Search Results (68)

Background/Objectives: The aim of this in vitro study was to determine the optimal combinations of wavelengths for short wavelength infrared (SWIR) multispectral transillumination and reflectance imaging of caries lesions on proximal and occlusal surfaces. Methods: The contrasts of (n = 76) caries lesions on the occlusal and proximal surfaces of extracted teeth were measured at 1050, 1300, and 1550 nm for occlusal transillumination and 1058, 1300, 1450, and 1675 nm for occlusal reflectance. All teeth were also imaged using radiography and microcomputed tomography (μCT) to verify lesion presence. A custom-fabricated handheld imaging probe suitable for clinical use and for the simultaneous acquisition of SWIR occlusal transillumination and reflectance (SWIR-OTR) images was used. Three high-power superluminescent diode lasers were used for transillumination, and a fiber-optic switch was used to switch between the transillumination wavelengths. Optical bandpass filters coupled with a tungsten halogen lamp were used for reflectance. All images were acquired at the same position and with the same field of view for comparison. Results: The highest contrasts in reflection were at 1450 and 1675 nm for occlusal and interproximal lesions, and the highest contrasts for transillumination were at 1050 and 1300 nm. Conclusions: This study suggests that the best wavelengths for SWIR-OTR are between 1000 and 1300 nm for transillumination and greater than 1400 nm for reflectance. Wavelengths beyond 1400 nm are advantageous for reflectance and yield significantly higher contrast. Wavelengths beyond 1300 nm are not promising for occlusal transillumination since internal water absorption leads to contrast inversion. Full article

In the current energy transition procedure, the application prospect of hydrogen as a clean energy material has attracted much attention. However, the widespread use of hydrogen is also accompanied by safety hazards, and how to detect hydrogen safely and efficiently has become a research focus. In this paper, we propose a fiber-optic hydrogen sensor based on the thermo-optic effect and nanomaterials, which combines the unique advantages of fiber-optic grating and platinum-loaded tungsten trioxide and is capable of detecting hydrogen concentration with high sensitivity. The principle of this sensor is to absorb hydrogen molecules by nanomaterials and trigger the exothermic effect, which leads to grating period change and refractive index change in the fiber, thus modulating the resonant wavelength of grating. By monitoring the wavelength drift in real time, the hydrogen concentration can be accurately detected. The experimental results show that the sensor can provide high sensitivity, fast response, wide detection range, and miniaturized design, which are suitable for hydrogen detection in complex environments. In addition, its dual-channel operational method further improves detection accuracy and environmental adaptability. This work provides technical support for safe hydrogen detection, which is suitable for hydrogen production, storage, industrial safety and environmental monitoring. Full article

Tungsten fiber reinforced tungsten–copper (W_f/W-Cu) composites have broad application prospects in fields such as electronic packaging due to their excellent comprehensive properties. However, the correlation between fiber parameters (content, aspect ratio, orientation) and the mechanical behavior of the materials is not yet clear. In this study, a combination of numerical simulation and experimental research was employed to construct a three-dimensional microstructural mechanic model and systematically investigate the influence of fiber parameters on the tensile properties and mechanisms of W_f/W-Cu composites. The results show that: (1) The critical fiber aspect ratio is 7.6. When below this value, fiber pullout dominates, and when above this value, fiber tensile fracture is the main mechanism. (2) As the fiber content increases from 1% to 6%, the tensile strength of the composite increases by 9.6%, the yield strength increases by 10.2%, while the elongation after fracture decreases by 18.6%. (3) As the fiber orientation angle increases from 0° to 90°, the material strength first increases and then decreases, while the toughness first decreases and then increases. (4) Short fibers achieve interface toughening through fiber pullout, crack deflection, and fiber bridging, while long fibers improve the strength and toughness of the composite through load transfer and fiber bridging effects. (5) The damage evolution mechanism reveals the regulation effect of fiber parameters on the multi-scale mechanical behavior of the material. The research results can guide the composition and structure optimization design of W_f/W-Cu composites, provide new ideas for the research of high-performance fiber composites, and have important significance for their engineering applications in extreme environments. Full article

