Absorption Phenomena Research Articles

Cascaded Graphene Frequency Selective Surface Integrated Tunable Broadband Terahertz Metamaterial Absorber

The quest of novel materials and structures to design an efficient absorber for realizing wave trapping and absorption at terahertz (THz) frequencies is an open topic. But the design of a thin, wideband, and tunable THz absorber is still an arduous job. Hence, in this paper, a hybrid THz metamaterial absorber integrated with a cascaded graphene frequency selective surface (FSS), with ultra-high absorbance over a wide frequency range is designed using an analytical equivalent circuit model. Such an approach provides a feasible way to optimize the device by interrelating the effective electromagnetic and circuit parameters with the unit cell dimensions of FSS. A systematic study and critical analysis over a wide range of device parameters including graphene chemical potential and FSS design variables is demonstrated. A peak dip in reflection coefficient of -30.27 dB is observed at 2.94 THz for an optimal device with a chemical potential (μ c ) of 0.38 eV (μ c1 ), and 0.25 eV (μ c2 ) in the range of 0.1-4.0 THz. The cascaded FSS configuration results in the unique anti-reflection-based absorption phenomena, which is responsible for the achievement of -10 dB absorption bandwidth of 2.34 THz (0.85-3.19 THz). In addition, the frequency-dependent effective permittivity, permeability, and impedance is extracted using reflection data, in order to understand the device physics. Such ultra-thin and broadband absorbing device architecture may confer potential application perspectives in THz sensing, imaging, and detection.

Bi0.9Ho0.1FeO3/TiO2 Composite Thin Films: Synthesis and Study of Optical, Electrical and Magnetic Properties

A visible light active Bi0.9Ho0.1FeO3 nanoparticles/TiO2 composite thin films with different mol.% of Bi0.9Ho0.1FeO3 were successfully prepared via non-aqueous sol-gel method. The incorporation of 5, 10 and 20 mol.% Bi0.9Ho0.1FeO3 nanoparticles in the precursor solution of TiO2 brings modifications in the functional properties of the composite thin films. XPS analysis indicates that interdiffusion of Fe3+, Ho3+, Bi3+/Ti4+ ions through the interfaces between Bi0.9Ho0.1FeO3 nanoparticles and TiO2 matrix reduces the concentration of Ti3+ ions. X-ray diffraction analysis affirms that TiO2 and Bi0.9Ho0.1FeO3 retain anatase and orthorhombic phase respectively in composite films. The composite thin film containing 20 mol.% Bi0.9Ho0.1FeO3 nanoparticles exhibits the most prominent absorption phenomenon in visible region and has significantly reduced indirect band gap of 2.46 eV compared to that of pure TiO2 (3.4 eV). Hall effect measurements confirm that the resistivity of composite film increases by ∼2.33 orders of magnitude and its carrier concentration decreases by 1.8 orders of magnitude at 5 mol.% Bi0.9Ho0.1FeO3 nanoparticles addition compared to those of pure TiO2 film. Moreover, the pure film exhibits diamagnetism, whereas the composite films have both large ferromagnetic and small diamagnetic components. The findings in this research justify that the composite film can be a potential candidate for making improved photocatalyst, resistors and spintronic devices.

Update of the HITRAN collision-induced absorption section

Correct parameterization of the Collision-induced Absorption (CIA) phenomena is essential for accurate modeling of planetary atmospheres. The HITRAN spectroscopic database provides these parameters in a dedicated section. Here, we significantly revise and extend the HITRAN CIA data with respect to the original effort described in Richard et al. [JQSRT 113, 1276 (2012)]. The extension concerns new collisional pairs as well as wider spectral and temperature ranges for the existing pairs. The database now contains CIA for N2N2, N2H2, N2CH4, N2H2O, N2O2, O2O2, O2CO2, CO2CO2, H2H2, H2He, H2CH4, H2H, HHe, CH4CH4, CH4CO2, CH4He, and CH4Ar collision pairs. The sources of data as well as their validation and selection are discussed. A wish list to eliminate remaining deficiencies or lack of data from the astrophysics perspective is also presented.

