Beam Configuration Research Articles

Direction Error Suppression of Mechanical Wind Sensors by Optimizing the Configuration of Supporting Beams

Direction Error Suppression of Mechanical Wind Sensors by Optimizing the Configuration of Supporting Beams

Intelligent Beam Configuration for Neighbor Discovery in Ad Hoc Networks with Directional Antennas

Intelligent Beam Configuration for Neighbor Discovery in Ad Hoc Networks with Directional Antennas

Genetic algorithm based terahertz multifunctional reconfigurable Dirac semi-metallic coded metasurface

Digitally encoded hypersurfaces show great potential in the field of electromagne-tic wave modulation. Currently, digitally encoded hypersurfaces in the terahertz band are mainly classified into two types: structure-encoded and controllable material-encoded. Once a structure-encoded hypersurface is fabricated, its function is fixed, which makes it difficult to adapt to changing application requirements. In contrast, the controllable material-encoded hypersurfaces can achieve dynamic regulation and multifunctional switching of terahertz beams by changing the external excitation, which shows good reconfigurability. To address this challenge, a Dirac semimetal-based encoded hypersurface is proposed in this paper. The Fermi energy level of the Dirac semimetal is varied by changing the bias voltage, which in turn dynamically adjusts its relative permittivity to obtain the coded unit. Besides, the traditional gradient-phase method encodes arrays by periodically arranging the cell structure, but there are limitations in the flexibility and accuracy of beam modulation. In order to break through these limitations, this paper employs a genetic algorithm for the inverse design of hypersurface coding arrays, which effectively improves the initiative and flexibility of beam modulation. In this paper, a three-layer terahertz-encoded hypersurface unit with a “back” structure composed of Dirac semimetallic materials is firstly designed, and the Dirac semimetallic dielectric constant is dynamically adjusted by using an applied bias voltage, so that the hypersurface unit is at 1.95 THz when the Fermi energy levels are 0.01 eV, 0.05 eV, 0.09 eV, and 0.55 eV can achieve 2bit coding. The results show that, for beam configuration, single-beam and multi-beam (two-beam to five-beam) modulation can be achieved at 1.95 THz within 40° pitch angle and 360° azimuth angle; for vortex beam generation, single-vortex beams with ±1 and ±2 topological charges can be generated, with mode purity exceeding 60%, and single-vortex, double-vortex and triple-vortex beams in pitch angle and 360° azimuth angle can be realised with the vortex-phase convolution. In terms of RCS reduction, in the frequency range of 1.72–2.51 THz, the hypersurface is able to achieve more than 10 dB of RCS reduction, especially in the frequency range of 1.82 THz, the maximum reduction value is up to 27.5 dB. achieves the diversity of functions, but also has a high degree of reconfigurability to meet the needs of complex application scenarios.

Bessel beams as a versatile tool to generate embedded devices in optical glasses

Beam shaping offers many opportunities to both streamline and accelerate laser fabrication processes, closing the gap between lab research and large-scale manufacturing. In the field of embedded devices, a Bessel beam configuration allows for large volume engraving of transparent materials in a single laser pass. In this work, we take advantage of femtosecond Bessel beams with a length of 340 μm and a diameter of 1 μm to generate diffractive elements within three distinct optical glasses. This strategy represents a chemical-free and cost-effective alternative to the conventional manufacturing of holographic elements based on photoresist micro-patterning. Despite the different nonlinear effects taking place in each material, we report the successful fabrication of diffraction gratings operating at either normal or Bragg incidence, with efficiencies in the first combined order of up to 70%. Our experimental results show the potential of Bessel beams as a tool to produce buried light devices in a wide variety of glass materials.

