The problem of wave propagation and scattering at terahertz (THz) frequencies has become increasingly important, in particular for accurate modeling of future indoor wireless communication channels. ...The reflective properties of indoor materials with different surface roughness and dielectric constants are important to explore diffuse scattering for accurate channel modeling. First and foremost, a terahertz Swissto12 system is adopted to obtain the first ever transmission measurements for a wide choice of indoor material groups, such as wood, plastic , and brick at frequencies from 750 GHz to 1.1 THz using up-conversion (frequency-domain) method. Both the reflection (<inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">S_{22} </tex-math></inline-formula>) and transmission coefficients (<inline-formula> <tex-math notation="LaTeX">S_{12} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">S_{21} </tex-math></inline-formula>) are measured using this novel and noninvasive electromagnetic technique. The inversion method based on Kramers-Kronig (K-K) relations is then applied to convert the calibrated scatter data into intrinsic material properties (i.e., refractive index, permittivity, absorption coefficient). Then, the surface topography of rough material samples is acquired using surface measurement instruments. Further, the optically smooth <inline-formula> <tex-math notation="LaTeX">(\sigma _{h} /\lambda \ll 1) </tex-math></inline-formula> materials are assorted as most to least rough based on Rayleigh roughness factor. Lastly, the ray tracer considering the Rayleigh-Rice (R-R) scattering model is employed to obtain the maximum achievable reflected paths of the above-mentioned indoor material samples at 300 GHz followed by their experimental validation.
Software tools for quantification of X-ray microtomography at the UGCT Vlassenbroeck, J.; Dierick, M.; Masschaele, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2007, Volume:
580, Issue:
1
Journal Article
Peer reviewed
The technique of X-ray microtomography using X-ray tube radiation offers an interesting tool for the non-destructive investigation of a wide range of materials. A major challenge lies in the analysis ...and quantification of the resulting data, allowing for a full characterization of the sample under investigation. In this paper, we discuss the software tools for reconstruction and analysis of tomographic data that are being developed at the UGCT. The tomographic reconstruction is performed using Octopus, a high-performance and user-friendly software package. The reconstruction process transforms the raw acquisition data into a stack of 2D cross-sections through the sample, resulting in a 3D data set. A number of artifact and noise reduction algorithms are integrated to reduce ring artifacts, beam hardening artifacts, COR misalignment, detector or stage tilt, pixel non-linearities, etc. These corrections are very important to facilitate the analysis of the 3D data. The analysis of the 3D data focuses primarily on the characterization of pore structures, but will be extended to other applications. A first package for the analysis of pore structures in three dimensions was developed under Matlab
®. A new package, called Morpho+, is being developed in a C++ environment, with optimizations and extensions of the previously used algorithms. The current status of this project will be discussed. Examples of pore analysis can be found in pharmaceuticals, material science, geology and numerous other fields.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•A revised rheological model is established for SMC materials with fiber-friction interactions.•It highlights the mechanical influence of the fibrous reinforcement on the flow of SMC materials.•The ...experimental compression molding stress is compared with an analytical model for different types of SMC materials.
Sheet Molding Compounds are composite materials made of chopped fiber bundles and thermoset resin processed by compression molding. Their high fiber content and relatively long fiber length classify them as concentrated suspensions. Experimental observations of mesostructures indicate the importance of contacts between the fiber bundles and friction forces during processing of these materials. They also reveal the presence of highly entangled networks of fiber bundles. Hence current models based on Jeffery's equation and the suspension theory are not able to predict the fiber orientation during flow and capture the rheological response during the compression of the suspension. A friction-based continuum model is proposed to describe the deformation of SMC mesostructures and their kinematics as a function of the fiber orientation tensor. An experimental study using tailored SMC materials confirm the rheological dependence of SMC materials on their mesostructures properties and validate the proposed friction model. The two material parameters of the model are identified experimentally and the results are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This article reports on an extensive interlaboratory comparison of measurements of material properties between 2 GHz and 1 THz using both vector network analyzer (VNA)-based and optical-based ...methods. For the former, techniques including open resonators, conventional free-space quasioptical systems, and a relatively new guided free-space approach through use of material characterization kits (MCKs) were utilized. The optical-based methods included both time-domain spectroscopy (TDS) and frequency-domain spectroscopy (FDS). Measurement setups for these five techniques located at five well-established laboratories have been employed in the measurements of seven types of commonly used dielectric materials. The results of the measurements by the participating laboratories using each of these techniques were compared to assess levels of agreement between the utilized techniques and thereby establish confidence in the characterizations of each material. Measurement results of these seven materials are presented, together with detailed discussion. This is the first time that an interlaboratory measurement comparison of material properties has been conducted over nearly three decades of frequency and involving such a range of techniques. This work should prove beneficial to applications where material properties need to be known accurately in the microwave to terahertz region.
