Semitransparent Materials Research Articles

Full-field analysis of semi-transparent cenosphere-filled composites using backlight illumination

This study introduces a novel approach for measuring deformations in semi-transparent composites using digital image correlation (DIC). Unlike traditional approaches relying on artificial speckle patterns, this method uses backlighted cenosphere particles dispersed in a semi-transparent matrix as intrinsic speckle patterns, eliminating the need for surface painting. The effectiveness of the intrinsic pattern is evaluated by comparing global parameters, such as speckle size, distribution, coverage, Shannon entropy and Mean Intensity Gradient, with those of a conventional pattern. Results indicate a relationship between speckle characteristics and measurement accuracy. A factorial design is employed to optimize DIC analysis parameters, including facet size, grid spacing, and filtering, resulting in a significant reduction in noise. Rigid displacement and four-point bending tests confirm the pattern’s traceability, with results compared against a numerical model. This approach lays the groundwork for future investigations of transparent and semi-transparent materials using DIC, allowing comprehensive mechanical characterization without altering material transparency.

Experimental study on the thermal insulation performance of semi-transparent materials based on convection heating method

Radiation heat transfer inside the aerogel materials belongs to medium radiation, so different heating methods have different measurement results of thermal conductivity. For aerogel materials applied in high temperature air flow environment (aerospace field), since the real boundary conditions of aerogel materials during operation can be simulated by convection heating method (CHM), the combustion-gas wind tunnel device based on two-stages atomization, two-stages combustion/mixing mode is constructed, and the performance test is conducted. The operation safety and combustion performance of the device meet the test requirements, so the thermal conductivity test of aerogel materials can be carried out. When the average temperatures are 469 K, 622 K and 763 K respectively, the effective thermal conductivity (ETC) measured by the CHM is smaller than that measured by the thermal conduction heating method (TCHM), which decreases by 2.7 %, 7.84 % and 9.23 % respectively. The CHM solves the limitations of the TCHM, so the ETC of aerogel materials measured by CHM is more valuable for the design of thermal protection system.

The Influence of Background Materials on the Radiative Cooling Performance of Semi-Transparent and Opaque Textiles: A Theoretical and Experimental Analysis.

This paper investigates the theoretical and experimental cooling performance of textile materials utilizing radiative cooling technology. By applying Kirchhoff's law, the emissivity of surfaces is determined, revealing that materials with high transmission values can achieve comparable cooling performance to those with high reflection values. Notably, materials exhibiting moderate reflectance and transmittance in the solar range tend to absorb minimal solar radiation, thus offering high theoretical cooling performance. However, practical applications like building envelopes or clothing present challenges due to the impact of background radiation on overall cooling capacity. Despite their intrinsic cooling properties, a significant portion of solar radiation is transmitted, complicating matters as the background can significantly affect overall cooling performance. This study provides a solution that accounts for the influence of background materials. Based on spectral data, various background materials and their impact on different semi-transparent comparison materials can be considered, and cooling performance can be simulated. This enables the simulation of cooling performance for various application scenarios and facilitates comparisons between transparent, semi-transparent, and opaque textile materials.

Artificial Intelligence Applied to Microwave Heating Systems: Prediction of Temperature Profile through Convolutional Neural Networks

Microwave heating, which is caused by the interaction of electromagnetic radiation and materials, has become an important component in industrial operations across numerous industries. Despite their importance, conventional numerical simulations of microwave heating are computationally intensive. Concurrently, advances in artificial intelligence (AI), particularly machine learning algorithms, have transformed data processing by increasing accuracy while decreasing computational time. This study tackles the difficulty of efficient and accurate modelling in microwave heating by combining convolutional neural networks (CNNs) with traditional simulation techniques. The major goal of this research is to use CNNs to forecast temperature profiles in a variety of industrial materials, including susceptors, semi-transparent, and microwave-transparent materials, under varying power settings and heating periods. This unique strategy greatly reduces prediction times, with up to 60-fold speed increases over standard methods. Our research is based on examining the electromagnetic and thermal responses of these materials under microwave heating. This study’s findings emphasise the need for extensive datasets and show the transformational potential of CNNs in optimising material processing. It uses artificial intelligence to pave the way for more effective and exact simulations, supporting breakthroughs in industrial microwave heating applications.

Integrated approach for simultaneously measuring thermophysical parameters of semi-transparent materials

To concurrently determine the thermophysical parameters of semi-transparent materials, a novel, to the best of our knowledge, integrated approach for concurrent measurement is proposed. In the measurement setup, a high-temperature radiation source and a beam reducer are employed to minimize the influence of background radiation. In order to differentiate between the transmitted and emitted radiation in the detection signal, the radiation signals from the radiation source are measured under four different conditions, enabling the calculation of transmissivity, emissivity, and reflectivity. The reliability and accuracy of the measurement method are validated by the thermophysical parameters of sapphire, and the results demonstrate a strong agreement between the measured data and previous findings. The combined uncertainties of transmissivity and emissivity for the sapphire at 753 K are estimated, highlighting the novel contribution of this method in investigating the thermophysical parameters of semi-transparent materials.

