Acoustic Energy Dissipation Research Articles

Improved Sound Absorption Properties in Polyurethane Foams by the Inclusion of Al2O3 Nanoparticles

At present, the scale of China’s power grid is becoming larger and larger, and the control of low‐frequency noise in substations (especially for transformers) is very important. The sound‐absorbing materials have become one of the important ways to control low‐frequency noise. The single polyurethane material cannot satisfy the requirements for reducing low‐frequency noise, so it is very necessary to study its composite with other materials. In the paper, the flexible polyurethane foam and Al2O3 nanoparticle composites were obtained by the impregnation method. The method was simple, safe, and easy to control. The morphology and sound absorption coefficient of the foam materials before and after filling were analyzed. Single‐hole acoustic cavity models of PU and Al2O3‐PU composite were established through the finite element. The absorption and dissipation process of sound pressure for single hole was studied to understand the energy dissipation process. Meanwhile, through studying acoustic energy storage and acoustic energy dissipation, the loss factor of a single hole was obtained, which can predict the change rule of the sound absorption coefficient for PU foam and Al2O3‐PU.

A new eccentric resonance matching layer with anti-reflection characteristics for underwater acoustic scattering suppression

The narrow frequency bandwidth and the effective frequency which cannot be low enough are two major challenges in underwater acoustics. To overcome these drawbacks, a new eccentric resonance matching layer with anti-reflection characteristics is proposed for underwater acoustic scattering suppression. Homogenization method and anti-reflection theory are applied for the design of anti-reflection structure. The complete mathematical model is developed based on the finite element method (FEM). Numerical simulations are carried out by COMSOL to verify the accuracy of the mathematical model. The results show that the proposed matching layer can significantly improve the broadband absorption capacity and can effectively suppress underwater acoustic scattering, especially at relatively low frequencies. It is a breakthrough in underwater low-frequency acoustic absorption, indicating that the structure has application prospects in underwater acoustic stealth, acoustic energy dissipation and acoustic wave regulation.

Design, fabrication and sound absorption test of composite porous metamaterial with embedding I-plates into porous polyurethane sponge

Nowadays the use of porous polyurethane sponge (PPS) is very common for sound absorption, thanks to its light-weight feature and easy fabrication. However, in many circumstances the traditional PPS has very limited absorption capabilities, due to the slow wave phenomenon and/or to insufficient sub-wavelength sound absorption. In this paper, we propose a composite porous metamaterial (CPM) consisting in a porous polyurethane sponge with embedded multi-layer I-plates to mitigate this problem. To characterize the sound absorption coefficient of the proposed CPM, we resort to the Johnson-Champoux-Allard (JCA) model, where five acoustic parameters, namely porosity, flow resistivity, tortuosity, viscous, and thermal characteristic lengths, are determined by acoustic test methods. Numerical and experimental results show that the sound absorption performance of PPS in the CPM is remarkably improved, compared to a contrast structure and a pure porous material, taking advantage of a twofold mechanism of local acoustic energy dissipation of the I-plates and the slow wave phenomenon cancellation inside the structure. Finally, the effects of the geometrical parameters on average sound absorption coefficient are presented and discussed in detail. The scheme of this paper possesses potential application value for the design of broadband and efficient sound absorbers, providing a reference for researches of new acoustic functional devices with high absorption performances.

