Acoustic Cavity Research Articles

Acoustic Resonance Tuning by High-Order Lorentzian Mixing.

Nanoscale mechanical resonators have attracted a great deal of attention for signal processing, sensors, and quantum applications. Recent progress in ultrahigh-Q acoustic cavities in nanostructures allows strong interactions with various physical systems and advanced functional devices. Those acoustic cavities are highly sensitive to external perturbations, and it is hard to control those resonance properties since those responses are determined by the geometry and material. In this paper, we demonstrate a novel acoustic resonance tuning method by mixing high-order Lorentzian responses in an optomechanical system. Using weakly coupled phononic-crystal acoustic cavities, we achieve coherent mixing of second- and third-order Lorentzian responses, which is capable of the fine-tunability of the bandwidth and peak frequency of the resonance with a tuning range comparable to the acoustic dissipation rate of the device. This novel resonance tuning method can be widely applied to Lorentzian-response systems and optomechanics, especially active compensation for environmental fluctuation and fabrication errors.

Coherent optical coupling to surface acoustic wave devices

Surface acoustic waves (SAW) and associated devices are ideal for sensing, metrology, and hybrid quantum devices. While the advances demonstrated to date are largely based on electromechanical coupling, a robust and customizable coherent optical coupling would unlock mature and powerful cavity optomechanical control techniques and an efficient optical pathway for long-distance quantum links. Here we demonstrate direct and robust coherent optical coupling to Gaussian surface acoustic wave cavities with small mode volumes and high quality factors (>105 measured here) through a Brillouin-like optomechanical interaction. High-frequency SAW cavities designed with curved metallic acoustic reflectors deposited on crystalline substrates are efficiently optically accessed along piezo-active directions, as well as non-piezo-active (electromechanically inaccessible) directions. The precise optical technique uniquely enables controlled analysis of dissipation mechanisms as well as detailed transverse spatial mode spectroscopy. These advantages combined with simple fabrication, large power handling, and strong coupling to quantum systems make SAW optomechanical platforms particularly attractive for sensing, material science, and hybrid quantum systems.

Rabi‐Like Splitting in Acoustic Cavity Coupled with Membrane‐Type Metasurface

Rabi‐like splitting effect in acoustics is demonstrated in a hybrid metasurface. The hybrid metasurface is composed of a membrane‐type acoustic metasurface and a Fabry–Perot (F–P) cavity. It is found that the transmission resonance of the F–P cavity is modulated to spectrum with two peaks around the resonant frequencies. The transmission valley in the middle of the two transmission peaks is caused by the antiresonance effect, and the phenomenon is similar to the Rabi‐splitting effect in quantum physics. The results are promising for utilization in designing acoustic wave devices like filtering and acoustic sensors with new mechanisms in hybrid metasurfaces.

Unsteady Subsonic/Supersonic Flow Simulations in 3D Unstructured Grids over an Acoustic Cavity

Unsteady Subsonic/Supersonic Flow Simulations in 3D Unstructured Grids over an Acoustic Cavity

Molding the acoustic cavity–analyzing the influence of toroidal vortex development on acoustic multi-bubble macrostructures under different ultrasonic horn tip diameters

The acoustic cavity structure typically experiences a sequence of transfigurations during its sinusoidal growth–collapse cycle. However, upon examining the cavity structure in aqueous bodies, it appears that the growth structure attained falls between two geometrical structures, namely, mushroom-like structure (MBS) and cone-like bubble structure (CBS), based on the actuated ultrasonic horn tip diameter. With the recurring observations of the emergence of proximal toroidal vortices, the present investigation conducts a numerical analysis exploring the vortex development under 3, 6, 13, 16, and 19 mm horn tips to establish a potential correlation between the vortex and the cavity structure. The study presents a computational fluid dynamic investigation to capture the nature of the vortex evolution, in terms of size and position, and its respective cavitation development. The first indicator of potential correlation was the equivalency of the vortex expansion–contraction frequency and the cavity's sub-harmonic frequency. It has been found that the cavity structure is molded into MBS by the presence of a symmetric locomotive vortex structure that extends up to 1.5 times the horn tip diameter. Meanwhile, CBS is observed to take shape in the presence of an eccentric locomotive vortex that attains a size within 0.2–0.6 times the horn tip diameter. The significance of the vortex size and position is also observed in the cavity's collapse, as the vortex appears to govern the ability of the cavity impinging jet to initialize the collapse phase.