Numerical simulation on the influence of metal radiation shield on the thermal insulation performance of the semi-transparent materials

Foams, flexible felt and thermal barrier coatings are widely used in the thermal insulation fields. This type of material has lower density and thermal conductivity, as well as higher specific surface area and porosity, and is generally referred to as the semi-transparent materials. The radiation heat transfer inside the semi-transparent materials belongs to medium radiation, so the radiation thermal conductivity is larger at high temperature. However, the metal radiation shields (MRSs) play an important role in weakening radiation heat transfer. In order to study the effect of MRSs on the thermal insulation performance of the semi-transparent materials, the numerical simulation of coupling heat transfer of heat conduction and heat radiation is carried out. The effective thermal conductivity (ETC) of the semi-transparent materials with different extinction coefficient is calculated when the different layers of MRSs are evenly inserted into the semi-transparent materials at the specific temperature, so that the influence of MRSs on the thermal insulation performance of the semi-transparent materials can be obtained. The simulation results show that whether it is an optical thin medium or an optical thick medium, when 7 layers of MRSs are inserted into the semi-transparent materials, the thermal insulation performance is greatly improved. After that, the ETC changes little with the increase of the layer of MRSs.

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Measurement of the thermal diffusivity of optical materials and products by a new thermographic express method that does not require cutting samples from bulk

Thermal diffusivity a and thermal conductivity λ are important for many building, structural and functional material applications. They determine the intensity of heat transfer, the quality of thermal insulation, the rate of heating / cooling, reaching a stationary mode, and the efficiency of power equipment. In laser technology, the radiation strength of the optical components of the system depends upon them, and in laser technologies with material removal they determine the speed and quality of processing. Most methods for measuring a and λ in solid materials require cutting out samples of a certain geometry, which makes them unsuitable for testing finished products. The paper proposes and describes an express method for determining a and λ in translucent materials, which does not require cutting a sample from a controlled object. It consists in the analysis of a non-stationary temperature field on the surface of the test object using a high-speed thermal imaging camera. The unsteady heating spot was created by a focused laser beam. It was switched on abruptly and operated in the mode of continuous irradiation with a constant intensity during the entire time of measurements. Heat propagated from this spot to the periphery, creating a non-stationary temperature field containing information about a and λ. The a value was extracted from the primary data using original algorithms and software. A thermal imager, as a recorder of a dynamic temperature field, provides a number of advantages – non-contact, high speed and a large amount of information (each of the many hundreds of thousands of pixels of a professional thermal imager matrix is a temperature sensor in a small surface area). Measurements of a and λ in semitransparent materials of laser optics have their own specifics. The low radiation absorption coefficient and the possible curvature of the surface (for example, in lenses) require special measures, which are described in the article. Due to the large amount of information contained in the dynamic patterns of the thermal field and the possibility of averaging over a large data array, the RMS of the thermal diffusivity measurement does not exceed 2 %.

Spectral Radiation Characteristic Measurements of Absorption and Scattering Semitransparent Materials—A Review

The obtainment of spectral radiation characteristics of semitransparent materials mainly includes the use of a theoretical method or experimental method. As the experimental method can better characterize the real radiation transmission results inside the material, it is generally considered more reliable and used as the basis for the verification of theoretical results. In this paper, the absorbing and scattering semitransparent materials are taken as the analysis object to illustrate the research status and future development direction in the field of measurement and identification of spectral radiation characteristics. According to the physical quantities measured and the temperature range, research status is discussed for the spectral radiation characteristic measurements of absorbing and scattering semitransparent materials, which specifically involves the measurement principle, measuring system, measuring physical quantity, identification model and application range. This research will have guiding significance for the following research directions in the field of the acquisition of spectral radiation characteristic parameters of other new materials in the future.

Nonstationary radiative–conductive heat transfer problem in an absolutely black body with semitransparent inclusions

We consider a nonstationary initial‐boundary value problem governing a radiative–conductive heat transfer in an absolutely black body with semitransparent inclusions. To describe the radiative transfer, the integro‐differential radiative transfer equation is used. We do not take into account the dependence of the radiation intensity and the properties of semitransparent materials on the radiation frequency. We proved at the first time the unique solvability of this problem. In addition, we proved the stability of solutions with respect to data, established a comparison theorem and results on improving the properties of solutions with an increasing on the summability of the data.

