Backing Layer Research Articles

The Effects of Target Thicknesses and Backing Materials on a Ti-Cu Collision Weld Interface Using Laser Impact Welding

This study demonstrates that the thickness of the target and its backing condition have a powerful effect on the development of a wave structure in impact welds. Conventional theories and experiments related to impact welds show that the impact angle and speed of the flyer have a controlling influence on the development of wave structure and jetting. These results imply that control of reflected stress waves can be effectively used to optimize welding conditions and expand the range of acceptable collision angle and speed for good welding. Impact welding and laser impact welding are a class of processes that can create solid-state welds, permitting the formation of strong and tough welds without the creation of significant heat affected zones, and can avoid the gross formation of intermetallic in dissimilar metal pairs. This study examined small-scale impact using a consistent launch condition for a 127 µm commercially pure titanium flyer impacted against commercially pure copper target with thicknesses between 127 µm and 1000 µm. Steel and acrylic backing layers were placed behind the target to change wave reflection characteristics. The launch conditions produced normal collision at about 900 m/s at the weld center, with decreasing impact speed and increasing angle moving toward the outer perimeter. The target thickness had a large effect on wave morphology, with the wave amplitude increasing with target thickness in both cases, peaking when target thickness is about twice flyer thickness, and then falling. The acrylic backing showed a consistently smaller unwelded central zone, indicating that impact welding is possible at a smaller angle in that case. Strength was measured in destructive tensile testing. Failure was controlled by the breakdown of the weaker of the two base metals over all thicknesses and backings. This demonstrates that laser impact welding is a robust method for joining dissimilar metals over a range of thicknesses.

Theoretical Studies of 2D Electron Gas Distributions and Scattering Characteristics in Double‐Channel n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN High‐Electron‐Mobility Transistors

A detailed analysis of self‐consistent potentials, electric fields, electron distributions, and transport properties of dual‐channel (DC) n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN high‐electron‐mobility transistors (HEMTs) is performed in this article. The 2D electron gas (2DEG) densities and mobility states limited by different scattering mechanisms in channel 1 and channel 2 are obtained, with varying values of doping concentrations, ambient temperatures, Al components, and thicknesses of the back barrier layer. The reduced and increased 2DEG densities are respectively observed in channel 1 and channel 2 with growing Al fractions and thicknesses of the AlxGa1−xN layer. Alloy disorder scattering exhibits a superior effect on carriers in channel 2 due to the lower barrier height and higher permeable electrons, which together with the interface roughness scattering severely depends on the thicknesses and Al fractions of the back barrier layer. Polar optical phonon scattering becomes important at higher temperatures. The trend of individual mobility in channel 1 is exactly opposite to that in channel 2. The parameter variation of the back barrier layer can effectively change the scattering characteristics of the main channel. Low‐temperature mobilities of n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN HEMTs under varied doping concentrations are also obtained. Finally, the results are verified by comparison with the technology computer‐aided design simulations for DC HEMTs.

Development of n-Type, Passivating Nanocrystalline Silicon Oxide Films via Plasma-Enhanced Chemical Vapor Deposition

Nanocrystalline silicon oxide (nc-SiOx:H) is a multipurpose material with varied applications in solar cells as a transparent front contact, intermediate reflector, back reflector layer, and even tunnel layer for passivating contacts, owing to the easy tailoring of its optical properties. In this work, we systematically investigate the influence of the gas mixture (SiH4, CO2, PH3, and H2), RF power, and process pressure on the optical, structural, and passivation properties of thin n-type nc-SiOx:H films prepared in an industrial, high-throughput, plasma-enhanced chemical vapor deposition (PECVD) reactor. We provide a detailed description of the n-type nc-SiOx:H material development using various structural and optical characterization techniques (scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Raman spectroscopy, and spectroscopic ellipsometry) with a focus on the relationship between the material properties and the passivation they provide to n-type c-Si wafers characterized by their effective carrier lifetime (τeff). Furthermore, we also outline the parameters to be kept in mind while developing different n-type nc-SiOx:H layers for different solar cell applications. We report a tunable optical gap (1.8–2.3 eV) for our n-type nc-SiOx:H films as well as excellent passivation properties with a τeff of up to 4.1 ms (implied open-circuit voltage (iVoc)~715 mV) before annealing. Oxygen content plays an important role in determining the crystallinity and hence passivation quality of the deposited nanocrystalline silicon oxide films.