Dynamic stiffness formulations for exact modal and dynamic response analysis of three-dimensional acoustic cavities in cylindrical coordinates

Exact dynamic stiffness (DS) models for three-dimensional (3D) cavities in cylindrical coordinates under any classical acoustic boundary conditions (BCs) are proposed in this paper. The paper first derives the exact general solutions that satisfy the governing differential equations. Then, these general solutions are used to develop the DS matrices for 3D cavities in cylindrical coordinates by substituting them into the acoustic pressure and normal velocity BCs. Subsequently, the Wittrick–Williams algorithm, along with the analytical expressions of the j0 count for various shaped cavities, is applied to compute natural frequencies. Finally, reliable and efficient techniques for dynamic response solution are employed. The DSM provides benchmark solutions for various 3D cavities. The convergence, universality, and efficiency of the proposed method in modal and response analysis are illustrated by comparing the results obtained using the DSM and FEM. The calculation time when using the DSM is only 0.1% of that when using the commercial finite element method, while maintaining the same accuracy. This research not only provides an effective technique for analyzing the cylindrical acoustic pressure field in engineering, but also establishes a foundation for the analysis of structural–acoustic coupling in tubular structures.

Acoustic tunnel lining cavity detection using cepstral coefficients with optimized filter bank

Tunnels are an essential component of modern transportation infrastructure, and their structural health is critical to traffic safety, which can be seriously affected by tunnel lining cavities. In this paper, an acoustic-based detection approach for assessing the integrity of tunnel linings is studied. By tapping the tunnel lining surface, acoustic signals are sampled and analyzed using a novel feature parameter extraction algorithm-the energy-frequency cepstral coefficient, which uses wavelet packet decomposition to obtain energy distribution statistics in the frequency domain of the signal, and constructs a signal-dependent filter bank to achieve the cepstral coefficient extraction. Compared with the traditional Mel filter bank, this method can adaptively adjust the resolution of the filter bank according to the frequency characteristics of the classified samples. This allows for higher frequency resolution in regions where the energy distribution is concentrated. As a result, the extracted feature parameters achieve both dimensional compression and superior information retention. Experimental results show that the proposed energy-frequency cepstral coefficient feature outperforms the traditional Mel-frequency cepstral coefficient feature, resulting in a higher accuracy of tunnel lining detection. The convolutional neural network model achieves an accuracy of 99.2%, with a 78.9% reduction in error rate compared with the traditional Mel-frequency cepstral coefficient feature parameters. Additionally, a particle swarm optimization support vector machine model is trained to achieve an accuracy rate of 99.6% and an error rate reduction of 76.5%.

Realization of nonreciprocal acoustic energy transfer using an asymmetric strong nonlinear vibroacoustic system

AbstractIn this paper, an asymmetric vibroacoustic system that can passively realize nonreciprocal transmission of acoustic energy is reported. This experimental system consists of a waveguide, a strongly nonlinear membrane, and three acoustic cavities with different sizes. The theoretical modeling of the system is verified by experiments, and parametric analysis is also carried out. These intensive studies reveal the nonreciprocal transmission of acoustic energy in this prototype system. Under forward excitation, internal resonance between the two nonlinear normal modes of the vibroacoustic system occurs, and acoustic energy is irreversibly transferred from the waveguide to the nonlinear membrane. However, under backward excitation, there is no internal resonance in the system. Energy spectra and wavelet analysis are used to highlight the mechanism of nonreciprocal transfer of acoustic energy. Consequently, nearly unidirectional (preferential) transmission of acoustic energy transfer is shown by this system. The nonreciprocal acoustic energy transfer method illustrated in this paper provides a new way to design the odd acoustic element.

