Dissipation Of Acoustic Waves Research Articles

Mechanochemically responsive polymer enables shockwave visualization

Understanding the physical and chemical response of materials to impulsive deformation is crucial for applications ranging from soft robotic locomotion to space exploration to seismology. However, investigating material properties at extreme strain rates remains challenging due to temporal and spatial resolution limitations. Combining high-strain-rate testing with mechanochemistry encodes the molecular-level deformation within the material itself, thus enabling the direct quantification of the material response. Here, we demonstrate a mechanophore-functionalized block copolymer that self-reports energy dissipation mechanisms, such as bond rupture and acoustic wave dissipation, in response to high-strain-rate impacts. A microprojectile accelerated towards the polymer permanently deforms the material at a shallow depth. At intersonic velocities, the polymer reports significant subsurface energy absorption due to shockwave attenuation, a mechanism traditionally considered negligible compared to plasticity and not well explored in polymers. The acoustic wave velocity of the material is directly recovered from the mechanochemically-activated subsurface volume recorded in the material, which is validated by simulations, theory, and acoustic measurements. This integration of mechanochemistry with microballistic testing enables characterization of high-strain-rate mechanical properties and elucidates important insights applicable to nanomaterials, particle-reinforced composites, and biocompatible polymers.

Spectral distortions from acoustic dissipation with non-Gaussian (or not) perturbations

A well-known route to form primordial black holes in the early universe relies on the existence of unusually large primordial curvature fluctuations, confined to a narrow range of wavelengths that would be too small to be constrained by Cosmic Microwave Background (CMB) anisotropies. This scenario would however boost the generation of μ-type spectral distortions in the CMB due to an enhanced dissipation of acoustic waves. Previous studies of μ-distortion bounds on the primordial spectrum were based on the assumptions of Gaussian primordial fluctuations. In this work, we push the calculation of μ-distortions to one higher order in photon anisotropies. We discuss how to derive bounds on primordial spectrum peaks obeying non-Gaussian statistics under the assumption of local (perturbative or not) non-Gaussianity. We find that, depending on the value of the peak scale, the bounds may either remain stable or get tighter by several orders of magnitude, but only when the departure from Gaussian statistics is very strong. Our results are translated in terms of bounds on primordial supermassive black hole mass in a companion paper.

Denoising deep brain stimulation pacemaker signals with novel polymer-based nanocomposites: Porous biomaterials for sound absorption

<p>Deep brain stimulation (DBS) pacemakers are sophisticated medical devices that deliver electrical signals to targeted areas of the brain via implanted electrodes, effectively regulating abnormal brain activity and relieving symptoms of treatment-resistant neurological disorders. However, proximity to other electromagnetic equipment may introduce additional noise, which can be disruptive to individuals. To mitigate this issue, we propose a novel polymer-based nanocomposite for pacemakers for signal denoising. This research focused on the development and analysis of nanocomposites comprising polypropylene (PP) combined with montmorillonite nanoclay and graphene nanosheets (GNs). The nanocomposites were created by blending them through melting, using varying ratios of clay to GNs, with a total loading of 4 wt.%. This study focused on enhancing the signal-to-noise ratio for brain pacemakers by using nanocomposites. It investigated the noise reduction properties of PP nanocomposites, specifically in the outlet gate of the pacemaker. This research aimed to find the ideal ratio of clay to GNs in the PP matrix. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were conducted to analyze the crystalline structure and filler dispersion, as well as thermal behavior and filler–matrix interactions in the material. Scanning electron microscopy was employed to observe the dispersion of the nanofillers in the PP, and sound tube testing was conducted to evaluate the noise levels of the composites. The findings indicated that a porous structure of the nanocomposite with dispersed microspheres within the PP matrix and a long pathway facilitated increased dissipation of acoustic waves, making it suitable for denoising in brain pacemakers. Furthermore, the nanocomposite containing 2.75 wt.% of nanoclay and 1.25 wt.% of graphene components within the polypropylene matrix demonstrated a favorable signal-to-noise ratio compared to other evaluated nanocomposites.</p>

Dynamics of acoustic waves in a liquid with solid particles and gas bubbles

A mathematical model that determines the propagation of acoustic waves in a mixture of a liquid with gas bubbles and solid particles is presented. The system of differential equations is written, the dispersion equation is obtained. Low-frequency and high-frequency asymptotics of the sound speed in the specified mixture are found and illustrated. The influence of solid particles and gas bubbles on the dispersion and dissipation of acoustic waves is indicated. For a mixture of liquid and solid particles, a comparison of the speed of sound with known experimental data is presented.

