Typical Beam Research Articles

3D Polarisation of a Structured Laser Beam and Prospects for its Application to Charged Particle Acceleration

A Structured Laser Beam (SLB) is a type of optical beam with spatially inhomogeneous 3D polarisation structures. Generating SLBs from vector beams allows the creation of Hollow Structured Laser Beams (HSLB) with a dark central core. In this way, atypical electric and magnetic field vectors, which are purely longitudinally polarized in the dark zones of the beam, are obtained. The SLB spatial distribution can also include regions with both the electric and magnetic fields longitudinally polarized and oriented in the same or opposite directions. The SLB has a transverse distribution similar to that of a Bessel beam but can theoretically propagate to infinity, therefore giving the potential to generate strong, longitudinally oriented electric fields over long distances, which could possibly allow the acceleration of charged particles. The results of the study of this phenomenon, including simulations of the spatial distribution of the electromagnetic field components, are presented in this paper.

Experimental Investigation into the Flexural Behaviour of Basalt FRP Reinforced Concrete Beams

This study involved conducting four-point bending tests on three types of rebar-reinforced concrete beam: those reinforced with steel bars, those reinforced using basalt fiber-reinforced polymer rods, and hybrid reinforced concrete beams that used both Basalt fiber-reinforced plastic and reinforcing steel. Various reinforcement ratios and configurations were used to analyze mid-span deflection, flexural capacity, fracture distribution, and Basalt FRP bars strain. The results suggest that using a hybrid reinforcement system that combines Basalt fiber-reinforced plastic and reinforcing steel can improve the transverse rupture strength of rebar-reinforced concrete beam, reduce deflection and cracking, and use the high-strength characteristics of Basalt FRP bars.

Study on the Hydrodynamic Performance of the Beam Used in the Antarctic Krill Beam Trawl

The beam trawl is one of the primary operational trawls for Antarctic krill, and its beam provides horizontal expansion support for the trawl net. The hydrodynamic performance of the beam significantly affects the vertical expansion and sinking performance of the trawl, as well as impacts the energy consumption of the fishing vessel. In this study, the beam of the Antarctic krill trawl used on the “Shen Lan” fishing vessel served as a prototype. Three types of beams, cylindrical, airfoil, and elliptical, were designed. The hydrodynamic performances of beams with different shapes at different angles of attack were studied using numerical simulation, and the accuracy of the numerical simulation was validated through the flume test. The results show that the cylindrical beam has a higher drag coefficient and a lower lift coefficient, compared to the airfoil beam and the elliptical beam. Under different angles of attack, the cylindrical beam’s drag coefficient is, on average, 49.54% higher than that of the airfoil beam and 59.74% higher than that of the elliptical beam. Its lift coefficient is 87.79% lower than that of the airfoil beam and 85.06% lower than that of the elliptical beam, respectively. At different angles of attack, the hydrodynamic coefficients of the airfoil beam and the elliptical beam are similar, and their trends, with respect to the angle of attack, are generally consistent. The drag coefficients increase with an increasing angle of attack, while the lift coefficients show a trend of initially increasing and then decreasing with an increasing angle of attack. The absolute values of the lift coefficients for the airfoil beam and the elliptical beam both reach their maximum values at an angle of attack of 45°, with values of 0.703 and 0.473, respectively. Compared to the cylindrical beam, the hydrodynamic performances of the airfoil beam and elliptical beam are superior.

High frequency analysis of the functionally graded sandwich nanobeams embedded in elastic foundations using nonlocal quasi-3D theory

This study focuses on the high frequency analysis of the functionally graded sandwich nanobeams resting on elastic foundations for the first time. In the current work, two types of sandwich structures, namely hard-core and soft-core sandwich beams, are considered. The elastic foundations are modeled using a two-parameter foundation model with a spring layer and a shear layer. For the size-dependent effects, the nonlocal elasticity theory is employed in conjunction with a quasi-3D theory. Hamilton's principle is applied to establish the governing equations of the motion of the nanobeams. A comprehensive parametric study is provided to demonstrate the free vibration behaviors of the sandwich nanobeams in both low and high frequency modes, with more focus on the high frequency analysis. Therefore, the present results contribute to a deeper understanding of the dynamic response of the functionally graded sandwich nanobeams in the high frequency range.