АКУСТИЧНА ПОМІТНІСТЬ БЕЗПІЛОТНИХ ЛІТАЛЬНИХ АПАРАТІВ З СИЛОВИМИ УСТАНОВКАМИ НА БАЗІ ПОРШНЕВИХ ДВИГУНІВ

The presence in operation of many prototypes of UAVs with propeller propellers, the use of such devices at relatively low altitudes and flight speeds makes the problem of noise reduction from UAVs urgent both from the point of view of acoustic imperceptibility and ecology.The aim of the work is to determine a set of methods that help to reduce the visibility of UAVs in the acoustic range. It is shown that the main source of noise from the UAV on the ground is the power plant, which includes the engine and the propeller. The parameters of the power plants influencing the processes that determine the acoustic signature of the UAV were investigated. A comprehensive analysis of the factors affecting visibility was carried out. The power plants include two-stroke and four-stroke engines, internal combustion and two-blade propellers. The use of silencers on the exhaust of the internal combustion engine was considered. The spectral characteristics of the acoustic fields of the propeller-driven power plants for the operating sample of the UAV "Eco" were obtained. The measurements were carried out in one-third octave and 1/48 octave frequency bands under static conditions. The venue is the KhAI airfield. Note that the propellers that were part of the power plants operated at Reynolds numbers (Re0,75<2*105), which can significantly affect its aerodynamic and acoustic characteristics. It is shown that when choosing a UAV control system, one should take into account the fact that two-stroke piston engines are the dominant source in the noise of propeller-driven control systems in the absence of a hood and mufflers in the intake and exhaust tracts. The use of a four-stroke internal combustion engine significantly reduces the noise of the control system. In the general case, the position of the boundaries of the zone of acoustic visibility of a UAV at the location of the observer is determined by the ratio between the intensity of acoustic radiation perceived by the observer from the UAV and the intensity of sound corresponding to the natural acoustic background and depends on the degree of manifestation of acoustic effects accompanying the propagation of sound in a turbulent atmosphere - the refraction of sound waves. Absorption and dissipation of acoustic energy. The calculation and comparison of the UAV detection range was carried out taking into account the existing natural maskers.The results of experimental studies are presented that allow assessing the degree of acoustic signature of the UAV. A set of measures aimed at reducing the intensity of the acoustic signature of the UAV in various regions of the radiation spectrum has been determined.

Influence of Joint Angle on the Acoustic Emission Evolution Characteristics and Energy Dissipation Rule of Rock Mass

Influence of Joint Angle on the Acoustic Emission Evolution Characteristics and Energy Dissipation Rule of Rock Mass

Failure analysis of water-bearing sandstone using acoustic emission and energy dissipation

We performed uniaxial compression tests on sandstone with variable water contents (dry, natural, and fully saturated) and monitored deformation and failure in real-time using acoustic emission (AE) techniques. We propose sandstone damage variables on the basis of accumulative AE energy and dissipated energy theory. The results provide a useful framework for evaluating rock failure and structural design of rock engineering to improve service life. The peak strength of sandstone in the natural and saturated state is 18.75% and 51.70% lower than that in the dry state, respectively. The stress-time results show a gradual change of the sandstone deformation mode from brittle to ductile with increasing water content. The AE data are closely related to crack compression and formation and the propagation and evolution of new fractures, which reflect the sandstone’s internal damage. Increasing water content also shows a clear influence on accumulate AE energy but does not affect the strong increase prior to damage. The damage variables can accurately reveal the evolution of rock damage during compression.

Auxetic graphene oxide-porous foam for acoustic wave and shock energy dissipation

Auxetic cellular structures have garnered huge research interest as a candidate for energy absorption due to their appealing features, including extremely high indentation resistance and fracture resistance. However, auxetic foams reported so far typically can only sustain a very limited loading force and impact with a counter-intuitive behavior. Here, we report a highly efficient sound and shock absorber based on three-dimensional (3D) auxetic foam with two-dimensional (2D) wrinkled graphene oxide. Compared with pure polyurethane foam, the auxetic heterostructured polyurethane foam interconnected with 2D corrugated graphene oxide shows a sound absorbing capacity of 99.7% at a frequency of 2,236 Hz and a shock energy absorbing time of 189% during the impact loading. The synergistic effects between 3D auxetic foam and 2D wrinkled graphene oxide result in stable compressive cycling performance, more indentation resistance, and more energy dissipation during local impact loads. This 3D engineered auxetic porous structure with 2D crumpled graphene oxide provides a new and cost-effective strategy to effectively absorb acoustic and shock energy.