Airborne dust is an important contaminant affecting the health and the environment, and a crucial concern in many workplaces such as animal facilities and potash mines. One of the techniques used for dust control is electrostatic particle ionization (EPI). This technology has been proven effective in reducing airborne dust; however, it has downsides, such as the generation of ozone and corrosion of electrodes. Thus, this study tested a corrosion-resistant carbon-fiber discharge electrode and compared it with electrodes commonly used in EPI systems, that is, stainless-steel and tungsten electrodes, in terms of collection efficiency for potash dust and wheat flour (representative of livestock dust), ozone production, and power consumption. The carbon-fiber electrode performed comparably to stainless-steel electrodes, particularly for potash dust, and performed better than the tungsten electrode in terms of dust collection efficiency. Moreover, it had the lowest energy consumption and generated the least amount of ozone. However, because of the limitations of this study (e.g., fewer samples, low air velocity, controlled conditions, and the use of wheat flour instead of livestock dust), tests under real barn or mining conditions are necessary to confirm the results. Full article

The purpose of this paper was to develop fiber lasers in the 2.7–2.8 μm range based on the tungsten–tellurite glass fiber that is technically robust compared to the other fibers currently used in laser engineering. Using an advanced technology for producing ultra-dry tellurite glasses, we manufactured Er³⁺-doped tungsten–tellurite glass preforms with extremely low absorption and obtained active single-mode tungsten–tellurite fibers. Based on a 70 cm long fiber, we developed a laser oscillator pumped by a low-cost, high-efficiency diode laser at 976 nm. At the highest used pump power, the laser output reached 33 mW, which may be interesting for practical applications. We also measured the single-pass on/off gain of the fibers and showed that with increasing pump power amplification, as high as 5 can be reached, showing that such active fibers may also be used for increasing laser output. Full article

Exposure to high levels of radiation can cause acute, long-term health effects, such as acute radiation syndrome, cancer, and cardiovascular disease. This is an important occupational hazard in different fields, such as the aerospace and healthcare industry, as well as a crucial burden to overcome to boost space applications and exploration. Protective bulky equipment made of heavy metals is not suitable for many advanced purporses, such as mobile devices, wearable shields, and manned spacecrafts. In the latter case, the in-space manufacturing of protective shields is highly desirable and remains an unmet need. Composites made of polymers and high atomic number fillers are potential means for radiation protection due to their low weight, good flexibility, and good processability. In the present work, we developed electrospun composites based on polycaprolactone (polymer matrix) and tungsten powder for application as shielding materials. Electrospinning is a versatile technology that is easily scalable at an industrial level and allows obtaining very lightweight, flexible sheet materials for wearables. By controlling tungsten powder size, we engineered homogeneous, stable and processable suspensions to fabricate radiation composite shielding sheets. The shielding capability was assessed by an in vivo model on prototype composite sheets containing 80 w% of W filler in a polycaprolactone (PCL) fibrous matrix by means of irradiation tests (X-rays) on mice. The obtained results are promising; as expected, the shielding effectivity of the developed composite material increases with the thickness/number of stacked layers. It is worth noting that a thin barrier consisting of 24 layers of the innovative shielding material reduces the extent of apoptosis by 1.5 times compared to the non-shielded mice. Full article

In recent years, increased attention to air pollutants such as NO_x has led the scientific community to focus meaningfully on developing strategies for NO_x reduction. Selective catalytic reduction of NO_x by ammonia (NO SCR by NH₃) is currently the main method to remove NO_x from diesel engine exhaust emissions. The catalysts with typical V₂O₅-WO₃/TiO₂ (VWTi) composition are widely used in NH₃-SCR for their high NO_x conversion activity, low cost, and robustness, especially concerning sulfur poisoning. However, in real diesel engine working conditions, the thermal and hydrothermal aging of catalysts can occur after several hours of operation at high temperature, affecting the catalytic performance. In this study, the stability of a commercial VWTi monolith, self-supported and containing glass fibers and bentonite in its matrix, was investigated as a case study. In laboratory conditions, NO SCR tests were performed for 50 h in the range of 150 to 350 °C. Subsequently, the VWTi monolith was thermally and hydrothermally aged at 600 °C for 6 h. The thermal aging increased the NO_x conversion, especially at low temperature (<250 °C), while the hydrothermal aging did not affect the SCR. The differences in NO_x conversion before and after aging were associated with the change in vanadium and tungsten oxide surface coverage and with the reduction in the surface area of catalysts. In order to correlate the change in SCR activity with the modifications occurring after aging processes, the monolithic samples were characterized by several techniques, namely XRD, SSA and pore analysis, TPR, XPS, Raman, TGA and SEM/EDX. Full article