Detection and differentiation of semi-transparent materials simulating biological structures using optical coherence tomography: a phantom study.

.SignificanceLymphatic and peripheral nervous system imaging is of prime importance for monitoring various important pathologic processes including cancer development and metastasis, and response to therapy.AimOptical coherence tomography (OCT) is a promising approach for this imaging task but is challenged by the near-transparent nature of these structures. Our aim is to detect and differentiate semi-transparent materials using OCT texture analysis, toward label-free neurography and lymphography.ApproachWe have recently demonstrated an innovative OCT texture analysis-based approach that used speckle statistics to image lymphatics and nerves in-vivo that does not rely on negative contrast. However, these two near-transparent structures could not be easily differentiated from each other in the texture analysis parameter space. Here, we perform a rigorous follow-up study to improve upon this differentiation in controlled phantoms mimicking the optical properties of these tissues.ResultsThe results of the three-parameter Rayleigh distribution fit to the OCT images of six types of tissue-mimicking materials varying in transparency and biophysical properties demonstrate clear differences between them, suggesting routes for improved lymphatics-nerves differentiation.ConclusionsWe demonstrate a novel OCT texture analysis-based lymphatics-nerves differentiation methodology in tissue-simulating phantoms. Future work will focus on longitudinal in-vivo lymphangiography and neurography in response to cancer therapeutics toward adaptive personalized medicine.

How far is the upper bound of photovoltaic conversion efficiency from the paramount efficiency of work extraction from statistically deformed thermal radiation energy?

The paper theorizes on the ultimate potential of the photovoltaic way of extracting work from thermal radiation. Two materials very well suited for photovoltaic energy conversion are considered: the constant energy bandgap and the graded energy bandgap materials, respectively. The common techniques of using these materials is described and quantified for both materials. Two models are developed. One model estimates the maximum work rate which can be extracted from a radiation energy flux. This model does not take into account the specific mechanisms of energy conversion inside the work extractor. It provides paramount performance indicators which can be used as a reference for any particular method of work extraction. The second model takes into account specificities of photovoltaic conversion. The performance indicator is the work content factor, which is denoted κtot,max and κel,max for the first and second model, respectively. Solar energy conversion into work is treated as an application. Photovoltaic conversion based on materials with constant energy bandgap is able to extract electric work which is up to a half of the maximum work that can be generated. When materials with graded energy bandgap are used, in the ideal case of transparent atmospheres and null reflectances, κtot,max is around 0.93 while κel,max ranges between 0.73 and 0.86, depending on the material temperature and the radiation concentration ratio. In the more realistic case of semi-transparent atmospheres and materials provided with antireflection layers the two indicators range around 0.87 (for κtot,max) and between about 0.78 and 0.85 (for κel,max). Therefore, photovoltaic conversion based on materials with graded energy bandgap is able to extract a large part (but not all) of the work that can be generated.

Simultaneously measurement of strain field and Poisson’s ratio by using an off-axis phase-sensitive optical coherence elastography

Phase-sensitive optical coherence elastography (PhS-OCE) is a novel functional imaging modality capable of mapping strain fields inside semi-transparent materials. In this work, an off-axis PhS-OCE was further developed to measure strain field and Poisson’s ratio simultaneously. Based on the intrinsic equations of continuum mechanics, the relationship between the elastic parameters of the measured material and the physical quantity (i.e. optical path difference) of PhS-OCE was first established. For validation, the depth-resolved strain field and Poisson’s ratio of a silicone rubber film were quantitatively measured during tensile tests. The experimental results, such as the estimates for Poisson’s ratio, agreed with the reference values. Moreover, phase difference maps of bilayer composites were discussed, indicating the effectiveness and potential of the proposed off-axis measurement method.

Influence of radiation heat transfer on parallel hot-wire thermal conductivity measurements of semi-transparent materials at high temperature

This paper presents a study of the influence of the radiation transfer on the thermal conductivity measurement in a parallel hot-wire method at high temperature. Simulations of the temperature evolution are first carried out with COMSOL Multiphysics® using the coupled conduction–radiation module based on the P1 approximation for the radiation calculation. A wide range of conditions were investigated: a low and a high density insulator were considered with various radiation characteristics (purely scattering, absorbing and scattering, purely absorbing) and with temperature varying up to 1500°C. This study enables the determination of the validity limit of the modeling of the temperature by a purely conductive model with an equivalent conductivity based on the Rosseland approximation. When this assumption is valid, a new estimation process was proposed to improve the estimation accuracy of the thermal properties. A calibration process of the distance between the hot-wire and the thermocouple has also been proposed and validated, enabling a more accurate estimation of the volume heat capacity.An experimental study carried out on three insulating materials with densities ranging from 581kgm−3 to 910kgm−3 and at temperatures ranging from 20°C to 1200°C confirms the results of the theoretical study. Finally, a method enabling the estimation of the extinction coefficient from thermal conductivity measurements at various temperatures is presented and successfully applied to the three tested materials.

