Measurement Of Absorption Coefficient Research Articles

Influence of water-repellent admixtures ( Sitren and Stearate materials) on the microstructure and mechanical performance of conventional Portland cement paste and mortar

The longevity of mortar and concrete structures can be compromised by the absorption of water and other fluids, leading to deterioration and aesthetic issues. To address this, water-repellent admixtures are employed to enhance the service life of mortar and concrete components by improving their mechanical and microstructural characteristics. This study focus on the effects of incorporating Sitren P 750 and various stearate materials (calcium, zinc, aluminum, and barium) as admixtures with ordinary Portland cement at mortar and paste dosages of 0.5%, 1.0%, and 1.5% of the cement content. We found that mortars with water-repellent admixtures exhibited competitive mechanical properties at all curing ages. Additionally, the study confirmed the contribution of these admixtures to the production of hydration products and the structural development of the mortars, as investigated through scanning electron microscopy, thermogravimetric–derivative thermogravimetric, and X-ray diffraction analyses. Despite alterations in several physical properties and hydration kinetics due to the water-repellent compounds and their dosages, all admixtures provided effective water-repellent protection. This was further corroborated by water contact angle tests and the measurement of the capillary water absorption coefficient for all samples. Identifying the optimal mixture ratio for construction technology and effectively incorporating repellence features is a crucial aspect of this research.

Effects of multiple reflections on nonlinear absorption measurements.

Accurate measurement of nonlinear absorption coefficients by transmission-based techniques, such as Z-scan and its modifications, remains challenging due to high measurement errors. In this Letter, we claim that one of the reasons for that could lie in ignoring multiple reflections of light in plane-parallel samples in the presence of multi-photon excitation. Closed-form formulations for transmittance and reflectance coefficients, considering both linear and multiphoton absorption, are obtained in the geometrical optics approximation. The contributions of multiple reflections to the total transmittance are calculated for several II-VI materials reported in the literature. The results show a nonlinear dependence on incident intensity, ranging from 15.7% down to 7.9% for CdS, from 10.3% down to 5.8% for CdSe, and from 18.1% down to 9.1% for ZnSe. The dependence of the contribution of multiple reflections on the sample thickness is shown to exhibit a near exponential decay.

Absorption Measurement in Ultrapure Crystalline Quartz with the Eliminated Influence of Ambient Air Absorption in the Time-Resolved Photothermal Common-Path Interferometry Scheme

We demonstrate measurements of the absorption coefficient α ≈ 2.5 × 10−7 cm−1 in synthetic crystalline quartz at a wavelength of 1071 nm with a signal-to-noise ratio of 10/1 using the Time-resolved photothermal common-path interferometry (TPCI) scheme. It utilized cells filled with flowing argon and eliminated the influence of ambient air absorption. The scheme elements limiting the sensitivity of measurements at the level of ≈7.8 × 10−8 cm−1 were revealed. When these elements are replaced by better ones in terms of their thermal influence, the sensitivity of absorption coefficient measurements in crystalline quartz is ~10−8 cm−1. The calculation of the correction due to these optical elements of the values of the measured absorption coefficients is also described, which makes it possible to achieve the same sensitivity without replacing the elements. The improved scheme confirms the presence of the spatial inhomogeneity of absorption with a minimum coefficient of 2.5 × 10−7 cm−1 in synthetic crystalline quartz. The discrepancy of the absorption coefficient values in different regions of the crystal in the presented series of experiments was 2.5 × 10−7 cm−1 to 4 × 10−6 cm−1. Taking into account the ratio of thermo-optical parameters and the heat diffusion effect, the calculation shows that for quartz glasses the corresponding sensitivity of the absorption coefficient measurements equals ≈1.5 × 10−9 cm−1.

Validation of an absorption coefficient measurement technique using two cardioid microphones in any impedance tube

We have proposed a technique for measuring sound pressure and particle velocity using a combination of cardioid microphones and then applied it to obtain the acoustic absorption coefficient in a tube. So far, we have revealed that either using one cardioid microphone measured twice or using a pair of cardioid microphones measured once are both suitable for the measurement and that the calibration of the cardioid microphones is required. If the technique works correctly, this technique holds promise for measuring the acoustic absorption coefficient of various specimens in any tube and with any cardioid microphones. To validate the technique's effectiveness, we conducted experiments in multiple square-section wooden or round-section steel tubes, with specimens of glass wool and polyester terephthalate (PET) wool. As a result, this technique can provide accurate absorption coefficient measurements in any tube configuration.

