Measurement Of Absorption Coefficient Research Articles

Measurement of refractive indices and absorption coefficients for glass materials and nematic liquid crystals in THz frequency band

Measurement of refractive indices and absorption coefficients for glass materials and nematic liquid crystals in THz frequency band

Characterization of water-soluble organic carbon absorption at an urban background site in the south-eastern Iberian Peninsula

Measurements of absorption coefficients (σap,λ) and carbonaceous components (OC, EC, WSOC and levoglucosan) in PM1 were conducted at an urban background site in southeastern Spain throughout 2021. The main goal of this research was to determine the contribution from different sources to WSOC light absorption (σWSOC). For this, σBrC,λ values were previously obtained. The mean contribution of BrC to total aerosol absorption was ∼29% at 370 nm, revealing a significant influence of BrC to light absorption in the study area. Assuming that BrC light absorption was from WSOC and WIOC, a multilinear regression (MLR) model was used to estimate σWSOC and σWIOC. Average values (mean ± SD) were very similar for both components: σWSOC,370 = 1.6 (±0.7) Mm−1 and σWIOC,370 = 1.9 (±0.7) Mm−1. Finally, the PMF technique coupled with MLR analysis was used to identify the sources of WSOC light absorption and estimate their contribution. Our findings point to biomass burning as the dominant source of σWSOC during the cold season, with a contribution of ∼37%. The Mineral Dust and Secondary Nitrate sources, that were not included in the model due to their low contribution to WSOC mass concentrations, accounted for a significant percentage of σWSOC during this period. Secondary organic aerosol was the major source during the warm season (∼56%), followed by traffic emissions (∼30%).

Which absorption coefficients are correct?

Each year absorptive material samples are sent to various accredited acoustic laboratories around the country by manufacturers who want to verify the performance of their products. Results are published as indisputable validation of the product absorption performance by the manufacturer. As no recent interlaboratory study results for ASTM C423—Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method are available, the Owens Corning Acoustic Research Center initiated a private interlaboratory study. A small set of accredited acoustical laboratories tested a set of the original National Voluntary Laboratory Accreditation Program reference panels. The resulting data and differences in the measured absorption coefficients will be reviewed.

Moving Beyond Simulation: Data-Driven Quantitative Photoacoustic Imaging Using Tissue-Mimicking Phantoms.

Accurate measurement of optical absorption coefficients from photoacoustic imaging (PAI) data would enable direct mapping of molecular concentrations, providing vital clinical insight. The ill-posed nature of the problem of absorption coefficient recovery has prohibited PAI from achieving this goal in living systems due to the domain gap between simulation and experiment. To bridge this gap, we introduce a collection of experimentally well-characterised imaging phantoms and their digital twins. This first-of-a-kind phantom data set enables supervised training of a U-Net on experimental data for pixel-wise estimation of absorption coefficients. We show that training on simulated data results in artefacts and biases in the estimates, reinforcing the existence of a domain gap between simulation and experiment. Training on experimentally acquired data, however, yielded more accurate and robust estimates of optical absorption coefficients. We compare the results to fluence correction with a Monte Carlo model from reference optical properties of the materials, which yields a quantification error of approximately 20%. Application of the trained U-Nets to a blood flow phantom demonstrated spectral biases when training on simulated data, while application to a mouse model highlighted the ability of both learning-based approaches to recover the depth-dependent loss of signal intensity. We demonstrate that training on experimental phantoms can restore the correlation of signal amplitudes measured in depth. While the absolute quantification error remains high and further improvements are needed, our results highlight the promise of deep learning to advance quantitative PAI.

