Unidirectional Beam Research Articles

Methodology study for determining the half-value layer using the Monte Carlo code PHITS

For most purposes, the quality of a beam can be specified in terms of the half-value layer (HVL), which is the thickness of material required to reduce the air kerma to half, at one meter from the source, from a unidirectional beam of infinitesimal width. Just like many other radiological quantities of interest, the HVL can be estimated via simulations employing the Monte Carlo Method (MCM). Among the variety of MCM based codes available, the Particles and Heavy Ions Transport Code System (PHITS) was the one adopted in this study. Primarily, simulations were conducted to determine the X-ray spectra resulting from the interaction of electron beams with different energies with a tungsten anode. Each of these spectra was then defined as a probability distribution for the photon source energies in a second round of simulations, where it was possible to estimate the X-ray beam qualities as specified by the reference literature. At this stage, it was possible to estimate the mean energy of the beam and the conversion coefficient for air kerma per unit fluence for each of the qualities. The results obtained in this phase were used to define the sources for other groups of simulations, where the air kerma was quantified for each source configuration, for different thicknesses of an aluminum metallic attenuator, which was also done with spectra for the same X-ray beam qualities obtained from a reference catalog. Curve fitting on the scatter of kerma points as a function of attenuation allowed the estimation of the HVL. The results obtained are consistent with the values described in the literature and demonstrate the efficiency of the developed methodology, as well as the use of the code in the evaluated energy range for X-rays.

The effect of fiber bridging on mode I fatigue delamination propagation—Part II: Cohesive zone model

AbstractThis is Part II of a series of two papers in which the effect of fiber bridging on fatigue delamination propagation is assessed. In Part I, unidirectional double cantilever beam specimens composed of the carbon fiber‐reinforced polymer prepreg AS4/8552 were tested by means of fatigue cycling. Fiber bridging in beam specimens composed of unidirectional plies causes the apparent fatigue delamination curves to exhibit growth which is slower than that for the case when fiber bridging does not occur. Generally, fiber bridging does not occur in laminate structures. In Part II of this study, a cohesive zone model (CZM) is developed and used to carry out finite element analyses to simulate the experiments. The CZM is employed to quantify and eliminate the contribution of fiber bridging to the fatigue delamination growth curves. In this way, more realistic results are obtained. These results are compared to an upper bound curve determined in Part I.

The effect of fiber bridging on mode I fatigue delamination propagation—part I: Testing

AbstractThe purpose of this investigation is to assess the effect of fiber bridging on fatigue delamination propagation. Fiber bridging occurs when testing beam type laminates specimens consisting of unidirectional plies. Unidirectional double cantilever beam specimens composed of the carbon fiber reinforced polymer prepreg AS4/8552 were tested by means of fatigue cycling. A Paris relation was determined based on these tests. Fiber bridging in beam specimens composed of unidirectional plies causes the apparent fatigue delamination curves to exhibit slower growth predicting overly conservative results. In Part I of this study, the effect of fiber bridging was eliminated experimentally from the results. In Part II of this study, a cohesive zone model is developed and used to carry out finite element analyses to simulate the experiments, as well as to eliminate the influence of fiber bridging.

Analytical determination and numerical validation of the shear factor in annular sector cross sections

In the present study, the shear factor of an annular sector cross section, including the thickness effect, has been analytically determined for the first time. The shear factors depend on the angle of the sector and on the mean radius to thickness ratio. Two approaches were used to determine circumferential and radial shear stresses. The limits of validity of the approach were established, based on the similarity of the shear factors determined from both approaches. The results obtained from the present analytical approach were compared with the results of another analytical approach developed for thin sections. To check the suitability of analytically determined shear factors, unidirectional composite cantilever beams have been analysed by the finite element method, for different cross sections and cantilever lengths. With the material properties and displacement at the cantilever tip known, shear factors were determined and compared with those obtained from the analytical approach. The script used to calculate the shear factors is included as an appendix.

