Sound Attenuation Measurements Research Articles

Study of the acoustic attenuation of 2D axisymmetric models of the human ear equipped with hearing protection

The ear is the organ responsible for auditory perception. Its role is to amplify, transmit, and convert an acoustic wave present in the environment into an electrical pulse that the brain can interpret via the auditory nerve. The objective of this study was to develop two axisymmetric 2D finite element models of the human ear to predict insertion loss when a porous earplug is introduced into the ear canal. In these models, the structure-acoustic interaction was resolved by finite element analysis. For a better representation, assumptions and boundary conditions (such as fixe boundary condition, spring-mass-damping boundary condition, etc...) are considered. The tympanic ring and the earplug are assumed to be fixed, and a load of what comes after the posterior part of the tympanic ring (the ossicular chain) has been replaced by an equivalent mechanical impedance mass-spring-damper system. The first model has a regular geometry, and the second model is obtained by reconstructing a 3D model. These two models were inspired by our previous work. For each model, the insertion loss (IL) is predicted and the results obtained are compared with those of the sound attenuation measurements of hearing protection performed in the laboratory.

Biogeoacoustic variability in muddy ocean bottom sediment

Both physical and biological benthic processes can influence seabed heterogeneity and contribute to spatiotemporal variability in geoacoustic properties. In particular, how biological processes affect both sediment acoustic properties and their variability is poorly understood. To address this deficiency, recent measurements investigated spatial variability in the upper few decimeters of sediment near the water-seabed interface within a fine-grained sediment deposit on the New England shelf. At each measurement location, acoustic probes were inserted into the sediment to collect direct in situ measurements of sediment sound speed and attenuation at near-ambient conditions, after which cores were collected from the inter-probe propagation paths for ex situ analysis of sediment physical, biological, and acoustic properties. Relationships among sediment properties, such as bulk density, porosity, grain size distribution, organic matter composition, infaunal community composition, and acoustic measurements spanning several frequency decades (10–1000 kHz) will be explored in this paper. Frequency dependence of sediment acoustic properties will also be discussed in the context of sediment acoustics models for mud based on the viscous grain shearing and extended Biot theories. [Sponsored by ONR.]

Acoustic performance of screens designed to act as metamaterials

Metamaterials are, nowadays, a mature field of research in acoustic and many applications with metamaterials have been developed in recent years. In metamaterials, the attenuation of sound is due to the interaction of the sound waves with their geometrically regular structures. The frequency at which the attenuation occurs is calculated with Braggs' law. This work presents sound attenuation measurements of structures made with metamaterials carried out in an anechoic chamber. The arrangements considered are both two- dimensional and three-dimensional: the 2D arrangement was obtained with a regular distribution of linear elements made with bars with diameters of 9, 15, and 20 mm; the 3D arrangement was obtained with a regular distribution of a lattice of spheres with a diameter of 23 mm. The results of the acoustic measurements are reported in terms of insertion loss in the range from 1000 to 10 000 Hz.

Diurnal measurements of sound attenuation (100 Hz—10 kHz) in a shallow (1-2 m), seagrass (Zostera marina) meadow are impacted by photosynthetic activity and water column height

Seagrass meadows are important habitats that provide a variety of ecosystem services. As the seagrasses photosynthesize, they fill their vascular tissues with oxygen which is also released as bubbles into the water column. Measurements of sound attenuation were made in August 2022 in a shallow (1–2 m water depth) Zostera marina meadow in Shinnecock Bay, New York. Sound sources included tones (100 Hz–2 kHz) transmitted over an 8hour period (0800–1600 local time) and a 10 kHz Fishtek pinger operating over a 3 day period. Hydrophones were placed in the seagrass meadow at ranges of 1, 3, and 7 m from the source to determine attenuation. Vertical profiles of temperature, salinity, and dissolved oxygen were measured at the study site during the 8 hour tonal source experiment, and solar irradiance and tide level for Shinnecock Bay were obtained for the 3 day study period. Peak to peak sound pressure levels varied by more than 31 dB over a diurnal period for the 10 kHz signals. Sound attenuation of lower frequency tones varied from 9 to 30 dB both with dissolved oxygen (a proxy for photosynthetic activity of the seagrass) as well as water column height.