Numerical Equivalent Acoustic Material for Air-Filled Porous Absorption Simulations in Finite Different Time Domain Methods: Design and Comparison

Extracting the microscopic parameters of a porous material is a complex task, and attempts have been made to develop models that can simulate their characteristics, gathering the least amount of information possible. As a case in point, tests to evaluate macroscopic behaviors such as tortuosity, which depends directly on the microscopic fluid velocities, are highly susceptible to generate errors if the precision of the measurement devices is not correct, and the same goes for the other parameters. For this reason, in this paper, a sound propagation model in porous materials with a rigid frame is presented based on a local theory, which tries to simplify, even more, the way to obtain the basic characteristics of porous materials, such as their absorption coefficient at normal and random incidence, and their normal surface impedance. The proposed linearized equivalent fluid model presents four phenomenological coefficients, which characterize acoustic propagation trough the material. Their values are obtained from the material thickness and a measurement in an impedance tube following the ISO 10534 standard. Thus, what is only required is the measured absorption coefficient, either on one third or one octave bands, to fully represent the acoustic behavior in the finite different in time domain (FDTD) method. The model has been simulated with FDTD in porous and fibrous kernels, and the results show a strong agreement with the laboratory measurements and with the analytical results calculated with well-established semi-phenomenological models.

Measurements of sound absorption coefficients of raked audience seating in a rectangular scale model room

Despite its significance, the sound absorption property of seating has not been fully understood compared to the other surfaces in an auditorium. In particular, the lack of information for sound absorption by seating with changes in section may lead to a failure in accurate prediction of room acoustics. This research investigates the effect of floor rake angle change on the sound absorption property of seating through a series of measurements performed in a rectangular scale model room. Both the sound absorption coefficients (αA) of unoccupied and occupied seating are measured using combinations of three different types of scale model chairs and two different types of scale model auditors while the floor rake angle is systematically varied. The results suggest that the αA’s for both unoccupied and occupied seating significantly increase as the floor rake angle becomes larger. However, the relationship between the floor rake angles and the corresponding αA’s is not monotonous. The effect of changing floor rake is highly associated with the upholstering of chairs for unoccupied seating, whereas it critically depends on the sound absorption property of auditors rather than the upholstering for occupied seating.

Mycelium-Based Composites as a Sustainable Solution for Waste Management and Circular Economy.

The global population is expected to increase by nearly 2 billion individuals over the next three decades, leading to a significant surge in waste generation and environmental challenges. To mitigate these challenges, there is a need to develop sustainable solutions that can effectively manage waste generation and promote a circular economy. Mycelium-based composites (MBCs) are being developed for various applications, including packaging, architectural designs, sound absorption, and insulation. MBCs are made by combining fungal mycelium with organic substrates, using the mycelium as a natural adhesive. Mycelium, the vegetative part of fungi, can be grown on various organic feedstocks and functionalized into a range of diverse material types that are biobased and thus more sustainable in their production, use, and recycling. This work aims to obtain mycelium-based composites with acoustic absorption properties, using coffee grounds and agricultural waste as raw materials. The topic approached presents a new method of recovering spent coffee grounds that does not involve high production costs and reduces two current environmental problems: noise pollution and abundant waste. Measurements of the normal-incidence sound absorption coefficient were presented and analyzed. Mycelium-based composites offer an innovative, sustainable approach to developing bio-composite sound-absorbing surfaces for interior fittings. The material by Ganoderma lucidum exhibits exceptional sound-absorbing properties at frequencies below 700 Hz, which is a crucial aspect of creating sound-absorbing materials that effectively absorb low-frequency sound waves. The modular construction system allows for a high degree of flexibility to adapt to short-term changes in the workplace.

ANALISIS TINGKAT REDAM BUNYI DARI BEBERAPA JENIS BAHAN AKUSTIK KAIN PERCA

Research was carried out on the analysis of the sound absorption level of several types of patchwork acoustic materials which aims to find out whether patchwork can be used as a sound dampening material, to determine the sound absorption level of several types of patchwork acoustic materials and to determine the best attenuation level of several types of patchwork acoustic materials. the type of patchwork acoustic material. The background of this research is due to the acoustic quality of the room which has received less attention for the comfort of listeners when they are in a room. The study used variations of sound absorbing materials, namely cotton and denim patchwork. Measurement of the sound absorption coefficient of patchwork is done by making a sample chamber with a length of 13.5 cm, a width of 13.5 cm and a height of 8.5 cm. Sound Level Meter is a tool used to measure the level of sound pressure. Variations in the thickness of the patchwork used were 3, 5, and 10 mm. In measuring the entire inner wall surface of the sample room will be covered with patchwork, then the speaker is placed in the sample room. The sound source comes from speakers with a frequency of 90 dB which is arranged in a frequency range of 125, 250, 500, 1000, 2000 and 4000 Hz. The best damping level of the three materials is a mixture of cotton and denim with a thickness of 10 mm, because the thicker the patchwork layer, the α value obtained is 0.629.

