Acoustic Wave Research Articles

Revisit of electron temperature effect on stimulated Brillouin scattering in homogenous plasma

Stimulated Brillouin scattering (SBS) has complex dependence on the plasma electron temperature via the Landau damping, particle trapping, and consequent nonlinear frequency shift. It is found from our numerical simulation that the SBS reflectivity in its saturation stage tends to increase with the plasma electron temperature within a certain range, although the linear growth rate of SBS normally reduces with the increasing electron temperature. This is because the phase velocity of an ion acoustic wave (IAW) increases with the electron temperature, which tends to reduce the Landau damping of the IAWs and hence reduce ion trapping. In the nonlinear saturation stage, ion trapping will modify the ion distribution function and induce a negative frequency shift in the IAW. This nonlinear frequency shift will break the three-wave coupling, thereby causing saturation of the SBS. With further increase in the electron temperature, however, electron trapping will dominate over ion trapping, which induces a positive frequency shift in the IAW and can lead to the SBS saturation as well. As a result, the SBS reflectivity first increases and then decreases with increase in the electron temperature. At around the peak of the SBS reflectivity, the positive frequency shift of IAW induced by electron trapping roughly offsets the negative frequency shift induced by ion trapping.

Investigation of the Properties of Surface Acoustic Waves in a Lithium Niobate Single Crystal with a Silicon Dioxide Film by the Finite-Element Method

Investigation of the Properties of Surface Acoustic Waves in a Lithium Niobate Single Crystal with a Silicon Dioxide Film by the Finite-Element Method

An introduction to acoustic location Template-based positioning model

Indoor location information, which is an indispensable label for linking the vast amount of data circulating in the world of IoT, 5G, and AI, is essential. This paper proposes a novel template pattern matching-based acoustic positioning method, Location Template-based Positioning Model, for indoor acoustic source localisation. This innovative technology, similar to the passive SONAR systems on submarines, uses audible acoustic waves to locate acoustic sources in complex indoor environments. The proposed LTPM is a statistical model, and it calculates the coordinates of acoustic sources by matching input acoustic signals with template acoustic signals that are pre-collected from preset locations. A comprehensive overview of the principles and implementations of LTPM is provided, and its feasibility is verified through preliminary positioning tests in this paper. It is hoped to provide research references for the advancement of pattern matching-based acoustic indoor positioning technologies.

Hybrid integration of BAW resonators with an on‐chip inductor to improve the stopband rejection of the N78 band filter

AbstractThis paper demonstrates a 3.4 GHz micro‐acoustic filter with excellent in‐band insertion loss, rectangle coefficient, and out‐of‐band rejection. The proposed filter was based on a novel topology by integrating the bulk acoustic wave (BAW) resonators with an on‐chip clamping inductor, the introduction of the lumped components is beneficial for improving the filters' stopband rejection while having minimal influence on the rectangle coefficient and in‐band insertion loss. Al0.8Sc0.2N material was selected as the piezoelectric film of the BAW device and the inductor was fabricated on the same wafer with BAW devices. The manufactured filter has a minimum in‐band insertion loss of ~ 1.5 dB, a 3 dB bandwidth of about 170 MHz, and a stopband rejection of nearly ‐30 dB. The experimental results verify the design and show great applications for 5G communication and beyond.

Continuous and explosive synchronization transition in turbulent combustors

Thermoacoustic instabilities in turbulent combustors have disastrous consequences and present notorious challenges in their modeling, prediction, and control. Such instabilities are characterized by self-excited periodic oscillations, arising from a positive feedback between the acoustic pressure and heat release rate fluctuations. We present a mean-field approach to model thermoacoustic transitions. The nonlinear flame response is modeled using an ensemble of phase oscillators constrained to collectively evolve at the rhythm of acoustic fluctuations. Starting from the acoustic wave equation coupled with the phase oscillators, we derive the evolution equations for the amplitude and phase for acoustic oscillations. The model captures abrupt and continuous transitions to thermoacoustic instability observed in disparate combustors. We also discover that continuous and abrupt transitions happen through paradigmatic continuous and explosive synchronization, respectively. Importantly, our approach explains spatiotemporal synchronization and pattern formation underlying the transition to thermoacoustic instability. The versatility of the model in capturing different types of transitions suggests promising prospects for its extension to encompass a wide range of fluid dynamics phenomena.