Investigation of surficial sediment acoustic, physical, and biological properties in the New England Mud Patch

Measurements of surficial sediment properties at five locations in the New England Mud Patch (NEMP) were conducted during a coring survey in April 2022. At each location the Acoustic-Multi-Corer (AMC) sampled the upper few decimeters of sediment near the water-seabed interface. The AMC inserted acoustic probes into the sediment to collect in situ measurements of compressional waves (30–140 kHz) and shear waves (0.8–1.2 kHz) at near ambient conditions, after which cores were collected from the inter-probe propagation paths for ex situ analysis of the sediment properties. Onboard the ship, the cores were scanned with a Core and Resonance Logger (CARL), which provided high-frequency sound speed and attenuation measurements (100–1000 kHz) along the lengths of the cores, as well as resonance-based measurements of sound speed at 12–16 kHz. A subset of cores was sieved for infauna onboard the vessel, and the remaining cores were later analyzed in an onshore laboratory for porosity, bulk density, mineral and organic matter composition, and grain size. The frequency dependence of the surficial sediment acoustic properties will be discussed in the context of the mud’s physical and biological properties as well as sediment acoustics models. [Work sponsored by ONR.]

Broadband core and resonance logger measurements of sound speed and attenuation in the New England mud patch

Extensive measurements of sound speed and attenuation have been performed on sandy sediments over the last few decades, which have motivated a variety of physical sediment acoustics models. Recently, the seabed characterization experiment (SBCEX) was performed in 2015–2017, in part, to quantify the geoacoustic properties of a clayey-silt accumulation, known as the New England Mud Patch (NEMP). Due to the variability and frequency range reported by the various direct measurements and geoacoustic inversions, the sound speed measured in the NEMP lacked any noticeable frequency dependence. In 2022, an additional coring cruise was completed in the NEMP area and included shipboard core and resonance logger (CARL) measurements, expanding upper limit of the band to 1 MHz. CARL measured sound speed and attenuation as a function of depth from 100 kHz to 1 MHz using a time-of-flight technique, and sound speed along the entire core length from 12 kHz to 16 kHz using a resonance technique. Positive dispersion and depth dependance was observed in the 200 kHz to 1 MHz band. The frequency and depth dependence of the CARL measurements will be presented and compared with previously published model fits to the 2015–2017 SBCEX dataset. [Work sponsored by ONR.]

Impacts of infauna, worm tubes, and shell hash on sediment acoustic variability and deviation from the viscous grain shearing model.

Infauna influence geoacoustic parameters in surficial marine sediments. To investigate these effects, an experiment was conducted in natural sand-silt sediment in the northern Gulf of Mexico. In situ acoustic measurements of sediment sound speed, attenuation, and shear speed were performed, and sediment cores were collected from the upper 20 cm of the seabed. Laboratory measurements of sound speed and attenuation in the cores were conducted, after which the core contents were analyzed for biological and physical properties. Since no model currently accounts for the effects of infauna, a deviation from model predictions is expected. To assess the extent of this, acoustic measurements were compared with the viscous grain shearing model from Buckingham [J. Acoust. Soc. Am. 122, 1486 (2007); J. Acoust. Soc. Am. 148, 962 (2020)], for which depth-dependent profiles of sediment porosity and mean grain size measured from the cores were used as input parameters. Comparison of acoustic results with distributions of infauna, worm tubes, and shell hash suggests biogenic impacts on acoustic variability and model accuracy are important in surficial marine sediments. The presence of infauna and worm tubes were correlated with higher variability in both sound speed and attenuation and greater deviation from the model near the sediment-water interface.

Direct measurements of acoustic and physical properties in mud and comparison to sediment acoustics models

Sediment acoustics models relate seabed physical properties to acoustic wave speed and attenuation, and direct measurements of sediment acoustic and physical properties provide a means to test such models. We examine direct measurements from two field experiment sites with muddy sediments that contain different ratios of clay, silt, sand, and organic components, comparing the acoustic data with sediment acoustic model predictions using parameters obtained from cores as model inputs. In the New England Mud Patch, sediment sound speed profiles up to several meters below the seabed surface were measured using in situ acoustic probes mounted to a gravity corer. At a second site near Mobile Bay, in situ probe measurements of sound speed, attenuation, and shear speed were obtained in the upper 20 cm of sediment, and diver cores were collected and scanned with an acoustic core logger. Sediments from both sites were analyzed for porosity and grain size distribution. The applicability of various models to the mud found at each site will be discussed, as well as effects of infauna and organic matter, which were also measured, but are not explicitly included in the models. [Work sponsored by ONR.]

