Semitransparent Materials Research Articles

A Spatially Offset Raman Spectroscopy Method for Non-Destructive Detection of Gelatin-Encapsulated Powders.

Non-destructive subsurface detection of encapsulated, coated, or seal-packaged foods and pharmaceuticals can help prevent distribution and consumption of counterfeit or hazardous products. This study used a Spatially Offset Raman Spectroscopy (SORS) method to detect and identify urea, ibuprofen, and acetaminophen powders contained within one or more (up to eight) layers of gelatin capsules to demonstrate subsurface chemical detection and identification. A 785-nm point-scan Raman spectroscopy system was used to acquire spatially offset Raman spectra for an offset range of 0 to 10 mm from the surfaces of 24 encapsulated samples, using a step size of 0.1 mm to obtain 101 spectral measurements per sample. As the offset distance was increased, the spectral contribution from the subsurface powder gradually outweighed that of the surface capsule layers, allowing for detection of the encapsulated powders. Containing mixed contributions from the powder and capsule, the SORS spectra for each sample were resolved into pure component spectra using self-modeling mixture analysis (SMA) and the corresponding components were identified using spectral information divergence values. As demonstrated here for detecting chemicals contained inside thick capsule layers, this SORS measurement technique coupled with SMA has the potential to be a reliable non-destructive method for subsurface inspection and authentication of foods, health supplements, and pharmaceutical products that are prepared or packaged with semi-transparent materials.

Performance analysis of optically semi-transparent material packed-bed solar air heater

This paper deals with theoretical analysis of performance of solar air collector having its duct packed with optically semitransparent materials. The heat transfer equations for two dimensional fully developed fluid flows under quasi-steady state conditions have been developed in order to analyze the thermal, thermo-hydraulic and exergy performance and to study the effect of system and operating parameters. A computer programme is developed in c++ language to estimate the temperature rise of entering air for evaluation of performance by solving the governing equations numerically using relevant correlations for heat transfer coefficient for packed bed systems. Results of air temperature rise and thermal efficiency obtained from the analysis have been compared with available experimental results and results are found fairly in closed agreement. It has been found that there is considerable enhancement in thermal efficiency with packed bed collector. Effect of total bed depth on efficiency show that there is an upper limiting value of total bed depth beyond which the thermal efficiency begins to fall again and this type of characteristics behavior is observed at all mass flow rate. It is also noticed that there exists an optimal value of effective and exergy efficiencies for a given mass flow rate.

Energy Saving Assessment of Semi-Transparent Photovoltaic Modules Integrated into NZEB

Photovoltaic semi-transparent materials (STPV) integrated into glazing systems can offer good potential for energy saving to buildings, influencing heating loads, cooling loads, and lighting, as well as electricity production. Moreover, with the new stringent regulations issued by various European countries, following the Energy Performance of Buildings Directive (EPBD, 2010/31/EC), the building envelope, including the glazing elements, needs to have high thermal performance to guarantee Nearly Zero Energy Building (NZEB) behavior. This work presents an assessment of energy saving potential of 4 different types of STPV with respect to conventional double pane glass. Dye sensitized solar modules (DSM) and thin film modules were considered in the study. Simulations based on an IEA reference office building (STD) and on reference buildings prescribed by the new Italian building energy performance regulation (NZEB) were carried out. All the glazing peculiarities could be simulated using only one simulation tool, namely IDA ICE 4.7.1. Dye sensitized solar modules resulted as the best performing devices for all orientations and climate zones. The work also evidenced how the requirements of NZEB seem to be too stringent for insulation properties, especially for the climate zone of Rome.

On a phase transition for semitransparent materials in terms of the Stefan problem

The paper deals with justification of the formula for the latent heat of phase transition of the first kind, taking into account superheating and subcooling of the formed two-phase system, in application to the solution of Stefan problem in semitransparent materials.