Numerical Beamforming and Parametric Descriptions of Laguerre-Gaussian Vortex Beams

Vortex beams are beams with a helical wavefront that have found applications in optical or acoustic tweezers to manipulate microscopic particles. Vortex beam imposes torque or force to particles, allowing them to trap the object within the beam's field and induce motion or displacement in a non-contact manner. One type of such beam is a Laguerre-Gaussian beam, where the solution of a Gaussian wave is modified by the Laguerre polynomial term that determines the pattern and helical characteristic of the beam. In this paper, a numerical method based on the mathematical expression of the Laguerre-Gaussian beam is implemented to describe how the parameters change the physical behavior of the beam. This work has shown that a straightforward numerical method is capable of producing this kind of beam. Therefore, this approach can be used for generating vortex beams for physical emissions, complex numerical simulations, or demonstrations for teaching purposes

STRENGTH CHARACTERISATION AND CLASSIFICATION OF COMBINED GLULAM BEAM MADE FROM OPEPE (Nauclea diderrichii) AND OBECHE (Triplochiton scleroxylon) TIMBERS

Quality timber species are declining due to over-exploitation in Nigeria. This has propelled the utilisation of low-grade timbers species that are considered for low-end constructions in the past which called for concern. This study establishes the viability of a typical beam made from locally sourced non-durable Obeche (Triplochiton scleroxylon) with highly durable Opepe (Nauclea diderrichii) timber specie in a combined glulam form, using polyvinyl acetate (PVA) adhesive which serves the impact of environmental sustainability and reduced cost of engineering construction. Seasoned timber samples and PVA adhesive were all obtained locally in Nigeria. Beam specimens were tested in the Department of Civil Engineering, Ahmadu Bello University, Zaria according to EN 338 (2009). Based on tests, it is evident that solid Opepe and Obeche timber specimens exhibited more durable characteristics than their homogenous glulam when fabricated with PVA adhesive. The combined Opepe/Obeche (GLc OP/OB) glulam beam specimen was proposed into GL18c strength class according to EN 338 based on minimum constraints which it satisfies, reflecting a 41 % greater Modulus of Elasticity (MoE) in comparison with EN 338 experimental value. This study recommends the enhancement of the bending strength, density and modulus of elasticity of a typical non-durable solid Obeche timber beam by 38 %, 47 % and 35 % respectively with 40 % durable Opepe timber in a combined glulam form using PVA adhesive for engineering construction purposes.

Tunable vortex beams generation in visible band via Pr3+:YLF laser with a spot defect

The generation of optical vortex beams with user-configurable topological charge and spatial profile is a topic of intense research due to the numerous potential applications for these types of laser beams. In this work, we demonstrate the direct generation of vortex laser beams with controllable topological charge and tunable spatial profile from a Pr3+:YLF laser cavity using a spot-defect technique. A theoretical model is established to examine the relationship between the topological charge of the generated vortex beam and how this relates to laser cavity parameters. Experimentally, the selective operation of first- and second-order vortex beams and tunable optical vortex lattices with one to four singularities at 607 nm can be achieved by adjusting the position of the defect spot. This work offers insight into methods for the generation of visible optical vortex beams with controllable topological charge and tunable singularities for a range of applications.

Experimental and numerical studies on unsteady galloping driving mechanism of a truss beam with solid barriers

The long-span bridges with truss beam are widely recognized as typical wind-sensitive structures, and its wind-induced divergence events may become a very predominant issue. This work evaluates the galloping performance of a typical truss beam with wind barriers, which is detected to be susceptible to the infrequent vertical instability at specific attack angles, as evidenced by experimentation and numerical analysis. Since the truss beam constitutes a complex cross section, this study employs energy analysis to distinguish the crucial parts affected by vibration and discovers that the galloping vibration is mostly caused by the surfaces of the deck. Rather than relying on conventional quasi-steady theory, this study explores the unsteady aerodynamic forces to identify the underlying galloping driving mechanism. Our findings reveal that the instigator of galloping instability is the phase rising of lift with increasing wind speed. Additionally, the nonlinear mechanical damping is not a decisive parameter. Furthermore, we have investigated the impact of an essential ancillary facility, the wind barrier, and discovered that its galloping stability can be enhanced by increasing its porousness and decreasing its height. However, the underlying mechanisms behind this improvement are distinct.