Diffusion equation-based modelling of reverberation chambers for sound absorption measurements

Recent research in reverberation chambers has revealed unacceptably large variations resulting from round-robin tests of the standardized measurements of random-incidence absorption coefficients. These variations have prompted active research activities in architectural acoustics. This study applies a diffusion equation model (DEM) in acoustics of reverberation chambers for random incidence absorption measurements by predicting both reverberant sound energies and energy flows. The DEM is of high computational efficiency when compared with other existing geometrical acoustics and wave-based methods. The DEM modeling of the sound energy flows in a reverberation room further reveals violations of the diffuse field assumption near the boundary area of absorbing sample under test. Due to its computational efficiency and higher order of the reverberant energy prediction of the statistical room-acoustic modeling, this work investigates an estimation approach to the absorption coefficients of the sample under test. The proposed approach estimates the absorption coefficients by pursuing both the DEM simulations and the chamber-based measurements. This paper investigates sound energy flux over varied absorbing degrees of absorber samples in standardized sizes, computational efficiency of the DEM for reverberant energy decays in reverberation chambers, and potential significance applied to random-incident absorption coefficient measurements.

A finite element study of absorption coefficient measurement at low frequencies

The frequency-dependent absorption coefficients of an acoustically absorbent material sample can be measured using the reverberation chamber method, defined by the ISO standard 354:2003. The lower frequency bound for the measurement defined in the standard is 100 Hz, since measurement data below this frequency may be unreliable. However, the ability to measure absorption coefficients at low frequencies is becoming increasingly more important, to facilitate the enhanced control of low frequency sound fields. This paper presents a finite element method study of the reverberation chamber measurement method at frequencies below 100 Hz, and the predicted performance of the ISO standard method is reported. Additionally, a recently proposed method that makes use of finite element-based eigenvalue analyses to estimate the locally reacting complex-valued impedance of a sample at modal frequencies is applied to the problem. It is shown that the proposed method can be used to estimate frequency-dependent absorption coefficients at modal frequencies below 100 Hz.

Application of TDLAS for measuring absorption coefficients of H2S rotational absorption lines near the wavelength of 2 µm

This paper presents the experimental measurement of hydrogen sulfide absorption coefficients in the pressure range of 75–460 mbar of two rotational absorption lines of the vibrational band of H2S molecule at 021-000 transition using the tunable diode laser absorption spectroscopy technique. The obtained results are compared with the data of the HITRAN spectroscopic database.

Sound absorption coefficient measurement for various building elements

The current sound absorption coefficient testing measurement method, ISO 354, primarily focuses on materials used for surface coverings or equivalent sound absorption objects. However, there are other building elements such as lightweight partition walls and windows that do not have solid structures behind them. These elements may allow sound to transmit to adjacent interior spaces or escape to the outside. On the other hand, the transmitted sound is expected to be rebounded into the measurement room when the test material is placed on a hard and thick surface as described in ISO 354. The test was conducted in a reverberation chamber located at the center of three consecutive acoustic testing chambers: reverberation-reverberation-anechoic. The testing chambers are equipped with test openings between them and are fully isolated from one another. The purpose of the test was to confirm whether the current measurement method reflects the influence of the assumed rebounded sound. The sound absorption coefficients were measured with the specimen installed on the floor, representing the ISO 354 condition, and comparisons were made to the conditions where the specimen was installed in another reverberation chamber opening and in the anechoic chamber opening.