Evaluation of Monolayer and Bilayer Buccal Films Containing Metoclopramide.

The objective of this study was to develop buccal film formulations containing metoclopramide hydrochloride monohydrate (MCP) with and without a backing layer and to evaluate their release properties and physiochemical stability. The crystallization of MCP in the polymer matrix was monitored with image analysis techniques for rapid and scalable observation. The results showed that the addition of a protective layer and its thickness significantly affected the release rate and crystallization behavior of MCP in the formulations. The crystallization of MCP increased over time, and certain formulations showed higher susceptibility to crystallization. To understand the factors affecting the crystallization of MCP, the relationship between the viscosity and pH of the casting solution was examined, but no significant correlation was found. A significant correlation was observed between the plasticizer concentration and the physical state of MCP. Through a systematic Design of Experiment (DOE) approach, an optimal formulation was devised, successfully preventing crystallization of the active ingredient. However, enhancing the overall chemical stability of the formulated product remains a challenge.

A Theoretical Model of Enhanced Adhesion of Bioinspired Micropillar Arrayed Surfaces

To achieve better adhesion, micropillar arrayed surfaces inspired by the gecko adhesion system have gained significant attention. However, debate continues on whether micropillar arrayed surfaces actually enhance interfacial adhesion compared to smooth surfaces. To clearly understand the factors influencing the adhesion force of micropillar arrayed surfaces and provide a criterion for achieving enhanced adhesion of such the surfaces, a theoretical model of a micropillar arrayed surface containing an elastic backing layer is established. Under a vertically uniform displacement load, the micropillars will detach from the rigid substrate. The adhesion behavior of each micropillar and the variation pattern of the entire adhesion force influenced by the geometry of the micropillars, materials of the micropillars and backing layer during the detaching process are analyzed. A load sharing efficiency is defined, and is found to increase with an increase in the micropillar aspect ratio, Young's modulus ratio of the backing layer to the micropillars, and separation distance between neighboring micropillars, but decrease with an increase in sample size. The entire adhesion force of a micropillar arrayed surface can be quantified, which is larger than that of a smooth surface if the micropillar aspect ratio, Young's modulus ratio of the backing layer to the micropillars and separation distance between neighboring micropillars are appropriate. Detailed diagrams are respectively provided for the load sharing efficiency of all the micropillars and the comparison of the adhesion forces between micropillar arrayed and smooth surfaces with different geometric and material parameters, from which the design strategies of approaching equal load sharing regime and stronger adhesion force of the micropillar arrayed surface than that of the smooth one can be clearly found. The obtained results can not only deepen the understanding of the adhesion behavior of fibrillar surfaces but also provide theoretical guidance for achieving robust adhesion of the micropillar arrayed surfaces.

MgO@polydopamine Nanoparticle-Loaded Photothermal Microneedle Patches Combined with Chitosan Gel Dressings for the Treatment of Infectious Wounds.

As for wound drug delivery, microneedles (MNs) have attracted wide attention. However, while effective at increasing the depth of drug delivery, traditional MNs often have limited drug loads and have difficulty penetrating scabs on wounds. Herein, we develop a drug delivery system combining MgO@polydopamine (MgO@PDA) nanoparticle-loaded photothermal MN patches and chitosan (CS) gel to inhibit the formation of scabs and deliver sufficient drugs into deep tissue. When inserted into the wound, the MN system can keep the wound bed moist and weakly acidic to inhibit the formation of scabs and accelerate wound closure. The released MgO@PDA nanoparticles from both the tips and the backing layer, which immensely increase the drug load, continuously release Mg2+ in the moist, weakly acidic wound bed, promoting tissue migration and the formation of microvessels. MgO@PDA nanoparticles show excellent antibacterial activity under near-infrared irradiation synergized with the CS gel, and the PDA coating can also overcome the adverse effects of oxidative stress. Through in vitro and in vivo experiments, the MN system showed remarkable antibacterial, antioxidant, anti-inflammatory, and pro-angiogenic effects, indicating its potential in the treatment of infectious wounds.

