Off-axis Angle Research Articles

Broadband Multi-layer Anti-reflection Coatings with Mullite and Duroid for Half-wave Plates and Alumina Filters for CMB Polarimetry

A broadband two-layer antireflection (AR) coating was developed for use on a sapphire half-wave plate (HWP) and an alumina infrared (IR) filter for cosmic microwave background (CMB) polarimetry. Measuring tiny CMB B-mode signals requires maximizing the number of photons reaching the detectors and minimizing spurious polarization due to reflection with an off-axis incident angle. However, a sapphire HWP and an alumina IR filter have high refractive indices of \(\simeq\) 3.1, and an AR coating must be applied to them. Thermally sprayed mullite and Duroid 5880LZ were selected in terms of index and coefficient of thermal expansion for use at cryogenic temperatures. With these materials, the reflectivity was reduced to about 2% at 90/150 GHz and <1% at 220/280 GHz. The design, fabrication, and optical performance evaluation of the AR coatings are described. The coatings were used in a current ground-based CMB experiment called the Simons Array. Also, they could be applied to next-generation CMB experiments, such as the Simons Observatory.

Off-axis tearing properties of the biaxial warp-knitted fabrics

This study presents an experimental and analytical investigation of the tearing properties of the biaxial warp-knitted fabrics with different off-axis angles. Firstly, the off-axis tensile tests, central tearing tests, single edge notch tearing tests, and trapezoidal tearing tests were carried out at seven off-axis angles. The strength, failure mode, and failure mechanism of the specimens under each test condition were studied. The results show that in the off-axis tensile tests, the lowest values of the tensile strength of the biaxial warp-knitted fabrics appear at the off-axis angles of 15° and 75° rather than the conventional 45°. Under the coupling effect of tensile strength and shearing strength, the yarn layers peeling occurs instead of yarn fracture, which is a unique failure mode of biaxial warp-knitted fabrics. The yarns of the biaxial warp-knitted fabrics can fully deform to balance the load due to the warp-knitting method, which improves the tearing strength and makes the failure brittle.

Preparation of β-Ga2O3 films on off-angled sapphire substrates and solar-blind ultraviolet photodetectors

β-Ga2O3 films have been prepared on (0001) sapphire substrates with different off-axis angles toward by sol–gel method and the solar-blind ultraviolet photodetectors (PDs) with metal-semiconductor-metal structure have been fabricated on these films. The effects of off-angled sapphire substrates on the surface morphology and crystal quality of β-Ga2O3 films have been systematically investigated. All the results indicate that to some extent the larger off-angled sapphire substrate could lead to the smoother surface morphology and higher crystal quality of β-Ga2O3 films. Reduction in the numbers of in-plane rotational domains for β-Ga2O3 films on off-angled substrates may result in the above-mentioned improvement, which have been confirmed by x-ray diffraction ϕ-scan. β-Ga2O3 film grown on ∼7° off-angled sapphire substrate has () preferred orientation with the single-domain growth mode. Besides, the performance of β-Ga2O3 PDs fabricated on different off-angled substrates show the same trend with changing the off-axis angles. The β-Ga2O3 PD fabricated on ∼7° off-angled sapphire substrate has excellent optical characteristics with large photocurrent to dark current ratio of 430.53 and high UV–visible rejection ratio of 1.42 × 103. These results would be helpful for improving the crystal-quality of hetero-epitaxy β-Ga2O3 films by using off-angled sapphire substrates and fabricating the cost-effective mass-producible solar-blind ultraviolet PDs by sol–gel method.

Off-Axis Compressive Behaviour of Fibre Reinforced Thermoplastic Composites.

This paper presents an experimental investigation on the mechanisms of damage onset and evolution in unidirectional PEEK/AS4 carbon fibre reinforced thermoplastic (CFRTP) composites subjected to off-axis compressive loadings. A test fixture was designed to prevent buckling, splitting, and end collapsing of the specimens during the test. A series of compression tests were conducted with specimens of various off-axis angles. The displacement and strain fields of all specimens during the tests were evaluated by the digital image correlation (DIC) method. In combination with the DIC results, the influence of the off-axis angles on the failure mechanisms and nonlinear stress–strain responses were analysed. The corresponding failure mechanisms were examined by scanning electron microscopy (SEM). The fracture angles of the tested specimens were evaluated and analysed according to Puck’s theory. The off-axis compression failure envelope based on LaRC05 and Hashin criteria was presented and compared to the experimental results. It was shown that the LaRC05 criterion can provide accurate predictions when the off-axis angle is larger than 15°. The complex failure mechanisms were analysed to better understand the effect of ductility of the thermoplastic matrix to the composites. The series of tests provide an experimental failure envelope in combined stress states and can be used for the evaluation of failure theories and the criteria of thermoplastic composites.