Metasubstrate-based SH guided wave piezoelectric transducer for unidirectional beam deflection without time delay

Focusing the energy of a guided wave along a desired direction is of great significance in structural health monitoring (SHM), since it can improve the sensitivity to defects and reduce the complexity of signal interpretations. The phased array method is the most common approach for beam deflection, which requires a high uniformity of each element and the support of expensive and complex electronics. Moreover, the mirrored wave beam cannot be avoided for a linear array, resulting in the difficulty of distinguishing the defects at the symmetric positions. In this work, a metasubstrate-based piezoelectric transducer (MSBPT) is developed for unidirectional SH0 wave (the fundamental shear horizontal wave) beam deflection under a single driving source. The proposed MSBPT is constituted by a metasubstrate and two columns of thickness-shear mode PZT wafers. The metasubstrate is designed to provide the required phase gradient for unidirectional beam deflection, so no extra time delay is needed during excitation and reception. An analytical model is proposed to guide the design of the transducer to obtain the desired wave beam. The beam deflection properties of the MSBPT are validated by finite element simulations and experiments. It is observed that the MSBPT can concentrate the energy of the generated SH0 mode only in one desired direction with a small divergence angle. Moreover, the MSBPT can also serve as a sensor that only receives the SH0 mode propagating from the deflection angle and filters out the wave energies from other incident angles. Due to the simple configuration, the proposed MSBPT will be helpful in the controllable generation and reception of SH0 mode in SHM.

Regarding the Theory of Power Lines Emission Propagation to the Space

AbstractThe analytical theory is presented that describes the propagation of power lines emission (PLE) with frequency of 50/60 Hz in the heights range from the Earth surface to the magnetosphere. Validation of the theory is made by the comparison with earlier published results of numerical modeling. It is shown that the actual source of emission is a magnetic dipole formed by the power line current and by the secondary image current in the ground. The emission is propagating to the lower boundary of ionosphere, where its main part is reflected back, but some of the energy (a few percent) penetrates into the ionosphere. There it is transformed into a quasi‐flat whistler wave. The generation of current in ground and the reflection from the ionosphere are the main factors that reduce the emission into space. In the ionosphere wave fronts propagate approximately vertically, and the energy propagates in a certain direction that depends on the geomagnetic field inclination. Thus, the ionosphere acts as a focusing system that collects PLE into a unidirectional beam. The PLE intensity does not change with altitude within the total range of ionospheric heights. In the magnetosphere PLE is transformed to both magnetosonic and Alfvén waves and the emission splits into two rays: one propagates along the wave vector and the other one—along the geomagnetic field lines. A set of analytical solutions is presented allowing determining the change in PLE parameters with altitude depending on the source parameters and ionospheric conditions.

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.

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.

Tunable Narrowband Carbon Quantum Dots Laser Based on Self‐Assembled Microstructure

AbstractPhotonic integrated circuits (PICs) are coupled with the laser to create active devices for optical communication, optical interconnection, and optical computing. Consequently, the light source remains a focal point of extensive research and development. Currently, the utilization of carbon quantum dots as a gain medium in photonic cavity lasers is accomplished and suggested as a viable approach for achieving active PICs. Nevertheless, challenges persist in achieving narrowband lasing beam output in one direction that is real‐time tunable while minimizing energy losses. These issues represent an active area of ongoing research. This article presents a self‐assembled microstructure and proposes a method for obtaining tunable, narrowband, unidirectional lasing beams. The objective is to stimulate further development in integration of PICs with lasers, extending beyond these applications, to realize substantial performance gains, eco‐friendly solutions, and efficient mass production.