A novel time domain measurement technique is proposed to facilitate the simultaneous measurement of electrical properties (complex relative permittivity) and geometrical parameters (thickness) of the ...material under test (MUT). The overall process is noninvasive and noncontacting, which uses the measured scattering data of the MUT in the equivalent time domain or spatial domain. The effective time domain scattering data are employed to detect the primary and secondary peaks of the overall reflection and transmission coefficients. To this end, a novel algorithm is proposed to obtain the complex permittivity and thickness of the MUT in terms of extracted reflection and transmission power peaks. From the practical point of view, the main advantage of the proposed scheme is that one avoids the complicated calibration procedure normally required to define the reference plane. For increasing the accuracy of the overall reconstruction process, an automated optimization procedure based on parameter sensitivity analysis is proposed, which uses standard time gating procedure to implement the corresponding direct problem. The proposed technique is validated by extracting the relative permittivity, the dielectric loss (effective conductivity), and the thickness of various standard materials, such as polyethylene, Plexiglas, PVC, mortar, nylon, and so on, and comparing the extracted data with their values available in the literature.
Coupling links and hooked plates constitute the primary components of automatic couplers in trains, enduring substantial tensile and compressive loads during train connections. This study endeavours ...to enhance the strength of S45C material through heat treatment techniques. The research commenced with the preparation of JIS S45C tensile test specimens adhering to ASTM E8 standards. The material's chemical composition was validated using an Optical Emission Spectrometer (OES). Six heat treatment variations were employed, including quench oil without tempering (QO), quenching water without tempering (QW), quenching oil tempered at 660°C (QOT660), quenching water tempered at 660°C (QWT660), quenching oil tempered at 550°C (QOT550), quenching water tempered at 550°C (QWT550), alongside untreated conditions (NT) for comparison. The efficacy of heat treatment was evaluated through tensile testing, optical metallographic analysis, and micro-Vickers hardness tests. QO and QW scenarios were excluded from the tensile tests. Results revealed that QWT550 demonstrated the most substantial enhancement in material yield, exhibiting a 115% increase. Moreover, hardness testing indicated superior hardness in QWT550 specimens compared to other tempered variants. The metallographic analysis illustrated the formation of identical and smooth martensitic structures. Overall, the combination of cooling heat treatment and tempering proved sufficient to meet the design requirements of hooked plates and coupling links for automatic couplers.
It has been proved previously that in the field of microwave absorption, film and material are confused, and that the impedance matching theory (IM) which is usually applied to metal-backed film is ...inadequate. By analysis of experimental data from a novel theoretical perspective, it is shown here that the problems with IM cannot be solved even if different criteria such as the value of |Zin - Z0| or the phase difference between Zin (input impedance of film) and Z0 (characteristic impedance of open space or a layered material) are used and therefore the current theories related to IM need to be replaced by wave cancellation theory. The analysis in this work applies to published data and supports the new theories against the current ones. The conditions for the minima of reflection loss |RL| at large values of |Zin - Z0| have also been determined by transmission-line theory.
•Theories against the mainstream ones have been confirmed by new experimental data•Conclusions against accepted theories have been confirmed from different perspectives•Conditions contradicting impedance matching theory have been identified•Impedance matching theory is a misapplication of transmission line theory
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The diffusion coefficient is a key property of materials. Electrochemical impedance spectroscopy (EIS) is a routine tool to determine the diffusion coefficient. Albeit being versatile for varied ...electrochemical systems and powerful in distinguishing multiple processes in a wide frequency spectrum, the EIS method usually needs a physical model in data analysis; misuse of models leads researchers to provide unwarranted interpretation of EIS data. Regarding diffusion, the simple and elegant formula developed by Warburg has been serving as the canonical model for more than a century. The classical Warburg model has very strict assumptions, however, it is used in a wide range of scenarios where assumptions may not be satisfied. It is the main purpose of the present article to define the boundary of applicability of the Warburg model and develop alternative models for cases beyond the boundary. In so doing, the Warburg model is revisited and its limitations and assumptions are scrutinized. Afterwards, new impedance models for more complicated and realistic scenarios are developed. The present article features: (1) generalization of the boundary condition when treating diffusion in bounded space and geometrical variants; (2) diffusion impedance in porous electrodes and fractals; (3) the effect of electrostatic interactions and coupling between diffusion and migration on the diffusion impedance in electrolytic solutions; (4) introduction of homotopy perturbation method to treat the convective diffusion; (5) physical interpretations of diffusion impedance behaviors.
•Assumptions of Warburg impedance are scrutinized.•Diffusion impedance in more realistic structures is modelled.•Diffusion impedance of ions in electrolytic cells is discussed.•Pitfalls in estimating diffusion coefficient in battery materials.•How the porous structure affects the diffusion impedance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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