Deterministic and stochastic flexural behaviors of laminated composite thin-walled I-beams using a sinusoidal higher-order shear deformation theory

In this study, a novel sinusoidal higher-order shear deformation thin-walled beam theory is presented to examine the effects of material properties and external load uncertainty on static responses of laminated composite thin-walled beams with open sections. The solution for the deterministic flexural analysis is based on Hamilton’s principle and Ritz-type exponential shape function series. Several mechanical parameters of laminated composite materials are randomized and plugged into the beam solver to investigate the thin-walled beam’s stochastic flexural behaviors. The computational cost and accuracy of the polynomial chaos expansion (PCE) method with both projection and linear regression approaches are presented and evaluated by comparing its results with crude Monte Carlo simulation (MCS). This comparison allows for a thorough assessment of the PCE method’s performance. Additionally, a sensitivity analysis is conducted to compare the relative significance of the uncertainty in material properties and loads on the stochastic responses. The supervised training of the artificial neural network based on the MCS beam data is also conducted and compared to the PCE and MCS methods. The findings about the stochastic outputs are introduced in various statistical metrics and illustrations to demonstrate the influences of material properties’ randomness on different laminated composite thin-walled beam configurations.

The Poynting Vector Field Singularities: Effects of Symmetry and Its Violation

AbstractThe phenomenological theory revealing the generic effects of the problem symmetry, its violation, and energy conservation law on the singularities of the Poynting vector field is presented. The bifurcation scenario of formation (annihilation) of the singularities under variations of the problem parameters is elucidated. The results describe the singularities in scattering a linearly polarized plane electromagnetic wave. However, they are valid for any configuration of the incident beam at its scattering by a subwavelength particle. The author shows that topological changes in the pattern of the Poynting vector field occur through a finite number of pitchfork bifurcations. It means that the patterns are topologically stable under variations of the problem parameter(s) that lie between the bifurcation values. The latter ensures that the discussed topological properties of the problem are robust to weak symmetry violation, which is inevitable in any actual experiment. The general consideration is illustrated by a detailed study of singularities in scattering by an infinite right circular germanium cylinder. The results open the possibility of fitting and controlling radiation patterns on subwavelength scales important for various nanotechnologies.

The coupled band gap of the double beam with attached periodic spring-mass structure

This study presents a novel investigation into the phenomenon of coupled band gaps within double beam structures and achieves the construction of beam configurations featuring inherent coupled band gaps. Initially, the identification of coupled band gaps in double beam structures is discussed, and it is engineered within the low-frequency range by adjusting the thickness ratio of the two beams. Subsequently, double beam models are constructed using various methods. A comparative analysis between the Spectral Element Method and the Plane Wave Expand method validates the existence of coupled band gaps. Furthermore, through systematic exploration using the Plane Wave Expand method, we investigate the effect of different parameters on coupled band gaps. The attenuation properties within the identified coupled band gap are experimentally validated using double beam Finite Element models and a dedicated experiment for forced vibration testing. Consequently, controlled variations in thickness ratio confirm well-defined coupled band gaps exist in conventionally thick beam structures. Within this specific frequency range (254–279 Hz) for the double beam with thicknesses 0.01 m and 0.002 m, respectively, average attenuation rates of −3.79 dB and −11.16 dB are recorded correspondingly. It significantly contributes to applying theories on coupled band gaps to large-scale architectural frameworks.

Design, simulation, and measurement of near-zero-index shells for electromagnetic beam generation

We present design and simulation of three-dimensional (3D) shell structures, which generate directional radiation patterns from isotropic sources thanks to their near-zero-index (NZI) characteristics, as well as realizations of these shells via low-cost 3D printing. Throughout the design process of NZI beam generators, both homogenized structures, for which near-zero relative permittivity and/or permeability values are enforced, and actual models involving periodic arrangements of dielectric rods are considered. Solutions of the electromagnetic problems are obtained by using rigorous implementations of the state-of-the-art surface-integral-equation (SIE) formulations in frequency domain. Iterative solutions of matrix equations derived from SIEs are accelerated by different forms of the multilevel fast multipole algorithm (MLFMA) and suitable preconditioners, when necessary. In the design process of NZI shells, alternative strategies are employed to obtain customized radiation patterns. In this context, various cavities with strong resonance behaviors are designed as source regions. At the same time, outer surfaces are modified to either enhance or suppress outgoing electromagnetic fields. In addition to comprehensive simulations and analyses of NZI beam generators, their capabilities are verified by measurements, specifically at 10.3 GHz, on different prototypes fabricated via 3D printing. Measurements of diverse NZI shell structures are presented to demonstrate that NZI properties can successfully be achieved by well-designed arrangements of dielectric rods with proper materials. The results demonstrate the feasibility of efficient, effective, low-cost, and reconfigurable NZI shells to generate alternative beam configurations that can be useful in a plethora of microwave applications.

