Acoustic Cavity Research Articles

Highly Sensitive Capacitive MEMS for Photoacoustic Gas Trace Detection.

An enhanced MEMS capacitive sensor is developed for photoacoustic gas detection. This work attempts to address the lack of the literature regarding integrated and compact silicon-based photoacoustic gas sensors. The proposed mechanical resonator combines the advantages of silicon technology used in MEMS microphones and the high-quality factor, characteristic of quartz tuning fork (QTF). The suggested design focuses on a functional partitioning of the structure to simultaneously enhance the collection of the photoacoustic energy, overcome viscous damping, and provide high nominal capacitance. The sensor is modeled and fabricated using silicon-on-insulator (SOI) wafers. First, an electrical characterization is performed to evaluate the resonator frequency response and nominal capacitance. Then, under photoacoustic excitation and without using an acoustic cavity, the viability and the linearity of the sensor are demonstrated by performing measurements on calibrated concentrations of methane in dry nitrogen. In the first harmonic detection, the limit of detection (LOD) is 104 ppmv (for 1 s integration time), leading to a normalized noise equivalent absorption coefficient (NNEA) of 8.6 ⋅ 10-8 Wcm-1 Hz-1/2, which is better than that of bare Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS), a state-of-the-art reference to compact and selective gas sensors.

Acoustic Radiation From Stiffened Double Concentric Large Cylindrical Shells: Part I Circumferential Harmonic Waves

Abstract Acoustic radiation from stiffened double concentric large cylindrical shells with periodic cavities is analytically investigated via circumferential harmonic waves driven by a point force. The vibration of double isotropic circular cylindrical shells is described by the first-order shear deformation shell theory. One set of uniformly spaced annular bulkheads connects the inner and outer cylindrical shells. In-plane motion equations of the annular bulkheads are expressed by two displacement potential functions. Sound pressure loadings of periodic cavities exerting on the inner and outer cylindrical shells are derived according to the Fourier transform and Poisson summation formula. Far-field sound pressure of the stiffened double cylindrical shells is obtained using the stationary phase method and acoustic radiation features of stiffened double concentric large cylindrical shells with periodic cavities are analyzed in terms of sound pressure power spectra and sound pressure level. Acoustic propagation features of stiffened double cylindrical shells with or without acoustic cavities are shown.

Dual-frequency anti-nonlinear sound-absorbing metasurface via multilayer nested microslit resonators

We propose a dual-frequency anti-nonlinear sound-absorbing metasurface (DASM) based on multilayer nested microslit resonators. Under the assumption of a linear system, the theoretical acoustic impedance of the DASM is derived by the transfer matrix method. Furthermore, the influence of structural parameters on sound absorption is also explored. The numerical and experimental results show that the proposed DASM can achieve quasi-perfect sound absorption at two low frequencies corresponding to the first two orders of the acoustic cavity mode frequencies of the structural unit, and enjoys strong anti-nonlinear performance and robustness to incident angles.

Dissipation-induced acoustic nonreciprocity

Linear acoustic transmission through a stationary elastic medium possesses Rayleigh reciprocal symmetry with respect to pressure produced by a source at point A(B) and measured at point B(A), pA(rB) = pB(rA). In ideal (inviscid) fluids, pressure plays the role of the scalar potential for velocity, v∼∇p. The Rayleigh reciprocity theorem is formulated for velocity potentials but not for their gradients. Any function of the absolute value of velocity, v(r), lacks reciprocal symmetry. In particular, acoustic intencity I = pv is not symmetric, IA(rB) ≠ IB(rA). Dynamics of ideal fluid is time-reversible, and lack of reciprocal symmetry is attributed to asymmetry in scattering. However, in a viscous environment dissipation breaks T symmetry making fluid dynamics irreversible. We report that acoustic transmission is not only irreversible but also becomes nonreciprocal due to different amount of dissipated energy for forward and backward propagation, provided that mirror symmetry (P symmetry) is broken. Since dissipation occurs within a narrow viscous layer at solid–fluid interface, the amount of nonreciprocity in transmission strongly depends on the quality of the surface of scatterers. Experiments performed with scatterers of different surface quality show how surface roughness affects the level of nonreciprocity. In a series of experiments with asymmetric phononic crystal, Tesla valve, and acoustic cavity, we demonstrate dissipation-induced nonreciprocity in transmission. [This work is supported by the NSF under EFRI Grant No. 1741677.]