Fractional-order modelling and dynamic analysis on a typical beam structure incorporated with a semi-active particle damping equipment

Semi-active particle damping equipments exhibit considerable adaptability when implemented in flexible structures. However, their dynamic characteristics become complex due to the presence of a substantial quantity of particles within the damping equipment, and the influence of the internal magnetic field necessitates careful consideration. The fractional-order model of this kind of equipment is established, wherein the designed parameters kp and α are respectively associated with the filling ratio and the input current. Depending on the Hertz-Mindlin contact model, the multi-body dynamic issues inner the damping equipment are addressed using the Discrete Element Method, and then the fractional-order parameters kp and α are identified based on the energy distribution observed within a single vibration period. The numerical simulations, conducted using the fractional-order model, show a fundamental consistency with the experimental results. This alignment serves to validate the accuracy and feasibility of the fractional-order model. Finally, the fractional-order model is utilized to investigate the optimized value of the input current and to analyze the motion trajectory of the damping equipment under various scenarios. The results indicate that the optimized input current is approximately 2.5 A; and as the parameter kp and α increase, the motion trajectory of the system will rotate in a counterclockwise direction, accompanied by a gradual outward displacement of the outermost curve relative to the origin position.

Optimization of a YAP(Ce) prompt X-ray camera for imaging with spot scanning proton beams at clinical dose levels

Prompt secondary electron bremsstrahlung X-ray (prompt X-ray) imaging using a low-energy X-ray camera is a promising method for observing the beam shape from outside a subject. However, it has sometimes been necessary to conduct such imaging at a higher dose than the clinical level to acquire images with acceptable quality. To solve this problem, we optimized a prompt X-ray imaging system to use for spot scanning proton therapy system. The new camera had more than one order higher sensitivity to image several types of beams, including those at the clinical dose level. The optimized prompt X-ray imaging system uses a 4 mm diameter pinhole collimator to increase sensitivity, and it is combined with a larger YAP(Ce) scintillator to increase the magnification ratio and thus improve spatial resolution. We used a list-mode data-acquisition system with high count rate capability. Prompt X-ray images were acquired by irradiating a water phantom with proton beams from the spot scanning proton therapy system. Measurements were taken for pencil beams, spread-out Bragg peak (SOBP) beams, and a beam utilized in actual clinical therapy. For all of the beams, we could measure scanning spot images within a spill and evaluate the ranges for the accumulated images at the clinical dose level. From the list-mode data, we measured the temporarily altered positions of the scanning beams as well as the accumulations of the prompt X-ray images. The optimized prompt X-ray imaging system could improve sensitivity while maintaining better spatial resolution. The new system realized prompt X-ray imaging at the clinical dose level and holds promise for future clinical imaging of prompt X-rays.

Impact of laser beam shaping on weld pool and seam geometry in butt-joint welding with filler wire

Beam shaping offers a promising solution to address various challenges in laser-based processes. This study explores the use of an adaptive beam shaping solution using a deformable mirror for high-power continuous wave lasers. Specifically, the impact of three different elliptical beam shapes on weld pool geometry, weld cross section in butt-joint welding with a filler wire is investigated. The results reveal that beam shaping significantly affects the weld pool and cross section, with elliptical beam shapes resulting in wider fusion zones in two tested cases and more uniform weld bead compared to a typical circular beam. These findings highlight the potential of beam shaping for enhancing consistency and quality in laser beam welding.

Simulation of the spatial distribution of scattered light under illumination of a resonant diffraction grating with structured light

In this paper, a comparative theoretical analysis and numerical simulation of the operation of various types of diffraction gratings in the far field is carried out using a Fourier transform. In more detail is discussed the spatial spectrum of binary amplitude gratings, including the diffraction patterns in the far field and in the focal plane and while taking into account variations in the fill-factor. When analyzing characteristics of experimentally created halide perovskite resonant gratings, the influence of the illuminating beam type on the formation of the first three diffraction orders is considered.

Mechanical properties prediction and design of curved beams by neural network

It is known that curved beams are used widely in vibration isolation and noise reduction. The curved beam can show bistable, negative stiffness and other mechanical characteristics in the compression process through design. The preflex beam absorbs energy during the multi-state jump process and can recover its initial configuration after undergoing loading and unloading, so it is an ideal energy absorb component. In this paper, preflex beams are designed and the mechanical properties are studied and predicted by neural network. Firstly, a large number of finite element models for sinusoidal preflex beams are built by using Python randomly selected the parameters of beams. Secondly, the dataset corresponding to the parameters of the beams and mechanical properties is established. The variation trend of mechanical properties such as initial stiffness, force threshold, negative stiffness and total absorbed energy with the change of structural parameters and the sensitivity of structural parameters to the above mechanical indexes are obtained. Thirdly, by substituting the data set into the artificial neural network, the trained neural network can predict the mechanical properties of the beams within the allowable error range. At last, a new type of preflex beam with porous section is proposed in order to optimize the specific absorbed energy of the preflex beam. After data screening and optimization, the specific absorbed energy of the porous preflex beam is increased by 15.56 % compared with the beam whose section without porous. The results obtained show that the data-driven method can greatly shorten the structural design time and expand the design space. This study will provide a theoretical basis for the wider application of preflex beams in engineering field.