Analysis of negative stiffness structures with B-spline curved beams

With unique mechanical properties, negative stiffness (NS) structures have presented significant advantages in energy absorption. In recent years, NS structures consisting of periodically arranged curved beams have attracted comprehensive attention. However, the curved beams of the current report mainly focus on geometrical parameters in specific configurations, and the variety of the reported geometrical configurations of the flexible beams is relatively limited. In this paper, a B-spline curved beam design method is proposed. A static analysis model of a B-spline curved beam is developed to investigate the force-displacement relations of curved beams in different configurations. The configuration for the B-spline curved beam is obtained, and the relation between the geometric parameters and the mechanical properties of the B-spline curved beam is discussed. Then the mechanical properties of NS structures with periodically arranged B-spline curved beams are analyzed by the finite element method, and the experiments verified the correctness of the simulation method. Finally, the force-displacement relation and energy-absorption properties of gradient NS structures with B-spline curved beams are discussed. The results indicate that the NS structure with B-spline curved beams has repeatability and effective energy absorption properties. The deformation form of the NS structure can be modulated by gradient NS design, and the energy absorption properties of the NS structure can be improved effectively. The research can provide a reference for the design of NS structures.

Empirical Analysis of Electron Beam Lithography Optimization Models from a Pragmatic Perspective

Electron Beam (EB) lithography is a process of focussing electron beams on silicon wafers to design different integrated circuits (ICs). It uses an electron gun, a blanking electrode, multiple electron lenses, a deflection electrode, and control circuits for each of these components. But the lithography process causes critical dimension overshoots, which reduces quality of the underlying ICs. This is caused due to increase in beam currents, frequent electron flashes, and reducing re-exposure of chip areas. Thus, to overcome these issues, researchers have proposed a wide variety of optimization models, each of which vary in terms of their qualitative & quantitative performance. These models also vary in terms of their internal operating characteristics, which causes ambiguity in identification of optimum models for application-specific use cases. To reduce this ambiguity, a discussion about application-specific nuances, functional advantages, deployment-specific limitations, and contextual future research scopes is discussed in this text. Based on this discussion, it was observed that bioinspired models outperform linear modelling techniques, which makes them highly useful for real-time deployments. These models aim at stochastically evaluation of optimum electron beam configurations, which improves wafer’s quality & speed of imprinting when compared with other models. To further facilitate selection of these models, this text compares them in terms of their accuracy, throughput, critical dimensions, deployment cost & computational complexity metrics. Based on this discussion, researchers will be able to identify optimum models for their performance-specific use cases. This text also proposes evaluation of a novel EB Lithography Optimization Metric (EBLOM), which combines multiple performance parameters for estimation of true model performance under real-time scenarios. Based on this metric, researchers will be able to identify models that can perform optimally with higher performance under performance-specific constraints.

Changes in Target Coverage and Dose to the Normal Brain during Fractionated Stereotactic Radiotherapy for Metastatic Brain Tumors