Acoustic Higher-Order Topological Insulators Induced by Orbital-Interactions.

The discovery of higher-order topological insulator metamaterials, in analogy with their condensed-matter counterparts, has enabled various breakthroughs in photonics, mechanics, and acoustics. A common way of inducing higher-order topological wave phenomena is through pseudo-spins, which mimic the electron spins as a symmetry-breaking degree of freedom. Here, this work exploits degenerate orbitals in acoustic resonant cavities to demonstrate versatile, orbital-selective, higher-order topological corner states. Type-II corner states are theoretically investigated and experimentally demonstrated based on tailored orbital interactions, without the need for long-range hoppings that has so far served as a key ingredient for Type-II corner states in single-orbital systems. Due to the orthogonal nature of the degenerate p orbitals, this work also introduces a universal strategy to realize orbital-dependent edge modes, featuring high-Q edge states identified in bulk bands. These findings provide an understanding of the interplay between acoustic orbitals and topology, shedding light on orbital-related topological wave physics, as well as its applications for acoustic sensing and trapping.

Higher-order Non-Hermitian skin effect in an acoustic lattice

Non-Hermitian physical systems offer a distinct band topology that gives rise to the interesting phenomenon known as the non-Hermitian skin effect (NHSE). However, the exploration of higher-order NHSE in classical wave systems by leveraging non-reciprocity has been largely unexplored. In this study, we introduce a novel approach to experimentally realize the higher-order NHSE in a two-dimensional non-reciprocal breathing acoustic Kagome lattice. This lattice is composed of acoustic cavities with non-reciprocal coupling achieved through electrically controlled active acoustic elements. We successfully observed second-order corner modes using a 3 × 3 lattice, which manifest as localized pressure distributions at specific frequencies in both parallelogram and triangular topological acoustic lattices. We delve into the underlying mechanisms and their implications, thereby paving the way for a deeper understanding of higher-order NHSE and potentially innovative applications rooted in the acoustic non-reciprocity.

A battery-free anti-inflammatory brain remote for spatiotemporal guiding movement of mice

The brain-machine-interface (BMI) system designed for the regulation of neural activity represents a cutting-edge technology in contemporary society, holding promising potential for applications in sensory substitution, neural disease treatment, and behavioral intervention. In this study, a novel battery-free anti-inflammatory brain remote has been innovated to guide the movement of mice. Characterized by a biologically inspired design, the device is capable of wireless power reception and control through a mobile phone utilizing the piezoelectric effect triggered by audio playback. Comprising two essential components—namely, the pedestal and the crest—the former is semi-invasively implanted on the head, featuring strategically positioned electrodes within specific brain regions. Additionally, the pedestal incorporates a drug-delivery microneedle array with antibacterial properties (PEG-ZnO nanorods), effectively mitigating the risk of postoperative infection and ensuring long-term wearability. The crest is constructed with an acoustic resonant cavity and a piezoelectric transducer, facilitating the reception of programmed acoustic waves and the subsequent output of neural electrostimulation signals. In vivo experiments involving the stimulation of the primary somatosensory barrel cortex (S1BF) in freely moving mice demonstrated the device's real-time influence on their body-turning behaviors. These findings underscore a wireless, self-powered, and biologically friendly approach, contributing to the advancement of remote brain-machine interfaces.

Robust temporal adiabatic passage with perfect frequency conversion between detuned acoustic cavities

For classical waves, phase matching is vital for enabling efficient energy transfer in many scenarios, such as waveguide coupling and nonlinear optical frequency conversion. Here, we propose a temporal quasi-phase matching method and realize robust and complete acoustical energy transfer between arbitrarily detuned cavities. In a set of three cavities, A, B, and C, the time-varying coupling is established between adjacent elements. Analogy to the concept of stimulated Raman adiabatic passage, amplitudes of the two couplings are modulated as time-delayed Gaussian functions, and the couplings’ signs are periodically flipped to eliminate temporal phase mismatching. As a result, robust and complete acoustic energy transfer from A to C is achieved. The non-reciprocal frequency conversion properties of our design are demonstrated. Our research takes a pivotal step towards expanding wave steering through time-dependent modulations and is promising to extend the frequency conversion based on state evolution in various linear Hermitian systems to nonlinear and non-Hermitian regimes.