Compact quad-band polarization independent metamaterial absorber using circular/square metallic ring resonator

In the paper, a compact quad-band polarization-independent metamaterial absorber has been presented for different microwave frequency bands. The proposed absorber unit cell comprises of two square and two concentric circular rings and it exhibits the absorption peaks greater than 90% at 3.1 GHz, 5.5 GHz, 7.6 GHz and 10.98 GHz respectively under the normal incidence. The full width at half maximum (FWHM) bandwidth is 150 MHz (3.03–3.18 GHz), 180 MHz (5.38–5.56 GHz), 330 MHz (7.44–7.77 GHz), and 560 MHz (10.70–11.26 GHz) at the four frequency bands. The proposed absorber is polarization and incidence angle insensitive due its symmetrical. The proposed structure also shows more than 90% absorptivity up to 60° incidence angle. The absorber unit cell is compact in configuration with size of 0.12 λo × 0.12 λo and ultrathin thickness of 0.016 λo, where λo is the wavelength at lowest frequency absorption peak. To recognize the absorption phenomenon of the absorber, input impedance, E-field and surface current distribution characteristics have been demonstrated. The structure has been fabricated and it shows good agreement between simulated and measured results.

Luminescent properties of stoichiometric Er:LiTaO3 submicron particles synthesized by a modified solid-state combustion route

Erbium-doped lithium tantalate submicron phosphor particles were produced by an efficient one-step solid-state combustion method. Well-crystallized products with uniform grain morphology were confirmed by X-ray diffraction and field-emission scanning electron microscopy. Thermogravimetric and differential thermal analysis were used to further analyze the combustion reaction process. In addition, down- and up-conversion luminescence (DCL, UCL) as well as the relationship between luminescence intensity and erbium doping level were revealed. The luminescence spectra for the UCL processes under different excitation intensities showed a remarkable three-photon absorption phenomenon in Er-doped system. These results demonstrate that the modified solid-state combustion method possesses practical value for large-scale synthesis of rare earth-doped submicron phosphors and has great potential for application in solid-state laser and display fields.

Evaporated porphyrin films as nitrogen dioxide gas sensors

In this work, metal-free and copper(II) 5,10,15,20-tetrakis(-4-(methyl 2-phenoxyacetate)) porphyrin films were employed as nitrogen dioxide gas sensors. The films were vacuum evaporated and the sensor response was evaluated as changes in the optical absorption spectra, hydrophobic properties and conductivity at different gas concentrations. The morphology of the films obtained with scanning electron and atomic force microscopy before and after gas exposure indicated different interaction mechanisms. For instance, metal-free film exhibited an absorption phenomenon due to gas diffusion towards the bulk film because of the presence of pores at the film interface, while the copper-porphyrin film showed interfacial film degradation. From UV–vis results, differences in the gas content within the film were detected due to the formation of new peaks around 680 nm in agreement with morphological findings. Contact angle results exhibited less hydrophobic films after gas adsorption as a result of changes in the surface roughness. In addition, the conductivity values were not only dependent on the gas concentration but also on the molecular structure. For instance, gas absorption within the metal-free films truncated electron mobility paths decreasing the conductivity response in comparison with the copper system. Finally, the molecular packing arrangement and gas absorption were also investigated by using density functional theory, which provided some insights into the molecular-gas interactions and supported experimental results.

Numerical and experimental study of absorption of H2O vapor in wavy falling film of LiBr aqueous solution in vertical tubes and in presence of non-absorbables

One of the main reasons for the discrepancies between theoretical predictions of absorption phenomena made by mathematical models when they are compared against experimental results under real conditions, are the presence of non-absorbable gases. It is well known that these non-absorbable gases inside the shell of the absorption chiller are produced mainly for two reasons: (i) air leakages (Oxygen-Nitrogen); (ii) gases produced by corrosion (Hydrogen). In order to evaluate the influence of the presence of non-absorbable gases, an experimental set-up which reproduces vapor absorption in a vertical falling film has been designed and built with a mass spectrometer analyzer. Parallelly, a mathematical model of falling film absorption of H2O by LiBr aqueous solution that considers the influence of non-absorbable gases has been implemented. The model is semi-empirical, based on Navier–Stokes equations together with energy and mass species simplified under the boundary layer hypotheses. Several experimental tests have been performed to determine the influence of the air concentration in the absorption performance. Moreover, a comparison of numerical results against experimental data has been performed under different working conditions with reasonable agreement.

Polarization and incident angle independent metasurface absorber for X-Band application

In the article, polarization and incident-angle independent metasurface absorber for X-band application has been proposed. Proposed absorber unit cell composed of a circular sector attached to a cross-shaped structure. The proposed absorber is symmetrical along the horizontal and vertical axis, which supports polarization angle insensitivity. Metasurface absorber shows the very good impedance matching with free space at 10.48 GHz along with 97% absorptivity. The full width at half maximum (FWHM) bandwidth is 480 MHz (10.24–10.72 GHz). In transverse electric and magnetic (TE and TM), modes the absorptivity of the proposed absorber is maintained above 90% up to 60° incidence angle. The absorber has an ultrathin thickness of 0.028λo, where λo is the wavelength of absorption peak. The absorption phenomenon is explained by normalized impedance, E-field distribution and surface current density. To analyze the metasurface properties effective permittivity, permeability and dispersion diagram has been demonstrated. The metasurface absorber has been fabricated and it shows the good accord between simulated and measured results.