Mechanical response and damage mechanism of 2D woven SiCf/SiC ceramic matrix composites under tension-shear coupling load

The macroscopic mechanical behavior and coupling damage mechanism of 2D woven SiCf/SiC ceramic matrix composites (CMC) prepared by chemical vapor infiltration (CVI) process under tension-shear coupling load were experimentally analyzed. At macroscale, the uniaxial tension, uniaxial shear and off-axis tension tests were completed and the results were compared. The tensile modulus and proportional limit have no significant difference with the increase of off-axis angle, while failure strength decreases by 22.3% compared the 45° tensile (165.4 MPa) with the 0° tensile (212.8 MPa). Based on the strain-difference analysis, the coupling damage effect of SiCf/SiC-CMC was characterized. At microscale, the main damage types of SiCf/SiC-CMC during loading were analyzed by scanning electron microscope (SEM), and the corresponding laws between micro damage development and macro mechanical behavior under different loading conditions were revealed by cluster analysis of acoustic emission (AE) signals. The test results show that the micro damage caused by tensile and shear stress components promote each other. The macro mechanical behavior of SiCf/SiC-CMC under complex loading is controlled by basic micro damage forms such as matrix cracking, interface debonding and fiber fracture. The tension-shear coupling load affects the evolution process of the basic damage forms, and then change the macro properties of SiCf/SiC-CMC.

Multiplexed Holographic Combiner with Extended Eye Box Fabricated by Wave Front Printing

We present an array-based volume holographic optical element (vHOE) recorded as an optical combiner for novel display applications such as smart glasses. The vHOE performs multiple, complex optical functions in the form of large off-axis to on-axis wave front transformations and an extended eye box implemented in the form of two distinct vertex points with red and green chromatic functions. The holographic combiner is fabricated by our extended immersion-based wave front printing setup, which provides extensive prototyping capabilities due to independent wave front modulation and large possible off-axis recording angles, enabling vHOEs in reflection with a wide range of different recording configurations. The presented vHOE is build up as an array of sub-holograms, where each element is recorded with individual optical functions. We introduce a design and fabrication method to combine two angular and two spectral functions in the volume grating of individual sub-holograms, demonstrating complex holographic elements with four multiplexed optical functions comprised in a single layer of photopolymer film. The introduced design and fabrication process allows the precise tuning of the vHOE’s diffractive properties to achieve well-balanced diffraction efficiencies and angular distributions between individual multiplexed functions.

Effect of N and Al Doping on 3C-SiC Stacking Faults

This study offers a comprehensive examination of the behavior of 3C-SiC crystals grown on 4° off-axis (100) Si substrates with different off-axis angles along &lt;110&gt; and &lt;100&gt; for N and Al doping, respectively. The investigation takes advantage of molten KOH etching to conduct an in-depth investigation of the average density and size of the SFs inside the crystal for both n- and p-type doped 3C-SiC epitaxial layers. Moreover, 3C-SiC grown on a &lt;100&gt; off-cut substrate was revealed to have a greater concentration of SFs due to the absence of self-annihilation along the plane (-1-10). Considering two different doping ranges suitable for IGBTs and MOSFETs development, the impact of doping and off-angle on the crystal quality, concentration, and length distribution of SFs was then investigated in order to quantify the influence of N and Al incorporation on the structural and optical characteristics of the semiconductor. It turned out that under heavy nitrogen doping (~1019 cm-3), when the dopant concentration grew, the average length of the stacking faults (SFs) expanded while their density dropped.

Effect of off-axis angle on mesoscale deformation and failure behavior of plain-woven C/SiC composites with digital image correlation

In this study, the deformation response and failure behavior of a plain-woven C/SiC composite were investigated under on-axis and off-axis tensile loading. Digital image correlation (DIC) was utilized to characterize the full-field deformation and mesoscale strain distribution. The test results indicate a strong influence of the woven architecture on the mechanical properties and strain distribution, and the materials exhibit failure modes dependent on the loading directions or off-axis angles: the fracture positions of different layers are the same under off-axial load, while for on-axil loading, the fracture positions of different layers do not affect each other. SEM results provide direct evidence that the width of the off-axis specimen has a great influence on the mechanical properties. The reduction of the modulus and strength of off-axis specimen, is not only due to the off-axis loading, but also due to the reduction of effective bearing area or effective bearing fiber.