On optimum speaker placement with a model-based approach for indoor local active noise control applications

In this study, a control system actively canceling the noise will be developed through a model-based algorithm to reduce the noise generated in the room on individuals in an environment as much as possible. The model-based design approach is preferred because it is convenient for optimization and can be applied much more effortlessly than real experiments; it is applied using the finite difference method. The model developed within this scope has been validated by comparing it with the acoustic test data performed in an empty room. The positioning of loudspeakers was accomplished through a heuristic search algorithm to obtain the highest local cancellation of noise originating in the acoustic cavity from any position(s) in the targeted area. The feedforward adaptive control system chosen to drive the control loudspeakers is implemented using the least mean squares algorithm. The efficiency of the designed system under different noise conditions was examined, and two of them were included in the study.

Two Dimensional Heterostructures for Optoelectronics: Current Status and Future Perspective.

Researchers have found various families of two-dimensional (2D) materials and associated heterostructures through detailed theoretical work and experimental efforts. Such primitive studies provide a framework to investigate novel physical/chemical characteristics and technological aspects from micro to nano and pico scale. Two-dimensional van der Waals (vdW) materials and their heterostructures can be obtained to enable high-frequency broadband through a sophisticated combination of stacking order, orientation, and interlayer interactions. These heterostructures have been the focus of much recent research due to their potential applications in optoelectronics. Growing the layers of one kind of 2D material over the other, controlling absorption spectra via external bias, and external doping proposes an additional degree of freedom to modulate the properties of such materials. This mini review focuses on current state-of-the-art material design, manufacturing techniques, and strategies to design novel heterostructures. In addition to a discussion of fabrication techniques, it includes a comprehensive analysis of the electrical and optical properties of vdW heterostructures (vdWHs), particularly emphasizing the energy-band alignment. In the following sections, we discuss specific optoelectronic devices, such as light-emitting diodes (LEDs), photovoltaics, acoustic cavities, and biomedical photodetectors. Furthermore, this also includes a discussion of four different 2D-based photodetector configurations according to their stacking order. Moreover, we discuss the challenges that remain to be addressed in order to realize the full potential of these materials for optoelectronics applications. Finally, as future perspectives, we present some key directions and express our subjective assessment of upcoming trends in the field.

임의 형상 음향 공동의 전 주파수 대역 고유치 추출을 위한 개선된 NDIF법: 제2부(예제 연구 및 고찰)

The eigenvalues of acoustic cavities in the low-frequency range are not extracted as the number of nodes increases in the original NDIF method. The study demonstrates, using example studies for two types of arbitrarily shaped acoustic cavities that a modified NDIF method successfully improves the problem of the original NDIF method. The modified NDIF method for arbitrarily shaped acoustic cavities also provides accurate and valid results not only for eigenvalues but also for mode shapes, as demonstrated in the example studies. Meanwhile, the accuracy of the eigenvalues decreases slightly as the number of nodes increases in the case of the quadrilateral acoustic cavity considered in the example studies. The causes of the decrease in accuracy will be thoroughly investigated in future studies, and the research results to prevent it will be presented.