Fatigue delamination behavior in composite laminates at different stress ratios and temperatures

This study provides an investigation on mode I fatigue delamination growth (FDG) with fibre bridging at different R-ratios and temperatures in carbon-fibre reinforced polymer composites. FDG experiments were first conducted at different temperatures of R-ratios 0.1 and 0.5 via unidirectional double cantilever beam (DCB) specimens. A fatigue model, employing both the strain energy release rate (SERR) range and the maximum SERR around crack front as similitude parameter, was proposed to interpret FDG behavior. The use of this model can collapse FDG data with fibre bridging at different R-ratios into one master curve, obeying well with the similitude principles. Accordingly, it was found that FDG can accelerate with elevated temperature, but decrease at sub-zero temperature. Furthermore, there are strong correlations between the fatigue model parameters and temperature using this model in FDG interpretations. Taking these correlations into account can extend the model to accurately predict FDG behavior of other temperatures. Fractographic examinations demonstrated that temperature has effects on the FDG damage mechanisms. Both fibre/matrix interfacial debonding and matrix brittle failure were observed in FDG of −40℃. Fibre/matrix interfacial debonding becomes the dominant failure in FDG of RT and 80℃. No obvious difference on the fracture morphology was identified for FDG at different R-ratios of a given temperature.

Real-time-controlled artificial quiet channel for acoustic cloaking under varying detection conditions

We consider the problem of hiding non-stationary objects from acoustic detection in a two-dimensional environment, where both the object’s impedance and the properties of the detection signal may vary during operation. The detection signal is assumed to be an acoustic beam created by an array of emitters, which scans the area at different angles and different frequencies. We propose an active control-based solution that creates an effective moving dead zone around the object, and results in an artificial quiet channel for the object to pass through undetected. The control principle is based on mid-domain generation of near uni-directional beams using only monopole actuators. Based on real-time response prediction, these beams open and close the dead zone with a minimal perturbation backwards, which is crucial due to detector observers being located on both sides of the object’s route. The back action wave determines the cloak efficiency, and is traded-off with the control effort; the higher is the effort the quieter is the cloaking channel. We validate our control algorithm via numerical simulations in a two-dimensional acoustic waveguide, testing variation in frequency and incidence angle of the detection source. Our cloak successfully intercepts the source by steering the control beams and adjusting their wavelength accordingly.

Unidirectional beam splitting in acoustic metamaterial governed by double fractional stimulated Raman adiabatic passage

In this work, we take fractional stimulated Raman adiabatic passage (f-STIRAP) for the design of functional acoustic waveguide (WG) coupler into account. Assisted by the agreement in the form between Schrödinger equation in quantum mechanics and the coupled-mode equation of classical waves, the quantum three-level system is mapped onto the acoustic three-WG system with space-varying coupling actions between composing WGs. The output port of the coupler can be selected by adopting different superposition forms of incident waves, which is utilized to build a one-way acoustic mode converter based on double f-STIRAP. By further constructing a functional acoustic metamaterial arrayed by mode converters, a desired beam splitting behavior can be generated unidirectionally in a broadband. Our work bridges f-STIRAP and the design of acoustic metamaterial, which may have profound impacts on exploring quantum technologies for promoting advanced acoustic functional devices with simple configuration and excellent performance.

Analisis Karakteristik Aliran Irigasi Perforasi Pada Lahan Datar

Perforation irrigation is a unidirectional beam irrigation system that can be used for crop irrigation on dry land, due to the efficient use of water and the ability to wet land with a limited area. Therefore, the perforation irrigation system needs to be studied further in relation to the area of land that can be irrigated and the distribution of discharge to each perforated pipe. By testing several variations of the water level, the perforation irrigation emission capability will be obtained in the form of irrigation distribution, uniformity, emission capability and discharge amount used in irrigation on flat land. This study aims to determine the perforation irrigation capacity on flat land, the distribution of irrigation and the amount of discharge required. The test was carried out on three perforated pipes made of ½” PVC as lateral pipes, three transmission pipe length variations, such as 0.8m, 1m, and 1.2m with a distance between the perforations of 60 cm. The source of irrigation water comes from a 3 m tall tower with a capacity of ± 200 𝑙𝑖𝑡𝑒𝑟. The test uses three variations of head height, namely h1 350 cm, h2 360 cm, h3 370 cm and h4 380 cm. The results showed that the perforation irrigation jet length was around 100cm -120 cm, the uniformity of CU irrigation was above 97% with a total discharge on h1 QT = 0.689 lt/s, h2 QT = 0.690 lt/s , h3 QT = 0.695 lt/s and on h4 QT = 0.701 lt/s. While the range of flow rates for perforation 1 pipe Q1 (0.42 lt/s – 0.429 lt/s), perforation 2, Q2 (0.13 -0.145 lt/s) and perforation 3, Q3 (0.129 - 0.135 lt/s)