Comparison of off-axis angle on the low velocity impact behaviors for carbon-fiber-reinforced polymer laminates

Three types of composite specimens with different off-axis angles after indentation were subjected to progressive tensile loading, and the results showed that although the tensile strength is reduced with an increase in off-axis fiber orientation angle, such off-axial structure can enhance the impact-resistance capacity. An acoustic emission (AE) signals analysis showed that data can be divided into categories that correlate with three damage modes. The AE peak frequency characteristics of each damage mode were also identified for both specimens with and without indentation, and the results also showed that indentation can change the order of appearance of different damage modes during loading. Additional characterization was provided by using Micro-computed tomography (Micro-CT) during a progressive tensile loading process, and the CT images provided visualization of damage location and evolution in the composites, with the data exhibiting good correlations with the AE data for defect prediction. The use of AE and Micro-CT technology was shown to effectively characterize composite damage evolution, and such data can potentially serve as a reference for the structural health monitoring (SHM) of such composites when used in structures.

Insight into the formation mechanism and interaction of matrix/TiB whisker textures and their synergistic effect on property anisotropy in titanium matrix composites

Considerable studies on processed pure titanium and titanium alloys have proved the possibility of property anisotropy induced by crystallographic textures, but limited information is available for the intrinsic coupling of matrix and reinforcement textures and their synergistic effect on property anisotropy in titanium matrix composite (TMCs). In the present work, an advanced EBSD/EDS coupling method was used to investigate the formation mechanism of primary α and secondary α textures in the matrix alloy. It is revealed for the first time that the reinforcement TiBw displays a {100}〈010〉 texture after hot rolling and has little effect on the matrix texture component but weakens texture intensity. Significant anisotropies in the tensile strength and ductility can be all noted at room and high-temperatures, which is the synergistic effect of the matrix texture and the aligned TiBw. The mean Schmid factor of each slip system was calculated to evaluate the influence of matrix texture on the minimum active stress of slip deformation in the different tensile directions. The analysis shows that the strong T-type matrix texture results in higher strength but lower ductility when loaded in the transverse direction. Moreover, a generalized shear-lag model was modified to quantitatively evaluate the strengthening contribution of aligned TiBw, which decreases with increasing off-axis angle and test temperature. A new parameter, defined as the critical aspect ratio of the off-axis whisker, was proposed to rationalize why the TiBw failure mechanism converts from TiBw fracture to TiBw/matrix interfacial debonding with increasing off-axis angle and test temperature.

Experimental study of carbon/glass fiber-reinforced hybrid laminate composites with torsional loads by using acoustic emission and Micro-CT

In this work, a torsion experiment was carried out on composite specimens with different off-axis angles to study the damage-evolution behavior of carbon/glass fiber-reinforced hybrid composites. The results show that the off-axis angle can improve the toughness of the specimen during the torsion process and enhance anti-torsion performance in the early stage. After applying Micro-CT and scanning-electron-microscope (SEM) technology, the damage distribution for a composite specimen under torsion was determined. AE technology for monitoring the entire torsion process was also applied, and for damage characterization post-processing based on Fuzzy C-Means (FCM) cluster analysis was performed on collected AE signals. AE signals were clearly divided into three categories that correspond to three damage modes, and frequency characteristics of the AE signal for each damage mode were found. The results can offer guidance for structural health monitoring (SHM) for composites under torsion.

A Beam Search-Based Channel Allocation Method for Interference Mitigation of NGSO Satellites with Multi-Beam Antennas

In the past few years, non-geostationary orbit (NGSO) satellite communication constellations have regained popularity due to their conspicuous advantages. Nevertheless, with more NGSO satellites getting involved in communications, the spectrum resources should become much more scarce. Multi-beam high throughput satellite and spectrum sharing are two major techniques in communication design. The two techniques can significantly mitigate interference and highly augment the capacity of the communication system. Thus, they are commonly used in satellite communication systems nowadays. With a massive number of NGSO satellites comprising the communication system and moving in their orbits, interference scenarios are pretty complex. In this article, the relationship between the level of interference and the beam distance is deduced. Moreover, for beams with different tilting angles, the different off-axis angles may correspond to the same beam distance, which is directly related to the interference level. Through the interference analysis, we propose a channel allocation method that uses a beam search algorithm to optimize the channel allocation problem and achieves outstanding time efficiency. The performance of the proposed method is validated by a coexisting scenario of the geostationary orbit and NGSO satellite communication systems. The results show that the level of interference can be largely mitigated, and the capacity of communication systems is significantly augmented.