The frame around a test specimen and its influence on the measured sound absorption coefficient

For most practical cases of reverberation room measurements of sound absorption coefficient according to ISO 354:2003, the standard requires the edges of the test specimen to be covered by a reflective frame. The purpose of this requirement is to keep the edges of the test specimen from absorbing sound. While this statement is consistent with practical measurement results at medium to high frequencies, it has been shown that the low frequency performance of a high-absorbing test specimen worsens when a frame is not in place. To further investigate this phenomenon, a series of reverberation room measurements have been carried out on several variations of a porous absorber test specimen. The goal of the measurements has been to determine whether the size and dimensions of the test specimen affect the test results, and if any such affections are dependent on the presence of a frame. Additionally, the sound absorption area of the frame itself has been measured to elucidate whether the frame is likely to give a significant contribution to the total sound absorption area of a framed test specimen. The results will be presented and discussed in this paper.

Experimental investigation of the sound absorption characteristics of unconsolidated granular materials

In the context of a wider research project investigating the use of Granular Material (GM) within floor and wall structures to increase their sound insulation, this study presents the sound absorption coefficient (SAC) measurements of different thicknesses for a range of GM. A primary aim has been to extend the understanding of the behaviour of GM layers in absorbing the propagated incident sound wave. Equally important has been an assessment of what GM could be sourced from waste and be acceptable for use in buildings from the point of view of fire insulation, handleability, economy, etc. Samples of GM were placed in an 88mm diameter vertical impedance tube and SACs measured up to 2kHz. The results show the effect GM's different structure (size and shape), bulk volume, and mechanical characteristics have on the range and value of the SAC. These determine the extent to which GM could be a replacement for traditional sound absorption materials.

Validation of an eigenvalue-based inverse method for estimating locally-reacting surface impedance

Accurate boundary condition descriptions are essential for creating accurate computational models for room acoustics. These descriptions are often defined in terms of absorption coefficients or surface impedances. However, obtaining complex-valued, frequency-dependent values for an acoustically absorbing material sample at low frequencies is a challenging task. In fact, the current measurement standard ISO 354:2003 does not provide a method for measuring absorption coefficients below 100 Hz. In this paper, a recently proposed eigenvalue-based inverse method for estimating locally-reacting impedance at measurement system resonance frequencies is validated. The validation uses data from three samples measured in an impedance tube. The method is also used to estimate complex-valued, frequency-dependent impedances at frequencies below 100 Hz in a measured reverberant room and in a simulated reverberation chamber.

Sound absorbers from walnut shell waste: measurement and models

Waste walnut shells have been cleaned, dried, chopped, glued, pressed, and molded to form porous cylinders for measurement of normal incidence sound absorption coefficient spectra in an impedance tube. Porosities and flow resistivities have been measured non-acoustically. Field Emission Scanning Electron Microscopy images, used to obtain fragment size for determining shell density, reveal that the fragment surfaces are rough, which may influence acoustical performance. Measured absorption spectra have been compared with predictions of two analytical models for acoustical properties of rigid porous media, which assume microstructures of identical uniform parallel slanted slits (SS) and non-uniform cylindrical pores with a log normal radius distribution (NUPSD) respectively. Measured values of flow resistivity and porosity are used in the models but tortuosity is adjusted to give best agreement with the quarter wavelength resonance in the measured absorption coefficient spectra. Predictions agree best with data for samples made from the smallest shell fragments. These samples have the highest values of tortuosity, flow resistivity and offer good absorption at speech frequencies which suggests that recyclable and sustainable sound absorbers made from walnut shell wastes could be useful for controlling indoor reverberation..

Interlaboratory comparison of ISO 354 sound absorption coefficient measurements for four sound absorbing materials

Sound absorption coefficients are among the most important acoustic parameters of building materials. The coefficients are measured in reverberation chambers using the ISO354 measurement procedure. The complex reverberant sound field that builds up in such facilities is closely related to the concept of the diffuse sound field and is difficult to characterize experimentally. Due to the limited quantitative assessment of the sound field, there is no general agreement in the scientific community on how to improve the method of measuring sound absorption coefficients, although significant differences have been reported between the results of different laboratories. To address part of this challenge, we investigate how specific the variations between laboratory results are for a particular material. In our investigation, we evaluated four different sound absorbing materials in five independent acoustics laboratories. Four of the reverberation chambers used suspended diffusers, while the complex shape of one chamber was designed to achieve a diffuse sound field. The results show that the interlaboratory deviations are not very specific to the material tested, while general differences between the facilities can be observed. Furthermore, the meticulous geometric design of the chambers can be seen as an alternative to the use of suspended diffusers.