Fractionated stereotactic radiotherapy (SRT) has been applied to large brain metastases to reduce the risk of radiation necrosis. For fractionated SRT, potential of interfractional tumor changes during the treatment period, such as tumor size, shape, and geometry, must be considered to improve the tumor local control. Our center performs adaptive re-planning for large brain metastases based on repeat MRI verification with a contrast agent in the middle of the treatment period. Purpose of this study is to evaluate the dosimetric impact of the changes in tumor size, shape, and geometry on the doses to the targets and normal brain in patients with brain metastases undergoing fractionated SRT. Fifteen solitary large intracranial metastatic lesions treated with fractionated SRT were investigated. Standardized planning MRI (MRI-1) and repeat verification MRI (MRI-2) were performed during the middle of the irradiation period. The GTV on the MRI-1 and MRI-2 scans was contoured by the same oncologist. The PTV was created by adding an isotropic margin of 1 mm from the GTV in all directions. Volumetric modulated arc therapy (VMAT) with beam energies of 6 MV (flattening filter-free mode) was used and plans were normalized such that PTV D95% or D98% was equal to the prescribed dose. Beam configuration and intensity on the initial VMAT plan were used to evaluate the dose to the tumor and the normal brain on MRI-2. We evaluated the impact of D98% on the GTV using the plans on the MRI-1 and MRI-2 scans. For the normal brain, the V90%, V80%, and V50% were investigated. The median GTV changed from 9.8 cc (range of 3.2-33.0 cc) to 9.7 cc (range of 2.8-36.5 cc) (p = 0.482). Three and four tumors exhibited volume shrinkage and enlargement changes of >10%. Five tumors exhibited volume shrinkage and enlargement changes of <10%. Three tumors showed no volume changes. Of the 15 large brain metastases, 12 tumors required treatment plan modification. The dosimetric parameters of the GTV, PTV, and normal brain did not significantly differ between the MRI-1 and MRI-2 scans. Regarding the tumor dose, the D98% to the GTV increased in patients with tumor shrinkage because of dose inhomogeneity and decreased in patients with tumor enlargement. The V90%, V80%, and V50% increase with decreasing tumor volumes and were linearly related to the tumor volume difference, with a coefficient of determination of 0.97, 0.98, and 0.97, respectively. Our study demonstrated the usefulness of repeat verification MRI for adaptive radiotherapy in the middle of the treatment period due to changes in tumor size, shape, and geometry in patients with brain metastases. Repeated MRI should be considered to evaluate the dose to the target and normal brain, which improves tumor local control and reduces brain necrosis, to reduce the magnitude of underdosing to the target or overdosing to the normal brain during the treatment period.

Test and design of built-up cold-formed steel-lightweight concrete (CFS-LWC) composite beams

Cold-formed steel (CFS) products are extremely versatile and can be used in multiple applications. To further extend their applicability, this investigation assesses the structural behaviour of innovative built-up CFS-lightweight concrete (LWC) composite beams through experimental testing and numerical modelling. First, four full-scale CFS-LWC simply supported composite beams were tested. The specimens included two distinct configurations of the innovative CFS built-up composite beams. The tested CFS-LWC composite beams comprised a lightweight concrete slab supported by profiled metal decking, connected to a CFS built-up beam using bolted shear studs. Following EN 1994-1-1, the degree of shear connection attained in the specimens ranged from 21 % to 57 %. The test procedure, setup, and collected results are described in detail, including load-bearing capacity, deformation, flexural stiffness, and failure modes. Numerical simulations and calibration against the experimental data were then performed, and the CFS-LWC composite beams with different degrees of shear connections were investigated using the calibrated finite element model. The validity of the available design code for the innovative CFS-LWC composite beams was assessed by comparing experimental findings and analytical predictions using EN1994-1-1 (equilibrium and simplified methods) and AISC 360 methodologies. The results showed that the maximum bending resistance of the composite beam obtained from the equilibrium method of EN1994-1-1 and AISC 360 was unconservative due to the overprediction of shear resistance for the bolted shear connectors. Consequently, a calibrated finite element modelling technique determined the bolted shear connectors’ shear resistance. Finally, the bending resistance design prediction of CFS-LWC composite beams following EN1994-1-1 and AISC 360 methodologies, incorporating the shear connector resistance obtained from simulations, was compared with experimental and numerical results from the parametric study. An excellent agreement was observed between experimental and numerical results with the design predictions according to EN1994-1-1.