Sisal-fiber-reinforced composites have garnered significant attention across various industries owing to their favorable attributes, including cost-effectiveness, biodegradability, and lightweight characteristics. Nevertheless, the need to enhance their mechanical and tribological properties has become imperative to meet the growing demand for high-performance materials. This study explores the impact of tungsten carbide (WC) particle reinforcement on the mechanical and tribological properties of sisal fiber composites. Composites were prepared by incorporating varying WC percentages (3%, 6%, and 9%) into the sisal-fiber–epoxy matrix. Flexural tests revealed a notable increase in flexural strength as WC content increased. Izod impact tests demonstrated superior impact resistance with higher WC content. Furthermore, pin-on-disc wear testing identified enhanced wear resistance in composites containing 9% WC reinforcement. These findings illustrate the potential of WC-reinforced composites for applications necessitating improved strength, impact resistance, and wear resistance, positioning them as promising materials for diverse industries. Full article

A new method for the synthesis and deposition of tungsten oxide nanopowders directly on the surface of a carbon-fiber-reinforced polymer composite (CFRP) is presented. The CFRP was chosen because this material has very good thermal and mechanical properties and chemical resistance. Also, CFRPs have low melting points and are transparent under ionized radiation. The synthesis is based on the direct interaction between high-power-density microwaves and metallic wires to generate a high-temperature plasma in an oxygen-containing atmosphere, which afterward condenses as metallic oxide nanoparticles on the CFRP. During microwave discharge, the value of the electronic temperature of the plasma, estimated from Boltzmann plots, reached up to 4 eV, and tungsten oxide crystals with a size between 5 nm and 100 nm were obtained. Transmission electron microscopy (TEM) analysis of the tungsten oxide nanoparticles showed they were single crystals without any extended defects. Scanning electron microscopy (SEM) analysis showed that the surface of the CFRP sample does not degrade during microwave plasma deposition. The X-ray attenuation of CFRP samples covered with tungsten oxide nanopowder layers of 2 µm and 21 µm thickness was measured. The X-ray attenuation analysis indicated that the thin film with 2 µm thickness attenuated 10% of the photon flux with 20 to 29 KeV of energy, while the sample with 21 µm thickness attenuated 60% of the photon flux. Full article

Tungsten carbide (WC) has been widely utilized in recent years in the hardware, mechanical, and chemical industries and in national defense because of its high hardness, anti-wear, low temperature, and anti-corrosion properties. However, using it for grinding is also challenging because the WC material has high hardness and brittle characteristics. The typical hub of a diamond wheel is made of steel. In high-speed grinding, the steel hub of the diamond wheel is subjected to gravity and centrifugal forces, which cause grinding wheel vibration, poor workpiece processing quality, and a short machine life. Therefore, this study used a carbon-fiber-reinforced thermoplastic (CFRP) hub to replace the steel hub when grinding the WC workpiece. It aimed to investigate methods to reduce oscillation, improve chip efficiency, and increase accuracy in the WC workpiece. The research results demonstrated that using a CFRP hub in the grinding wheel can reduce the oscillation when the peripheral speed of the grinding wheel is at 20–100 m/s. Additionally, the surface roughness average (Ra) of the workpiece can be reduced to 3.2–25.4% and the ten-point height of irregularities (Rz) can be reduced to 18.9–44% compared to using a steel hub in the grinding wheel. Full article

This research presents an experimental study focused on measuring temperature at the tool flank during the up-milling process at high cutting speed. The proposed system deals with emissivity compensation through a two-photodetector system and during calibration. A ratio pyrometer composed of two photodetectors and a multimode fiber-optic coupler is employed to capture the radiation emitted by the cutting insert. The pyrometer is calibrated using an innovative calibration system that addresses theoretical discrepancies arising from various factors affecting the measurement of cutting temperature. This calibration system replicates the milling process to generate a calibration curve. Experimentally, AISI 4140 steel is machined with coated tungsten carbide inserts, using cutting speeds of 300 and 400 m/min, and feed rates of 0.08 and 0.16 mm/tooth. The results reveal a maximum recorded cutting temperature of 518 °C and a minimum of 304 °C. The cutting temperature tends to increase with higher cutting speeds and feed rates, with cutting speed being the more influential factor in this increase. Both the pyrometer calibration and experimental outcomes yield satisfactory results. Finally, the results showed that the process and the device prove to be a convenient, effective, and precise method of measuring cutting temperature in machine processes. Full article