Non-metallic magnetostatically tunable metasurface absorber for terahertz waves

A non-metallic metasurface absorber containing VO2, InSb, and Teflon has been designed, simulated, and investigated for normally incident plane waves in the terahertz spectral regime. When the temperature exceeds 72°C, a backing layer of VO2 in its rutile phase instead of a conventional metal virtually eliminates transmission. Peak absorptance as high as 0.998, quality factor on the order of 200, and magnetostatic tunability of about 16GHz\, T−1 are achievable. Such metasurfaces can be made using standard microfabrication techniques.

Multi-material 3D printed eutectogel microneedle patches integrated with fast customization and tunable drug delivery

Microneedle patches are emerging multifunctional platforms for transdermal diagnostics and drug delivery. However, it still remains challenging to develop smart microneedles integrated with customization, sensing, detection and drug delivery by 3D printing strategy. Here, we present an innovative but facile strategy to rationally design and fabricate multifunctional eutectogel microneedle (EMN) patches via multi-material 3D printing. Polymerizable deep eutectic solvents (PDES) were selected as printing inks for rapid one-step fabrication of 3D printing functional EMN patches due to fast photopolymerization rate and ultrahigh drug solubility. Moreover, stretchable EMN patches incorporating rigid needles and flexible backing layers were easily realized by changing PDES compositions of multi-material 3D printing. Meanwhile, we developed multifunctional smart multi-material EMN patches capable of performing wireless monitoring of body movements, painless colorimetric glucose detection, and controlled transdermal drug delivery. Thus, such multi-material EMN system could provide an effective platform for the painless diagnosis, detection, and therapy of a variety of diseases.

An ultrasensitive and broadband transparent ultrasound transducer for ultrasound and photoacoustic imaging in-vivo

Transparent ultrasound transducers (TUTs) can seamlessly integrate optical and ultrasound components, but acoustic impedance mismatch prohibits existing TUTs from being practical substitutes for conventional opaque ultrasound transducers. Here, we propose a transparent adhesive based on a silicon dioxide-epoxy composite to fabricate matching and backing layers with acoustic impedances of 7.5 and 4–6 MRayl, respectively. By employing these layers, we develop an ultrasensitive, broadband TUT with 63% bandwidth at a single resonance frequency and high optical transparency ( > 80%), comparable to conventional opaque ultrasound transducers. Our TUT maximises both acoustic power and transfer efficiency with maximal spectrum flatness while minimising ringdowns. This enables high contrast and high-definition dual-modal ultrasound and photoacoustic imaging in live animals and humans. Both modalities reach an imaging depth of > 15 mm, with depth-to-resolution ratios exceeding 500 and 370, respectively. This development sets a new standard for TUTs, advancing the possibilities of sensor fusion.

Towards a locally constructed multi-element ultrasound imaging transducer for resource poor environments

This paper investigates techniques and materials for making a multi-element ultrasound imaging transducer with craft-based techniques available in resource poor environments. The transducer housing can be conveniently divided into three parts: the body supporting the piezoelectric (PZT) elements and other components; the matching layer between the PZT elements and the human body; and the backing layer behind the PZT elements. Low-cost 3D printing systems based on photopolymers were found to be suitable for manufacturing the body. Finite Element Modelling (FEM) showed that the material characteristics of the backing layer and the thickness of the matching layer were much less critical than predicted by ultrasound plane wave theory and transmission line theory, respectively. The backing and matching layers are normally made from epoxy-tungsten composites that are pourable in the uncured state. However, the composite required for the backing layer was putty-like when uncured. When the tungsten was allowed to settle under gravity during curing, a 20 % by volume uncured tungsten-epoxy composite gave a 30 % by volume concentration of tungsten at the bottom when cured at 20–30 °C. These findings, when coupled with the findings from the FEM modelling, suggests that constructing a multi-element ultrasound imaging transducer using craft-based techniques is feasible.