Evidence for a Square-Square Vortex Lattice Transition in a High-T_{c} Cuprate Superconductor.

Using sound velocity and attenuation measurements in high magnetic fields, we identify a new transition in the vortex lattice state of La_{2-x}Sr_{x}CuO_{4}. The transition, observed in magnetic fields exceeding 35T and temperatures far below zero field T_{c}, is detected in the compression modulus of the vortex lattice, at a doping level of x=p=0.17. Our theoretical analysis based on Eilenberger's theory of the vortex lattice shows that the transition corresponds to the long-sought 45° rotation of the square vortex lattice, predicted to occur in d-wave superconductors near a van Hove singularity.

Gas discrimination by simultaneous sound velocity and attenuation measurements using uncoated capacitive micromachined ultrasonic transducers

Chemically functionalized or coated sensors are by far the most employed solution in gas sensing. However, their poor long term stability represents a concern in applications dealing with hazardous gases. Uncoated sensors are durable but their selectivity is poor or non-existent. In this study, multi-parametric discrimination is used as an alternative to selectivity for uncoated capacitive micromachined ultrasonic transducers (CMUTs). This paper shows how measuring simultaneously the attenuation coefficient and the time of flight under different nitrogen mixtures allows to identify hydrogen, carbon dioxide and methane from each other and determine their concentration along with identification of temperature and humidity drifts. Theoretical comparison and specific signal processing to deal with the issue of multiple reflections are also presented. Some potential applications are monitoring of refueling stations, vehicles and nuclear waste storage facilities.

Tests for the correct insertion of earplugs in the ear canal performed with the use of a portable device

The aim of the study was to assess the correct insertion of earplugs in the ear canal by people with different knowledge regarding this matter. The use of hearing protectors leads to a reduction in the risk of hearing loss, which is part of environmental engineering. Measurements of sound attenuation by earplugs were carried out with the participation of 21 people with no experience in the use of earplugs. The measurements were repeated until the subjects had read the instructions for the use of earplugs, and then after the subjects had been trained in the correct insertion of earplugs in the ear canal. The tests were carried out using a newly developed portable device for quick measurements of sound attenuation. Familiarizing the subjects with the instructions for use resulted in a sound attenuation value being 6.7 and 3.3 dB higher, at 250 and 4000 Hz, respectively, compared to the measurement when the subjects inserted earplugs in the ear canal without any guidance. An even greater increase in attenuation was observed when the subjects were trained to insert earplugs, at 9.2 dB (250 Hz) and 5.4 dB (4000 Hz), respectively. In most cases, the changes in attenuation as a result of providing guidance were statistically significant. Persons who have no experience in using earplugs have significant problems with their correct insertion. Reading the instructions for use does not guarantee that earplugs will be inserted correctly. Only the training showing how to insert the earplugs correctly results in people being able to do it correctly in most cases. Med Pr. 2021;72(5):521-8.

In Situ Measurement of Sound Attenuation by Fish Schools (Japanese Horse Mackerel, Trachurus japonicus) at Mid-Frequency Bands

Acoustic waves are attenuated by fish schools as they propagate through the ocean. The attenuation by fish schools is not currently considered in fishery acoustics and sonar applications, especially at mid-frequency bands. In this study, fish school attenuation experiments were conducted with a number of individual fish in situ in a net cage at mid-frequency bands (3–7 kHz). The target fish species was the Japanese horse mackerel (Trachurus japonicus), which typically forms fish schools in the coastal ocean of northeastern Asia. The attenuated acoustic waves were measured for the cases of non-net, only net (0), 100, 200, 300, 400, and 500 individual horse mackerels in the net cage. Results showed that the acoustic signal attenuation increased with the number of horse mackerels. The mean and maximum attenuation coefficients were approximately 6.0–15.4 dB/m and 6.5–21.8 dB/m for all frequencies, respectively. The measured attenuation coefficients were compared with the ones from previous studies to propose new regression models with normalized extinction cross-sections of weight and length of fish. This study confirmed that the fish school attenuation could not be ignored and compensated at mid-frequencies in the ocean. These results would be useful for fishery acoustics, especially in the development of scientific echo-sounder, and naval applications of sonar operations and analysis.