Influence of Radiation Heat Transfer on Parallel Hot-Wire Thermal Conductivity Measurements of Semi-Transparent Materials at High Temperature

Influence of Radiation Heat Transfer on Parallel Hot-Wire Thermal Conductivity Measurements of Semi-Transparent Materials at High Temperature

Non-contact heat transfer models identification for laser hyperthermia of semi-transparent materials

The identification of mathematical models of heat transfer traditionally involves the installation of temperature sensors inside the sample under study and registration of the response to external thermal effects. In cases where the use of contact methods for measuring temperature is impossible, it is necessary to develop new approaches to determining the unknown thermophysical and radiation-optical characteristics. Laser hyperthermia of superficial tissues is one such case. The paper proposes a method for identifying a model of one-dimensional unsteady heating of a semitransparent sample using non-contact thermometry. A feature of the physical process under consideration is the possibility of its discretization. Due to this, a two-stage iterative procedure for solving the inverse heat transfer problem was formulated. The implementation of the proposed algorithm using software made it possible to carry out a computational experiment. The results showed the effectiveness of this approach. The presented method can be used in the development of means for monitoring and regulating the laser hyperthermia procedure.

Experimental study of radiative transfer in semi-transparent composite materials at different temperatures

This study deals with the analysis of the propagation of radiation within a diffusing semi-transparent composite medium with rough boundaries. The two-phase medium (resin matrix and glass fibers reinforcement) is treated as an equivalent homogeneous medium characterized by volumetric radiative properties (extinction coefficient, albedo and phase function) and boundary scattering properties. The aim is to identify the radiative properties at different temperatures ranging from room temperature to 200°C. The identification method (Gauss-Newton) uses bidirectional reflectance and transmittance values. The experimental results are obtained using a spectrophotometer equipped with a goniometer and a heated sample holder. The Monte Carlo method is used to solve the Radiative Transfer Equation (RTE) in order to obtain the theoretical values.

Measurements of spectral emissivity, reflectance and transmittance at high temperatures using laser heating and auxiliary light source

A multi-wavelength measurement method for the high-temperature radiation properties of semi-transparent materials heated by high power laser and irradiated by the infrared source with alternating spectral distributions is introduced. The method avoids the strong dependence of existing methods on accurate temperature measurements or emissivity model of semi-transparent samples. The spectral emissivity, reflectance, transmittance and temperature of semi-transparent samples can be determined simultaneously. Furthermore, we established the experimental device, including a FTIR spectrometer (spectral range of 2.0∼16 μm), a 500 W 915 nm fiber laser, and an infrared SiC emitter irradiation source. The radiation properties of the oxidized stainless-steel sample (opaque materials) and n-type, phosphorous-doped silicon wafer sample (semi-transparent materials) were investigated experimentally at different temperatures (400∼800 °C). With the increase of laser power, the upper limit of sample temperature can be extended to higher temperatures. The measurement results show that the infrared spectral emissivity of stainless-steel increases with the increase of temperature. The spectral emissivity of semi-transparent n-type, phosphorous-doped silicon wafer increases with the increase of temperature, while the spectral directional-hemispherical reflectance decreases with the increase of temperature. The results of temperature and wavelength dependent emissivity of silicon wafer sample are consistent with the literatures, which verifies the applicability of the device. The research work provides a useful reference for measuring the high-temperature radiation properties of semi-transparent materials.

Unique solvability of a stationary radiative‐conductive heat transfer problem in a system consisting of an absolutely black body and several semitransparent bodies

We consider a stationary boundary value problem describing a radiative‐conductive heat transfer in a system consisting of one absolutely black body and several semitransparent bodies. To describe the radiative transfer, the integro‐differential radiative transfer equation is used. We do not take into account the dependence of the radiation intensity and the properties of semitransparent materials on the radiation frequency. We proved at the first time the unique solvability of this problem. Besides, we proved the comparison theorems and established the results on improving the properties of solutions with increasing exponents of data summability.

Unique solvability of a stationary radiative–conductive heat transfer problem in a semitransparent body with absolutely black inclusions

We consider a stationary boundary value problem describing a radiative–conductive heat transfer in a semitransparent body with absolutely black inclusions. To describe the radiative transfer, the integro-differential radiative transfer equation is used. We do not take into account the dependence of the radiation intensity and the properties of semitransparent materials on the radiation frequency. We proved at the first time the unique solvability of this problem. Besides, we proved the comparison theorems and established the results on improving the properties of solutions with increasing exponents of data summability.