半透明材料红外热像检测的光谱特性和光源选择

半透明材料红外热像检测的光谱特性和光源选择

半透明材料红外热像检测的光谱特性和光源选择

半透明材料红外热像检测的光谱特性和光源选择

Effect of radiative heat transfer on determining thermal conductivity of semi-transparent materials using transient plane source method

The theoretical basis of transient plane source method is the unsteady differential equation of heat conduction which is suitable for opaque medium. Extremely low density materials such as aerogels and foaming materials are not opaque for thermal radiation at high temperature. For these semi-transparent materials, radiation will participate in the thermal transport process. When applying transient plane source method to measure the thermal conductivity of semi-transparent materials, the existence of thermal radiation within the materials will affect the test accuracy. In present study, the effect of radiative heat transfer on determining thermal conductivity of semi-transparent materials using transient plane source method is numerically studied. The results show that the thermal conductivity of semi-transparent materials measured by transient plane source method will be overestimated at temperature higher than 600K and extinction coefficient less than 2000m−1 where radiative heat transfer is dominant. The deviation increases with temperature and reaches to 19.6% at 1000K for materials with extinction coefficient of 500m−1. It illustrates that the thermal conductivity of semi-transparent materials measured by transient plane source method has taken into account part of the influence of radiative heat transfer within the materials.

Analysis of the Thermo-Reflectivity Coefficient Influence Using Photothermal Pump-Probe Techniques.

Recent improvements in the modeling of photo-induced thermo-optical-mechanical effects have broadened the application of photothermal techniques to a large class of solids and fluids. During laser excitation, changes in optical reflectivity due to temperature variation may affect the photothermal signal. In this study, the influence of the reflectivity change due to heating is analyzed for two pump-probe photothermal techniques, thermal lens and thermal mirror. A linear equation for the temperature dependence of the reflectivity is derived, and the solution is tested using optical properties of semi-transparent and opaque materials. For semi-transparent materials, the influence of the reflectivity change in photothermal signals is less than 0.01%, while for opaque materials it is lower than 3%.

Optical properties of graphene-based materials in transparent polymer matrices

Different aspects of graphene-based materials (GBMs) and GBM-nanocomposites have been investigated due to their intriguing features; one of these features is their transparency. Transparency of GBMs has been of an interest to scientists and engineers mainly with regard to electronic devices. In this study, optical transmittance of structural, purpose-made nanocomposites reinforced with GBMs was analyzed to lay a foundation for optical microstructural characterization of nanocomposites in future studies. Two main types of GBM reinforcements were studied, graphene oxide (GO) and graphite nanoplates (GNPs). The nanocomposites investigated are GO/poly(vinyl alcohol), GO/sodium alginate, and GNP/epoxy with different volume fractions of GBMs. Together with UV-visible spectrophotometry, image-processing-assisted micro and macro photography were used to assess the transparency of GBMs embedded in the matrices. The micro and macro photography methods developed were proven to be an alternative way of measuring light transmittance of semi-transparent materials. It was found that there existed a linear relationship between light absorbance and a volume fraction of GBMs embedded in the same type of polymer matrices, provided that the nanocomposites of interest had the same thicknesses. This suggests that the GBM dispersion characteristics in the same type of polymer are similar and any possible change in crystal structure of polymer due to different volumetric contents of GBM does not have an effect on light transmittance of the matrices. The study also showed that the same types of GBMs could display different optical properties in different matrix materials. The results of this study will help to develop practical microstructural characterization techniques for GBM-based nanocomposites.

The effect of molecular structure on the secondary transitions and their influence on the decoloration kinetics of photochromic dyes in co‐polycarbonates

ABSTRACTPhotochromic dyes have restricted use in rigid polycarbonates because of slow coloration and decoloration kinetics. In this study, it is shown that the decoloration kinetics of two photochromic dyes can be controlled by tuning the chain stiffness and free volume of the host matrix. The introduction of flexible moieties in rigid BPA‐based polycarbonate chain accelerates the decoloration of these dyes whereas a rigid co‐monomer delays the decoloration kinetics. Although Tg might be used as a parameter to improve photochromism in polymer matrices, dynamic mechanical analysis demonstrates that the decoloration kinetics of the dyes in host polymer matrices having similar Tg depends primarily on the secondary relaxations and, thus, on the polymer architecture. The effect of the co‐monomer type on the characteristic ratio is also discussed underlining the potential relationship between the free volume and chain stiffness. These results open the possibility to develop transparent or semitransparent photochromic materials based on tailor‐made co‐polycarbonates. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1593–1601

Flow Synthesis of Silver Nanowires for Semitransparent Solar Cell Electrodes: A Life Cycle Perspective.