Volatile organic compounds (VOCs), often invisible but potentially harmful, are prevalent in industrial and laboratory settings, posing health risks. Detecting VOCs in real-time with high sensitivity and low detection limits is crucial for human health and safety. The optical sensor, utilizing the gasochromic properties of sensing materials, offers a promising way of achieving rapid responses in ambient environments. In this study, we investigated the heterostructure of SnO₂/WO₃ nanoparticles and employed it as the primary detection component. Using the electrospinning technique, we fabricated a sensing fiber containing Ag NPs, poly(methyl methacrylate) (PMMA), and SnO₂/WO₃ (PMMA-Ag-SnO₂/WO₃) for acetone vapor detection. Following activation via UV/ozone treatment, we observed charge migration between WO₃ and SnO₂, resulting in a substantial generation of superoxide radicals on SnO₂ nanoparticles. This phenomenon facilitates structural deformation of the fiber and alters the oxidation state of tungsten ions, ultimately leading to a significant change in extinction when exposed to acetone vapor. As a result, PMMA-Ag-SnO₂/WO₃ fiber achieves a detection limit of 100 ppm and a response time of 1.0 min for acetone detection. These findings represent an advancement in the development of sensitive and selective VOC sensing devices. Full article

In recent years, great progress has been made in the technology of high-purity and ultra-dry tellurite glasses, which has enabled the creation of high-purity single-mode tellurite fibers doped with rare-earth ions. This technology has made it possible to demonstrate laser generation in the range of about 2.7 μm in erbium-doped tungsten tellurite fibers. In this paper, we present an experimental study of broadband amplification in erbium-doped zinc-tellurite fibers. Zinc-tellurite glasses containing modifying components, such as Na₂O, La₂O₃, Bi₂O₃, or rare-earth metal oxides, are known to have noticeably lower phonon energy than heavy metal-tellurite systems, namely, tungsten tellurite glasses, which leads to better lasing output. The on-off gain of 30- and 60-cm long zinc-tellurite fibers has been measured in a wide range of diode pump powers. It has been shown for the first time that the amplification band is essentially extended, with pump power reaching over 250 nm (2600–2850 nm) at a peak power of about 40 W for a 30-cm long fiber. Full article

Fiber laser sources in the spectral range near 1.7–1.8 μm are in highly demand for a lot of applications. We propose and theoretically investigate a dual-wavelength switchable Raman tungsten-tellurite fiber laser in the 1.7–1.8 µm range which can produce two stable modes at frequencies separated by ~7 THz with a pump at 1.55 µm. The Raman waves shifted by 19.8 THz (mode 1) and 27.5 THz (mode 2) from the pump frequency can be generated near two different maxima of the Raman gain spectrum (gain is higher at 19.8 THz and twice lower at 27.5 THz). We numerically simulate two-mode Raman lasing with allowance for energy transfer from the pump wave to modes 1 and 2, and from mode 1 to mode 2 due to inelastic Raman scattering. Diagrams of generation regimes depending on system parameters are constructed. We demonstrate controlled switching between two modes by changing the pump power. For the same intracavity losses for both Raman modes at relatively low pump powers, only mode 1 is generated. At medium pump power, generation occurs simultaneously in both modes. At relatively high pump power, only mode 2 is generated near the weaker maximum. This effect seems surprising, but a rigorous explanation with allowance for the nonlinear interaction between mode 1 and mode 2 is found. When losses for one of the modes change, switching of the generated regimes is also predicted. Full article

With the unprecedented development of green and renewable energy sources, the proportion of clean hydrogen (H₂) applications grows rapidly. Since H₂ has physicochemical properties of being highly permeable and combustible, high-performance H₂ sensors to detect and monitor hydrogen concentration are essential. This review discusses a variety of fiber-optic-based H₂ sensor technologies since the year 1984, including: interferometer technology, fiber grating technology, surface plasma resonance (SPR) technology, micro lens technology, evanescent field technology, integrated optical waveguide technology, direct transmission/reflection detection technology, etc. These technologies have been evolving from simply pursuing high sensitivity and low detection limits (LDL) to focusing on multiple performance parameters to match various application demands, such as: high temperature resistance, fast response speed, fast recovery speed, large concentration range, low cross sensitivity, excellent long-term stability, etc. On the basis of palladium (Pd)-sensitive material, alloy metals, catalysts, or nanoparticles are proposed to improve the performance of fiber-optic-based H₂ sensors, including gold (Au), silver (Ag), platinum (Pt), zinc oxide (ZnO), titanium oxide (TiO₂), tungsten oxide (WO₃), Mg₇₀Ti₃₀, polydimethylsiloxane (PDMS), graphene oxide (GO), etc. Various microstructure processes of the side and end of optical fiber H₂ sensors are also discussed in this review. Full article