Improved Terahertz Time-Domain Spectroscopy via the Extended Kalman Filter

To implement terahertz time-domain spectroscopy (THz-TDS) systems that have short integration time and maintain performance, the extended Kalman filter (EKF) has been used. Performance of EKF with THz-TDS on vapor samples and solid samples is untested. Previous EKF methods were not adaptive for use on multiple THz-TDS systems. We provide an adaptive EKF method that can work on any THz setup, to improve maximum measurable absorption coefficient. Our adaptive EKF method responds to THz pulse properties. The adaptive EKF is exhaustively demonstrated for six different time-constant data sets spanning 1 ms to 300 ms for THz-TDS on vapor with electro-optic THz detection. The acquisition time saved is quantified and shown to significantly reduce acquisition time from 2.58 ms to 1 ms. This improvement of 2.58 times will have a significant effect to move spectral imaging from taking hours to taking minutes. Vapor absorption lines are maintained. We show the adaptive EKF maintain correct spectral information when compared to the high-resolution transmission molecular absorption (HITRAN) database. The adaptive EKF is also demonstrated for THz-TDS on vapor with photoconductive THz detection, thus demonstrating adaptability, and is applied for THz-TDS of a solid sample of polyethylene terephthalate glycol.

Enhanced tunable terahertz Mie resonance and magnetoplasmonic effect through chain formation in ferrofluid

We present experimental and theoretical evidence demonstrating the Mie resonance effect in the terahertz (THz) range, utilizing Fe3O4/Kerosene ferrofluid. Our findings indicate a significant and rapid change in the complex refractive indices at 0.5 THz with an increase in the magnetic field strength. Moreover, we observed a prominent absorption peak at 0.5 THz in transmittance and absorption coefficient measurements, corresponding to a magnetic field intensity of 178.0 mT. This phenomenon occurs due to the adjustment of particle spacing, leading to resonance under different magnetic field conditions. These research results hold immense potential in advancing the development of magneto-optical THz modulators for imaging and communication applications.

Influence of Alkali Treatment on Microstructure Transformation and Mechanical Properties of Palm-Fiber Cell Wall

ABSTRACT Utilizing agricultural waste and natural fibers minimizes environmental impact and can improve the acoustic and thermal conditions of buildings. Natural fibers can be an alternative to non-biodegradable synthetic sound-absorbing materials. This study aimed to investigate the acoustic and thermal properties of insulating materials made from wool and sugarcane bagasse. Thermal conductivity, thermal resistance, acoustic and moisture absorption, and fire properties of five insulating materials made from sheep wool, goat fiber, camel wool as well as pith and fiber bundles of sugarcane bagasse were determined. The measurement of the sound absorption coefficient was performed in an impedance tube. The thermal resistance and thermal conductivity coefficient were measured according to the ASTM D5334–08 Standard. The findings show that camel wool has the highest sound-absorbing performance, thermal insulation, and fire-resistant properties. The lowest value of the noise reduction coefficient (NRC) was 0.52 for goat fiber, and the highest was 0.74 for camel wool. The maximum sound absorption coefficient of camel wool was 0.95 at a frequency above 1000 Hz. Thermal conductivity varies between 0.038 and 0.046W/(M.K). Hence, all materials tested can be considered thermally insulating. The results showed insulating materials made from wool, especially camel wool, had better performance than fiber and pith of sugarcane bagasse.

Effect of Fiber’s Size on Acoustic Absorption of Abaca Fiber/Epoxy Resin Composites

This study develops an absorber containing abaca fiber (Musa Textiles) and epoxy resin as a binder. The ability to absorb sound energy is related to the pore’s size present in the absorber. One of the methods to create porosity is to vary the length of fiber, which is 1, 10 mm, 15 mm and 20 mm. Before the fiber is cut to be certain length, it is treated employing NaOH alkalization and acetic acid hydrolysis. The characterization carried out includes density, morphology and absorption coefficient measurement using impedance tubes. Moreover, the fibers are measured for the density, then continued to determine the porosity and air flow resistivity using the Konzeny-Carman equation. The air flow resistivity parameter is utilized to determine the absorption coefficient using Delany-Bazley model. The value of the absorption coefficient from experiments using impedance tubes and based on theoretical analysis shows a similar trend curve. The results show that the fiber with the length of 20 mm exhibits the highest sound absorption coefficient.