Impact resistance performance and structural optimization of lightweight composite target plate

AbstractThe finite element model of a 7.62 mm armor‐piercing incendiary bomb penetrating lightweight composite target is established. The structure of the target plate is composed of boron carbide ceramic/carbon fiber laminate/aramid fiber laminate/damping material. The reasonable distribution position of damping material is explored by designing the material structure and geometric parameters. Genetic algorithm is used to optimize the structure of the lightweight composite target plate, and the feasibility of the optimization results is verified through experiments. The results show that under the same surface density, the energy absorption value of the target plate with a certain thickness of back layer damping is 1.36% higher than that of the target plate without damping. And the damping material on the back layer can act as a buffer layer to reduce blunt trauma caused by bullets to the human body. The surface density of the optimized lightweight composite target plate is reduced by 21.6% under the same protection capability. This work provides a theoretical foundation for the impact resistance design and optimization of lightweight composite target plates.Highlights Impact resistance performance of lightweight composite target plate is investigated. The impacting analytical model of the structure is established. The validity of the optimized impacting analytical model is verified by numerical simulation.

Ultrasound transducers with both imaging and power output capabilities by anti-matching at backing layers

Precise ultrasound therapy requires long-term power output and imaging guidance. However, traditional therapeutic transducers do not have imaging capabilities due to the low bandwidth and long ringing. Whereas for a diagnostic transducer, 20%–30% of the energy is dissipated as heat in the backing layer, resulting in degradation of the transducer under high duty cycle and high voltage excitation. Therefore, the transducers with both power output and imaging capabilities are unmet demands for precise ultrasonic treatment. To address this problem, we propose an ultrasound transducer with both imaging and power output capabilities. An anti-matching layer is designed at the position of the backing layer of the transducer, which reflects the backward ultrasound waves to forward waves. Therefore, the majority of the energy is transmitted efficiently and little energy is dissipated in the backing layer. Finite element simulations demonstrated that a double-layer anti-matching design reflects 99.8% of the backward energy, resulting in an insertion loss of −27.7 dB. The performance was validated by a transducer prototype with transmission measurement using hydrophone and pulse-echo test. This design of transducers with both imaging and power output capabilities indicates a promising application of self-guided ultrasound therapy.

Optimal design of ultrasonic transducer based on multi-layer backing with adjustable impedance

Ultrasonic transducers, especially used in medical imaging, strike a balance between sensitivity and bandwidth to yield high-quality images. This challenge centers on the optimal transmission of acoustic energy across the layers of transducer. The backing layer stands as a critical component of transducers, orchestrating the conversion of acoustic impedance to enhance bandwidth. While traditional designs often utilize metal particle-polymer composites, issues arise from material limitations, complex fabrications, and deviations in sample properties. This study introduces an optimized multilayer backing (MLB) design using a metal-polymer structure. Implementing an equivalent circuit model, an MLB of epoxy-aluminum composite is designed. The ultrasonic transducer has an operating frequency of about 6 MHz, in which the backing layer is a stacking composite of 19.3 μm epoxy resin and 30 μm aluminum foil. Notably, this optimized design increased the -6dB bandwidth from 27.72 % to 33.44 % and verified its superior electro-acoustic performance based on ultrasonic imaging. Furthermore, this innovative design approach provides a wider range of acoustic impedance, improves the efficiency of ultrasonic energy transmission, and provides a streamlined approach to miniaturized transducer design.

An accurate forming model for capturing the nonlinear material behaviour of multilayered binder-stabilised fabrics and predicting fibre wrinkling