Enhanced wave transmission in random media with mirror symmetry

We present an analysis of enhanced wave transmission through random media with mirror symmetry about a reflecting barrier. The mathematical model is the acoustic wave equation, and we consider two setups, where the wave propagation is along a preferred direction: in a randomly layered medium and in a randomly perturbed waveguide. We use the asymptotic stochastic theory of wave propagation in random media to characterize the statistical moments of the frequency-dependent random transmission and reflection coefficients, which are scalar-valued in layered media and matrix-valued in waveguides. With these moments, we can quantify explicitly the enhancement of the net mean transmitted intensity, induced by wave interference near the barrier.

Vortex-induced noise suppression of a cylinder with blowing through porous media

To mitigate vortex shedding for flow and noise control of a circular cylinder, an experimental approach combining air blowing and porous coating was implemented simultaneously as a hybrid method. Localized air blowing was symmetrically applied through structured porous media at four angles, corresponding to different regions of the flow field: boundary layers, shear layers on the cylinder, separated shear layers, and the cylinder's base. The study involved synchronizing near-field pressure fluctuation and far-field noise measurements with flow field measurements obtained via particle image velocimetry. Near-field pressure measurements were taken around the cylinder's circumference using a remote sensing method. This comprehensive investigation revealed that vortex shedding primarily induced pressure fluctuations at the cylinder's shoulders, resulting in the propagation of acoustic waves to the far field. The hybrid method, alongside the separate application of porous coating and local blowing, showcased substantial efficacy in mitigating near-field pressure, consequently leading to a reduction in far-field noise. These techniques achieved this by strategically shifting the vortex formation region further downstream and expanding the wake region compared to the baseline. Notably, the hybrid method, particularly when local blowing was applied at the base of the porous coated cylinder, exhibited a significantly enhanced impact in this regard, resembling the behavior observed with the individual application of porous coating.

A complex boundary wave superposition method for solving external acoustic problems

This paper proposes a complex boundary wave superposition method with a unique solution of full wavenumber based on the similarity between the acoustic wave superposition method (WSM) and the external excitation response of dynamic systems and combined with the idea that a damping system has a unique solution in dynamic theory. By placing the virtual equivalent source on the virtual boundary of complex space, the conventional WSM acquires damping properties comparable to those of the dynamical system. This approach successfully addresses the non-uniqueness of the solution at the eigenfrequency and is more efficient than the conventional combined layer potential method. The paper presents a comprehensive description of the proposed method, with a focus on theory, modeling, and parameter selection. The effectiveness of this method is evaluated by applying it to two types of acoustic problems, namely, radiation and scattering. The numerical results indicate that this method effectively addresses the non-unique problems encountered in conventional WSM. Furthermore, the proposed method is as accurate and efficient as the conventional WSM.

Nonlinear Burgers Type Equation for Acoustic Waves in the Ray Approximation in a Moving Atmosphere (Theory, Experiment)

Nonlinear Burgers Type Equation for Acoustic Waves in the Ray Approximation in a Moving Atmosphere (Theory, Experiment)

Simultaneous Protein Adsorption and Viscosity Measurement using Micropillar-Enhanced Acoustic Wave (μPAW) Device for Pharmaceutical Applications

At the early stages of drug development, the amount of drug materials is rather limited. In this case, viscosity measurement is often postponed to the later stages, where grams of proteins can be produced. Therefore, it is necessary to develop a viscometer capable of measuring the viscosity with high accuracy while requiring low sample volume. This study presents a novel viscosity measurement technique based on measuring the resonance frequency and motional resistance of a micropillar-enhanced acoustic wave (μPAW) device. The μPAW was developed by fabricating micropillars on the quartz crystal microbalance substrate in order to achieve ultra-high sensitivity, thanks to a unique coupling between the micropillar and the resonator. The experimental measurements demonstrated a nonlinear relationship between the density and viscosity of the fluid and the response of μPAW. A calibration correlation was developed using the response of μPAW in aqueous glycerol and sucrose solutions. The measurements were then extended using high-concentration BSA solutions as the model of protein solution. The main advantage of the μPAW device in this work over other viscometers is the ability to simultaneously measure solution viscosity and protein adsorption on the surface. This is a huge step forward in the development of sensing systems for the pharmaceutical industry, where real-time sensing of target biological proteins and measuring the viscosity of a solution is required.

