Interaction Of Acoustic Waves Research Articles

Effect of undulating bottom on wave interaction with a floating flexible plate coupled with a flexible porous barrier

In the present study, under the assumption of small amplitude water wave theory and structural response, effect of bed undulation on the wave interaction with a combination of flexible porous barrier and a flexible floating plate, is studied. The flexible porous barrier is modelled using the porous wave maker-theory while the elastic floating plate is modelled using thin plate theory. The physical problem is handled for solution using eigenfunction expansion method by matching pressure and velocity at interface boundaries while finite difference method is used to deal with modified mild-slope equation. In the present study, two types of plate configurations are namely (a) finite plate and (b) semi-infinite plate. To understand the role of undulating seabed, wave and structural parameters, in attenuating wave force and plate deflection, numerical results are computed and compared with available literature. It is found that full wave reflection occurs for certain critical angle and wave force acting on the barrier vanishes for the same critical angle for the semi-infinite plate case while the wave reflection tends to attain maximum value at critical angle for the finite case and these maximum value increases with the increase of plate length. It is observed that less wave reflection occurs for sloping bed profile compare to rest of the bed profile. The study reveals that positioning a barrier between plate and undulated region, helps in the reduction of plate deflection significantly. As special case, wave interaction problem with a finite floating elastic plate is studied experimentally and the experimental result has shown good agreement with the numerical result. The findings of the present study are likely to be of immense help in the design of various types of marine structures for protecting very large floating structures (VLFS). The present theory can be extended to handle large class of acoustic wave interaction problems with flexible porous structures.

Interaction of Phase-Conjugate Acoustic Waves with Discrete Modes of Elastic Vibrations in a Magnet

Experimental investigation is given to overthreshold parametric phase conjugation of ultrasound waves with the frequency of 22 MHz under resonant excitation of discrete acoustic modes with the frequencies of 0.214 and 1.248 MHz in the antiferromagnetic single crystal of α-Fe2O3. It is shown that nonlinear interaction with discrete modes is accompanied by amplitude and phase modulation of traveling phase-conjugate ultrasound waves. In processes of Raman scattering by discrete modes the modulation depth can amount to 100%.

Nonlinear Interaction of Acoustic Waves with a Spheroidal Particle: Radiation Force and Torque Effects

The nonlinear interaction of a time-harmonic acoustic wave with an anisotropic particle gives rise to the radiation force and torque effects. These phenomena are at the heart of the acoustofluidics technology, where microparticles such as cells and microorganisms are acoustically manipulated. We present a theoretical model considering a generic acoustic beam interacting with a subwavelength spheroidal particle in a nonviscous fluid. Concise analytical expressions of the radiation force and torque are obtained in the scattering dipole approximation. The radiation force is given in terms of a gradient and scattering force; while the radiation torque has two fundamental contributions, namely, the momentum arm and acoustic spin (spin-torque effect). As a practical example, we use the theory to describe the interaction of two crossed plane waves and a prolate spheroidal particle. The results reveal the particle is transversely trapped in a pressure node and is axially pushed by the radiation force. Also, the momentum arm aligns the particle in the axial direction. At certain specific positions, only the spin-torque occurs. Our findings are remarkably consistent with finite-element simulations. The success of our model enables its use as an investigation tool for the manipulation of anisotropic microparticles in acoustofluidics.

Interaction of Acoustic and Electromagnetic Waves in Nondestructive Evaluation and Medical Applications

Nonlinear acoustic nondestructive evaluation (NA NDE) methods have a higher sensitivity for defect detection than standard methods. These methods use various kinds of acoustic wave interactions. In this paper, we suggest augmenting the acoustic framework and use the interaction between acoustic and electromagnetic waves. A brief review of NA NDE and medical nonlinear acoustic imaging methods is presented. Medical methods based on electromagnetic wave modulation by an acoustic radiation force are discussed where improvements using ultrasound contrast agents are suggested. The estimation of the modulation of a radar signal by a crack vibration were made based on standard static measurements. The effects of modulation of an acoustic wave by an electromagnetic field are briefly considered for the method of crack detection in metal materials. The effects considered in this paper may be used in the new methods of NDE and medical diagnostics.