Lengthwise Fracture Analysis of Inhomogeneous Viscoelastic Cantilever Beam Subjected to Sinusoidal Strains

This paper describes a research of lengthwise fracture in a viscoelastic inhomogeneous cantilever beam under strain that is a sinusoidal function of time. The beam mechanical behavior is investigated by a model having two linear springs and a linear dashpot. The beam material is continuously inhomogeneous along thickness. Therefore, the modules of elasticity of the springs and the coefficient of viscosity of the dashpot vary smoothly in the thickness direction. The compliance method is applied to derive the strain energy release rate (SERR) for the lengthwise crack in the beam structure. The integral J is applied for verification. The stress-strain-time dependence of the viscoelastic model is used for describing the behavior of the beam when obtaining solutions of the SERR and the J-integral. Solutions are derived for both positive and negative rotation angle of the lower crack arm end (when the angle is positive, the upper crack arm is load free, while at negative angle both crack arms are loaded). The effects of various factors including the sign of the angle of rotation on the SERR are analyzed.

Buckling analysis of multi-span non-uniform beams with functionally graded graphene-reinforced foams

This paper conducts the buckling analysis of multi-span functionally graded (FG) beams reinforced by three-dimensional graphene foams (3D-GFs) restrained by elastic supports. The graphene foams are considered as graded variation in the thickness direction according to four different porosity distributions. The width and height of the non-uniform beams vary in the longitudinal direction in accordance with the power-law principle, and the multi-span beams consist of two types of optional beams. The governing equations of buckling behavior are derived based on the Timoshenko beam theory and the principle of virtual displacements, and solved by the discrete singular convolution (DSC) method. The purpose of this paper is to obtain the critical buckling load of FG 3D-GFs reinforced beams under the consideration of variable cross-section and multi-span beams with 2–4 spans. The effect of porosity coefficients, slenderness ratio, and spring constants on the buckling characteristic also are studied. The results suggest that the taper ratio of beams and the configuration of multi-span beams lead to remarkable changes in the critical buckling load of beams.

Dual beam polarization interferometry for roll angular displacement measurement

This study presents a polarization interferometry-based technique for the measurement of roll angular displacement with high resolution and excellent stability. The proposed technique uses a polarization camera to detect the phases of a light beam passed through a birefringent crystal. Variations in the phase difference are used to determine the angular displacement of the birefringent crystal. The dual beam configuration of the proposed measurement scheme helps to overcome the effects of fluctuating incident angular displacement on measurements of roll angular displacement. In experiments, the proposed system achieved resolution of 0.58 arcsec within a 10-degree measurement range. Disturbance from the incident angular displacement was much lower than that of our previous technique measurement methods. This study also investigated the occurrence of nonlinear periodic system errors. The proposed technique offers several advantages over existing methods, including higher resolution, wider range measurement capabilities, and robustness against external disturbance.

Electro-mechanical behavior of multi-functional glass fiber composites under dynamic Mode-I fracture loading

An experimental study was performed to investigate damage sensing and fracture toughness of multifunctional conductive glass fiber composites under dynamic mode-I fracture loading. Carbon nanotubes (CNTs) were dispersed within the epoxy matrix using a shear mixing and sonicating process. An electrostatic wet flocking process was used to reinforce milled short PAN-based carbon fibers onto each of the layers of glass fiber fabric along the thickness direction in the composites. These layers of flocked fabric were stacked, and a vacuum infusion process was employed to fabricate the composites. The parametric study consisted of two carbon fiber lengths (80 μm and 150 μm) and two fiber densities (1000 fibers/mm2 and 2000 fibers/mm2) and was performed to investigate the damage sensing capabilities of a three-dimensional conductive network generated through CNTs and carbon fibers. A double cantilever beam (DCB) configuration was considered, and a modified Hopkinson pressure bar setup along with a high-speed camera was used to investigate dynamic fracture toughness of the composites. The piezo-resistance response of the composites during dynamic fracture was measured using a modified system of four probes. For comparison, composites were also characterized for fracture toughness and piezo-resistance under quasi-static fracture loading conditions. The addition of short, milled PAN-based carbon fibers significantly increased the fracture toughness of glass/epoxy composites. The piezo-resistance response of the composites was easily correlated with instances of sudden crack growth during static fracture loading.