О возможности создания эффективных устройств на поверхностных акустических волнах на частотах выше 6 ГГц

In the paper the interaction of surface acoustic waves (SAWs) with reflectors and interdigital transducers (IDTs) with high aspect ratio electrodes (HAR-electrodes) are investigated. The conditions for the SAW resonant reflection and propagation and the effective IDT conversion of the SAW power into electrical power at the load have been obtained. The real possibility of the effective SAW devices creation (filters, delay lines, resonators, RFID tags) at frequencies above 6 GHz (up to 12-15 GHz) using HAR-electrodes was demonstrated.

Activated carbon-reinforced polyurethane composite foams with hierarchical porosity for broadband sound absorption

The generation of various noise has caused severe noise pollution issues across a wide frequency spectrum, urgently requiring the development of sound-absorbing materials. Herein, we introduce composite polyurethane (PU) foams incorporating extremely nanoporous activated carbon (AC) including both meso- and macro-sized pores as an eco-friendly sound-absorbing material with superior and broadband sound absorption capabilities. The composite foam absorbs 95.8 % of the incident acoustic waves in the 2,000–5,000 Hz frequency range, i.e., the most sensitive range for the human auditory system, far outperforming pristine PU foam, which absorbs only 70.6 %. We demonstrate that sound absorption properties can be fine-tuned by adjusting the pore type and content of the AC. Significantly, the optimized composite foam structure absorbs 100 % of the incident waves at a specific frequency of 2,550 Hz. Collectively, we propose a master curve for the sound absorption properties derived from various composite foams, demonstrating that the properties can be precisely predictable and subsequently used for designing the pore characteristics and content of AC. Incorporating AC can also improve the mechanical properties of foams through interfacial adhesion phenomena. Our methodology provides valuable insights into the fabrication of composite foams with tunable sound absorption properties as a promising solution to noise pollution.

Application of dust acoustic waves as THz polarizer: Numerical investigations

Application of dust acoustic waves as THz polarizer: Numerical investigations

Analysis Method for the Influence of Parasitic Surface Conductivity on Silicon-Based Surface Acoustic Wave Devices

Analysis Method for the Influence of Parasitic Surface Conductivity on Silicon-Based Surface Acoustic Wave Devices

Advancements in One-Port Surface Acoustic Wave (SAW) Resonators for Sensing Applications: A Review

Advancements in One-Port Surface Acoustic Wave (SAW) Resonators for Sensing Applications: A Review

Low-frequency Acoustic Collimation Modulation Based on Monopole Mie Resonance Acoustic Metamaterials

Acoustic metamaterials show great flexibility in manipulating acoustic waves and exhibit important applications. However, an increasing number of applications are suitable for the low-frequency range, which makes it challenging to design acoustic metamaterials for low-frequency modulation. Here, we propose a subwavelength monopole Mie resonance acoustic metamaterial that can flexibly control the propagation route of acoustic waves. Compared to the background medium, the designed Mie unit has a higher refractive index and can achieve directional manipulation of low-frequency acoustic waves based on monopole Mie resonance. Furthermore, an array formed by multiple Mie units in a specific arrangement can achieve the acoustic collimation phenomenon. The designed monopole Mie resonance acoustic metamaterial has potential application prospects in fields such as low-frequency filtering, noise suppression, and nondestructive testing.

Valley edge states with opposite chirality in temperature dependent acoustic media

The valley degree of freedom in phononic crystals and metamaterials holds immense promise for manipulating acoustic and elastic waves. However, the impact of acoustic medium properties on valley edge state frequencies and their robustness to one-way propagation in valley topological phononic crystals remains unexplored. While significant attention has been devoted to scatterer design embedded in honeycomb lattices within acoustic and elastic media to achieve valley edge states and topologically protected nontrivial bandgaps, the influence of variations in acoustic medium properties, such as wave velocity and density affected by environmental temperature, has been overlooked. In this study, we investigate the effect of valley edge states and topological phases exhibited by topological phononic lattices in a temperature-dependent acoustic medium. We observe that a decrease in wave velocity and density, influenced by changing environmental temperature, shifts the topological valley edge states to lower frequencies. Therefore, alongside phononic lattice design, it is crucial to consider the impact of acoustic medium properties on the practical application of acoustic topological insulators. This issue becomes particularly significant when a topological phononic crystal is placed in a wave medium that transitions from incompressible to compressible, where wave velocity and density are no longer constant. Our findings offer a novel perspective on investigating topological insulators in variable acoustic media affected by changing thermodynamic and fluid properties.