Silver nanowires (AgNWs) were prepared on a 5 g scale using either the well-known batch synthesis following the polyol method or a new flow synthesis method. The AgNWs were employed as semitransparent electrode materials in organic photovoltaics and compared to traditional printed silver electrodes based on micron sized silver flakes using life cycle analysis and environmental impact analysis methods. The life cycle analysis of AgNWs confirms that they provide an avenue to low-impact semitransparent electrodes. We find that the benefit of AgNWs in terms of embodied energy is less pronounced than generally assumed but that the toxicological and environmental benefits are significant.

Apparent directional spectral emissivity determination of semitransparent materials**Project supported by the National Natural Science Foundation of China (Grant Nos. 51476043 and 51576053) and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51421063).

An inverse estimation method and corresponding measurement system are developed to measure the apparent spectral directional emissivities of semitransparent materials. The normal spectral emissivity and transmissivity serve as input for the inverse analysis. Consequently, the refractive index and absorption coefficient of the semitransparent material could be retrieved by using the pseudo source adding method as the forward method and the stochastic particle swarm optimization algorithm as the inverse method. Finally, the arbitrary apparent spectral directional emissivity of semitransparent material is estimated by using the pseudo source adding method given the retrieval refractive index and absorption coefficient. The present system has the advantage of a simple experimental structure, high accuracy, and excellent capability to measure the emissivity in an arbitrary direction. Furthermore, the apparent spectral directional emissivity of sapphire at 773 K is measured by using this system in a spectral range of 3 μm–12 μm and a viewing range of 0°–90°. The present method paves the way for a new directional spectral emissivity measurement strategy.

Hybrid Methodology for Retrieving Thermal Radiative Properties of Semi-Transparent Ceramics

Semitransparent materials, like silica or alumina, are highly used by high-temperature industries as refractory materials in blast or glass-making furnaces, first for their good mechanical properties. The knowledge of their radiative properties is also essential to improve thermal transfers. However, characterizing experimentally the high temperature dependence of radiative properties of semitransparent ceramic materials remains nowadays a difficult task. This paper reports a hybrid methodology to address this problem. The approach relies on two or more experimental emittance measurements, performed by infrared spectroscopy on samples of increasing thicknesses, and application of emittance models. The efficiency of the method is illustrated by using experimental data obtained on Jargal M samples, an industrial electrofused ceramic, and a virtual media built from X-ray computed tomography images. Two emittance models, a model from the literature and a new model proposed in this work, are selected to be a p...

Iterative and FEM methods to solve the 2−D Radiative Transfer Equation with specular reflexion

The present paper deals with iterative algorithms coupled with finite element methods (FEM) to solve the Radiative Transfer Equation (RTE) within semi-transparent heterogenous materials where specular reflexions occur on their boundaries. As our intention is to use such solution for inversion, the forward model should be solved as fastly as possible. This communication compares, in terms of both accuracy and CPU, the Discontinuous Galerkin (DG) method with the Streamline Upwind Petrov-Galerkin (SUPG) method, both being coupled with the Discrete Ordinate Method. Next, several iteratives methods used to accelerate the convergence are compared. These methods are the Gauss-Siedel (GS), the Source-Iteration (SI) and the Successive Over-Relaxation (SOR) methods.

Spectral data of specular reflectance, narrow-angle transmittance and angle-resolved surface scattering of materials for solar concentrators.

The spectral specular reflectance of conventional and novel reflective materials for solar concentrators is measured with an acceptance angle of 17.5 mrad over the wavelength range 300−2500 nm at incidence angles 15–60° using a spectroscopic goniometry system. The same experimental setup is used to determine the spectral narrow-angle transmittance of semi-transparent materials for solar collector covers at incidence angles 0–60°. In addition, the angle-resolved surface scattering of reflective materials is recorded by an area-scan CCD detector over the spectral range 350–1050 nm. A comprehensive summary, discussion, and interpretation of the results are included in the associated research article “Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators” in Solar Energy Materials and Solar Cells.

Enhanced adaptive focusing through semi-transparent media.

Adaptive optics can focus light through opaque media by compensating the random phase delay acquired while crossing a scattering curtain. The technique is commonly exploited in many fields, including astrophysics, microscopy, biomedicine and biology. A turbid lens has the capability of producing foci with a resolution higher than conventional optics, however it has a fundamental limit: to obtain a sharp focus one has to introduce a strongly scattering medium in the optical path. Indeed a tight focusing needs strong scattering and, as a consequence, high resolution focusing is obtained only for weakly transmitting samples. Here we describe a novel method allowing to obtain highly concentrated optical spots even by introducing a minimum amount of scattering in the beam path with semi-transparent materials. By filtering the pseudo-ballistic components of the transmitted beam we are able to experimentally overcome the limits of the adaptive focus resolution, gathering light on a spot with a diameter which is one third of the original speckle correlation function.