Quantum critical thermal transport in the unitary Fermi gas

Strongly correlated systems are often associated with an underlying quantum critical point which governs their behavior in the finite temperature phase diagram. Their thermodynamical and transport properties arise from critical fluctuations and follow universal scaling laws. Here, we develop a microscopic theory of thermal transport in the quantum critical regime expressed in terms of a thermal sum rule and an effective scattering time. We explicitly compute the characteristic scaling functions in a quantum critical model system, the unitary Fermi gas. Moreover, we derive an exact thermal sum rule for heat and energy currents and evaluate it numerically using the nonperturbative Luttinger-Ward approach. For the thermal scattering times we find a simple quantum critical scaling form. Together, the sum rule and the scattering time determine the heat conductivity, thermal diffusivity, Prandtl number and sound diffusivity from high temperatures down into the quantum critical regime. The results provide a quantitative description of recent sound attenuation measurements in ultracold Fermi gases.

Apparent attenuation by opto-acoustic defocus in phonon microscopy

Understanding the mechanical properties of biological cells is a challenging problem for the life sciences partly because there are limited methods for mapping elasticity with high resolution. Phonon microscopy is a form of Brillouin light scattering which uses coherent phonons for imaging with elasticity-related contrast, phonon resolution and without labels. It can measure material properties such as sound velocity, acoustic impedance and attenuation. To use it as a contrast mechanism in microscopy, high numerical aperture (NA) lenses are key to high resolution. However, increasing NA induces apparent attenuation, a premature decay of the detected signal. To reduce signal decay and quantify the sound attenuation coefficient in cells, it is necessary to understand the mechanisms that affect signal decay. Here we define opto-acoustic defocus as a signal decay mechanism and propose methods to achieve quantitative sound attenuation measurements, and to optimise in-depth imaging at high resolution which is crucial for cell imaging.

In situ observation of sediment sound speed and attenuation from coarse to fine-grained sediments

The long-term objective is to address the impact of spatial variability of sediment properties on sound propagation and reverberation from a few hundred hertz to 10 kHz. In this band, the frequency dependences of sound speed and attenuation are important for applications, but cannot be inferred from high-frequency data, hence direct measurement is necessary. In this talk, a summary of in situ measurements of sediment sound speed and attenuation collected from three major field experiments, i.e., Shallow Water 2006 (SW06), Target and Reverberation Experiment 2013 (TREX13), and Seabed Characterization Experiment 2017 (SCE17), are presented. Sediment sound speed and attenuation within the surficial 3 m of sediments were obtained through penetration, using the Sediment Acoustic-speed Measurement System (SAMS). In TREX13, i n situ measurements were carried out at five sites along a 5-km track, with sediment types ranging from coarse sand to a mixture of soft mud over sand. SAMS was deployed at 18 sites within the 10 × 30 km SCE17 study area. Significant variation of sediment geoacoustic properties was observed in range (TREX13) and depth (SCE17), respectively. Preliminary sediment acoustic modeling work is presented, using SAMS data taken from the wide range of sediment types. [Work supported by ONR.]The long-term objective is to address the impact of spatial variability of sediment properties on sound propagation and reverberation from a few hundred hertz to 10 kHz. In this band, the frequency dependences of sound speed and attenuation are important for applications, but cannot be inferred from high-frequency data, hence direct measurement is necessary. In this talk, a summary of in situ measurements of sediment sound speed and attenuation collected from three major field experiments, i.e., Shallow Water 2006 (SW06), Target and Reverberation Experiment 2013 (TREX13), and Seabed Characterization Experiment 2017 (SCE17), are presented. Sediment sound speed and attenuation within the surficial 3 m of sediments were obtained through penetration, using the Sediment Acoustic-speed Measurement System (SAMS). In TREX13, i n situ measurements were carried out at five sites along a 5-km track, with sediment types ranging from coarse sand to a mixture of soft mud over sand. SAMS was deployed at 18 sites within ...