Prefabricated stacks of binder-stabilised dry fabrics are used to increase reinforcement deposition rates in the manufacturing of large composite structures such as wind turbine blades. To ensure optimal part quality, accurate simulation tools may be used to avoid costly trial-and-error experiments. This paper introduces a new modelling framework for predicting wrinkle defects that arise from forming thick binder-stabilised stacks of quasi-unidirectional non-crimp fabric. In this context, quasi-unidirectional non-crimp fabrics are unidirectional rovings stabilised with a backing layer. The non-constant bending stiffness of the fabric is modelled using an asymmetric compressive modulus, while a mixed-mode cohesive formulation with user-defined damage evolution is used for modelling the initial non-constant elastic binder interface stiffness and interface degradation. The model is verified against cantilever bending tests of single fabric layers and transverse shear experiments of bindered fabric layers. Comparison with experimental results on the forming of preforms shows that the model accurately predicts wrinkle location and geometry during the forming of thick binder-stabilised preforms. The error between the wrinkle geometry predicted by the new modelling approach and the experimentally measured wrinkle geometry is reduced by 35% to 94% compared to wrinkles predicted by conventional modelling approaches. The modelling framework is freely available at https://doi.org/10.5281/zenodo.10077428.

Simulation study of Perovskite/Si Monolithic Multijunction Solar Cell

The utilization of perovskite and crystalline-silicon (c-Si) light absorbers in multijunction solar cells presents an exciting opportunity to surpass the efficiency limit of the industry's leading single-junction c-Si solar cells. In this work, we used the Solar Cell Capacitance Simulator (SCAPS-1D) to simulate a monolithic tandem junction solar cell. The solar cell consists of two types of materials: low bandgap and high bandgap. These are layers of perovskites and Si, divided by a window layer of zinc oxide (ZnO), a buffer layer of cadmium sulfide (CdS), a recombination layer of Spiro-MeOTAD/silicon, and a heavily doped back surface field layer formed from n++Si to prevent recombination at the back surface. The impact of di fferent series and shunt resistances, as well as perovskite layer thickness and bandgap, on solar cells' photovoltaic performance has been investigated.

A detachable dissolving microneedles patch as a new effective platform to deliver Japanese encephalitis live attenuated chimeric vaccine

The purpose of this study was to develop a detachable dissolving microneedles (dDMNs) patch incorporating Japanese encephalitis live attenuated chimeric vaccine (JE-CV) via skin intradermal (ID) immunization. JE-CV-loaded dDMNs (JE-CV:dDMNs at a mass ratio of 1:4) were successfully formulated from NaHCO3:CS:PVA (sodium bicarbonate:chitosan:polyvinyl alcohol) at 0.25:1:4 mass ratio with 121 needles per patch of 1 cm2. The MN patches showed sufficient mechanical strength to resist compression and maintain their appearance after penetrating excised neonatal porcine skin. After application, the MNs arrays were completely detachable from the backing layer at 1 h (∼91 % of delivery efficiency) as wearing time required, and over 80 % of the needles had dissolved after 2 h. For immune responses, the results found that mice immunized with a half-dose of the JE-CV via ID using a JE-CV-loaded dDMNs patch elicited seroprotection (PRNT50 ≥ 10 titers, recommended by the World Health Organization (WHO)) comparable to mice who received a full dose of the JE-CV via subcutaneous (SC) injection. In contrast, mice immunized with a half-dose of the JE-CV via SC injection did not elicit seroprotection. Mice immunized with a half-dose of the JE-CV-loaded dDMNs via ID stimulated IgA higher than mice immunized with the full-dose ∼1.4 times in saliva and nasal wash. For cytokines’ levels, mice immunized with the full-dose of the JE-CV solution via SC induced interferon-gamma (IFN-ɤ) and interleukin-4 (IL-4), the levels were similar to the half-dose of the JE-CV-loaded dDMNs patch ID immunization (p > 0.05). The results revealed that the JE-CV-loaded dDMNs showed promise for effectively stimulating humoral immune responses (HIR) and cell-mediated immune responses (CMIR) to protect against JEV.

Effect of angular distortion and axial misalignment on the fatigue strength of welded and ground mild steel cruciform joints

AbstractThe focus of this work is to investigate the fatigue strength of a cruciform joint one-sided through-welded by a HV seam with a backing layer made of a 10-mm-thick S355 mild steel. The aim is firstly to analyse the effect of the deformation state incorporating angular distortion and axial misalignment on the fatigue strength of the tested specimens and secondly, the analysis of the benefit by grinding as post-treatment method on the resulting fatigue performance. The deformation impact is numerically investigated utilizing geometry measurements of the specimens as well as strain gauge measurements for validation. Thereby, the near notch stress under clamping condition without any load and under an additional static nominal load is analysed. Based on these investigations, the applied stress range for each tested specimen is converted to a “deformation-free” condition by means of the IIW-recommended km factor. The statistical analyses of the data points with and without this modification reveal a significant impact by the deformation state on both the evaluated fatigue strength and the scatter band. Moreover, this affects the evaluated benefit by grinding as post-treatment, whereas an increase of more than 40% in the fatigue strength at 2 million cycles is observed using the modified data points.