임의 형상 음향 공동의 전 주파수 대역 고유치 추출을 위한 개선된 NDIF법 개발: 제1부(이론 정립)

A modified NDIF method for highly accurate eigenvalue analysis of arbitrarily shaped two-dimensional acoustic cavities is proposed in the paper. The original NDIF method has the weak point of not extracting lower-order eigenvalues when the number of nodes increases to obtain more accurate eigenvalues. It turns out in the study that this weak point is because the system matrix of the acoustic cavity of interest becomes ill-conditioned and doesn’t have full rank. The paper proposes a practical way to extract eigenvalues and mode shapes of acoustic cavities in the entire frequency range by means of calculating accurately the determinant of the system matrix ill-conditioned in the low frequency range. It is confirmed through the example study for the circular acoustic cavity having an exact solution that eigenvalues and mode shapes obtained by the proposed method using only 32 nodes agree exactly with the exact solution although eigenvalues obtained by ANSYS using 2840 nodes have some errors with respect to the exact eigenvalues.

Effect of the electric field on the sound transmission loss of double-walled electro-rheological fluid sandwich plates with functionally graded carbon nanotube reinforced composite facesheets

Numerous studies have been conducted to examine the vibroacoustic characteristics of lightweight double-walled structures due to the anticipated applications of these structures in noise reduction engineering. In this study, third-order shear deformation theory (TSDT) is used to develop a theoretical model that predicts sound transmission loss (STL) across double-walled electro-rheological fluid (ERF) sandwich plates with functionally graded carbon nanotube reinforced composite (FG-CNTRC) facesheets. The extended rule of mixture is utilized to evaluate the properties of the FG-CNTRC material in the thickness. Depending on the four FG models, the CNT volume fraction varies. A sufficient displacement continuity condition is taken into account between layers. Furthermore, it should be noted that changing the electric field affects the pre-yield zone’s ERF features. The vibroacoustic equations are derived using Hamilton’s principle and solved utilizing weighted residual (Galerkin) technique considering simply supported and clamped boundary conditions. Several studies are done to compare the results of the suggested model with other results found in the literature. An extensive numerical study is conducted to examine the dependence of STL on several parameters, including electric field strength, volume percentage of the CNTs, CNTs distribution, depth of acoustic cavity.

Analysis and Control of Acoustic Modes in Cylindrical Cavities with application to Direct Field Acoustic Noise (DFAN) Testing.

It is well known that acoustic cavities have frequencies at which certain free-response 'modes' of propagation respond especially strongly. In the absence of significant damping, these cause peaks of high SPL in the frequency response as well as spatial non-uniformity and temporal ringing. The spatial non-uniformity is especially problematic since it means the room cannot be 'EQ'd' to compensate, since the SPL is different in different positions. This phenomenon has been studied extensively in the room acoustics literature and various strategies for mitigation proposed. Many of these make use of the theoretical mode shapes for a cuboid with a rigid boundary condition, since this is a common shape of room and a reasonable approximation for a solidly constructed wall. But modes exist for other shape spaces too. Of particular interest is the cylindrical cavity that is formed when large enclosing arrays of loudspeakers are used to perform high-intensity acoustic tests on space hardware. These possess problematic modes that can cause over-testing in some positions and under-testing in others. In this work, it is investigated how a simple FEM simulation can compute Q-factors for these modes and identify which will be problematic. How this might inform control system design is discussed.

Topology optimization of single and double panels for improved sound insulation in specific frequency bands

Single and double panels are commonly employed in noise control, e.g., as partitioning elements between rooms and to enclose noisy machines. In presence of narrowband disturbances, related for example to rotating machines, further improvements in sound insulation can be obtained by properly distributing the material within the area of the panels. This allows maximizing the sound Transmission Loss (TL) in the frequency band of interest by controlling structural resonances and antiresonances. In order to achieve this goal, in this work, we apply numerical topology optimization to find the optimal material thickness distribution for single and double panels. In the iterative design process, single panels are schematized through a simple mechanical Finite Element (FE) model, while double panels are modelled considering the vibroacoustic coupling between the two mechanical plates and the internal acoustic air cavity. The sound insulation properties of the designed solution are evaluated by TL computations through hybrid Finite Element-Statistical Energy Analysis (FE-SEA) simulations. The method is applied targeting different frequency bands in the audible range and focusing on practically relevant design cases, such as single and double PMMA and glazing panels.