Spectral reflectance, transmittance, and angular scattering of materials for solar concentrators

The narrow-angle spectral specular reflectance and angular scattering of conventional and novel reflective materials for solar concentrators are measured over the wavelength range 300–2500nm at incidence angles ranging from 15° to 60° using a spectroscopic goniometry system. The solar-weighted specular reflectance at near normal incidence and an acceptance half-angle of 17.5mrad is 0.941 for back-silvered glass, 0.908–0.926 for silvered polymer films, 0.895 for aluminized polyester film, 0.939–0.954 for silvered aluminum sheets, and 0.860 for aluminized aluminum sheet. The angular scattering, quantified in terms of the standard deviation of a Gaussian distribution, is found to be negligible for aluminized polyester (<0.05mrad) and back-silvered glass (<0.07mrad), and noticeable for silvered polymer films (0.27–1.12mrad) and silvered aluminum sheets (0.12–1.66mrad). In addition, the spectral transmittance of semi-transparent materials suitable for protective covers is measured, yielding solar-weighted normal transmittance values of 0.913 and 0.946 for 100μm thin films of ETFE (ethylene-tetrafluoroethylene) and FEP (fluorinated ethylene propylene), respectively. The measured optical properties are incorporated in a Monte Carlo ray-tracing program and applied to analyze the optical performance of solar concentrators.

A new method to retrieve spectral absorption coefficient of highly-scattering and weakly-absorbing materials

A significant uncertainty in the absorption coefficient of highly scattering dispersed materials is typical in the spectral ranges of very weak absorption. The traditional way to identify the main absorption and scattering characteristics of semi-transparent materials is based on spectral measurements of normal-hemispherical reflectance and transmittance for the material sample. Unfortunately this way cannot be used in the case of in vivo measurements of optical properties of biological tissues. A method suggested in the present paper is based on thermal response to the periodic radiative heating of the open surface of a semi-transparent material. It is shown that the period of a variation of the surface temperature is sensitive to the value of an average absorption coefficient in the surface layer. As a result, the monochromatic external irradiation combined with the surface temperature measurements can be used to retrieve the spectral values of absorption coefficient. Possible application of this method to porous semi-transparent ceramics is considered. An example problem is also solved to illustrate the applicability of this method to human skin. The approach suggested enables one to estimate an average absorption coefficient of human skin of a patient just before the thermal processing.

Direct measurement of photo-induced nanoscale surface displacement in solids using atomic force microscopy

The interaction between light and solid matter causes localized heating and surface displacement in the nanometer scale. The deformed surface can be analyzed by probing the time-dependent intensity of a laser reflected off of the surface using the thermal mirror (TM) method. This method provides quantitative measurements of thermal, optical and mechanical properties of a variety of materials. Here, we propose an alternative method to measure laser-induced surface deformation using atomic force microscopy (AFM). AFM is employed to determine the time evolution of the surface deformation and a theoretical model is proposed to determine physical properties of semi-transparent materials. The results are found to be in excellent agreement compared to those obtained using TM.

A new method for the thermal characterization of transparent and semi-transparent materials using outdoor measurements and dynamic simulation

The work presents a new method to evaluate the thermal performance of transparent and semi-transparent materials under real operating conditions. The methodology could be particularly useful to test innovative materials and composites whose thermal properties are not known. It is easily reproducible, low cost, with a low technical impact. The proposed method uses experimental devices named “Solar Test Boxes” (STB) and a dynamic simulation software: IDA Indoor Climate and Energy. The outdoor measurements inside and outside the test boxes are used to accurately calibrate the dynamic simulation model of STB with the objective to obtain the global thermal transmittance (U) and Solar Heat Gain Coefficient (SHGC) of the test sample.The paper illustrates the methodology and the application of the method for the determination of the thermal characteristics of a light diffusing insulating glass. The application of the method to the case study allowed estimating SHGC with accuracy below ±10%. The U-value yields a poor result due to the lack of measurement range (required temperature difference) to assess this parameter.