Investigation on energy dissipation by polarization switching in ferroelectric materials and the feasibility of its application in sound wave absorption

In the current paper, energy dissipation via stress-induced polarization switching in ferroelectric material is investigated, and the feasibility of its application in sound wave absorption is analysed. For the system design and analysis, a phenomenological model based on the modified Landau phase transition theory is constructed to describe the polarization switching. A simple and robust energy dissipation prototype is introduced. The hysteretic dynamics associated with the polarization switching process and the energy dissipation process are investigated. The dependence of the energy dissipation on the bias voltage, frequency, and resistance is analysed in detail. The energy dissipation density in one cycle is calculated. It is shown that the resistance has a strong influence on the energy dissipation. Meanwhile, a better energy dissipation effect could be obtained by setting an appropriate resistance for the low-frequency excitation. The feasibility of using ferroelectric materials for low-frequency sound wave absorption is validated. For a specific acoustic energy dissipation device, corresponding design and analysis will be discussed in our future papers.

Signal attenuation simulation of acoustic telemetry in directional drilling

Acoustic telemetry is preferred to conventional mud pulse telemetry because of its faster data transmission rate. However, acoustic telemetry requires a repeater for signal amplification because of the large signal attenuation that depends on the depth of drilling, which makes the system complicated and expensive. To improve communication performance by overcoming signal attenuation, developing a simulator capable of simulating the signal is necessary. However, the existing research models are limited to certain types of wave equation models that do not reflect the signal attenuation. In this study, the viscous dissipation term is added to the existing model, assuming that viscous friction caused by the relative movement between the mud and the drill string vibrating by acoustic waves is the main factor causing acoustic energy dissipation. A transient numerical model has been developed and tuned to simulate the attenuation rate reported in Drumheller's experiment on depth-dependent signal attenuation. The model shows that mud viscous flow is a major contribution to acoustic energy dissipation. The model developed in this study can be applied as a virtual simulator to develop various communication algorithms, as it can simulate signal attenuations at various drilling sites.

Acoustic absorption measurement for the determination of the volume viscosity of pure fluids / Messverfahren für die akustischen Absorption zur Bestimmung der Volumenviskosität reiner Fluide

Abstract A realistic description of fluid mechanical and acoustic processes requires the volume viscosity of the medium to be known. This work describes how the volume viscosity of pure fluids can be determined by measuring acoustic absorption with the pulse-echo method. The challenge in realizing such a measurement method lies in the separation of the different dissipative effects that superimpose on absorption. Diffraction effects ultimately cause a dissipation of acoustic energy and acoustic reflector surfaces have a small, but finite transmission coefficient. Further, influences of the transducer (in particular its frequency response), as well as the system’s electrical components have to be taken into account. In contrast to the classical approach relying on the amplitude ratio, the absorption is determined by the moments of the amplitude spectrum. The measurement system applied is originally designed for precision measurements of the sound velocity by means of the propagation time difference of two acoustic signals.

Acoustic Emission and Energy Dissipation Characteristics of Gas-Bearing Coal Samples Under Different Cyclic Loading Paths

Cyclic loading widely exists in coal mining activities, and it can significantly change the mechanical and seepage characteristics of coal. In this study, raw gas-bearing coal with different coal rank was mechanically tested under three stress paths: cyclic loading with stepwise increased peak stress (path 1), with step-by-step increased peak stress (path 2) and with crossed peak stress (path 3) using a tri-axial seepage testing machine. The acoustic emission (AE) signals under different loading and unloading paths indicate different mechanical properties of the coal sample. The Kaiser point is not a good indicator of the stress history of coal. The ratios of the quiet effect of the three coal samples under the three stress paths show that loading path 1 can increase defects such as micro-cracks in the coal samples (the AE quiet period decreases), while the other two paths decrease the number of defects (the AE quiet period increases). The cumulative dissipated energy of the coal shows an exponential growth with axial effective stress. The damping coefficient of coal first decreases then increases under cyclic loading. The damage variables can be used to predict the failure of coal samples, regardless of the stress path. Our results provide theoretical support and insight into the permeability increase mechanism and strengthened permeability increase mechanism of coal seams based on cyclic-loading-induced fracturing (repetitive hydraulic fracturing) under multiple protections and gas drainage engineering.