CMB spectroscopy at third-order in cosmological perturbations

Early energy injection to the Cosmic Microwave Background (CMB) from dissipation of acoustic waves generates deviations from the blackbody spectrum not only at second-order but also at third-order in cosmological perturbations. We compute this new spectral distortion $\mathcal \kappa$ based on third-order cosmological perturbation theory and show that $\kappa$ arises as a result of mode coupling between spectral distortions and temperature perturbations. The ensemble average of $\kappa$ can be directly sourced by (integrated) primordial non-Gaussianity. In particular, we roughly estimate the signal as $\kappa=f^{\rm loc.}_{\rm NL}\times \mathcal O(10^{-18})$ for local type scale-independent non-Gaussianity. The signal is incredibly tiny; however, we argue that it carries a specific frequency dependence different from other types of CMB spectral distortions. Also, it should be noticed that $\kappa$ is sensitive to extremely squeezed shapes of primordial bispectra that cannot be constrained by the CMB anisotropies. Finally, we comment on other possible applications of our results.

Optically Controlled Topologically Protected Acoustic Wave Amplification

Acoustic topological insulators that lead to backscattering-immune edge states provide an important way to control and manipulate the behaviors of phonons. To date, most of these acoustic systems are based on single-particle Hamiltonians that conserve particle number. Here, we exploit particle-nonconserving phonon–photon interactions to engineer not only the band structure but also the dissipation of acoustic waves. We find a topologically protected edge state for phonons that can be parametrically amplified while all the bulk modes remain stable. This phenomenon can be exploited to realize topologically protected nonreciprocal traveling-wave amplification for phonons, which may find wide applications in classical and quantum acoustics.

Acoustic Absorption Characteristics of New Underwater Omnidirectional Absorber**Supported by the National Natural Science Foundation of China under Grant Nos 51575201 and 11204098.

We investigate a new underwater omnidirectional absorber with acoustic black hole effect to realize a broadband omnidirectional acoustic wave absorption. Based on multiple scattering theory, a two-dimensional axisymmetric model of underwater omnidirectional absorber comprised of an acoustic gradient refractive index structure and a hollow core is developed, and the mechanisms of omnidirectional absorption and dissipation of acoustic waves are studied. The numerical results indicate that the omnidirectional absorber developed here can achieve the omnidirectional absorption of incident acoustic waves in a broadband frequency and can effectively reduce the backscattering of acoustic waves. It potentially provides a new notion for underwater acoustic coating design.

Multi-stage phononic crystal structure for anchor-loss reduction of thin-film piezoelectric-on-silicon microelectromechanical-system resonator

Thin-film piezoelectric-on-silicon acoustic wave resonators are promising for the development of system-on-chip integrated circuits with micro/nano-engineered timing reference. However, in order to realize their large potentials, a further enhancement of the quality factor (Q) is required. In this study, a novel approach, based on a multi-stage phononic crystal (PnC) structure, was proposed to achieve an ultra-high Q. A systematical study revealed that the multi-stage PnC structure formed a frequency-selective band-gap to effectively prohibit the dissipation of acoustic waves through tethers, which significantly reduced the anchor loss, leading to an insertion-loss reduction and enhancement of Q. The maximum unloaded Qu of the fabricated resonators reached the value of ∼10,000 at 109.85 MHz, indicating an enhancement by 19.4 times.

CMB spectral μ-distortion of multiple inflation scenario

In multiple inflation scenario having two inflations with an intermediate matter-dominated phase, the power spectrum is estimated to be enhanced on scales smaller than the horizon size at the beginning of the second inflation, k>kb. We require kb>10Mpc−1 to make sure that the enhanced power spectrum is consistent with large scale observation of cosmic microwave background (CMB). We consider the CMB spectral distortions generated by the dissipation of acoustic waves to constrain the power spectrum. The μ-distortion value can be 102 times larger than the expectation of the standard ΛCDM model (μΛCDM≃2×10−8) for kb≲103Mpc−1, while the y-distortion is hardly affected by the enhancement of the power spectrum.