PIV measurements of coherent vortices and turbulence production inside acoustic liner cavity with offset slit

This paper reports an experimental investigation into the vortex dynamics purely excited by periodic acoustic waves within a slit–cavity structure, which is a typical unit element of an acoustic liner for aeroengine applications. Particle image velocimetry (PIV) was used to measure the instantaneous, time-averaged and phase-dependent flow dynamics inside the slit–cavity, which is exposed to high-intensity incident acoustic waves. Different with traditional literature mainly focusing on the acoustic characteristics, we primarily analyze the coherent vortex structures and turbulence production mechanism, accompanying with the variable of slit offset ratio being taken into consideration. The results demonstrate that the acoustic waves can excite the hydrodynamic velocities exceeding almost tens of times than the acoustic particle velocity, yielding multi-scale vortex structures appearing within the enclosed volume. Comparatively, in configuration with offset slit, the maximum hydrodynamic velocities were gradually intensified by wall confinement effect. Subsequent proper orthogonal decomposition analysis revealed the coherent vortex structures and demonstrated the offset configuration will increase their energy proportions and enhance their temporal correlations. However, the phase-dependent flow results revealed that the offset slit can oppositely attenuate the kinematics of the coherent vortices, which were represented by the convection trajectories and convection speeds, especially during the initial acceleration stage. Finally, analysis on turbulence production mechanism confirmed the attenuated turbulent kinetic energy by the offset slit, which was attributed to the less generation of shear stresses.

The Vibro-Acoustic Characteristics Analysis of the Coupled System between Composite Laminated Rotationally Stiffened Plate and Acoustic Cavities

In order to study vibro-acoustic characteristics between composite laminated rotationally stiffened plate and acoustic cavities in the coupled system, first-order shear deformation theory (FSDT) and modified Fourier series are used to construct a unified analysis model. The involved coupled systems primarily encompass three types: the coupled system between composite laminated rotationally stiffened plate and cylindrical-cylindrical cavities, spherical-cylindrical cavities, and conical-cylindrical cavities. First, the first-order shear deformation theory and the modified Fourier series are applied to construct the allowable displacement function of the composite laminated rotationally stiffened plate and the allowable sound pressure function of the acoustic cavities. Second, the energy functionals for the structural domain and the acoustic field domain are established, respectively. According to the continuity condition of the particle vibration velocity at the coupling boundary between the composite, laminated cylindrical shell and the enclosed cavity, the coupling potential energy between the stiffened plate and two acoustic cavities is introduced to obtain the energy functional of the coupled system. Third, the Rayleigh-Ritz method is utilized to solve the energy functional and, when combined with artificial virtual spring technology, the suggested theory may be used to study the vibro-acoustic characteristics of a coupled system with arbitrary elastic boundary conditions. Finally, based on validating the fast convergence and correctness of the model, this paper will analyze the impact of crucial parameters on vibro-acoustic characteristics. Furthermore, by incorporating internal point forces and point-sound source stimulation, a steady-state response analysis of the coupled system will be conducted. This research can give a theoretical foundation for the vibration and noise reduction of a vibro-acoustic coupling system.

Nonlinear supersonic flutter of a composite panel backed by an acoustic cavity with finite-amplitude sound waves

