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Microstructured and Solid Polymer Optical Fiber Sensors
Published in Krzysztof Iniewski, Smart Sensors for Industrial Applications, 2017
Christian-Alexander Bunge, Hans Poisel
Figure 2.1 provides a hierarchical structure of fiber optical sensors in general. They can be classified into glass and polymer fibers. Many glass-optical sensors are in use today. Most of them are based on single-mode fibers making use of interferometric or polarization effects in coherent light. These effects are well known and a lot of literature deals with this kind of sensors. We will therefore concentrate on polymer fiber sensors for the remainder of this chapter. Like in their glass counterparts, polymer fibers are available as solid fibers as well as microstructured with tiny holes in the cross section running along the whole length of the fiber. These holes alter the optical properties of the material they are embedded in and usually cause a decrease of the material’s effective refractive index so that the material acts like being doped with air (see, e.g., [1]). Another approach is to form a crystal-like structure around the fiber core, in which energy bands develop like in semiconductors. These bands stand for allowed energy states for the photons so that a fiber can be constructed with energy states that are allowed in the core, but not in the cladding. Then, photons cannot help remaining in the core region. This effect is called band-gap guidance and can even be used for fibers with air cores otherwise impossible to produce (see, e.g., [2]). This type of fibers offers the main advantage that the holes can be changed in terms of geometry (e.g., by pressure) or refractive index (e.g., by blowing in gases or liquids), or that they provide a means to bring the material to be studied closer to the light in order to interact.
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Published in J. Carmeliet, H. Hens, G. Vermeir, Research in Building Physics, 2020
M. Bomberg, M. Pazera, J. Zhang, F. Haghighat
These are materials in which the barrier is provided by a monolithic film that has been mechanically punctured to impart a level of water vapour permeability. The mechanically punctured holes are typically an order of magnitude larger than the pores in fibrous materials. Material properties will depend on the size and number of holes. These materials may be mechanically supported by a woven or non-woven scrim. (see Figure 3).
Sensors Based on Polymer Optical Fibers
Published in Krzysztof Iniewski, Optical, Acoustic, Magnetic, and Mechanical Sensor Technologies, 2017
Christian-Alexander Bunge, Hans Poisel
Figure 2.1 provides a hierarchical structure of fiber optical sensors in general. They can be classified into glass and polymer fibers. Very many glass optical sensors are in use today. Most of them are single-mode sensors making use of inter-ferometric or polarization effects. These effects are well known and a lot of literature deals with these sensors. We will therefore concentrate on polymer fiber sensors for the remainder of the chapter. As in their glass counterparts, polymer fibers are available as solid fibers as well as microstructured fibers with tiny holes in the cross section running along the whole length of the fiber. These holes alter the optical properties of the material they are embedded in and usually cause a decrease in the material’s effective refractive index so that the material acts like being doped with air (see, e.g., Reference [1]). Another approach is to form a crystal-like structure around the fiber core, in which energy bands develop as in semiconductors. These bands stand for allowed energy states for the photons so that a fiber can be constructed with energy states that are allowed in the core but not in the cladding. Then, photons cannot help remain in the core region. This effect is called band-gap guidance and can even be used for fibers with air cores that are otherwise impossible to produce (see, e.g., Reference [2]). The main advantage of this type of fiber is that the holes can be changed in terms of geometry (e.g., by pressure) or refractive index (e.g., by blowing in gases or liquids), or that they provide a means to bring the material to be studied closer to the light in order to interact. Solid POFs are usually large in diameter and numerical aperture and thus massively multimode. There are also a couple of single-mode POF applications, but the main advantages of POF sensors are their robustness, ease of handling, and the easy reception of light (e.g., for reflectance measurements). One can also differentiate between single fibers, multicore fibers, and bundles. Most of the sensor effects themselves are based on single fibers, but these sensors can be easily extended or multiplexed by fiber bundles or in a more compact form as multicore structures. In this way, one can design distributed sensors that can sense at many different locations and bring their sensing signal to one centralized detector. Some effects, however, make direct use of fiber bundles or multicore fibers; for example, one can use a bundle of fibers in order to receive the reflected light of a surface or use an additional fiber for calibration purposes. Solid POF sensors usually fall into several distinct categories. One can use their attenuation by a simple power measurement Other sensors rely on refraction, which finally also leads to an increased attenuation. Since standard POF are multimode, one can also measure the modal power distribution and detect for instance bends that change the modal structure of the fiber. Although multimode, one can also use phase measurements for the detection of elongation or other mechanical changes in the fiber. In this case, the optical phase cannot be measured, but a lower-frequency sine signal can be used and its phase can be compared with a reference signal.