Wideband High-Absorption Electromagnetic Absorber With Chaos Patterned Surface

A resistive metasurface featured by the Rossler chaos reaction-diffusion system patterns is proposed and realized in a wideband electromagnetic absorber. The chaos surface consists of units with both random shapes and dimensions. Simulation results show absorption phenomenon, and correlation function analysis indicates new wave-absorbing mode can be generated when correlation of the edges of the chaos patterns matches geometrical size of chaos units. Experimental results indicate unconventional bandwidth ratio with reflectivity lower than –10, –15, and –19 dB reaches 96.84%, 80.1%, and 56.1%, respectively. A high-absorption nature makes this structure have application potential in a modern anechoic chamber or other electromagnetic wave absorbers.

Modelling and experimental validation of an in-tube vertical falling film absorber with counter flow arrangement of solution and gas

In the present study, an in-tube vertical falling film absorber with gas and falling film in counter-current flow arrangement, which utilizes NH3−H2O pair as the working fluid, has been built and is then integrated with a single effect absorption heat pump. Twelve sets of tests have been designed and conducted, taking into account the standard operating range of these types of heat pumps. The results obtained from performing a testing procedure on this experimental setup have been utilized to assess the accuracy of a developed mathematical model in simulating the corresponding absorption phenomenon. The obtained results demonstrate an acceptable agreement between the values simulated by the model and the experimental data, while addressing various heat duties. Furthermore, it has been shown that the transfer coefficients between the liquid film and the interface are order/s of magnitude higher than the ones between the gas and the interface and therefore, the absorption process is controlled by the heat and mass transfer coefficients between the film and the interface. Moreover, it has been revealed that in falling film absorber modelling, insignificant errors in the evaluation of rate of absorption can lead to a notable miscalculation of the absorber size. It is concluded that the effect of hydrodynamic of the film on the heat and mass transfer process should be considered for future enhancement of the model.

Unidirectional absorption properties in a defective semiconductor-dielectric asymmetric triadic Cantor photonic crystal

It is well known that the defective asymmetric bilayer photonic crystal (PC), air/(DB)NA(BD)M/air, where A and B are dielectrics, D is lossy material, and N, M are stack numbers with N≠M, exhibits unidirectional absorption phenomena. In this work we theoretically study whether the defective asymmetric Cantor PC also exhibit the unidirectional optical property. The considered PC is the defective asymmetric Cantor PC, air/TCSN/A/TCSM/air, where TCSN is the N stage triadic Cantor structure composed of B and D; the semiconductor, n-InSb, is chosen as D. Our results show that their absorption spectra also exhibit unidirectional properties. Besides, the absorption peaks has defect mode depending on the defect layers just similar to the defect modes in the transmittance spectra of the usual symmetry photonic crystals.

Influence of Surface State in Micro-Welding of Copper by Nd:YAG Laser

Laser welding of copper is characterized by low and unstable light absorption around 1000 nm wavelength. Combination of high thermal conductivity and low melting point makes it difficult to obtain good welding quality and leads to low energy utilization. To improve efficiency and welding quality, a technique to enhance process stability using 1064 nm wavelength Nd:YAG laser has been proposed, and absorption rate and molten volume in laser micro-welding were discussed. Since the surface state of specimen affects absorption phenomena, effects of surface shape and surface roughness were investigated. Absorption rate and molten volume were increased by creating appropriate concave holes and by controlled surface roughness. Stable micro-welding process with deep penetration and good surface quality was achieved for transitional processing condition between heat conduction and keyhole welding, by enhanced absorption rate.

Liquisolid systems: Understanding the impact of drug state (solution or dispersion), nonvolatile solvent and coating material on simvastatin apparent aqueous solubility and flowability.