Low-frequency broadband valley transport for acoustic topology based on extended resonance

This paper proposes an extended resonant structure to solve the problem that topological acoustic waveguides have a narrow bandwidth at low frequencies. This acoustic structure consists of a two-dimensional structure and a resonant cavity in the three-dimensional direction, and its essence is to extend the resonant cavity in the two-dimensional structure to the three-dimensional direction. The problem that the size of the resonant cavity is limited by the size of the two-dimensional structure can be solved by this special extension. At the same time, the resonant cavity can be maximized in the three-dimensional direction. The topological properties of the original structure are not affected as long as the radius of the resonant cavity is widened without changing the symmetry of the overall composite structure. The rotating scatterer remains a reliable method for realizing topological phase transitions. The effect of the resonant cavity length on the band position is obtained using the finite element method, and it is demonstrated that the topological acoustic waveguide has a wide operating band at low frequencies. Simulation results show that this structure still has a bandgap width of 100 Hz at a low frequency of 350 Hz. The topological acoustic waveguide structure proposed in this paper can provide a new idea for the study of low-frequency broadband acoustic topology, which promotes the control of low-frequency acoustic waves by the topological acoustic waveguide.

Beam‐Driven Electron Cyclotron Harmonic and Electron Acoustic Waves as Seen in Particle‐In‐Cell Simulations

AbstractRecent study has demonstrated that electron cyclotron harmonic (ECH) waves can be excited by a low energy electron beam. Such waves propagate at moderately oblique wave normal angles (∼70°). The potential effects of beam‐driven ECH waves on electron dynamics in Earth's plasma sheet is not known. Using two‐dimensional Darwin particle‐in‐cell simulations with initial electron distributions that represent typical plasma conditions in the plasma sheet, we explore the excitation and saturation of such beam‐driven ECH waves. Both ECH and electron acoustic waves are excited in the simulation and propagate at oblique wave normal angles. Compared with the electron acoustic waves, ECH waves grow much faster and have more intense saturation amplitudes. Cold, stationary electrons are first accelerated by ECH waves through cyclotron resonance and then accelerated in the parallel direction by both the ECH and electron acoustic waves through Landau resonance. Beam electrons, on the other hand, are decelerated in the parallel direction and scattered to larger pitch angles. The relaxation of the electron beam and the continuous heating of the cold electrons contribute to ECH wave saturation and suppress the excitation of electron acoustic waves. When the ratio of plasma to electron cyclotron frequency ωpe/ωce increases, the ECH wave amplitude increases while the electron acoustic wave amplitude decreases. Our work reveals the importance of ECH and electron acoustic waves in reshaping sub‐thermal electron distributions and improves our understanding on the potential effects of wave‐particle interactions in trapping ionospheric electron outflows and forming anisotropic (field‐aligned) electron distributions in the plasma sheet.

Passive control of vibrations of a beam by means of Herschel–Quincke vibration filters

This work concerns the adaptation of the Herschel–Quincke filters (HQ) known in the case of plane acoustic waves in tubes to the case of bending waves in beams. The objective is to develop new techniques to design vibration filters in thin structures. In acoustics, an HQ filter consists of the insertion of a bifurcation in a primary tube, so as to create two tubes in parallel and of different length. The phase difference creates destructive interference at certain frequencies which gives rise to zero transmission. In the case of the bending waves considered here, the HQ interference is obtained by locally splitting a thin beam into two segments of the same length but of different thickness. The difference in travel time is then created by the difference in bending stiffness between the two segments. A semi-analytical wave decomposition model using Timoshenko’s theory is developed to perform parametric studies of behaviour of such a device. Finite element simulations and experimental demonstrations confirm the predictions of a semi-analytical model. The results highlight the link between the geometric parameters of the device and its filtering properties. Therefore, this paper establishes a novel strategy of design of vibration filters, which utilizes the HQ effect for bending waves in beams.