Acoustic Disturbances in Galaxy Clusters

Abstract Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is the dissipation of acoustic waves generated by active galactic nuclei. Fabian et al. showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self-limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semicollisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian et al. remains the most viable path to acoustic wave heating of galaxy cluster cores.

CMB spectral distortion constraints on thermal inflation

Thermal inflation is a second epoch of exponential expansion at typical energy scales V1/4 ∼ 106 ∼ 8 GeV. If the usual primordial inflation is followed by thermal inflation, the primordial power spectrum is only modestly redshifted on large scales, but strongly suppressed on scales smaller than the horizon size at the beginning of thermal inflation, k > kb = ab Hb. We calculate the spectral distortion of the cosmic microwave background generated by the dissipation of acoustic waves in this context. For kb ≪ 103 Mpc−1, thermal inflation results in a large suppression of the μ-distortion amplitude, predicting that it falls well below the standard value of μ ≃ 2× 10−8. Thus, future spectral distortion experiments, similar to PIXIE, can place new limits on the thermal inflation scenario, constraining kb ≳ 103 Mpc−1 if μ ≃ 2× 10−8 were found.

Weak waves in multifractional liquids with bubbles

The propagation of weak waves in multifractional mixtures of liquid with vapor-gas and gas bubbles of different sizes and different compositions with phase transitions is studied. The dispersed phase consists of N+M fractions having various gases in bubbles and different in the bubbles radii. Phase transitions accounted for N fractions. The total bubble volume concentration is small (less than 1%). The dispersion relation is derived and dispersion curves is built. Influence of the mass concentration is shown. It is shown that dispersion and dissipation of acoustic waves depends significantly on presence of different bubbles in fractions of the dispersed phase.

Acoustic wave propagation in multifraction gas suspensions

We investigate propagation of acoustic waves in gas mixtures with fractions of various materials and size particles. We propose a mathematical model; obtain the dispersion relations, the equilibrium and the frozen sound velocity, and the lowand the high-frequency asymptotes of the linear attenuation coefficient; and calculate the dispersion curves. We also analyze the influence of the particle size and the disperse phase parameters on the acoustic wave dissipation and dispersion for a multifraction gas suspension with sand, aluminum, and sand particles. The calculation results are compared to the experiment.

Numerical investigation of the nonlinear attenuation and dissipation of acoustic waves in a medium containing ultrasound contrast agents

The presence of microbubble ultrasound contrast agents (UCAs) in path of an ultrasound beam increases the attenuation of the medium. A detailed knowledge about the medium attenuation in the presence of UCAs is critical for optimizing ultrasound applications. In this study, a model incorporating the nonlinear attenuation of microbubbles is developed by deriving the complex and real part of the wave number from the Calfish model. Results showed that when UCAs are sonicated by their linear resonance frequency (fr), the effective attenuation of the medium can potentially decrease as the pressure increases, in agreement with experimental observations of the attenuation of monodisperse microbubbles. When sonicated with their pressure dependent resonance frequency (fs), the effective attenuation of the medium is smaller than the case of sonication with fr, but only below a pressure threshold (Ps). Above Ps, the effective attenuation increases abruptly (e.g. ~3 fold) and becomes significantly more than the attenuation during sonication with fr. The attenuation in the subharmonic (SH) regimes of oscillations (sonication with n*fr where n = 2, 3.) are considerably smaller compared to the cases of sonication with fr and fs (~10 times). The attenuation undergoes a sharp increase concomitant with the generation of SH oscillations.

Acoustic waves in multifractional bubbly liquids

The propagation of acoustic waves in multifractional mixtures of a liquid with vapor-gas and gas bubbles of different sizes and different compositions with phase transitions is investigated. The dispersed phase consists of N + M fractions having various gases in bubbles and different in the bubble radii. Phase transitions accounted for N fractions. The total bubble volume concentration is small (less than 1%). A system of differential equations of the mixture motion is developed, and the dispersion relation is derived. It is shown that the dispersion and dissipation of acoustic waves depends largely on the presence of bubbles of various proportions in the composition of the disperse phase. It is found that the replacement of a fraction of vaporgas bubbles in the monodisperse bubbly mixture with phase transitions for gas bubbles with different thermophysical properties, depending on the type of gas, can lead to both a decrease and an increase in the attenuation coefficient in the low-frequency region.