The drug in a solid dosage form must undergo dissolution before it is available for absorption from the gastrointestinal tract. Liquisolid system (LS) is a technology used for increasing aqueous solubility of the drugs, which has an important role in the dissolution and absorption phenomena. However, many factors can influence the performance and success of LS. Therefore this study aimed to evaluate through a factorial design, the factors such as drug state (solution or dispersion), nonvolatile solvent and coating material that influence the increase simvastatin (BSC II drug) apparent aqueous solubility and LS flow properties. Through numerical optimization the best formulation was selected to develop a liquisolid compact (LC) and it was evaluated by dissolution tests over commercial tablets using two dissolution media. Analyzing the data, the type of nonvolatile solvent and the state of the drug (solution or dispersion) were the factors with the greatest effects on the apparent aqueous solubility response (p < 0.0001 for both). Regarding the responses that evaluated the flow properties, the type of coating material and the type of nonvolatile solvent were the factors that influenced the Carr index (p < 0.0006, p < 0.0023, respectively) and Hausner ratio (p < 0.0006, p < 0.0014, respectively), where formulations containing Kollidon® CL were more efficient than Aerosil® (which is the most commonly used coating material for LS manufacture). These results enabled us to identify which factors were most influential and to move towards the use of new excipients in the case of Kollidon® CL. In addition, allowed a wider evaluation and understanding of LS, which is considered an important technological alternative for the increase of drug solubility.

Insights on the photocatalytic degradation processes supported by TiO2/WO3 systems. The case of ethanol and tetracycline

TiO2/WO3 composites are widely in the literature as engineered systems for photocatalytic and (photo)electrochemical applications, since the presence of WO3 can promote both visible light absorption and electron transfer phenomena of TiO2. The preparation of these system, depending on the preparation method, can also affect the surface feature with respect to TiO2, modifying adsorption and performance, as well as the reaction mechanisms. Here, TiO2/WO3 composites were prepared by precipitation of WO3 onto the TiO2 surface and characterized in terms of their structural, morphological, optical and surface properties. Raman and IR spectroscopy as well as a marked shift in the isoelectric point support the preferential surface location of WO3. Samples were photocatalytically tested towards the degradation of ethanol and of tetracycline and the adsorption and degradation behaviour were studied, suggesting, in both cases, significant variations of the reaction paths by the addition of WO3.

Multi-objective optimization of heat transfer mechanisms of microcellular polymeric foams from thermal-insulation point of view

In this study, a comprehensive investigation of heat transfer mechanisms of polymeric foams is performed using response surface methodology (RSM). Foam density, cell size and strut fraction are selected as variable parameters. A regression model is obtained to predict the overall thermal conductivity using analysis of variance (ANOVA) tool of RSM. The results indicate that this regression model with R2 = 95.22% and having an error smaller than 4% has an appropriate performance to estimate the overall thermal conductivity. Foam density is the most effective parameter on the overall thermal conductivity with contribution of 69.8%, as ANOVA results show. Reduction of foam density and cell size leads to decreasing the thermal conductivity while it is also decreased by increasing the strut fraction. It is reported for the first time that the cell walls are dominant components in comparison to struts in heat transfer mechanism by solid phase. On the other hand, it is discovered that the strut component is the predominant part in absorption phenomenon. The overall thermal conductivity is 23.69 mW/mK at the optimum condition (i.e. foam density of 25 kg·m−3, cell size of 1 μm and strut fraction of 0.2 in the studied range) using multi-objective optimization tool of RSM.

Masquelet membrane induction technique for reconstruction of bone defect

There are many reasons for bone defects. Trauma, malignant tumor resection, chronic osteomyelitis and congenital factors can all lead to bone defects. The treatment methods include autogenous cancellous bone grafting, vascularized fibular grafting, distraction osteogenesis and Masquelet techniques, etc. Masquelet technique was first discovered by Masquelet et al. in 1986. It provides a simple and safe method for the treatment of large bone defects. This technique has two stages, and the first stage includes wound thoroughly debridement, maintenance of the stability of fracture, placement of (antibiotic) cement spacer, and closure of the wound without tension, then 6 to 8 weeks later, the second stage will be conducted including performing a longitudinal incision of the induced membrane, removal of the bone cement and bone graft. Bone cement includes polymethyl methacrylate (PMMA), calcium phosphate, calcium sulfate and other materials, if necessary, antibiotics could be combined at the same time. Different bone cement induced biofilmhas different characteristics.Induced membrane can secrete transforming growth factor (TGF-β1), bone morphogenetic protein 2 (BMP-2), platelet endothelial cell adhesion molecule-1 (PECAM-1), and vascular endothelial growth factor (VEGF) and other osteogenesis growth and angiogenesis related factors, then an independent space is built to isolate the bone graft from outside environment, avoiding the phenomenon of bone graft absorption and providing a stable biological environment of bone defect. Masquelet technique is simple to operate, safe, accompanied by fewer complications, less demanding to the recipient area, easy to be accepted by patients and promoted clinically. It is applicable to bone defects in all parts and has great potential for clinical application and especially suitable for large segmental bone defectwhich is ineffective in other treatment methods.

