineering the geometrical parameters of the nanocavity for near-infrared frequency applications requires a fabrication tolerance of ±5 nm. This high accuracy is challenging for the mass production of devices. The fabrication accuracy can be relaxed greatly for mid-infrared frequency devices. As a showcase, we analyze and optimize the well-known PC L3 defect nanocavity for mid-infrared frequency applications in the framework of Feshbach resonance. We show that the optimal structure of this defect nanocavity requires a fabrication tolerance of ±50 nm. Our nanocavity design approach may be useful for near- and mid-infrared frequency applications.