In this paper, an implicit partitioned fluid-structure-acoustic interaction method is presented for predicting nonlinear aeroelastic response of an elastic composite laminated panel backed by an acoustic cavity and subject to a supersonic flow. The method is formulated in an arbitrary Lagrangian-Eulerian framework based on the unsteady Navier-Stokes equations for the supersonic flow, a geometrical nonlinear dynamics model for the composite laminated panel, and the nonlinear Westervelt equation for the finite-amplitude sound waves in cavity. A theoretical fluid-structure-acoustic model of the supersonic panel is proposed for validating the present numerical method, in which the nonlinear structural model of the panel, the first-order piston aerodynamics model of the supersonic flow and the nonlinear sound wave model of the cavity are coupled in a monolithic manner. It is found that cavity acoustic resonance can appear in the case a vibration mode of the panel coalescing with an acoustic mode of the cavity. Several new physical features of nonlinear acoustic resonance have been discovered, such as the presence of shock wave with high pressure gradients travelling along the resonant cavity in axial direction and the presence of higher-order harmonic wave components, which emphasize a nonlinear acoustic wave model of the cavity must be used to fully characterize these phenomena. In addition, the nonlinearity of the standing wave is quantitatively related to the acoustic modes by means of a proper orthogonal decomposition analysis.

Steering non-Hermitian skin states by engineering interface in 1D nonreciprocal acoustic crystal

Topological insulators, which possess robust topologically protected properties for manipulating the wave propagation against the disorder and defects, have grown into a large research field in photonic and phononic crystals. However, the conventional topological band theory is used to describe a closed photonic/phononic crystal that is assumed to be Hermitian system. In fact, practical physical systems often couple with outside environment, and induce non-Hermitian Hamiltonian with complex eigenvalues. Recently, many novel topological properties have been induced by the interacting between non-Hermitian and topological phases, a prominent example is non-Hermitian skin effect that all eigenstates are localized to the boundary in open system, which different from the conventional topological edge states. The unique physical phenomenon has stimulated various applications, such as wave funneling, enhanced sensing, and topological lasing. In this work, we describe the non-Hermitian skin effect using winding numbers. The sign of the winding number determines the rotation direction of the loops in the complex frequency plane, which the sign can be controlled by the nonreciprocal coupling direction. In this context, we designed different topological skin interface between different domains with opposite winding numbers to manipulate the energy focusing to middle or two-end of non-Hermitian 1D acoustic cavity chain. In experiment, we used an electroacoustic coupling method, employing a unidirectional coupler composed of microphones, speakers, phase shifters, and amplifiers, to introduce positive and negative non-reciprocal couplings between the two acoustic cavities and studied the characteristics of these non-reciprocal couplings. Then, the non-reciprocal coupling cavities were extended into a chain structure, and the magnitude and sign of the non-reciprocal couplings were flexibly controlled using phase shifters and amplifiers. Through this method, we successfully constructed interfaces between different winding numbers, achieving a one-dimensional non-Hermitian skin effect at various interfaces. The experimental results indicate that the sound can be focused at middle interface or two-end interfaces for different nonreciprocal coupling distributions, and the skin interface can also be switched from middle to two-end by exchanging the nonreciprocal coupling direction of the domains. Our research results offer greater flexibility in the design of acoustic devices and may provide a new platform for exploring advanced topological acoustic systems for controlling sound propagation.

Temporal Quasi-Phase Matching Assists Robust Acoustic Adiabatic Passage

Recent work demonstrated stimulated Raman adiabatic passage-type transfer of energy along 3 acoustic cavities. After brief comments on the stimulated Raman adiabatic passage method, remarks on the scientific and technological relevance of this work are presented, followed by noting other recent important applications of the process.

Tunable underwater sound absorption characteristics of 0-3 piezoelectric anechoic coating.

Piezoelectric composite materials (PCMs) with shunt damping circuits are used widely in hydroacoustics because of the flexible adjustability of their parameters. PCMs offer good underwater sound absorption, but shortcomings remain, such as poor low-frequency sound absorption, narrow bandwidth, and a single dissipation mechanism. In this paper, the tunable underwater sound absorption of a 0-3 PCM combined with a cavity structure and shunt circuit (PCMC) is studied systematically. First, the equivalent material parameters of 0-3 PCM are derived based on the Yamada model, and then a theoretical electroacoustic model is established for solving the absorption coefficient and is mutually verified with the numerical simulation method. On this basis, the tunable absorption characteristics of the structure are analyzed. The results show that coupling the energy dissipation mechanism of 0-3 PCM with the acoustic mechanism of the cavity structure not only achieves strong absorption at lower frequencies but also enriches the absorption mode in the mid-high frequencies by connecting the shunt circuits. Moreover, the influence of piezoelectric control variables and acoustic cavity morphology characteristics on structural sound absorption performance is further explored. Finally, the acoustic performance of PCMC is improved further via shape optimization and parameter optimization.