Ultra-Short Pulsed Laser Manufacturing and Surface Processing of Microdevices

Abstract Ultra-short laser pulses possess many advantages for materials processing. Ultrafast laser has a significantly low thermal effect on the areas surrounding the focal point; therefore, it is a promising tool for micro- and submicro-sized precision processing. In addition, the nonlinear multiphoton absorption phenomenon of focused ultra-short pulses provides a promising method for the fabrication of various structures on transparent material, such as glass and transparent polymers. A laser direct writing process was applied in the fabrication of high-performance three-dimensional (3D) structured multilayer micro-supercapacitors (MSCs) on polymer substrates exhibiting a peak specific capacitance of 42.6 mF·cm−2 at a current density of 0.1 mA·cm−2. Furthermore, a flexible smart sensor array on a polymer substrate was fabricated for multi-flavor detection. Different surface treatments such as gold plating, reduced-graphene oxide (rGO) coating, and polyaniline (PANI) coating were accomplished for different measurement units. By applying principal component analysis (PCA), this sensing system showed a promising result for flavor detection. In addition, two-dimensional (2D) periodic metal nanostructures inside 3D glass microfluidic channels were developed by all-femtosecond-laser processing for real-time surface-enhanced Raman spectroscopy (SERS). The processing mechanisms included laser ablation, laser reduction, and laser-induced surface nano-engineering. These works demonstrate the attractive potential of ultra-short pulsed laser for surface precision manufacturing.

Infrared Thermography technique (IRT) for the evaluation of the hydric behavior of building stones

The water distribution into stone specimens in laboratory conditions is evaluated through the infrared thermography method (IRT). Porous building stones samples (calcarenite and sandstone) are examined under stable laboratory conditions (controlled temperature and relative humidity) in order to simulate the same hydric behavior in real scale of material systems &lt;em&gt;in situ.&lt;/em&gt; Hydric tests monitored through IRT are performed in order to analyze the capillary water absorption and evaporation transport phenomena into stone samples. IRT technique allows to record thermal images at different intervals of time highlighting the internal capillary and evaporation rise heights, responsible for the majority of decay processes occurring in masonries. The geometric shape of the damped area and the time of spreading are directly related to the open porosity of the investigated stone materials. Hydric tests are repeated for each splitting plane of the specimens (faces), in order to obtain useful results that could be applied for real masonries. Results demonstrate the usefulness of IRT as a non-destructive and portable technique in the field of new construction and for restoration purposes, as well as its importance in characterizing the physical stone features and the effectiveness of applied conservation treatments.

Green synthesis of silver/silica nanocomposite in seconds at room temperature using reducing agents obtained from silicon nanoparticles

In this work, we present a single step, highly stable, energy efficient, green and economically scalable room temperature method for the synthesis of silver/silica (Ag/SiO2) nanocomposite. The Ag/SiO2 nanocomposites are synthesized from silver nitrate solution using extracts of silicon nanoparticles. The silicon nanoparticles, which are prepared through the laser ablation of silicon in ethanol with polyvinylpyrrolidone,are used as the reducing agent. The nanocomposites have been characterized by ultraviolet–visible spectroscopy, x-ray diffraction pattern and Fourier transform infrared spectrum. The ultraviolet–visible absorption spectrum of the colloidal nanocomposites shows a surface plasmon peak at 424 nm. The x-ray diffraction pattern of Ag/SiO2 nanocomposite powder only contains silver structures, and thus SiO2 nanoparticles are amorphous. The nonlinear properties of Ag/SiO2 colloidal nanocomposite solution are studied using the Z-scan method. The value of the nonlinear absorption is measured as 17 × 10−3 cm W−1 with a positive sign, which illustrates the two photon absorption phenomena. The Ag/SiO2 nanocomposite shows a large nonlinear absorption near the surface plasmon resonance frequency of Ag nanoparticles.

All-optical fiber optic coherent amplifier

A fiber optic-based all-optical amplifier is designed by using the coherent perfect absorption phenomenon. For this purpose, we use a deposited chromium thin layer as an absorbent material on the cross-section of a PM fiber. By placing another fiber in front of the deposited one, we show that by controlling the relative phase between the two counter-propagating beams, total absorbance can be controlled. In the interaction of two beams with unequal intensities, absorption control can be associated with amplification for the weaker beam. By using this mechanism, the effect of an external phase-shifting parameter can be amplified. Furthermore, it is possible to amplify a small signal riding on a CW background through this all-optical procedure.