Effect of uniform and nonuniform temperature distributions on sound transmission loss of double-walled porous functionally graded magneto-electro-elastic sandwich plates with subsonic external flow

Using the third-order shear deformation theory (TSDT), this research investigates the loss in sound transmission through air-filled rectangular double-walled sandwich smart magneto-electro-elastic (MEE) plates with a porous functionally graded material (PFGM) core layer, in the presence of external mean airflow and subjected to uniform and non-uniform temperature distributions. Multiple temperature profiles are evaluated in order to correctly capture the impact of the temperature rises over the thickness. Based on the power-law model, three different types of uneven porosity distributions are considered for the PFGM core layer. These distributions should change along the in-plane and thickness directions. Hamilton's concept is used to achieve the derivation of vibroacoustic equations as coupled relations. The sound transmission loss (STL) equation is obtained by using a double Fourier series in combination with an analytical method, i.e., the second velocity potential. The produced solution is evaluated in terms of accuracy and precision by comparing it to other accessible data from a previous study. The effects of the initial electric and magnetic potentials, porosity distributions, incidence angles, acoustic cavity depth, and changes in temperature profile on STL are shown by parameter investigations.

A piezoelectric-nonreciprocal metamaterial with shaped eigenvectors using shunted piezo-networks

This paper presents a class of passive nonreciprocal metamaterials (PNMM) which are designed to control the flow of acoustic waves along a one-dimensional periodic acoustic duct. The proposed PNMM consists of a multi-cell array of acoustic cavities which are provided with piezoelectric boundaries. These boundaries are connected to an optimally designed array of shunted inductive networks in order to spatially shape the eigenvectors of the array in such a manner that breaks the reciprocity of the acoustic duct. This approach distinguishes itself from other approaches where non-reciprocities are controlled either actively or passively . A finite element model (FEM) is developed to analyze and predict the dynamic characteristics and behavior of the proposed PNMM for various shunting strategies and distributions of the networks. The predictions of the FEM are validated experimentally using a five-cell array that is tested using the Transmission Loss and Impedance tube of ACUPRO (Sage Technologies). In the experimental model, the inductances are synthesized electronically to enable significant tailoring of the eigenvectors of the PNMM. The obtained results indicate significant breaking of the non-reciprocity when the characteristics of the PNMM are determined during forward and backward wave propagations.

Phonon Blockade in Parametrically Pumped Acoustic Cavity at Finite Temperature

In this study, we investigated the phonon blockade effect in a parametrically driven and dissipative acoustic cavity at finite temperature. With the approximated analytical results based on the steady-state density-matrix master equation, we found that a quantum-interference-induced phonon blockade exists at finite temperature. We found a crossover between the quantum and thermal regimes on the curve of the second-order correlation function of the acoustic mode as the temperature increases. This phenomenon implies an asymmetry about the quantum and classic regimes. We also numerically simulated the single-phonon emission using the Monte Carlo wave function method. The results showed that a wide and deep dip around the zero time delay exists on the curve of the time-delayed second-order correlation function, which implies the possibility of observing a strong phonon blockade with pulse driving. Our study outlines a potential candidate for a efficient single-phonon source and applications in quantum information and phononic quantum networks.

Electro-mechanical tuning of high-Q bulk acoustic phonon modes at cryogenic temperatures

We investigate the electromechanical properties of quartz bulk acoustic wave resonators at extreme cryogenic temperatures. By applying a DC bias voltage, we demonstrate broad frequency tuning of high-Q phonon modes in a quartz bulk acoustic wave cavity at cryogenic temperatures of 4 K and 20 mK. More than 100 line-widths of tuning of the resonance peak without any degradation in loaded quality factor, which are as high as 1.73×109, is seen for high order overtone modes. For all modes and temperatures, the observed coefficient of frequency tuning is ≈ 3.5 mHz/V per overtone number n corresponding to a maximum of 255.5 mHz/V for the n = 73 overtone mode. No degradation in the quality factor is observed for any value of an applied biasing field.