Fractional disclination charge as a probe in acoustical topological crystalline insulators

The body–boundary correspondence refers to the relationship between the body and boundary states of topological insulators (TIs). In TIs, the presence of boundary states is connected to the bulk topological properties of the material. The topology can be identified by studying the energy of the topological modes within the bulk bandgap. However, not all topological materials exhibit boundary states within the insulating energy gap. In many cases, the presence of boundary states can be hidden or masked by the bulk energy bands, making it difficult to measure TIs. Recent experiments have shown that defects, which are commonly found in crystalline materials, can be used as probes to explore higher-order topologies that have been recently realized on various platforms. These defects can generate fractional charges and stable bound states in the dispersion region, allowing us to observe the clear body–disclination correspondence. We have performed simulations using a coupled acoustic cavity system with C3 and C5 symmetries to investigate the body–disclination correspondence in topological crystal insulators (TCIs) in the field of acoustics. Simulation and theoretical results have demonstrated that defects such as disclinations can be used to probe higher-order topologies that were previously unobservable in three-dimensional structures. This approach allows us to detect fractional mode charges and stable bound states, which are crucial for understanding the topological nature of TCIs. Our work demonstrates the potential of using disclination defects to study the intricate relationship between the body and boundary states in topological materials, particularly in the context of acoustics.

Vibroacoustics of a membrane-finite cavity resonator: Traditional and alternative approaches for analysis

This paper investigates a vibroacoustic model consisting of a flexible rectangular membrane backed by an acoustic air cavity of large lateral extent. A traditional methodology (termed Approach I) for analyzing the interaction between the acoustic airfield in the cavity and the flexible membrane is initially revisited and employed. In this approach, the transversal deformation of the mid-membrane is represented as an infinite series of eigenfunctions (normal modes) that satisfy the clamped boundary conditions for the in-vacuo membrane, regardless of the presence of the cavity. However, numerical challenges and limitations are encountered in obtaining direct insights into system characteristics, as this method heavily relies on matrix inversions and computing the roots of determinants. These operations can be computationally expensive and prone to inaccuracies and numerical instabilities, particularly when dealing with high-dimensional, non-sparse (dense) and nearly singular matrices. To overcome these limitations, an alternative methodology (termed Approach II) is proposed, which enables a precise analysis of the acoustically forced membrane and provides explicit expressions for the steady-state response, mode shapes, governed by a single transcendental characteristic equation for determining the vibroacoustic natural frequencies. Through a comparative analysis, we demonstrate the effectiveness and reliability of the proposed approach, showcasing its potential advantages over the traditional method in addressing numerical challenges. The influence of cavity depth on the vibroacoustic natural frequencies is examined across various levels of membrane stiffness, including low, intermediate, and high values. The analysis reveals the presence of both softening and hardening effects with respect to the in-vacuo case, suggesting that the air pressure plays a dual role in the system, i.e., influencing both the overall stiffness and inertia. The vibroacoustic membrane mode shapes exhibit significant deviations for soft and intermediate-stiff membranes but resemble in-vacuo mode shapes for stiff membranes, with the resemblance dependent on the selected cavity depth. Additionally, two qualitatively distinct mode families for the acoustic pressure, namely, propagating, and localized modes, are identified. The propagating modes are spatially extended and are characterized by the deformation of the volume of the medium, rendering them volume modes. In contrast, the localized modes are distinguished by localized vibrations occurring in the near field close the membrane surface, without significant energy transport or sound wave propagation in the cavity; as a result, they can be regarded as surface modes. The proposed methodology reveals features common to more complex vibroacoustic systems and offers a comprehensive and efficient approach for predictively designing the dynamics of such systems.