Development of a quasi-ring airy vortex beam using an all-dielectric geometric phase metasurface

The quasi-ring Airy vortex beam (QRAVB) is a special type of vortex beam was recently proposed, which performs efficiently in turbulent environments. However, bulky optical elements, such as the spatial light modulator, used for generating the QRAVB hinder its application in modern integrated optical communication devices. Here, we present a type of compact optical element developed for generating the QRAVB by using an all-dielectric geometric phase metasurface. We simulate the performance of the designed metasurface and discuss several properties, such as autofocusing and self-healing of the metasurface-generated beams, are similar to Airy beams. This type of metasurface has potential applications in integrated free-space optical communication and on-chip optical information processing in the future.

Elimination of stochastic traffic flow effects on modal identification of beam type bridge under ambient excitation

Bridge modal parameters identified under ambient excitation are normally used for damage detection and condition assessment. However, stochastic traffic flow is often assumed as part of the ambient excitation without considering its additional mass attribution. This paper investigates the influence of stochastic traffic flow on the modal identification results of beam type bridge under ambient excitation and proposes an elimination method accordingly. Firstly, specific location of stochastic traffic flow acting on bridge is simulated by using cellular automata model. Then, finite element model is established to analyze the effects of stochastic traffic flow on the identified modal parameters of beam type bridge under ambient excitation. Finally, the empirical formula is proposed to eliminate the effects of stochastic traffic flow and verified by field monitoring data of a five-span continuous bridge with variable cross-section.

Improvement on the axial force accuracy of the ANCF Euler-Bernoulli beam element with the second-order approximate function of the centerline and precise constraint equations

The conventional Euler-Bernoulli beam element of the absolute nodal coordinate formulation (ANCF) yields incorrect axial force due to the existence of the first-order approximate function of the centerline and over-constraint equations. This work aims to improve the axial force accuracy of the element by using the second-order centerline approximate function and precise constraint equations. The second-order function includes the quintic Hermite shape function and the vector of nodal coordinates containing zeroth to second-order derivatives of position. The elastic force vector of the element and its tangent stiffness were then formulated based on the decoupled elastic line method. The exact kinematic requirements of three types of constraint points were fully clarified. On this basis, the corresponding concise constraint equations, constraint Jacobian and Hessian matrices were rigorously derived in the context of ANCF, where G2 continuity was demonstrated to be satisfied at the node acted by an inclined concentrated force, the relative rotation constraint of the rigid joint was described using the dot product of the gradients on both sides of the joint, and the fixing gradient direction at the partially-clamped end was expressed by using the zero cross product of the end gradients in the initial and deformed configurations. Large deformation problems of typical beams under fixed and follower loads were solved using five types of elements, where the results of the ABAQUS B22 elements were taken as a reference for validation. It is found that when using the first- and second-order beam elements having over-constraint equations of the three types of constraint points, obvious axial force error occurs near the corresponding constraint points. In comparison, a few second-order elements containing the derived constraint equations output correct axial force consistent with ABAQUS. However, a large number of the first-order elements containing the correct constraint equations still yield inaccurate axial force in certain beam regions.

Thinning of Poly(methyl methacrylate) and Poly(vinyl chloride) Thin Films Induced by High-Energy Ions of Different Stopping Powers.

Ion bombardment is an important tool of materials processing, but usually leads to erosion of the surface and significant thickness reductions when thin layers are used. The growing use of polymer thin films in a variety of applications, from coatings and membranes to biomedical and electronic devices, calls for a deeper understanding of the thinning process induced by energetic ions espe-cially for very thin films. Here, thinning and surface morphology changes induced by high-energy ion bombardment in PMMA and PVC thin films were investigated, focusing on the role of the initial thickness of the films and the stopping power of the ions. We used thin films with initial thicknesses varying from 13 to 800 nm, and light and heavy ions as projectiles in the energy range of 2-2000 MeV, where the electronic stopping dominates. Thickness reductions as a function of fluence were monitored and thinning cross sections were extracted from curves. A supralinear scaling between the thinning cross sections and the electronic stopping power of the beams was observed, with a much enhanced thinning efficiency for the swift heavy ions. The scaling with the stopping power dE/dx is almost independent of the initial thickness of the films. At intermediate and large fluences, changes in the physicochemical properties of the irradiated polymers may modulate and decelerate the thinning process of the remaining film. The importance of this secondary process depends on the stopping power and the balance between erosion and the chemical transformations induced by the beam. We also observe a trend for the thinning efficiency to become larger in very thin films. Depending on the type of beam and polymer, this effect is more or less pronounced. PMMA films irradiated with 2 MeV H+ show the most systematic correlation between initial thickness and thinning cross sections, while in PVC films the initial thickness plays a minor role for all investigated beams.