Acoustic waves in bubbly liquids for two kinds of gas bubbles with phase transitions

The propagation of acoustic waves in a mixture of liquid with vapor-gas bubbles is studied. The dispersed phase consists of two fractions of the bubbles differing on gas structure and radii (a two-fractional mixture). The phase transitions take place at each of the fractions. The volume content of the bubbles is the low (about 1%). The dispersion relation, unified for plane, cylindrical and spherical waves is obtained. It is shown that a presence of the second fraction in the structure of a disperse phase of the bubbles changes significantly a dispersion and a dissipation of acoustic waves.

Directional asymmetry of the nonlinear wave phenomena in a three-dimensional granular phononic crystal under gravity.

We report the experimental observation of the gravity-induced asymmetry for the nonlinear transformation of acoustic waves in a noncohesive granular phononic crystal. Because of the gravity, the contact precompression increases with depth inducing space variations of not only the linear and nonlinear elastic moduli but also of the acoustic wave dissipation. We show experimentally and explain theoretically that, in contrast to symmetric propagation of linear waves, the amplitude of the nonlinearly self-demodulated wave depends on whether the propagation of the waves is in the direction of the gravity or in the opposite direction. Among the observed nonlinear processes, we report frequency mixing of the two transverse-rotational modes belonging to the optical band of vibrations and propagating with negative phase velocities, which results in the excitation of a longitudinal wave belonging to the acoustic band of vibrations and propagating with positive phase velocity. We show that the measurements of the gravity-induced asymmetry in the nonlinear acoustic phenomena can be used to compare the in-depth distributions of the contact nonlinearity and of acoustic absorption.

Reheating the universe once more: the dissipation of acoustic waves as a novel probe of primordial inhomogeneities on even smaller scales.

We provide a simple but robust bound on the primordial curvature perturbation in the range 10(4) Mpc(-1)<k<10(5) Mpc(-1), which has not been constrained so far unlike low-wave-number modes. Perturbations on these scales dissipate the energy of their acoustic oscillations by the Silk damping after primordial nucleosynthesis but before the redshift z∼2×10(6) and reheat the photon bath without invoking cosmic microwave background distortions. This acoustic reheating results in the decrease of the baryon-photon ratio. By combining independent measurements probing the nucleosynthesis era and around the recombination epoch, we find an upper bound on the amplitude of the curvature perturbation over the above wave number range as P(ζ)<0.06. Implications for supermassive black holes are also discussed.

Studying the thermodynamic processes in excilamps by the pressure jump method (Review)

A review of studies of thermodynamic processes in KrBr (207 nm), KrCl (222 nm), and XeBr (282 nm) barrier-discharge excilamps and XeBr (282 nm) and XeCl (222 nm) microwave-discharge excilamps is presented. Using various pressure gauges, it was experimentally shown that a pressure jump that occurs upon excilamp switching-on (-off) contains a fast (with a characteristic time of ∼100 ms) and a slow (∼100 s) component. The fast pressure-jump component is associated with gas heating during the discharge and allows evaluation of the fraction of the discharge power that is thermalized in the gas. From the analysis of the pressure decay after the jump, it follows that the gas is heated as a result of two processes: direct gas heating during the discharge (∼100 ms) and the energy dissipation of acoustic waves in the gas (∼10 ms). The slow component of the pressure jump is caused by the general heating of the excilamp and can be used to determine the fraction of the discharge power that is converted to thermal energy and to study various excilamp cooling modes.

Effect of the phase transformations on acoustics of a mixture of gas with vapor, droplets, and solid particles

The propagation of acoustic waves in the two-fraction mixtures of gas with vapor, droplets, and solid particles of different materials and sizes with phase transformations has been studied. Nonstationary and nonequilibrium effects of the interphase exchange of the impulse, mass, and heat have been taken into account. A system of the differential equations of the motion of the mixture has been presented, and the dispersion relation has been deduced. The high- and low-frequency asymptotics of the attenuation coefficient have been obtained and analyzed. The effect of the heat and mass exchange on dispersion and dissipation of acoustic waves in the two-fraction mixtures of gas with vapor, droplet, and solid particles has been studied.