High-brightness 808 nm semiconductor laser diode packaged by SiC heat sink
Published in Journal of Modern Optics, 2020
Xingyu Li, Kai Jiang, Zhen Zhu, Jian Su, Wei Xia, Xiangang Xu
In the wavelength drift method, Rth can be determined by where Pt is the thermal power, and Po is the output power. The wavelength at different temperature for both lasers is given in Figure 4(a), and the value of Δλ/ΔT is estimated to be 0.294 nm·K−1. The wavelength at different test current for the both lasers is given in Figure 4(b). The wavelength drift of the laser packaged by SiC is 6.55 nm when the test current rises from 1 to 9 A, which is smaller than that of the laser packaged by AlN with a drift of 6.89 nm. The equation of Pt = UI–Po can be computed from the data in Figure 3. Ultimately, the calculated thermal resistance is 2.95 K·W−1 for SiC heat sink laser and 3.16 K·W−1 for AlN heat sink laser. SiC heat sink laser with lower thermal resistance shows good thermal performance. The experimental results of the thermal resistance value are larger than the previous simulation results, mainly because it is assumed in the calculation that the sintered surface between the chip and the heat sink is in perfect contact. In fact, as shown in Figure 5, there are generally holes in the sintered surface of the device. These holes hinder the downward transfer of heat, form local hot spots, and then increase the average thermal resistance of the device.
Fabrication of a multi-phase porous high-temperature Mo–Si–B alloy by in situ reaction synthesis
Published in Powder Metallurgy, 2019
Yongan Huang, Laiqi Zhang, Meng Wang, Mark Aindow
For the samples sintered at temperatures of 1200 and 1400°C (Figure 6(c,d), respectively), the Si and B particles appear to have been consumed leaving holes in the microstructure at these locations. Such holes are a major part of the total porosity, which will have an important effect on the mechanical properties and the permeability of the material. At the same time, sintering necks start to appear between the remaining particles, and these coarsen gradually to form the skeleton of the open porous structure. Since these two samples were sintered below the melting point of Si (1413°C), solid–solid diffusion reactions will dominate the phase transformations. Based on the literature concerning diffusion couples in the Mo–Si system, Kirkendall voids are anticipated because the intrinsic diffusion coefficient of Si is much larger than that of Mo [34,35]. Most of those pores should be located in the interfaces between different phases, although the formation of pores within the phases is also possible [44].
Microstructure characteristics in weld zone of the novel thick 08Cr9W3Co3VNbCuBN heat-resistant steel welded joint by fusion welding
Published in Philosophical Magazine Letters, 2023
Hong-ju Fan, Peng Liu, Yong-bin Wang, Xin-fang Guo
Figure 5 shows the SEM morphology with EDS results of the welded surface of the steel. The red boxes in Figure 5a, d, g represent the SEM magnification area, and the high magnification images are shown in Figure 5b, e, h. Figures 5c, f, i correspond to the EDS energy spectrum and element composition content of test points, respectively. According to Figure 4a and b, it can be seen that the microstructure of the welded cover was mainly composed of tempered lath martensite. There were several black holes and precipitated second-phase particles in and inside the grain boundary in the welded cover. The holes may be defects such as pores, enclosed slag or incomplete fusion. And part of the second phase was distributed on the grain boundary. The EDS analysis was performed on the surface of spectrum 1 and spectrum 2, respectively. Based on the element composition of literature [21], EDS results and XRD analysis (see Figure 6), it is indicated that the matrix of the original alloy α-Fe solid solution. A large number of Si-rich phases were detected in the chemical composition (see Figure 5c1) of the black hole at spectrum 1 in Figure 5b1, and it was speculated that the black hole may be a Si-rich inclusion. This was mainly due to the fact that Si was added to the electrode as a deoxidising element to prevent the oxidation of iron, and the products were difficult to float out of the molten pool, resulting in slag inclusion in the weld metal. According to the above analysis of process and microstructures, the grains at the weld cover were coarser, which often led to high brittleness and low toughness of the joint. In addition, the spectrum 2 pointed out in Figure 5b2 represented the chemical composition of the martensite matrix area (see Figure 5c2), which had 81.51 Fe, 10.95 Cr, 3.62 Co and 3.91 W (at. %). This result showed that the weld metal had a chemical composition similar to BM.