Identification of Elastic Characteristics of Unidirectional CFRP under Off-Axis Tension Taking into Account the Rates of Loading

Polymer-based fiber composites have a number of unique physical and mechanical properties and are widely used in the design of structural elements in rocket and space engineering. However, along with the high characteristics of strength and rigidity, there is a noticeable anisotropy of properties which contributes to occurrence and development of damage leading to degradation of the load bearing capacity of structures and their premature destruction. Along with development of micromechanical and phenomenological models, an important place has the procedure for identifying the basic characteristics of composite materials. Such characteristics, in particular, include those of layer elasticity which are usually used when designing structures. However, even such characteristics depend on the loading conditions and for their identification, computational methods based on statistical analysis should be used. This paper attempts to identify the elastic characteristics based on test results of unidirectional carbon plastic with AS4 carbon fibers and polyetheretherketone thermoplastic matrix. For identification, the least squares method was used for samples tested at off-axis angles of 0, 10, 30, 45, 60 and 90 ° and different values of strain rates.

Exact solutions for bimorph cross-ply and antisymmetric angle-ply plate piezoelectric energy harvesters

This paper presents the exact solutions for the plate type piezoelectric bimorph energy harvesters composed of laminated cross-ply or angle-ply substrate plate. Both series and parallel connections of the piezoelectric layers of the bimorphs are considered for deriving the exact solutions. Since the exact solutions for the layers of the laminated substrate plate are available in the open literature exact solutions for the piezoelectric layers are only derived here for finding the exact solutions of the harvesters. The piezoelectric layers should be orthotropic or generally orthotropic for deriving the exact solutions. Three sets of exact solutions for the piezoelectric layers are required to be derived. The electric potential induced by the bimorph in which the piezoelectric layers are connected in series is significantly larger than that in case of the bimorph with piezoelectric layers connected in parallel. The effects of the variations of the off-axis angle in the generally orthotropic piezoelectric layer, the length over width ratio of the harvester and the thickness of the piezoelectric layers on the induced electric potential have been studied. The expressions for the exact solutions can be used in a straight forward manner for verifying the experimental and the numerical results.

Excessive Derotational K-Wire Angulation Decreases Compression by Headless Compression Screw.

Background Scaphoid fracture is the most common carpal bone fracture. Open reduction internal fixation of scaphoid fractures typically undergo stabilization by a single headless compression screw (HCS). During screw insertion, a derotational Kirschner wire (K-wire) is often placed for rotational control of the near and far fragment. Questions/Purposes The aim of this study was to determine if there is an angle of derotational K-wire placement in relation to the axis of a HCS that compromises the amount of compression generated at a fracture site by the HCS. We hypothesize that increased off-axis angle will lead to decreased compression across the fracture site. Methods A Cellular Block 20 rigid polyurethane foam (Sawbones, Vashon, WA) scaphoid model was created to eliminate variability in bone mineral density in cadaveric bone. MiniAcutrak HCS screws (Acumed, Hillsboro, OR) were used for testing. Three conditions were tested: (1) HCS with derotational wire inserted parallel to the HCS (zero degrees off-axis); (2) HCS with derotational wire inserted 10 degrees off-axis; and (3) HCS with derotational wire inserted 20 degrees off-axis. Results A statistically significant difference in the mean compression of the control group (56.9 N) was found between the mean compression with the derotational K-wire placed 20 degrees off-axis (15.2 N) ( p = 0.001). Conclusions Compression at the fracture site could be impeded by placing an excessively angulated off-axis derotation wire prior to insertion of the HCS. Clinical Relevance Our study adds a new detail to the optimal technique of HCS placement in scaphoid fractures to improve compression and fracture union.

Growth of twin-free cubic In2O3(111) thick layers on c-plane sapphire substrates by halide vapor phase epitaxy

The growth of twin-free single-crystal cubic-indium oxide (c-In2O3) layers was investigated by halide vapor phase epitaxy on c-plane sapphire substrates with various off-axis angles. The growth rate of the c-In2O3 layer increased and twin formation was suppressed as the off-axis angle of the substrate was increased. A single-crystal c-In2O3(111) layer grown on a sapphire substrate with a 5° off-axis angle showed a room temperature carrier density and mobility of 1.4 × 1016 cm−3 and 232 cm2 V−1 s−1, respectively. Temperature-dependent Hall measurements of the layer revealed that the mobility is dominated by optical phonon scattering.