Focused Ultrasound Effects on Osteosarcoma Cell Lines.

MRI guided Focused Ultrasound (MRgFUS) has shown to be effective therapeutic modality for non-invasive clinical interventions in ablating of uterine fibroids, in bone metastasis palliative treatments, and in breast, liver, and prostate cancer ablation. MRgFUS combines high intensity focused ultrasound (HIFU) with MRI images for treatment planning and real time thermometry monitoring, thus enabling non-invasive ablation of tumor tissue. Although in the literature there are several studies on the Ultrasound (US) effects on cell in culture, there is no systematic evidence of the biological effect of Magnetic Resonance guided Focused Ultrasound Surgery (MRgFUS) treatment on osteosarcoma cells, especially in lower dose regions, where tissues receive sub-lethal acoustic power. The effect of MRgFUS treatment at different levels of acoustic intensity (15.5-49 W/cm2) was investigated on Mg-63 and Saos-2 cell lines to evaluate the impact of the dissipation of acoustic energy delivered outside the focal area, in terms of cell viability and osteogenic differentiation at 24 h, 7 days, and 14 days after treatment. Results suggested that the attenuation of FUS acoustic intensities from the focal area (higher intensities) to the “far field” (lower intensities) zones might determine different osteosarcoma cell responses, which range from decrease of cell proliferation rates (from 49 W/cm2 to 38.9 W/cm2) to the selection of a subpopulation of heterogeneous and immature living cells (from 31.1 W/cm2 to 15.5 W/cm2), which can clearly preserve bone tumor cells.

Power Dissipation in the Cochlea Can Enhance Frequency Selectivity

The cochlear cavity is filled with viscous fluids, and it is partitioned by a viscoelastic structure called the organ of Corti complex. Acoustic energy propagates toward the apex of the cochlea through vibrations of the organ of Corti complex. The dimensions of the vibrating structures range from a few hundred (e.g., the basilar membrane) to a few micrometers (e.g., the stereocilia bundle). Vibrations of microstructures in viscous fluid are subjected to energy dissipation. Because the viscous dissipation is considered to be detrimental to the function of hearing—sound amplification and frequency tuning—the cochlea uses cellular actuators to overcome the dissipation. Compared to extensive investigations on the cellular actuators, the dissipating mechanisms have not been given appropriate attention, and there is little consensus on damping models. For example, many theoretical studies use an inviscid fluid approximation and lump the viscous effect to viscous damping components. Others neglect viscous dissipation in the organ of Corti but consider fluid viscosity. We have developed a computational model of the cochlea that incorporates viscous fluid dynamics, organ of Corti microstructural mechanics, and electrophysiology of the outer hair cells. The model is validated by comparing with existing measurements, such as the viscoelastic response of the tectorial membrane, and the cochlear input impedance. Using the model, we investigated how dissipation components in the cochlea affect its function. We found that the majority of acoustic energy dissipation of the cochlea occurs within the organ of Corti complex, not in the scalar fluids. Our model suggests that an appropriate dissipation can enhance the tuning quality by reducing the spread of energy provided by the outer hair cells’ somatic motility.

The influence of schlichting vortices on the absorption of sound by a solid surface

The aim of this work is to study the mechanisms of acoustic energy dissipation due to the physical processes occurring in the acoustic boundary layer (APS), which occurs when the standing sound wave interacts with a solid surface. Unlike laminar APS in this case, in the wall layer of the medium, in addition to inhomogeneous viscous and thermal waves, acoustic Schlichting flows occur. Vortices can exist only due to the energy taken from the standing sound wave in consequence of which an additional mechanism of energy dissipation appears in the APS. A cylindrical tube with rigid walls, the ends of which are closed by impedance lids, was chosen as the object of research. When the longitudinal half-wave resonances are excited in the pipe, standing waves are excited in the pipe, formed due to the interaction of the normal zero-order sound waves running towards each other

Influence of Magnetic Nanoparticles on the Focused Ultrasound Hyperthermia.