Research on the Shear Performance of Cold-Formed Thin-Walled Steel-Glued Laminated Wood Composite Beams

This paper proposes a new type of composite box beam combined with cold-formed thin-walled steel and glued laminated timber to develop green building structures while improving the load-carrying capacity of a single steel girder and glued timber girder. Two composite beams composed of laminated timber and Q235 cold-formed thin-walled steel were designed and fabricated. Then, the shear performance test with quadratic loading was carried out to analyze the load carrying capacity, damage modes, and deformation characteristics of the test beams, as well as their influencing factors. Subsequently, a finite element model of the composite beam was established, and the loading mode was the same as that of the test to further study the parameters affecting the shear performance of the composite beam. The results of the study indicate that steel and glued timber in composite beams connected by adhesive bonding can work and deform together under load and each give full play to its material properties, especially the composite beams, which exhibit higher shear strength than a steel or timber beam. The effects of parameters such as steel cross-sectional area, shear span ratio, steel skeleton form, and steel cross-sectional strength on the shear capacity of the composite beams were observed, among which the shear span ratio had the greatest effect on the shear capacity of the composite beams. The shear capacity decreased by 14.3% and 19.5% when the shear span ratio was increased from 1.5 to 2.0 and 2.5, respectively. The shear capacity of the combined composite beams increased by 10.6%, 6.3%, and 5.8% when the thickness was increased from 1.5 mm to 2.0 mm, 2.5 mm, and 3.0 mm, respectively. When the combination of the steel cross-section was a box beam, the overall shear-bearing capacity could be increased by 12% compared with the “I” type composite beam, although its shear stiffness was close to that of the “I” section composite beam.

Design and Experimental Evaluation of a Dual-Cantilever Piezoelectric Film Sensor with a Broadband Response and High Sensitivity.

Cantilever-beam-type PVDF (Polyvinylidene Fluoride) piezoelectric film sensors are commonly utilized for vibration signal detection due to their simple structures and ease of processing. Traditional cantilevered PVDF piezoelectric film sensors are susceptible to the influence of the second-order vibration mode and have a low lateral stress distribution at the free end, which limit their measurement bandwidth and sensitivity. This study is on the design of a dual-cantilever PVDF piezoelectric film sensor based on the principle of cantilevered piezoelectric film sensors. The results of the experiments indicate that, compared to a typical single-arm piezoelectric cantilever beam vibration sensor, the developed sensor has a longer second-order natural frequency that ranges from 112 Hz to 453 Hz, while the first-order natural frequency is maintained at around 12 Hz. This leads to a better ratio of the second-order natural frequency to the first-order natural frequency and a wider frequency response range. At the same time, the sensitivity is increased by a factor of 3.48.

Conical Emission Induced by the Filamentation of Femtosecond Vortex Beams in Water

Conical emission is a typical nonlinear phenomenon that occurs during the filamentation of femtosecond laser pulses in transparent media. In this work, the conical emission induced by two kinds of typical vortex beams (i.e., Laguerre–Gaussian (LG) and Bessel–Gaussian (BG) beams) in water is experimentally studied. By recording the light spots of different spectra components from the supercontinuum induced by the vortex beams, the characteristics of the conical emission induced by femtosecond vortex beams are studied. It is found that the spots of the supercontinuum induced by the two kinds of vortex beams differ greatly from each other. The spots of the supercontinuum induced by the BG beams are a set of concentric rings like a rainbow with a white center, while the white light spots in the case of the LG beams are circular white disks, which are different from the commonly observed white light spots. By measuring the maximum divergence angle, it is observed that the divergence angle increases with a decrease in the wavelength, while it is merely affected by the topological charge, which is explained by the formation mechanism of conical emission in terms of self-phase modulation. Based on the observed results, we discuss the transfer of optical angular momentum during the supercontinuum induced by the filamentation of femtosecond vortex beams. This work may help to better understand the transfer of optical angular momentum in non-optical parametric processes as well as the interaction of high-intensity pulses with matter.