Improving Hyper-Kamiokande sensitivity to CP violation with high precision near detector electron neutrino cross-section measurements

The next generation long-baseline neutrino oscillation experiment, Hyper-Kamiokande, will consist of a 260 kt underground water Cherenkov detector, placed 295 km from the neutrino source at J-PARC. This is generated by a 1.3 MW proton beam striking a target. In addition, a suite of near detectors, both on and off-axis will be used. With this, Hyper-Kamiokande aims to perform precision measurements of the parameters governing neutrino oscillations, the observation of CP violation being one of the main aims of the experiment. To achieve these goals, Hyper-Kamiokande will require smaller systematic uncertainties than in any previous long-baseline experiment.Many of these systematic uncertainties are related to neutrino-nucleus interactions, and can be constrained by a detector placed close to the beam production point. For this, the Hyper-Kamiokande long-baseline programme includes an Intermediate Water Cherenkov Detector, the IWCD. This is a 500 tonne water Cherenkov detector located 1 km from the beam production point. This detector is able to move within a vertical shaft and span a range of off-axis angles relative to the beam, from 1 to 4 degrees. The combination of large target mass, precise water Cherenkov reconstruction and off-axis angle flux dependence allows for high purity and high statistics electron neutrino and electron antineutrino samples. This paper describes how this detector can be used to constrain the major systematic uncertainty affecting the measurement of CP violation at Hyper-Kamiokande: the electron neutrino and antineutrino interaction cross section.

Flexible thin-film acoustic wave devices with off-axis bending characteristics for multisensing applications

Flexible surface acoustic wave (SAW) devices have recently attracted tremendous attention for their widespread application in sensing and microfluidics. However, for these applications, SAW devices often need to be bent into off-axis deformations between the acoustic wave propagation direction and bending direction. Currently, there are few studies on this topic, and the bending mechanisms during off-axis bending deformations have remained unexplored for multisensing applications. Herein, we fabricated aluminum nitride (AlN) flexible SAW devices by using high-quality AlN films deposited on flexible glass substrates and systematically investigated their complex deformation behaviors. A theoretical model was first developed using coupling wave equations and the boundary condition method to analyze the characteristics of the device with bending and off-axis deformation under elastic strains. The relationships between the frequency shifts of the SAW device and the bending strain and off-axis angle were obtained, and the results were identical to those from the theoretical calculations. Finally, we performed proof-of-concept demonstrations of its multisensing potential by monitoring human wrist movements at various off-axis angles and detecting UV light intensities on a curved surface, thus paving the way for the application of versatile flexible electronics.

Off-axis compressive behavior of cross-laminated bamboo and timber wall elements

This work mainly focuses on the off-axis compressive behavior of cross-laminated bamboo and timber (CLBT) wall elements. In total, 224 off-axis specimens were tested, which were made from hem-fir lumber and bamboo mat-curtain panels or just hem-fir lumber. Based on the in-plane compressive failure criteria and prediction models for the off-axis apparent compressive modulus, the mechanical property parameters of the off-axis tests were predicted. Experimental results showed that the main failure modes were slender failure zones along the parallel or perpendicular to the off-axis angles and delamination failures between the layers. The orthogonal structures inside the off-axis specimens dispersed the compressive performance of the major strength direction. Compared with glued-laminated timber specimens, the off-axis compressive performance of cross-laminated timber and CLBT specimens varied more smoothly with the increase of the off-axis angle. In addition, the characteristics of the model forms and materials affected the accuracy of the off-axis compressive property prediction models. The results in this paper can provide some inspiration for a series of innovative full-size CLBT wall members.

Can we predict the microstructure of a non-woven flax/PLA composite through assessment of anisotropy in tensile properties?

Flax/Poly-(lactide) non-woven composites are an alternative to conventional glass/poly-(propylene), offering a potentially lower environmental impact solution for the automotive industry. To understand this complex material, its detailed architecture and void distribution are examined through 3D microtomography. Anisotropy in fibre orientation is also observed, further verified through off-axis tensile tests. Then micro-mechanics and laminate theory are used, taking into account fibre orientation distribution, to predict mechanical properties and compare with experimental measurements. Even though some deviation is observed at off-axis angles greater than 45°, we report that off-axis tensile tests (property) can be used to predict fibre orientation (structure) in industrial production facilities as a simple means of quality control and tailored design of new non-woven preforms.