Acoustical and Thermal Characterization of Insulating Materials Made from Wool and Sugarcane Bagasse

ABSTRACT Utilizing agricultural waste and natural fibers minimizes environmental impact and can improve the acoustic and thermal conditions of buildings. Natural fibers can be an alternative to non-biodegradable synthetic sound-absorbing materials. This study aimed to investigate the acoustic and thermal properties of insulating materials made from wool and sugarcane bagasse. Thermal conductivity, thermal resistance, acoustic and moisture absorption, and fire properties of five insulating materials made from sheep wool, goat fiber, camel wool as well as pith and fiber bundles of sugarcane bagasse were determined. The measurement of the sound absorption coefficient was performed in an impedance tube. The thermal resistance and thermal conductivity coefficient were measured according to the ASTM D5334–08 Standard. The findings show that camel wool has the highest sound-absorbing performance, thermal insulation, and fire-resistant properties. The lowest value of the noise reduction coefficient (NRC) was 0.52 for goat fiber, and the highest was 0.74 for camel wool. The maximum sound absorption coefficient of camel wool was 0.95 at a frequency above 1000 Hz. Thermal conductivity varies between 0.038–0.046W/(M.K). Hence, all materials tested can be considered thermally insulating. The results showed insulating materials made from wool, especially camel wool, had better performance than fiber and pith of sugarcane bagasse.

Self-referencing photothermal digital holographic microscope for characterization of low-loss liquids

Measurement of absorption coefficients of transparent samples is important for their characterization and identification; however, it is challenging to measure low values, e.g., 10−3–10−4 cm−1 with high accuracy. Here, we report a compact photothermal lateral shearing digital holographic device. It is based on the thermal lens effect and a common-path, self-referencing digital holographic microscope comprising a glass plate, probe beam, and a CMOS camera. The change in phase distribution caused by the temperature change due to light absorption is measured from the recorded holograms to extract the sample's absorbance and absorption coefficient. The feasibility of the proposed configuration is validated by the experimental results obtained with different concentrations of gold nanoparticles (AuNPs) in an aqueous solution. Determination of AuNPs concentration in the nM range is performed, and the obtained limits of detection and quantitation are 0.04 nM and 0.13, respectively. The calibration curve is linear at a low concentration range of 0.06–0.95 nM with 1% reproducibility. In addition, the method's versatility is demonstrated by measuring the absorption coefficient of low-loss solvents, such as ethanol and water. The determined absorption coefficients agree with the reported values, confirming that this method provides good spectrometric capabilities, such as high sensitivity and accuracy.

A Filter-Based Approach for the Measurement of Mass Absorption Coefficient of OC and EC Components in Soot

ABSTRACT There is a general consensus that soot produced by hydrocarbon combustion consists of two components, elemental carbon associated with the graphitic nanostructure and organic carbon. Despite the relevance of evaluating their radiative properties, particularly for organic carbon, the knowledge of the spectral absorption behavior remains limited. In this work, a dual-beam five wavelengths absorption photometer is used to estimate the optical properties of particulate matter generated by a laminar premixed ethylene-air flame at different residence times along the flame. The wavelength dependence of the light absorption of aerosols collected on filters is analyzed in terms of both the optical band gap and the absorption Ångström exponent, AAE. The aerosols are then analyzed in terms of the organic and elemental carbon content by a thermal-optical OC-EC analyzer. Combining the results of light absorption and OC-EC analysis, the spectral mass absorption coefficient of both the organic carbon and elemental carbon components in soot are obtained.

Sound absorption coefficient measurement and analysis of bio-composite micro perforated panel (BC-MPP)

Sound absorption coefficient measurement and analysis of bio-composite micro perforated panel (BC-MPP)