Flexural resistance of Cold‐formed steel‐lightweight concrete (CFS‐LWC) composite beam

AbstractThis paper discusses the flexural behaviour of innovative built‐up cold‐formed steel lightweight concrete (CFS‐LWC) composite beams through an experimental study. Two full‐scale CFS‐LWC composite beams were tested. The specimens included two distinct configurations of the innovative CFS composite beams. The tested CFS‐LWC composite beams consisted of a lightweight concrete slab supported by profiled metal decking, connected to a CFS built‐up using bolted shear connectors. Two degrees of shear connection were considered. The specimens were uniformly loaded, and the load was increased until failure occurred. The test procedure, setup, and results were recorded in detail, including load‐bearing capacity, deformation, and failure modes. The validity of the design predictions following EN 1994‐1‐1 for the innovative CFS‐LWC composite beams was investigated. Both equilibrium and simplified methods were used to predict the bending resistance of the CFS‐LWC composite beam. The results showed that the design predictions following EN 1994‐1‐1 (equilibrium method) accurately predicted the bending resistance of the CFS‐LWC composite beam, while the simplified method underpredicted the experimental results.

Large-incidence-angle multiple-beam two-plasmon decay instability in inertial confinement fusion

A multi-dimensional code FLAME-MD solving fluid-like laser-plasma instabilities' (LPIs) equations has been developed and is used to study multiple-beam two-plasmon decay (TPD) instability relevant to a laser-entrance-hole window burn-off scenario in inertial confinement fusion (ICF) experiments. It is found that TPD can be collectively driven by multiple beams incident at large incidence angles with respect to the electron density gradient at a very low threshold. The polarization configuration of the laser beams is a key factor determining the way of sharing common daughter electron plasma waves (EPWs). The p-polarized beams arranged on the same incidence cone can collectively drive common EPWs along the cone axis. The common-wave sharing mechanisms among the s-polarized beams are largely dependent on the geometry of the beams and are less robust. The simulation results also show that the p-polarized beams are dominating the multiple-beam TPD processes. The common EPWs along the cone axis can accelerate energetic electrons toward the capsule inside the hohlraum and, therefore, pose a fuel-preheat risk to ICF implosions.

Three-dimensional printed microcantilever with mechanical metamaterial for fiber-optic microforce sensing

Mechanical metamaterials can adjust mechanical properties of structures flexibly through a mechanical structural design based on the premise that the materials remain unchanged. Here, a cantilever probe microstructure is designed using mechanical metamaterials for an optical fiber microforce sensor tip that can be prepared by femtosecond laser-induced two-photon polymerization. The elastic constant k of the fabricated fiber-optic microforce sensor has been adjusted by two orders of magnitude from 0.165 to 46 N/m, and the geometric configuration of the cantilever beam can be tailored to match the mechanical properties of biological specimens. This fiber microforce sensor shows an ultra-high force sensitivity of 154 nm/µN and a force resolution of up to 130 pN. The optical fiber microforce sensor that shows the lowest force resolution in a direct-contact mode has high potential for biosensing applications, and the results reveal a potential design strategy for special scanning tunneling microscope probes with unique physical properties.

Flexible Generation and Manipulation of Microwave Bottle Beam Using a Reconfigurable Metamirror

Bottle beams have drawn considerable research interest due to their attractive features and applications in beam trapping. Herein, the flexible generation and modulation of bottle beams utilizing a reconfigurable metamirror over a non‐negligible frequency band ranging from 8.5 to 9.5 GHz is investigated. A varactor diode is embedded into each meta‐atom on the metamirror enabling the achievement of a nearly 2π phase coverage by varying the external bias voltage. Based on the caustic theory, several configurations of bottle beam with distinct radius a are realized as proof‐of‐concept validation. Besides, the flexible modulation of the operating frequency is analyzed by judiciously controlling the bias voltages applied to the metasurface. The experimental results are in good agreement with those obtained from numerical simulations. Such a flexible bottle beam generator shows good potential in the microwave regime for near‐field applications, such as imaging and power transmission.