Toughness Amplification via Controlled Nanostructure in Lightweight Nano-Bouligand Materials.

The enhanced properties of nanomaterials make them attractive for advanced high-performance materials, but their role in promoting toughness has been unclear. Fabrication challenges often prevent the proper organization of nanomaterial constituents, and inadequate testing methods have led to a poor knowledge of toughness at small scales. In this work, the individual roles of nanomaterials and nanoarchitecture on toughness are quantified by creating lightweight materials made from helicoidal polymeric nanofibers (nano-Bouligand). Unidirectional ( = 0°) and nano-Bouligand beams ( = 2°-90°) are fabricated using two-photon lithography and are designed in a micro-single edge notch bend (µ-SENB) configuration with relative densities between 48% and 81%. Experiments demonstrate two unique toughening mechanisms. First, size-enhanced ductility of nanoconfined polymer fibers increases specific fracture energy by 70% in the 0° unidirectional beams. Second, nanoscale stiffness heterogeneity created via inter-layer fiber twisting impedes crack growth and improves absolute fracture energy dissipation by 48% in high-density nano-Bouligand materials. This demonstration of size-enhanced ductility and nanoscale heterogeneity as coexisting toughening mechanisms reveals the capacity for nanoengineered materials to greatly improve mechanical resilience in a new generation of advancedmaterials.

A low‐profile wideband spiral antenna with multiple stopbands

AbstractA low‐profile spiral antenna with three stopbands (2.55 GHz band, 3.85 GHz band, and 5.45 GHz band) is developed. The stopbands are generated using three pairs of slots cut into the spiral arms. The antenna height is 0.077 wavelength at a low band edge frequency of 2 GHz. Firstly, the effects of the slot dimensions (length, width, ending angle, and position) on the stopbands are analysed, where the spiral antenna floating in free space radiates a bi‐directional beam. It is found that the stopband centre frequency is determined by the slot length, and the stopband bandwidth is determined by the slot width, ending angle, and position. Secondly, the fabrication tolerances are investigated. Thirdly, the bi‐directional beam from the floating spiral antenna is transformed into a unidirectional beam by using a low‐profile cavity. It is revealed that three stopbands are maintained. Finally, a prototype of the antenna is fabricated and measured to verify the analysed results.

An End‐Fed Programmable Metasurface Based on Substrate Integrated Waveguide for Novel Phased Array

A programmable metasurface antenna based on electrically tunable elements operating in 5G millimeter‐wave band, which has the features of low cost, easy manufacturing, low profile, easy integration with planar circuits, is proposed herein. The prototype consists of a 128‐element metasurface array, an 8‐channel beamforming chip as equal amplitude power divider networks, and a control network. Elements mounted with varactors to realize different states are controlled by DC bias signal from the back of a printed circuit board (PCB). By assigning different voltage values, array coding can be dynamically changed, thereby realizing beam steering. Both element dimensions and its location along substrate integrated waveguide (SIW) are optimized to better antenna performance. Experiment results show that the proposed metasurface can achieve not only the scanning range of ±70° for unidirectional beam in azimuth and ±40° in elevation but also ±50° for dual beam in azimuth. The whole prototype is fabricated based on PCB technologies, and good agreements among simulated and measured results are obtained. The proposed electrically tunable metasurface array is a good alternative to the traditional expensive phased array and has a great potential application prospect in radar and communication systems.