Copper doping effect in the back surface field layer of CdTe thin film solar cells

In this work, the Solar Cell Capacitance Simulator (SCAPS-1D) is employed to evaluate the characteristics of CdTe thin films with ZnTe as the Back Surface Field (BSF) layer and estimate the effective copper doping ratio at both the atomic scale and the device operational response perspective. The electrical characteristics of ZnTe, at varying levels of copper doping, were derived using density functional theory (DFT) by applying the generalized gradient approximation (GGA) and Hubbard U corrections (DFT+U). The performance of ZnTe with different Cu concentrations as a BSF layer was evaluated by analysing the values of four key parameters that are open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), and conversion efficiency (η). The results indicate that an increase in Cu concentration from 0% to 3%, 6%, 10%, and 12% resulted in a reduction of the energy band gap. Specifically, the energy band gap decreased from 2.24 eV to 2.10 eV, 1.98 eV, 1.92 eV, and 1.88 eV, respectively. Optimal Cu doping promotes the favourable shift in the valence band maxima (VBM) and formation of p + -ZnTe, lowering thermionic emission and improving carrier lifetime, which results in an improved ohmic contact, η = 18.73% for 10% of Cu content. Excessive doping in contrast degraded the overall device performance by forming an unmatched carrier band offset at the front interface with CdS, increasing the acceptor type defect and CdTe compensation rate. Overall, the findings suggest that incorporating a controlled level of Cu, which in this case is around 10%, promotes the efficiency and stability of the proposed CdTe device configuration to a certain extent.

Unconfined interfacial friction of Geosynthetic Cementitious Composite Mats

Geosynthetic Cementitious Composite Mats (GCCMs) are flexible, cementitious material-filled geosynthetics that harden on hydration to form thin concrete layers and are primarily used for surface erosion protection applications. When installing GCCMs on steep slopes and channels, the interfacial friction between the GCCM and the substrate must be understood to determine if anchoring is required to secure the material in place. Determining interface shear resistance using test methods such as ASTM D5321 require a shear box and confining load acting on the soil/GCCM, which may not accurately represent GCCM resistance, as when installed there is typically no confining load other than GCCM self-weight and water. To provide a more detailed understanding of ‘unconfined’ interfacial friction properties of GCCMs, the authors created a tilt table which could be filled with different substrates and inclined to record the angle of GCCM specimen slip on the substrate surface. This paper reviews the tilt table testing on two common GCCMs with different backing layers (PVC and LLDPE), tested on a number of substrates that are typically lined in GCCMs. Both the interfacial friction angle and adhesion are determined, with discussion on the relationship between adhesion and surcharge for some substrate types.

High-frequency wearable ultrasound array belt for small animal echocardiography.

Wearable ultrasound has been widely developed for long-term, continuous imaging without the need for bulky system manipulation and repeated manual locating. To potentially lead to more accurate and reliable imaging monitoring, this work presents the design, fabrication, and evaluation of a novel high-frequency wearable ultrasound array belt (WUAB) for small animal echocardiography. The fabrication process involved precise dicing technology for a λ-pitch design. The 20 MHz WUAB consists of two matching layers, piezoelectric composite with 128 channels, customized flexible circuit substrate, acoustic backing layer, and customized belt structure with designed end tip and insertion point for wearability. The resulting WUAB demonstrates sensitivity of -5.69 ± 2.5 dB and fractional bandwidth of 57 ± 5 %. In vivo experiments on rat model showed expected echocardiography and B-mode images of rat heart. These results represent significant promise for future longitudinal studies in small animals and real-time physiological monitoring.