Modeling Acoustic Cavitation Using a Pressure-Based Algorithm for Polytropic Fluids

A fully coupled pressure-based algorithm and finite-volume framework for the simulation of the acoustic cavitation of bubbles in polytropic gas-liquid systems is proposed. The algorithm is based on a conservative finite-volume discretization with collocated variable arrangement, in which the discretized governing equations are solved in a single linear system of equations for pressure and velocity. Density is described by the polytropic Noble-Abel stiffened-gas model and the interface between the interacting bulk phases is captured by a state-of-the-art algebraic Volume-of-Fluid (VOF) method. The new numerical algorithm is validated using representative test-cases of the interaction of acoustic waves with the gas-liquid interface as well as pressure-driven bubble dynamics in infinite and confined domains, showing excellent agreement of the results obtained with the proposed algorithm compared to linear acoustic theory, the Gilmore model and high-fidelity experiments.

Interaction of electron acoustic waves in the presence of superthermal electrons in terrestrial magnetosphere

We have investigated the propagation and interaction of nonlinear electron acoustic waves (EAWs) in a plasma comprising hot (superthermal) and cold electrons and immobile ions. We have derived the Korteweg-de Vries equation for EAWs in the small amplitude limit. Employing the Hirota's Direct method, we have investigated the multisoliton solutions for electron acoustic solitary waves (EASWs). It has been found that the system under consideration admits only rarefactive electrostatic solitary structures. As the observable data are available in terms of electric field rather than electric potential, therefore, we have discussed our results in terms of bipolar electric field structures. The numerical analysis has revealed that the ratio of hot to cold electrons and superthermality of hot electrons play a crucial role in changing the amplitude of EASWs. The interaction of the two solitons and its dependence on the choice of propagation vectors, superthermality, and density ratio have also been elaborated. The results of the present study may be beneficial to comprehend the interaction between two EASWs in astrophysical and laboratory plasmas.

Monitoring of Bioresources in Shallow Water by Parametric Systems

Hydroacoustic parametric systems and methods of nonlinear acoustics in the study of bioresources in shallow areas of the oceans are considered. Unique characteristics of parametric antennas are given. The general issues of nonlinear interaction of acoustic waves are considered. The features of the interaction and propagation of acoustic waves in shallow water are presented. The characteristics of parametric instruments are presented, and the results of their applications for monitoring bioresources in shallow areas of the oceans are considered

Surface Acoustic Waves-Localized Plasmon Interaction in Pillared Phononic Crystals

We study numerically the interaction of surface acoustic waves propagating at the surface of a multilayer structure (the so-called Sezawa waves) with localized surface plasmons at the bottom of metallic pillars deposited on the substrate. The pillars are made of gold and the multilayer structure is constituted by a layer of gold on a silicon substrate and covered by a thin spacer of dielectric material. We are interested in localized plasmons, which are the analog of metal-dielectric-metal surface plasmons. The physical characteristics of these plasmons, such as their eigenvalues and absorption or reflection spectra, are modulated by surface acoustic waves due to deformation of the structure in the vicinity of the pillars. The surface waves are generated in the area in front of the pillars deposited on the substrate. Two types of acoustic modes are envisioned to interact with the localized plasmons, namely, confined modes associated with the local resonances of the pillars and the propagating Sezawa modes that deform the structure in the vicinity of the surface. We discuss the efficiency of phonon-plasmon coupling for both types of modes and select those that can be useful for an experimental realization based on this platform. Also, we show that, besides the plasmon frequency, the phonon-plasmon coupling magnitude strength is sensitive to the distance between the pillars, which reveals the role of interactions between the pillars on the coupling. The geometrical parameters are chosen such that the acoustic waves are in the sub-GHz range and the plasmons are around the telecommunication wavelength of 1.55 mu m. This work may help with the design of optomechanical devices that can be controlled by fast coherent acoustics and facilitate applications involving enhanced sound-light interactions, such as light modulation.

Tunable semiconductor laser with two acousto-optic tunable filters in its external cavity

We report a laser with a linear external cavity containing a near-IR injection semiconductor optical amplifier as a gain element and two acousto-optic tunable filters (AOTFs) with quasi-collinear interaction of acoustic and light waves. At identical frequencies of RF signals that control the filters and ensure compensation for the Doppler frequency shift of light passing through the AOTFs, the steady-state laser emission linewidth can be reduced to about 25 MHz, which is almost three orders of magnitude smaller than that in the case of one filter (20 GHz). The position of the emission line, which remains narrow, slowly fluctuates within a spectral range about 3 GHz wide, which seems to be due to the large length of the external cavity and insufficient thermal stabilization of its components. This does not prevent us from obtaining light with a large coherence length. In emission wavelength sweep mode, the instantaneous emission linewidth increases with tuning rate, reaching 0.022 nm (8.8 GHz) at the highest tuning rate: 104 nm s−1. In the case of automatic control over the output optical power at a level of 3 mW, the tuning range is 815 – 875 nm. Such instruments are of practical interest for optical coherence tomography, spectroscopy, optical metrology, and other application areas.