Feasibility of a multigroup Boltzmann–Fokker–Planck solution for electron beam dose calculations

Legacy nuclear-reactor Boltzmann solvers start clinical deployment as an alternative to Monte Carlo (MC) codes and Fermi–Eyges semiemprical models in radiation oncology treatment planning. Today’s certified clinical solvers are limited to photon beams. In this paper, ELECTR, a state-of-the-art multigroup electron cross sections generation module in NJOY is presented and validated against Lockwood’s calorimetric measurements, EGS-nrc and GEANT-4 for 1–20 MeV unidirectional electron beams. The nuclear-reactor DRAGON-5 solver is upgraded to access the library and solve the Boltzmann–Fokker–Planck (BFP) equation. A variety of heterogeneous radiotherapy and radiosurgery phantom configurations were used for validation purpose. Case studies include a thorax benchmark, that of a typical breast Intra-Operative Radiotherapy and a high-heterogeneity patient-like benchmark. For all beams, 100% of the water voxels satisfied the American Association of Physicists in Medicine accuracy criterion for a BFP-MC dose error below 2%. At least, 97.0% of adipose, muscle, bone, lung, tumor and breast voxels satisfied the 2% criterion. The average BFP-MC relative error was about 0.56% for all voxels, beams and materials combined. By irradiating homogeneous slabs from Z=1 (hydrogen) to Z=99 (einsteinium), we reported performance and defects of the CEPXS mode [US. Sandia National Lab., SAND-89-1685] in ELECTR for the entire periodic table. For all Lockwood’s benchmarks, NJOY-DRAGON dose predictions are within the experimental data precision for 98% of voxels.

Evaluation of the effect of fiber bridging on mode I quasi‐static testing

AbstractThe purpose of this investigation is to evaluate the contribution of fiber bridging to the energy release rate of a fracture resistance curve. Fiber bridging occurs when testing beam‐type specimens consisting of unidirectional plies in a laminate. Unidirectional double cantilever beam specimens composed of the carbon fiber reinforced polymer prepreg AS4/8552 were tested using standard methods. In addition, a cohesive zone model was developed and used to carry out finite element analyses on the tested specimens. It was employed to calculate the contribution of fiber bridging to the ‐curve which was determined from the tests. Fiber bridging in beam specimens increases the apparent fracture toughness of a composite laminate. A method has been proposed for evaluating its contribution to the energy release rate. In that way, an ‐curve may be determined for which the effect of fiber bridging is eliminated.

Prototype of a unidirectional magnetic field-applied fast atom beam source for surface-activated bonding

Prototype of a unidirectional magnetic field-applied fast atom beam source for surface-activated bonding

Nonlinear vibration analysis of carbon fiber-reinforced composites with frequency-dependence and strain-dependence: Experimental and theoretical studies

In this paper, with 3 kinds of carbon fiber unidirectional composite beams as test specimens, a test system based on the resonance method is established to test both the frequency-dependence and strain-dependence for carbon fiber-reinforced composites. The test captures the variations of relevant mechanical parameters for carbon fiber-reinforced composites with frequency and strain under vibration load. The expressions of frequency-dependence and strain-dependence for relevant mechanical parameters obtained by testing data processing and numerical fitting are introduced into the numerical models for 2 kinds of carbon fiber-reinforced composite plates with different fiber alternating laying modes. The comparison of the results from the numerical analysis and the corresponding experimental tests verifies the correctness and applicability for the expressions describing the two dependency characteristics. Obviously, clarifying the laws of the mechanical parameters of carbon fiber-reinforced composites varying with frequency and strain has guiding significance for the design of carbon fiber-reinforced composite structures subjected to vibration loads.