Observations of the effects of benthic biology in measurements from the Acoustic Coring System collected in the New England Mud Patch

This paper presents in situ measurements of sediment sound speed and attenuation collected in the New England Mud Patch using the Acoustic Coring System (ACS) with comparisons to sound speed measurements from a multi-sensor core logger (MSCL). The ACS uses rod-mounted piezoelectric cylinders mounted below the penetrating tip of a gravity corer to obtain a continuous record of sound speed as a function of depth as the corer penetrates the seabed. The MSCL measurements of the recovered sediment cores were acquired in 2 cm increments. In both the ASC and MSCL measurements, an elevated sound speed is observed in the upper 25 cm of the seabed which is the portion of the seabed where most infauna live. The sediments collected in the cores were analyzed for density, porosity, bulk organic matter, carbonate content, mineral composition, and grain size. Additional surficial sediment samples recovered using a box core and a multi-core were sieved for infauna collection. The organisms were preserved, identified, and classified according to acoustically relevant traits. The acoustic measurements are interpreted in terms of the physical measurements of cores and the abundance of different types of organisms present in the seabed. [Work supported by ONR.]

Comparison of sound speed and attenuation measurements to the corrected effective density fluid model for gassy sediments.

To validate the corrected effective density fluid model for gassy sediments, an acoustic experiment was undertaken to measure the sound speed and attenuation in the frequency band of 10 to 120 kHz in a laboratory tank. Sound speed and attenuation each have four peaks, with a one-to-one correspondence between them. The optimal bubble size distribution modeled by five continuous modified Gaussian functions is obtained from inversion of sound speed and attenuation data. The measured sound speed and attenuation are in good agreement with the predicted results.

Suspended sediment assessment by combining sound attenuation and backscatter measurements – analytical method and experimental validation

Abstract The use of acoustic techniques has become common for estimating suspended sediment in water environments. An emitted beam propagates into water producing backscatter and attenuation, which depend on scattering particles concentration and size distribution. Unfortunately, the actual particles size distribution (PSD) may largely affect the accuracy of concentration quantification through the unknown coefficients of backscattering strength, ks2, and normalized attenuation, ζs. This issue was partially solved by applying the multi-frequency approach. Despite this possibility, a relevant scientific and practical question remains regarding the possibility of using acoustic methods to investigate poorly sorted sediment in the spectrum ranging from clay to fine sand. The aim of this study is to investigate the possibility of combining the measurement of sound attenuation and backscatter to determine ζs for the suspended particles and the corresponding concentration. The proposed method is moderately dependent from actual PSD, thus relaxing the need of frequent calibrations to account for changes in ks2 and ζs coefficients. Laboratory tests were conducted under controlled conditions to validate this measurement technique. With respect to existing approaches, the developed method more accurately estimates the concentration of suspended particles ranging from clay to fine sand and, at the same time, gives an indication on their actual PSD.

Attenuation of low-frequency underwater sound using an array of air-filled balloons and comparison to effective medium theory.

The ultimate goal of this work is to accurately predict the attenuation through a collection of large (on the order of 10-cm-radius) tethered encapsulated bubbles used in underwater noise abatement systems. Measurements of underwater sound attenuation were performed during a set of lake experiments, where a low-frequency compact electromechanical sound source was surrounded by different arrays of encapsulated bubbles with various individual bubbles sizes and void fractions. The measurements were compared with an existing predictive model [Church, J. Acoust. Soc. Am. 97, 1510-1521 (1995)] of the dispersion relation for linear propagation in liquid containing encapsulated bubbles. Although the model was originally intended to describe ultrasound contrast agents, it is evaluated here for large bubbles, and hence low frequencies, as a design tool for future underwater noise abatement systems, and there is good quantitative agreement between the observations and the model.

Temperature dependence of hypersound attenuation in silica films via picosecond acoustics

We report picosecond acoustic measurements of longitudinal sound dispersion and attenuation in an amorphous SiO2 layer at temperatures from 20 to 300 K over frequencies ranging from about 40 to 200 GHz. The sample is a radio frequency cathodic sputtered silica layer grown on a sapphire substrate with an aluminum film transducer deposited on top. Acoustic attenuation is evaluated from the simultaneous analysis of three successive echoes using transfer matrix calculation. Results are found to follow rather well a model combining coupling to thermally activated relaxations of structural defects and interactions with thermal vibrations. This leads to a nontrivial variation of the attenuation coefficient with frequency and temperature. The number density of relaxing defects in the SiO2 layer is found to be slightly higher than that in bulk v-SiO2. In contrast, similar anharmonic contribution to acoustic absorption is observed in both systems. The velocity variations are also measured and are compared to the dynamical velocity changes deduced from the sound attenuation.