THE RESEARCH FOR AN IDENTIFICATION OF CRACK – LIKE CORROSION – MECHANICAL DEFECT BY ACOUSTIC IN-LINE INSPECTION TOOLS

Problem of an identification of cracks in dents or corrosion damage, which is considered as a crack – like corrosion – mechanical defect type, is considered for acoustic in – line inspection tools during an in – line inspection of oil pipelines. For this purpose, a theoretical model has been provided and considered as a vertical notch with a convex base. For modeling an interaction of acoustic waves with the defect model there has been used a corresponded formula of an acoustic equation at a ray – acoustic approximation. Considering used simplifying assumptions there have obtained certain boundary conditions for acoustic equation of the crack – like corrosion mechanical defect. Based on this theoretical model here an experimental research were provided at specially manufactured test specimen which contained vertical notches with base of different curvature. At the specimen there are has been obtained a difference of echo signals amplitude from convex and flat surface based notches. Obtained results showed a sufficient agreement with provided by theoretical modeling and approve an adequacy of the proposed model for a theoretical description of considered interaction shear waves with the defect imitation. According to obtained trend of an echo – signal amplitude variation a method for identification of cracks in dents or corrosion damage during an oil pipeline inspection by inline inspection tools has been provided.

Nonlinear interaction of gravity and acoustic waves

Here we have investigated the possibility of an inertio-acoustic wave-mode to be unstable with regards to gravity mode perturbations through non-linear triad interactions in the context of a shallow non-hydrostatic model. We have considered highly truncated Galerkin expansions of the perturbations around a resting, hydrostatic and isothermal background state in terms of the eigensolutions of the linear problem. For a single interacting wave triplet, we have shown that an acoustic mode cannot amplify a pair of inertio-gravity perturbations due to the high mismatch among the eigenfrequencies of the three interacting wave-modes, which requires an unrealistically high amplitude of the acoustic mode in order for pump wave instability to occur. In contrast, it has been demonstrated by analysing the dynamics of two triads coupled by a single mode that a non-hydrostatic gravity wave-mode participating in a nearly resonant interaction with two acoustic modes can be unstable to small amplitude perturbations associated with a pair of two hydrostatically balanced inertio-gravity wave-modes. This linear instability yields significant inter-triad energy exchanges if the nonlinearity associated with the second triplet containing the two hydrostatically balanced inertio-gravity modes is restored. Therefore, this inter-triad energy exchanges lead the acoustic modes to yield significant energy modulations in hydrostatic inertio-gravity wave modes. Consequently, our theory suggests that acoustic waves might play an important role in the transient phase of the three-dimensional adjustment process of the atmosphere to both hydrostatic and geostrophic balances.

Numerical Investigation of Surface Acoustic Wave (SAW) Interacting with a Droplet for Point-of-Care Devices

A three-dimensional numerical simulation of the interaction of a surface acoustic wave (SAW) with a droplet of water is carried out. The mixing produced inside the droplet due to the incident with the SAW and the droplet is investigated by undertaking a parametric study, with parameters such as frequency, drop size, and the lateral position of the droplet on the surface of the substrate. The linear relationship between the input voltage and the mixing velocity inside the droplet is obtained with variation of the input voltage of the inter-digital transducer (IDT) of the SAW device within a 10--40 V range. With the variation in frequency, the maximum mixing velocity is observed at 20 MHz and it appears to be independent of the size of the droplet. Varying the substrate material with lead zirconate titanate and lithium niobate produces better mixing. Lithium niobate is preferred due to its availability and cost-effectiveness. A drop of 600 um diameter produces better mixing. The different velocities inside the drop and the SAW device are obtained by changing the droplet position in the lateral direction (asymmetrical position) from the centre of the substrate. Cut planes parallel and perpendicular to the SAW at the core of a half-spherical droplet are observed to visualise the mixing effects inside the droplet during the interaction. To achieve the best mixing criteria, the droplet is moved in a lateral direction. An efficient parametric design for the mixing phenomena in micro-fluidic devices is presented for point-of-care devices.

Quantum effects in bi-dust plasmas

In this paper a theoretical approach has been carried out using a fluid model on a bi-dust plasma which consist of two dusts negative charged different particles in an electron–ion plasma. In such system, this fluid model describe a dense strong coupled heavy dust grain together with a weak coupled light dusty particle. The bulk is immersed in a system of electrons and ions dominated by a Thomas–Fermi density distribution, where interaction and propagation of solitary dust acoustic solitary waves will be analyzed. This investigation will be carried out for arbitrary amplitude of solitary dust acoustic waves. These are originated through the presence of both dust grains in the plasma system. Therefore, it is used a set of fluid equation which determine general expressions for the concentrations of different dust particles. The onset of the Sagdeev method is then employed in order to look for influence of the light component on the quantum system. In this way there is an increasing or decreasing in the Sagdeev potential. This is a quantum effect phenomena.

Enhancement of diffuse correlation spectroscopy tissue blood flow measurement by acoustic radiation force.

The current research on acousto-optic effects focuses on the interactions of acoustic waves with static optical properties rather than dynamic features such as tissue blood flow. Diffuse correlation spectroscopy (DCS) is an emerging technology capable of direct measurements of tissue blood flow by probing the movements of red blood cells (RBCs). In this article, we investigated the relations between the acoustic radiation force (ARF) and ultrasonic patterns by the finite element simulations. Based on the outcomes, we experimentally explored how the ultrasound-generated ARF enhance the DCS data as well as the blood flow measurements. The results yield the optimal pattern to generate ARF and elucidate the relations between the ultrasonic emission and flow elevations. The flow modality combing the DCS with ARF modulations, which was proposed in this study for the first time, would promote disease diagnosis and therapeutic assessment in the situation wherein the blood flow contrast between healthy and pathological tissues is insufficient.

ВЛИЯНИЕ ТАЙФУНА VONGFONG 2014 г. НА ИОНОСФЕРУ И ГЕОМАГНИТНОЕ ПОЛЕ ПО ДАННЫМ СПУТНИКОВ SWARM: 2. ГЕОМАГНИТНЫЕ ВОЗМУЩЕНИЯ

Strong meteorological disturbances in the atmosphere, accompanied by the generation of waves and turbulence, can affect ionospheric plasma and geomagnetic field. To search for these effects, we have analyzed electromagnetic measurement data from low-orbit Swarm satellites during flights over the typhoon Vongfong 2014. We have found that there are “magnetic ripples” in the upper ionosphere that are transverse to the main geomagnetic field fluctuations of small amplitude (0.5–1.5 nT) with a predominant period of about 10 s caused by small-scale longitudinal currents. Presumably, these quasiperiodic fluctuations are produced by the satellite’s passage through the quasiperiodic ionospheric structure with a characteristic scale of ~70 km induced by the interaction of acoustic waves excited by the typhoon with the E-layer of the ionosphere. In one of the flights over the typhoon, a burst of high-frequency noise (~0.3 Hz) was observed, which can be associated with the excitation of the ionospheric Alfven resonator by atmospheric turbulence.

INFLUENCE OF THE VONGFONG 2014 HURRICANE ON THE IONOSPHERE AND GEOMAGNETIC FIELD AS DETECTED BY SWARM SATELLITES: 2. GEOMAGNETIC DISTURBANCES

Strong meteorological disturbances in the atmosphere, accompanied by the generation of waves and turbulence, can affect ionospheric plasma and geomagnetic field. To search for these effects, we have analyzed electromagnetic measurement data from low-orbit Swarm satellites during flights over the typhoon Vongfong 2014. We have found that there are “magnetic ripples” in the upper ionosphere that are transverse to the main geomagnetic field fluctuations of small amplitude (0.5–1.5 nT) with a predominant period of about 10 s caused by small-scale longitudinal currents. Presumably, these quasiperiodic fluctuations are produced by the satellite’s passage through the quasiperiodic ionospheric structure with a characteristic scale of ~70 km induced by the interaction of acoustic waves excited by the typhoon with the E-layer of the ionosphere. In one of the flights over the typhoon, a burst of high-frequency noise (~0.3 Hz) was observed, which can be associated with the excitation of the ionospheric Alfven resonator by atmospheric turbulence.

Partitioned Coupling for Structural Acoustics

Abstract We expand the second-order fluid–structure coupling scheme of Farhat et al. (1998, “Load and Motion Transfer Algorithms for 19 Fluid/Structure Interaction Problems With Non-Matching Discrete Interfaces: Momentum and Energy Conservation, Optimal Discretization and Application to Aeroelasticity,” Comput. Methods Appl. Mech. Eng., 157(1–2), pp. 95–114; 2006, “Provably Second-Order Time-Accurate Loosely-Coupled Solution Algorithms for Transient Nonlinear Computational Aeroelasticity,” Comput. Methods Appl. Mech. Eng., 195(17), pp. 1973–2001) to structural acoustics. The staggered structural acoustics solution method is demonstrated to be second-order accurate in time, and numerical results are compared to a monolithically coupled system. The partitioned coupling method is implemented in the Sierra Mechanics software suite, allowing for the loose coupling of time domain acoustics in sierra/sd to structural dynamics (sierra/sd) or solid mechanics (sierra/sm). The coupling is demonstrated to work for nonconforming meshes. Results are verified for a one-dimensional piston, and the staggered and monolithic results are compared to an exact solution. Huang, H. (1969, “Transient Interaction of Plane Acoustic Waves With a Spherical Elastic Shell,” J. Acoust. Soc. Am., 45(3), pp. 661–670) sphere scattering problem with a spherically spreading acoustic load demonstrates parallel capability on a complex problem. Our numerical results compare well for a bronze plate submerged in water and sinusoidally excited (Fahnline and Shepherd, 2017, “Transient Finite Element/Equivalent Sources Using Direct Coupling and Treating the Acoustic Coupling Matrix as Sparse,” J. Acoust. Soc. Am., 142(2), pp. 1011–1024).

A robust actively-tunable perfect sound absorber

Perfect sound absorption (PSA), producing an absorption coefficient of 1, can be achieved based upon the coherent interaction of acoustic waves, while it can merely be achieved within a narrow frequency-band due to critical impedance matching conditions. Here, we theoretically and experimentally study self-modulation and active-tunability in PSA created on account of a membrane-covered cavity. It is observed that due to the nonlinearity of the membrane, the frequency of PSA increases with the intensities of input acoustic waves, exhibiting a self-modulation property. Furthermore, we design an apparatus to control the elasticity of the membrane via four electromagnets, and thus, the PSA frequency can be freely and effectively adjusted by changing the direct-current driving voltage of the electromagnets. Despite the critical impedance matching conditions, the absorption coefficient achieved in our system holds at 1 when the PSA frequency is freely changed, which exhibits strong robustness in active-tunability.

Kinetic Theory of Ion Acoustic Waves Observed at Comet 67P/Churyumov–Gerasimenko

Abstract This work presents the resonance interaction of ion acoustic waves with the cometary plasma as observed at comet 67P/Churyumov–Gerasimenko. The plasma is comprised of cold, warm, and suprathermal electron populations and water ions such that the quasineutrality is satisfied. The cold electron population is found to play a dominant role in the damping of the waves, and its maximum Landau damping rate is observed when it is 2% of the total electron density in the system. It is determined that lowering the cold electron density supports the current-driven ion acoustic instability at a relatively lower drift speed of the warm and suprathermal electron species. In the absence of cold electrons, the wave phase speed does not change by populating the high-energy suprathermal electron species, therefore, the Landau damping rate of both warm and suprathermal electrons increases by increasing their respective densities. The growth rate of the current-driven ion acoustic instability decreases by elevating the concentration of suprathermal electrons in the case of drifting warm and stationary suprathermal electrons. In the case of stationary warm and drifting suprathermal electrons, the elevated density of suprathermal electron instead favors the instability.

The Influence of the Configuration and Material of Interdigital Transducers on the Excitation of Surface and Pseudosurface Acoustic Waves in Lithium Niobate Substrates

We have studied the excitation, propagation, and interaction of surface and pseudosurface acoustic waves in X-cut lithium niobate substrate. Resonance excitation frequencies, propagation velocities, and dispersion characteristics for the acoustic waves of each type are determined. It is established that the electrode material influences the efficiency of excitation and interaction between the acoustic waves of various types. Requirements for the material and configuration of electrodes in integrated acousto-optic devices are determined.