Ultrasound hyperthermia is a medical treatment used to increase temperature of tissues. It can be used independently or as a supportive method for an anticancer treatment. The therapeutic efficacy of focused ultrasound hyperthermia can be improved using sonosensitizers, nanoparticles enhancing the attenuation and dissipation of acoustic energy. As sonosensitizers, we propose magnetic nanoparticles owing to their biodegradability, biocompatibility, and simple positioning in tissues using a magnetic field. Focused ultrasound hyperthermia studies were performed using tissue-mimicking phantoms. Temperature changes were measured at various ultrasound powers and distances from the center of the ultrasound focus. Specific absorption rate (SAR) values, describing the power deposition in the tissues during the hyperthermia treatment, were evaluated for the center of the focus point and for various distances from it. The results show that the addition of nanoparticles increases the SAR almost two times compared to that for the pure phantom. The highest SAR is obtained in the ultrasound focus; it decreases with the increase of the distance from the focus.

Dual-frequency sound-absorbing metasurface based on visco-thermal effects with frequency dependence

We propose an acoustic metasurface with near-perfect absorption at two frequencies and design it by using two-dimensional periodic array of four Helmholtz resonators in two types. By considering how fluid viscosity affects acoustic energy dissipation in the narrow necks of the Helmholtz resonators, we obtain effective complex-valued material properties that depend on frequency and on the geometrical parameters of the resonators. We furthermore derive the effective acoustic impedance of the metasurface from the effective material properties and calculate the absorption spectra from the theoretical model, which we compare with the spectra obtained from a finite-element simulation. As a practical application of the theoretical model, we derive empirical formulas for the geometrical parameters of a metasurface that would yield perfect absorption at a given frequency. Whereas previous works on metasurfaces based on Helmholtz resonators aimed to absorb sound at single frequencies, we use optimization to design a metasurface composed of four different Helmholtz resonators to absorb sound at two target frequencies.

Acoustic energy absorption and dissipation characteristic of Helmholtz resonator enhanced and broadened by acoustic black hole

In the present analysis, a novelty Helmholtz resonator (HR) enhanced by the acoustic black hole (ABH) is established. Dynamic partial differential equations are formulated according to the equilibrium of the flexible plate under harmonic uniformly distributed load, and the load is generated by acoustic fluids in the coupled system. By applying the Wentzel–Kramer–Brillouin (WKB) method, two fundamental functions are respectively assumed to describe the characteristic in the fluid and solid fields, and then the functions are determined by the boundary conditions and continual properties of the coupled structures. Moreover, relationships between the two functions are identified. By utilizing the energy conservation theorem of the closed system, energy storage and absorption characteristic in HR and ABH are separately calculated, which is further depicted as the normalized energy absorbed according to the input and output of the system, then energy transmission loss of the coupled system is calculated. The factors influence on the energy transmission loss in the frequency domain are quantitatively and qualitatively analyzed, especially the ABH parameter m. Finally, comparison is presented, the analysis shows the advantage of the coupled system by comparing with traditionally HR.

Polycrystallinity of Lithographically Fabricated Plasmonic Nanostructures Dominates Their Acoustic Vibrational Damping.