Elastic bound states in the continuum by acoustoelastic interaction

One of the most widely-held beliefs was that no such thing as a bound state existed in a continuum. Notably, it only lately emerged to disclose such a state in several domains of wave physics. Here we report the presence of elastic quasi-bound states in the continuum (QBICs) by balancing local Fano and Fabry–Pérot resonant states, with vanishing linewidths nearby which indicate BICs. The rational design is made by directly integrating an acoustic cavity into an elastic bar, which enables the two to interact. The proposed continuum elastic bar is in analogy to the Fano–Anderson discrete model, which further satisfies a criteria for both Fano and Fabry–Pérot resonances to obtain optimal QBIC modes. Experiments are also carried out for proof-of-concept purposes to uncover these states with a good agreement. This platform would be versatile in illustrating generic Fano lineshapes and high Q-factors, bringing up a new avenue for using the acoustoelastic nature. We hope that our findings would also contribute to the understanding of quantum-driven phenomena in classical contexts with sharing the comparable underlying wave physics.

An efficient method for 3D Helmholtz equation with complex solution

<abstract><p>The Helmholtz equation as an elliptic partial differential equation possesses many applications in the time-harmonic wave propagation phenomena, such as the acoustic cavity and radiation wave. In this paper, we establish a numerical method based on the orthonormal shifted discrete Chebyshev polynomials for finding complex solution of this equation. The presented method transforms the Helmholtz equation into an algebraic system of equations that can be easily solved. Four practical examples are examined to show the accuracy of the proposed technique.</p></abstract>

Comparison Between Bézier Extraction and Associated Bézier Elements in Eigenvalue Problems

This paper shows that the control points which are implicitly encountered in the Bézier extraction during isogeometric analysis can be explicitly used to form Bézier elements of C^0-continuity in several ways, thus eventually leading to a superior accuracy and performance than the C^p-continuity. The study is reduced to the eigenvalue extraction in problems governed by the Helmholtz equation. Analysis is performed in conjunction with piecewise cubic interpolation for three benchmark tests in one and two dimensions. In the latter case a rectangular and a circular acoustical cavity under Neumann boundary conditions are analyzed. Several computational details are also discussed.

Design of Helmholtz resonator group in a lightweight aluminum alloy wheel for reducing tire acoustic cavity resonance noise

Tire acoustic cavity resonance (TACR) noise is one of the significant sources causing vehicle interior noise at low-frequency band. Since the rotating and loading conditions can split TACR frequencies, TACR noise exhibits a relatively narrow frequency band, which becomes a challenge to attenuate this type of noise. To deal with this problem, the reduction method of the Helmholtz resonator (HR) group installed inside a lightweight aluminum alloy wheel is adopted in this paper. By the combination welding of spoke and rim in aluminum alloy wheel of a passenger vehicle, the internal annular hollow area is generated as the installation space for this HR group. Great advantages of this manufacturing process are the lightweight and easy installation performances for the wheel. According to the theoretical analyses based on the superposition of traveling waves and its experimental validations, the frequency bands of TACR noise for a rotating tire are determined. To reduce the noise, HR group consisting of 5 different sizes is designed by the Finite Element Method (FEM). Meanwhile, the sound-reducing tire-wheel assembly incorporated with the designed HR group is manufactured and tested by the bench and vehicle experiments. A remarkable reduction can be observed at the peak and specified frequency range of TACR noise. Moreover, the performance also proves to be stable and robust under various road and speed conditions. This paper provides a comprehensive and feasible process strategy for the development of noise-reducing wheel.

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems