Frequency Acoustic Waves Research Articles

A composite acoustic black hole for ultra-low-frequency and ultra-broad-band sound wave control

Achieving ultra-low and ultra-broad-band sound absorption and full-band sound insulation is a major challenge. Here, we propose a composite structure of a multilayer micro-perforated plate and acoustic black holes to achieve this purpose. Combining the stable sound absorption effect of the multilayer micro-perforated plate in the full frequency band and the sound insulation effect of the acoustic black hole in the low frequency and the excellent sound absorption effect in the high frequency, the excellent sound control effect of 600–3150 Hz absorption coefficient greater than 0.8 and 100–3150 Hz sound transmission loss greater than 50 dB is achieved. The acoustic properties of different components and different acoustic black hole outlet were evaluated by finite element method, and the principles of sound absorption and insulation of the composite structure were elaborated. Finally, the results of finite element method are verified by impedance tube experiments. This work can make further progress in elucidating the acoustic properties of the ABH and open up new avenues in the control of ultra-low and ultra-wide frequency acoustic waves.

Study on the influence pattern and efficiency enhanced mechanism of acoustic–chemical spray dust reduction

To study the influence pattern and efficiency enhanced mechanism of acoustic–chemical spray method on dust reduction, a self-developed acoustic excitation test platform, viscosity test, surface tension experiment and sinking experiments were used to investigate the chemical spray properties and the wetting behavior of coal dust excited by acoustic waves. The self-developed acoustic–chemical spray dust reduction simulation platform was used to study the influence of acoustic waves on coal dust reduction effect and its efficiency enhanced mechanism. The results showed that the surface tension and viscosity of the chemical spray solution fluctuated between 0.4 mN/m and 0.4 mPa·s along with the variations in acoustic wave frequency and sound pressure level (SPL), thereby confirming that acoustic waves had on effected on chemical spray solution properties. However, the wetting time of the chemical spray solution on coal dust increased by 33.64 % at an acoustic frequency (f) of 1300 Hz and SPL of 120 dB because of the liquid interface vibrations caused by acoustic waves. With an increasing of acoustic frequency, the dust reduction efficiency demonstrated a parabolic trend and reached its maximum value at f = 1300 Hz. The dust reduction efficiency also increased exponentially along with increasing SPL. Acoustic waves not only increased the collision frequency between particles and droplets by changing the trajectory of dust but also accelerated the wetting and agglomeration effect of chemical spray reagents on coal dust by causing vibrations at the gas–liquid interface, thereby enhancing the dust reduction efficiency. Compared to the dust reduction efficiency of chemical spray technology, the total dust reduction efficiency was increased by 8.53 %, and the respirable dust reduction efficiency was increased by 21.93 %. The effect of acoustic waves on the respirable dust reduction efficiency was more significant than that on total dust.

Research on the audible acoustic field-enhanced heat transfer of double-pipe exchangers: Effect of laminar flow and turbulence, vertical and horizontal placement of pipes

The acoustic field is considered an efficient and reliable technique for enhancing convective heat transfer. This study investigates the optimal experimental conditions of acoustic field-enhanced heat transfer using an experimental platform for convective heat transfer in a double-pipe exchanger. The experiment mainly explored the enhancement effect of the acoustic field on heat transfer by comparing laminar flow and turbulent flow states, as well as the arrangement of horizontal and vertical pipes. Meanwhile, acoustic wave frequency and inlet temperature of the thermal fluid were also considered as experimental variables. The results showed that compared to the horizontal pipe which has the best reinforcement efficiency at a frequency of 0.6 kHz, the vertical pipe in the laminar flow condition showed a high heat transfer capacity in the range of 0.6–0.8 kHz, with the best reinforcement efficiency reaching up to 43.6%. The significant heat transfer enhancement effect is mainly because 0.6 kHz is close to the acoustic resonance frequency, which further enhances the heat transfer effect. In the turbulent flow condition, the effect of the acoustic field on enhancing heat transfer is obvious when the pipe is arranged horizontally, and the reinforcement efficiency reaches a maximum of 24.5% at a frequency of 0.7 kHz.

An improved analytical approach to establish the soliton solutions to the time‐fractional nonlinear evolution models

The time‐fractional Schrödinger (higher dimensional) and the Zakharov–Kuznetsov (ZK) models are the noteworthy modeling equations to interpret the propagation of signal in nonlinear optical fibers, small‐amplitude gravity waves on the surface water, high frequency acoustic waves, the interactions of small amplitude waves, the ion acoustic waves, nonlinear optics, Bose‐Einstein condensates, dynamics of plasma particles, etc. In this article, in order to develop advanced and broad‐spectrum closed‐form soliton solutions of the previously described nonlinear models, the advanced auxiliary equation approach has been put in used with reference to the beta‐derivative concept. The established soliton solutions are further comprehensive and typical and found in the form fractional, exponential, hyperbolic, and trigonometric functions and their variation. We depict 3D shape of the obtained solitons and explain the physical significance of the solitons. The accomplished solutions affirm that the method is effective and powerful and yields compatible solutions to fractional nonlinear evolution equations.

Investigating the Performance of the Multi-Lobed Leaf-Shaped Oscillatory Obstacles in Micromixers Using Bulk Acoustic Waves (BAW): Mixing and Chemical Reaction

Proper mixing in microfluidic devices has been a concern since the early development stages. Acoustic micromixers (active micromixers) attract significant attention due to their high efficiency and ease of implementation. Finding the optimal geometries, structures, and characteristics of acoustic micromixers is still a challenging issue. In this study, we considered leaf-shaped obstacle(s) having a multi-lobed structure as the oscillatory part(s) of acoustic micromixers in a Y-junction microchannel. Four different types of leaf-shaped oscillatory obstacles, including 1, 2, 3, and 4-lobed structures, were defined, and their mixing performance for two fluid streams was evaluated numerically. The geometrical parameters of the leaf-shaped obstacle(s), including the number of lobes, lobes’ length, lobes’ inside angle, and lobes’ pitch angle, were analyzed, and their optimum operational values were discovered. Additionally, the effects of the placement of oscillatory obstacles in three configurations, i.e., at the junction center, on the side walls, and both, on the mixing performance were evaluated. It was found that by increasing the number and length of lobes, the mixing efficiency improved. Furthermore, the effect of the operational parameters, such as inlet velocity, frequency, and intensity of acoustic waves, was examined on mixing efficiency. Meanwhile, the occurrence of a bimolecular reaction in the microchannel was analyzed at different reaction rates. It was proven that the reaction rate has a prominent effect at higher inlet velocities.

The effect of high-frequency acoustic wave vibration pattern on HKUST’s multi-level pore structure

The physical properties of materials are critical to their functionality, and the ability to control these properties using external forces is a significant challenge. In this study, we investigate the effect of three high frequency acoustic wave vibration patterns on the structure and morphology of MOF particles. Our results indicate that while regular vibration patterns generated by SAW can alter particle morphology, hybrid waves and Lamb waves with irregular vibration patterns can synthesise MOF crystals with multi-level pores. The vibration pattern of acoustic waves is shown to be a critical factor in controlling the particle morphology process. These results provide new insights into the precise control of crystal structure and the theory of crystallisation by particle attachment (CPA).

One-channel time reversal focusing of ultra-high frequency acoustic waves on a MEMS

This Letter reports on a work performed to fabricate and characterize a silicon micro-machined cavity dedicated to micro-resolution Ultra-High Frequency imaging in microfluidics and microbiological applications using one-channel time reversal. Time reversal provides the means to spatially and temporally localize elastic energy on a receiver. Here, the arrays of zinc oxide micro transducers are coupled with a 400 μm thick silicon wafer containing micromachined structures for acoustical field confinement. Characterization of the diffused acoustic field and time-reversal retro-focusing are reported. The transducers are wideband in the 0.2–2 GHz range with a central frequency of 0.9 GHz.

Acousto-optical camera for super-resolution imaging

I will present a hybrid acousto-optical imaging system that probes the environment with acoustic waves, converts the back-scattered sound into a coherent optical field on an aperture using an acousto-optical metasurface, and focuses the latter into an image with existing optical lenses. Preliminary theoretical analysis and experiments show that this approach can produce images of significantly higher resolution than possible with conventional methods, thus enabling high quality images produced with low frequency probing sound. Our imaging approach takes advantage of the best properties of optic and acoustic waves, namely, (1) the high image quality produced by existing optical systems and (2) the ability of low frequency acoustic waves to penetrate most materials. An additional advantage of our method is that it puts essentially no constraints on the sound source. For example, the source could have low directivity and may consist of a single transducer or it could even miss when imaging noisy environments. In the latter scenarios, our imaging method becomes purely passive.

Specialized finite element basis functions for mid-frequency simulations

Finite element analysis (FEA) has over the years become a common numerical tool for simulating time and frequency acoustic wave scattering and radiation problems due to its flexibility to model multiphysics coupling and complex geometries. For mid-frequency acoustic simulations, the computational mesh must be sufficiently fine to represent the wave field and the geometry, which becomes computationally expensive and impractical to use. Recent works in partition of unity FEA and isogeometric analysis have shown that using smooth basis functions that well-represent the local solution typically produce increased accuracy per degree of freedom compared to traditional FEA with Lagrange basis functions. In this work, the concept of designing accurate basis functions that can be easily incorporated into a finite element framework is explored. This process makes use of the Helmholtz-Kirchhoff integral defined along the edges of the mesh to locally represent the solution in the interior of each element. Therefore, this method only requires degrees of freedom on the element boundaries and does not require any a priori knowledge of the local solution for enrichment. Numerical dispersion results will be presented, and the practical implementation into FEA codes will be discussed.

Coexistence of two hole phases in high-quality p−GaAs/AlGaAs in the vicinity of Landau-level filling factors ν=1 and ν=(1/3)

We focused on the transverse AC magnetoconductance of a high-mobility $p$-GaAs/AlGaAs quantum well $(p=1.2\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{cm}}^{\ensuremath{-}2})$ in the vicinity of two values of the Landau-level filling factor $\ensuremath{\nu}$: $\ensuremath{\nu}=1$ (integer quantum Hall effect) and $\ensuremath{\nu}=1/3$ (fractional quantum Hall effect). The complex transverse AC conductance ${\ensuremath{\sigma}}_{xx}^{\mathrm{AC}}(\ensuremath{\omega})$ was found from simultaneous measurements of attenuation and velocity of surface acoustic waves propagating along the interface between a piezoelectric crystal and the two-dimensional hole system under investigation. We analyzed both the real and imaginary parts of the hole conductance and compared the similarities and differences between the results for filling factor 1 and filling factor 1/3. Both to the left and to the right of these values maxima of a specific shape, ``wings,'' arose in the $\ensuremath{\sigma}(\ensuremath{\nu})$ dependences at those two $\ensuremath{\nu}$. Analysis of the results of our acoustic measurements at different temperatures and surface acoustic wave frequencies allowed us to attribute these wings to the formation of collective localized states, namely, the domains of a pinned Wigner crystal, i.e., a Wigner solid. While the Wigner solid has been observed in 2D hole systems previously, we were able to detect it at the highest hole density and, therefore, the lowest hole-hole interaction reported.

Ion acoustic waves in lunar wake plasma

Kinetic theory of low frequency electrostatic waves is carried out in the lunar wake plasma modelled by kappa electrons, kappa-beam electrons, Maxwell–Boltzmann distributed protons and doubly charged Helium ions. The present work is motivated by observation of electrostatic waves on the outbound side of the first lunar wake flyby of the mission Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) probe P1. The dispersion characteristics of electrostatic waves which are identified as ion-acoustic waves are carried out for the observational plasma parameters. The frequencies of the ion acoustic waves derived from the model corresponding to peak growth rates are f⩽0.02fpe; (fpe being electron plasma frequency) which matches with the frequency of the waves observed by wave burst 1 (WB1) in the lunar wake (Tao et al., 2012). Our theoretical analysis reveals that in order to excite the low-frequency wave modes, low-energy electron beams are required which are not apparent in the observations.

Detection of the Large Surface Explosion Coupling Experiment by a Sparse Network of Balloon-Borne Infrasound Sensors

In recent years, high-altitude infrasound sensing has become more prolific, demonstrating an enormous value especially when utilized over regions inaccessible to traditional ground-based sensing. Similar to ground-based infrasound detectors, airborne sensors take advantage of the fact that impulsive atmospheric events such as explosions can generate low frequency acoustic waves, also known as infrasound. Due to negligible attenuation, infrasonic waves can travel over long distances, and provide important clues about their source. Here, we report infrasound detections of the Apollo detonation that was carried on 29 October 2020 as part of the Large Surface Explosion Coupling Experiment in Nevada, USA. Infrasound sensors attached to solar hot air balloons floating in the stratosphere detected the signals generated by the explosion at distances 170–210 km. Three distinct arrival phases seen in the signals are indicative of multipathing caused by the small-scale perturbations in the atmosphere. We also found that the local acoustic environment at these altitudes is more complex than previously thought.

Sensors on the surface acoustic waves for intelligent systems

The work is aimed at the study of surface processes on the dynamically deformed adsorbed surface of semiconductors, which will be used as a sensitive substrate in radiometric temperature sensors. The choice of semiconductors with a zinc blende structure is explained by the sensitivity of such electronic subsystem to the deformation of the crystal lattice, which can be caused by the self-consistent redistribution of defects, inconsistency of the parameters of the crystal lattice, or external factors, for example, the influence of mechanical or electric fields. Based on established regularities of the influence of the concentration and type of adsorbed atoms on the spectrum of surface electronic states and the distribution of electron density on the dynamically deformed adsorbed surface of a single crystal, the development of a new class of intelligent sensors with increased accuracy of measuring the concentration of adsorbed atoms and temperature on surface acoustic waves is proposed. Such a new approach is based on the self-consistent effect of the deformation of the crystal lattice on the dispersion law and the spectral width of the phonon mode, the electric charge density, and the energy displacement of the edges of the allowed zones. It is calculated the temperature-concentration coefficient of the resonance frequency of the surface acoustic wave and the regularities of its change depending on the concentration of adsorbed atoms are established. The relevance of this research is determined both by the needs of fundamental research and by applied aspects of development, optimization and cost reduction of the process of designing and creating devices, the functioning of which is carried out on surface acoustic waves.

Interpreting ultrasonic pulse velocities and elastic properties of lac du bonnet granite under compression

The measurement of ultrasonic velocities in rock core is a straightforward, non-destructive, economic method to estimate rock material properties conducted by emitting high frequency acoustic waves through the rock core. The velocities of compressional and shear waves (P- and S-waves, respectively) are influenced by the unique microstructural characteristics of the rock. Once wave velocities and bulk density for each sample have been determined, the dynamic elastic material constants such as Young’s modulus, Poisson’s ratio, and shear modulus can be calculated. In theory, it is expected that the dynamic properties would be similar to the static properties calculated in uniaxial compression strength (UCS) tests. In UCS tests, elastic parameters are estimated using stress-strain relationships at approximately 50% of the peak strength. However, dynamic properties from the UPV method often do not match static properties. In this study, dynamic testing of the rock core is completed under two broad stress conditions: no compression and axial compression (UCS). This allows for a direct comparison between dynamic UPV testing data, and static data, and should produce a closer match between the dynamic and static testing data when dynamic UPV testing is conducted under stress conditions similar to the static testing stress state.

Experimental study on laser propagation characteristics in local air turbulence disturbed by coherent acoustic waves

The existence of atmospheric turbulence seriously restricts the application of laser technology. However, the acoustic wave will affect the air density during the propagation process, change the original structure of the air turbulence, and then affect the propagation of the laser in the air turbulence. To study the effect of disturbance of atmospheric turbulence by acoustic waves on laser propagation, the propagation characteristics of lasers in local atmospheric turbulence under coherent acoustic wave perturbation are investigated experimentally. First, a coherent acoustic wave generator and a closed local air turbulence simulation device are designed. The propagation experiments of laser in a closed local air turbulence environment disturbed by coherent acoustic waves are carried out. It is found that the coherent acoustic wave will interfere with the wave reflected from the inner wall of the closed local air turbulence simulation device, and the sound pressure forms a regular standing wave intensity distribution pattern. Moreover, the variations of laser beam drift fluctuation variance, scintillation index, and beam diameter with coherent acoustic wave frequency, power, and sound source array position are studied. The results show that the original structure of air turbulence will be changed in the process of coherent acoustic wave propagation, which will affect the beam drift fluctuation variance, scintillation index, and beam diameter changes of laser propagation in air turbulence. The beam drift fluctuation variance, scintillation index, and beam diameter change regularly with the change of the frequency and power of the sound source. Changes of the fluctuations with frequency are relatively gentle, whereas changes with power are severe. This paper explores the influence of coherent acoustic waves disturbing air turbulence on laser propagation characteristics, and the research results provide a basis for improving or disturbing laser propagation performance in atmospheric turbulent environments.

Acoustically Stimulated Charge Transport in Graphene Film.

The process of acoustically stimulated charge transport in the graphene film on the surface of the YZ-cut of a LiNbO3 crystal was investigated. It was found that the dependence of the current in the graphene film on the frequency of the surface acoustic wave (SAW) excitation repeats the amplitude-frequency response of the SAW delay time line. It is shown that increasing the SAW amplitude leads to an increase in the current in the graphene film, and the current in the graphene film depends linearly on the amplitude of the high-frequency input signal supplied to the interdigital transducer (IDT, in dB). It is demonstrated that at a positive bias potential on the graphene film, the SAW propagation allows to change the direction of the current in the graphene film by changing the amplitude of the SAW. It is also shown that in the frequency range of the amplitude-frequency response of the SAW delay time line, the current in the graphene film can vary from positive to negative values depending on the frequency. The capability to control the SAW excitation frequency or the SAW amplitude makes it possible to control the value and direction of the current in the graphene film. The SAW propagation lets to collect and transport the photo-stimulated charges in the graphene film on the crystal surface.

Thermal effect of acoustic impact on the oil reservoir

The paper considers the effect of heating an oil-saturated reservoir during the propagation of high-frequency acoustic waves in it, due to their absorption by a saturated porous medium. It is assumed that in this case, volumetric heat sources are created in the reservoir. The density of distribution of heat sources in a porous medium at various capacities and frequencies of acoustic waves is shown. The paper presents a mathematical model for calculating the temperature field in a porous saturated medium under acoustic influence with an emitter located opposite the treated reservoir. It is assumed that the radius of the acoustic radiator is equal to the radius of the well, and the length of the radiator is equal to the power of the treated reservoir. In addition, the effect of increasing the effective thermal conductivity of the formation is taken into account when calculating the distribution of the temperature field. It is believed that the well works without stopping with a certain oil flow rate, depending on the viscosity of the oil. The problem is solved by the numerical method of finite differences according to an implicit scheme in a cylindrical coordinate system. In this paper, the author presents the results of studies of thermal effects occurring in the formation, namely, an increase in the effective thermal conductivity of the formation and the occurrence of heat sources during the propagation of acoustic waves in the formation. Thus, the article presents the results of computational studies that take into account only thermal effects during the treatment of the formation by the wave (acoustic) method. The treatment of the reservoir by wave methods (acoustic, sound, water hammer, elastic, and so on) is one of the promising methods for both increasing oil recovery and intensifying oil production, therefore, the theoretical study of the processes arising from the interaction of waves with a saturated porous medium is significant.

Experimental study on the transition process from partial discharge to arc discharge of oil–paper insulation based on fibre‐optic sensors

Arc discharge in the power transformer can bring enormous economic losses and safety risks. The transformer protection system for arc discharge faults is still not ideal. The physical characteristics of the whole process from partial discharge defects transition to arc faults are not fully recognized, mainly because it is difficult to establish and sense the relevant characteristic parameters. This paper built a research platform for studying the transition process from partial discharge to early arc discharge based on fibre-optic ultrasonic, temperature, pressure sensors with traditional electrical voltage and current sensors. Five discharge models are designed and the changing pattern of multiple parameters in the transition process of different models is studied. The experiment results show that the amplitude and frequency of acoustic waves drop significantly after the arc breakdown. Ultrasonic and high-frequency current sensing in the early warning of arc fault each has its own limitations. The pressure caused by the arc is not only related to the arc energy but also related to the discharge types. The overall oil temperature change after the early arc discharge is small and hard to detect. This work highlights the promise of using fibre-optic sensors for physical process research within a harsh electromagnetic environment.

Effect of acoustic waves on the flow and heat transfer around two tandem arranged cylinders

In this work, the effect of acoustic waves on vortex shedding and convective heat transfer of two tandemly arranged cylinders is investigated using experiments and numerical simulations. This paper focuses on the average Reynolds number Re = 200, the sound pressure level ranges from 127dB to145dB, and the sound frequency ranges from 100Hz to 1000Hz. Different acoustic wave frequencies and particle vibration velocity amplitudes were set as the entrance conditions. The average heat transfer in the upstream and downstream cylinders was enhanced due to the increase in the particle velocity amplitude of the fluid around the cylinder by acoustic oscillations. Moreover, with the increase in the acoustic frequency, the flow mixing is enhanced and irregular vortices appeared in the cylindrical wake. With regards to the particle velocity amplitude, the values of the Nusselt number of the two cylinders increase with the increase in particle velocity amplitude. With the increase in the particle velocity amplitude, the forced mixing and heat transfer of the gap flow between the two cylinders are enhanced. The comparison between the experimental and numerical results shows that acoustic waves can enhance convective heat transfer of two tandemly arranged cylinders in the cross-flow.

Investigation of critical response characteristics of micro-droplets under the action of low-frequency acoustic waves

For the droplets with different size distribution, reasonably selecting the frequency and period of acoustic waves are of great significance to acoustic agglomeration. To investigate critical responses of microdroplets under the action of low-frequency acoustic waves, laboratory experiments and numerical simulations of acoustic interference were conducted, and statistical test and theoretical analysis were carried out. A total of 1,680 sets of experiments were performed, from which about 300,000 particle size samples were collected, with sound frequency of 30–280 Hz and the sound pressure level (SPL) of 70–130 dB. Droplet size distribution (DSD), equilibrium response time (ERT), the nodal plane in the air chamber and entrainment coefficient were analyzed. The critical SPL of acoustic agglomeration was 110 ± 15 dB based on average droplet size increment, and the variation of droplet size indicated that the ERT of acoustic intervention on microdroplets under the critical SPL was 44 ± 12 s. In addition, lower sound frequencies corresponded to larger widths of droplet size with significant response (DSSR), which were jointly affected by sound pressure gradient (SPG), the entrainment coefficient and the droplet concentration. For microdroplets with unknown particle size distribution, acoustic intervention with variable frequencies is suggested for fog elimination and precipitation enhancement.