The study of acoustic vibrations in nanoparticles provides unique and unparalleled insight into their mechanical properties. Electron-beam lithography of nanostructures allows precise manipulation of their acoustic vibration frequencies through control of nanoscale morphology. However, the dissipation of acoustic vibrations in this important class of nanostructures has not yet been examined. Here we report, using single-particle ultrafast transient extinction spectroscopy, the intrinsic damping dynamics in lithographically fabricated plasmonic nanostructures. We find that in stark contrast to chemically synthesized, monocrystalline nanoparticles, acoustic energy dissipation in lithographically fabricated nanostructures is solely dominated by intrinsic damping. A quality factor of Q = 11.3 ± 2.5 is observed for all 147 nanostructures, regardless of size, geometry, frequency, surface adhesion, and mode. This result indicates that the complex Young's modulus of this material is independent of frequency with its imaginary component being approximately 11 times smaller than its real part. Substrate-mediated acoustic vibration damping is strongly suppressed, despite strong binding between the glass substrate and Au nanostructures. We anticipate that these results, characterizing the optomechanical properties of lithographically fabricated metal nanostructures, will help inform their design for applications such as photoacoustic imaging agents, high-frequency resonators, and ultrafast optical switches.

CALCULATION OF THE REFLECTION AND TRANSMISION COEFICIENTS OF A PLANE ULTRASONIC WAVE THROUGH A LAYER OF DISSIPATIVE BIOLOGICAL TISSUE

Background. Investigation of propagation of an ultrasound wave through layers of dissipative biological tissues along with theoretical interest has also a practical meaning in ultrasound therapy and diagnostics. It is well known that the result of the ultrasound therapeutic effect and the quality of ultrasound imaging depend on the fraction of ultrasound energy absorbed in the material of a tissue. Dissipation of acoustic energy leads to a thermal bio-effect and lowers a contrast of images received by ultrasound scanners.Objectives. We wanted to calculate the coefficients of transmission and reflection of a plane ultrasonic wave through a layer of dissipative biological tissue during the normal incidence of the wave on the surface of that layer.Materials and methods. The normal incidence of a plane ultrasonic wave on the layer of dissipative tissue was considered. Taking into account the continuity conditions for pressure and velocity in the ultrasonic wave at two boundaries of the tissue’s layer, the expressions for the reflection and transmission coefficients were obtained.Results. The explicit expressions for values of both coefficients in case of a normal incidence of ultrasonic wave were obtained and the parameters defining the magnitudes of these coefficients were determined. Namely, the relative acoustic impedances of the media through which ultrasonic wave propagates, the coefficient of absorption in the layer of a tissue, and the frequency of ultrasound.Conclusions. The results of this work allow calculating therapeutic effects produced by the ultrasonic wave. Particularly, they can be used for estimation of the intensity of the ultrasound wave in the human’s internal organs during non-invasive ultrasound interventions and the magnitude of temperature increase in the area of ultrasound irradiation. These results may be used for calculations of a therapeutic action of ultrasound wave, numerical simulations of the propagation of ultrasound wave through multilayered biological structures for improvement of ultrasound visualization of organs. Also, they can be used for improvement in the effectiveness in ultrasound applications, and for estimation of the magnitude of undesirable ultrasound side effects during diagnostic ultrasound screening.

Heating Induced by Therapeutic Ultrasound in the Presence of Magnetic Nanoparticles.

The efficiency of ultrasound hyperthermia for anti-cancer treatments such as radiotherapy or chemotherapy can be improved by using sonosensitizers, which are materials that enhance the attenuation and dissipation of acoustic energy. We propose the use of magnetic nanoparticles as sonosensitizers because of their biocompatibility, nontoxicity, and common use in several medical applications. A magnetic material was synthetized and then incorporated in the form of a magnetic fluid in agar tissue-mimicking phantoms. Ultrasound hyperthermia studies were conducted at various ultrasound frequencies and concentrations of magnetic nanoparticles in the phantoms. The theoretical modeling based on a heat transfer equation and the experimental results show good agreement and confirm that the temperature rise during ultrasound heating in tissue-mimicking phantoms doped with sonosensitizers is greater than that in a pure agar phantom. Furthermore, on the basis of Pennes' bio-heat equation, which takes into consideration the blood perfusion and metabolic heat, the thermal dose and lesion shapes after sonication were determined for a hypothetical tissue.