Reverberation room design optimisation for low-frequency diffuse sound absorption testing

The reproducibility of sound absorption testing with the reverberation room method is a long-standing concern. Absorptive samples induce directionality in the nearfield, while the farfield depends on the room geometry below the Schroeder frequency. Nevertheless, when properly accounting for nearfield effects, the theoretical diffuse absorption coefficient of a sample still represents its average performance across an ensemble of different rooms, even at very low frequencies. Recent research found that particular reverberation room designs allow for an accurate measurement of the diffuse sound absorption coefficient of highly absorptive samples at low frequencies. Pinpointing such designs hence opens up a possibility to sustainably improve the low-frequency reproducibility of sound absorption testing in reverberation rooms. The present paper introduces a numerical optimisation framework that serves this purpose. Specific room shapes are parametrised and the geometrical room parameters are optimised so as to minimise the difference between the measured and the diffuse absorption coefficient under appropriate constraints. The sound absorption testing of a sample in a particular reverberation room is numerically simulated using a method that is both accurate and computationally efficient at low frequencies. The diffuse absorption is computed with a hybrid deterministic-statistical energy analysis approach that accounts for the detailed absorber properties, geometry, and boundary conditions, as well as the nearfield effects. The methodology is applied to both cuboidal and hexahedral room shapes. Certain optimised designs are found not only to provide an excellent match for the absorber that was used during the optimisation, but they also maintain their performance across a range of absorptive samples. Additionally, potential geometrical deviations are found to be well tolerated by these reverberation room designs.

Measurement of nonlinear refraction and absorption coefficient in BaGa2GeSe6 crystal

The coefficients of nonlinear absorption and nonlinear refraction of the quaternary barium chalcogenide crystal BaGa2GeSe6 at a wavelength corresponding to half the band gap, as well as their dependence on the pulse repetition rate and peak on-axis irradiance, were measured for the first time. The third-order nonlinear optical properties were studied using the single-beam Z-scan technique. An Nd: YLF laser at 1.053 μm with a pulse duration of approximately 5.2 ns was used as a radiation source. In addition, a thermal Z-scan was carried out to investigate thermal lensing in the BaGa2GeSe6 crystal, employing a continuous wave Nd: YAG laser at 1064 nm. These studies represent an important step in comprehending the nonlinear optical properties of barium chalcogenide crystals and their behavior at different pulse intensities. The results might be significant for the modelling and design of mid-infrared optical systems.

A Full-Scale Analysis of Absorption Edges in Dye-Doped Nonlinear Optical Polymers.

A full-scale analysis of the absorption edges by modified Tauc-Lorentz models is essential in determining the optical bandgap and Urbach energy of semiconductors, transparent conductors, ionic compounds, and dielectric materials. This technique has not yet been applied to analyzing organic nonlinear optical (NLO) materials. This problem is tackled by preparing high-quality films of guest-host NLO polymers with a wide thickness range from sub-micron to 200 microns, allowing accurate measurement of full-spectral absorption coefficients of NLO materials over four orders of magnitude by the UV-VIS-NIR spectroscopy. The Tauc model and a new Monolog-Lorentz model are used to study the optical absorption edge of guest-host NLO polymers containing various push-pull chromophores and the dependence of optical bandgap and Urbach edge on the structure and composition of materials is analyzed. The results reveal the critical transition of the Urbach exponential tail to a low energy tail that overlaps with vibrational overtones of materials at the telecom wavelengths. Determining the fundamental absorption region of organic NLO films in this study provides quantitative insight into the research to harness the resonance-enhanced nonlinear coefficients of materials by operating at the wavelengths near the band edge with the control of optical loss.

Sound absorption coefficient measurement and analysis for multisection perforation microperforated panel

Sound absorption coefficient measurement and analysis for multisection perforation microperforated panel

Preparation of PPA based composite reinforcing with glass beads and clays: Investigation of sound absorbing

The research investigates the sound absorption properties of potassium polyacrylate (PPA) composites, particularly those augmented with clay and porous hollow glass beads within a hydrogel template. This unique material combination shows promise for efficient sound absorption, relevant in industries requiring effective noise control like acoustic engineering and construction. Experimental assessment focused on measuring the sound absorption coefficient, crucial for quantifying a material’s ability to absorb sound energy across various frequencies. Incorporating clay and porous hollow glass beads introduces complexities, emphasizing the need for precise acoustic performance prediction. Collected data from sound absorption coefficient measurements formed the basis for training an Artificial Neural Network (ANN) model. Leveraging the ANN’s pattern recognition capabilities, the model learned from diverse composite compositions, enabling accurate prediction of sound absorption coefficients for varying material compositions. This predictive model streamlines material design, offering a systematic approach to tailor composite acoustic characteristics. Integration of machine learning, particularly ANNs, enhances accuracy and expedites material design and optimization, contributing to innovative and customizable sound-absorbing materials for diverse industrial applications.

Discussion of “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”

In February 2024, Construction and Building Materials published the paper “Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR”, which claims to measure the capillary absorption of moisture in brick, sandstone, mortar and concrete by means of moisture content profiling with the ‘NMR mouse’, a low-field, single-sided, open-magnet NMR instrument. This critique formulates several serious concerns on the study’s outcomes and conclusions. The excessively large similarity of the capillary absorption behaviour of the four materials is peculiar, since it disregards the differences in their open porosities and pore sizes. The overly large capillary moisture contents are equally abnormal, as they exceed the moisture storage limit of the material’s pore structure. There appears to be an inconsistency between the moisture content profiles and the overall moisture masses. Finally, it is shown that the lengthy time interval necessary for a single NMR pass limits the applicability of the NMR mouse for capillary absorption coefficients of porous building materials.

Field comparison of dual- and single-spot Aethalometers: equivalent black carbon, light absorption, Ångström exponent and secondary brown carbon estimations

Abstract. The Aethalometer is a widely used instrument for black carbon (BC) mass concentration and light absorption coefficient (babs) measurements around the world. However, field intercomparison of the two popular models, dual-spot (AE33) and single-spot (AE31) Aethalometers, remains limited; in addition, the difference in secondary brown carbon (BrCsec) light absorption estimation between the two models is largely unknown. We performed full-year collocated AE33 and AE31 measurements in a megacity in southern China – Guangzhou. The babs values agree well between the two Aethalometers (R2 > 0.95), with AE33 / AE31 slopes ranging from 0.87 to 1.04 for seven wavelengths. AE33 consistently exhibits lower limits of detection (LODs) than AE31 for time resolutions of 2 to 60 min. The AE33 / AE31 slope for equivalent BC (eBC) was 1.2, implying the need for site-specific post-correction. The absorption Ångström exponent (AAE) obtained from different approaches does not agree very well between the two models, with the biggest discrepancy found in AAE880/950. The estimated BrCsec light absorption at 370 nm (babs370_BrCsec) was calculated using the minimum-R-squared (MRS) method for both Aethalometers. The babs370_BrCsec comparison yields a slope of 0.78 and an R2 of 0.72 between the two models, implying a non-negligible inter-instrument difference. This study highlights the high consistency in babs but less so in AAE between AE31 and AE33 and reveals site-specific correction for eBC estimation and non-negligible difference in BrCsec estimation. The results are valuable for data continuity in long-term Aethalometer measurements when transitioning from the older (AE31) to the newer (AE33) model, as anticipated in permanent global-climate and air-quality stations.

Measurement of light absorption by chromophoric dissolved organic matter using a type-II liquid capillary waveguide: assessment of an achievable accuracy

Light absorption by chromophoric dissolved organic matter (CDOM) in the ocean is often measured using liquid waveguide capillary cells coupled to spectral array detectors. This type of optical setup is affected by several sources of uncertainties related to the waveguide and the detector. Uncertainties from the waveguide arise from errors in the effective path length and the effects of water salinity, while errors related to the detector are due to the non-linearity in the response, internal stray light, and wavelength accuracy. Here, uncertainties in the measurements of the spectral absorption coefficient of CDOM due to the optical setup itself were investigated in detail. The related systematic errors were very often significant (2–15%) and larger than expected from simple measurement uncertainty (±1%). However, they can be corrected by characterizing the detector’s response for non-linearity and stray light, regularly performing calibrations for the detector’s wavelength response, and routinely measuring the waveguide’s effective path length. Including such corrections and timely calibrations reduces the uncertainties related to the spectrophotometric measurements to about ±2%. Uncertainties related to the necessary handling of samples are not included here.

Crystalline germanium high-Q microresonators for mid-IR

High-quality-factor optical microresonators have become an appealing object for numerous applications. However, the mid-infrared band experiences a lack of applicable materials for nonlinear photonics. Crystalline germanium demonstrates attractive material properties such as high nonlinear refractive index, large transparency window including the mid-IR band, particularly long wave multiphonon absorption limit. Nevertheless, the reported optical losses in germanium microresonators might not allow the potential of the Ge-based devices to be revealed. In this study, we report the fabrication of germanium microresonators with radii of 1.35 and 1.5 mm, exhibiting exceptional quality factors (Q-factors) exceeding 20 million, approaching the absorption-limited values at a wavelength of 2.68 µm. These Q-factors are a hundred times higher than previously reported, to the best of our knowledge. We measured the two-photon absorption coefficient combined with free-carrier absorption leveraging the high-Q of the resonators (obtained βTPA = (0.71 ± 0.12) · 10−8 m/W at 2.68 µm). This research underscores the potential of whispering gallery mode microresonators as valuable tools for measuring absorption coefficients at different wavelengths, providing a comprehensive analysis of various loss mechanisms. Furthermore, the exceptional Q-factors observed in germanium microresonators open intriguing opportunities for the advancement of germanium-based photonics within the mid-infrared spectral band.

First-principle investigation of lead-free double perovskites Cs2MScCl6 (M = Na, K) for optoelectronic and thermoelectric applications

Double perovskite optoelectronic devices are gaining popularity due to their advantageous features, such as an efficient and easy-to-manage crystalline structure. In this study, we looked into the optoelectronic, mechanical, and thermoelectric attributes of Cs2MScCl6 (with M being Na or K) using density functional theory. The obtained results show that both compounds can exist stably in cubic double perovskite structure, space group Fm3¯m . The electronic band structures of Cs2NaScCl6 and Cs2KScCl6 demonstrate a direct semiconducting band gap of 3.829 eV and 3.996 eV, respectively. As the pressure rises up to 200 GPa, Cs2KScCl6 reveals extraordinary tunability along with an indirect band gap of 2.000 eV. Moreover, optical analysis—comprising dielectric constant calculations, absorption coefficient measurements, refractive indices checks, reflectivity assessments, energy loss estimations, and electrical conductivity appraisals—shows promising results too. Specifically, the absorption coefficient and conductivity predominantly fall within the ultraviolet range under normal atmospheric pressure. The thermoelectric characteristics suggest a noteworthy Seebeck coefficient, low thermal conductance and good figure of merit implying it could be used in the domain of sustainable energy.

WSOC in accumulation mode aerosols: Distribution and relationship with BrC light absorption at an urban background site

This paper presents the outcomes of a one-month long campaign (Jan 11, 2021 to Feb 11, 2021) of size segregated particulate matter (PM) in the accumulation mode (AM). Samples were collected at an urban background station (southeastern Iberian Peninsula) using a micro-orifice uniform deposit impactor (MOUDI). PM mass and water-soluble organic carbon (WSOC) were subsequently measured. The main goals of this research were: (1) to explore differences in WSOC mass size distributions under different meteorological conditions and (2) to determine the most efficient size for light absorption by WSOC. For the second objective, measurements of absorption coefficients (σap,λ) were obtained by means of an Aethalometer (AE33). Significant differences in WSOC concentrations and σap,λ values during stagnation episodes compared to non-event days were observed. Increases in WSOC concentrations during these episodes were most likely associated with the photochemical production of secondary compounds (in small-size ranges of the AM) and with water uptake (in large-size ranges of the AM). The average σap,λ value during this type of event was 2.6 higher than for non-event days. No significant increases in WSOC levels were detected under Saharan dust events. The average contribution of BrC to light absorption at 370 nm was ∼35%, revealing a significant influence of BrC on the absorption process. High contributions from BrC to light absorption were associated with AAE values above 1.5 and, in general, with high WSOC concentrations. WSOC in the smallest size mode (0.25 μm) was mainly emitted from biomass burning (BB) and showed the highest light absorption efficiency.