High Acoustic Transmission Research Articles

A multi-objective optimization design method for underwater composite sandwich structures with high acoustic transmission and low vibration performance

ABSTRACT To address the issue of reduced structural integrity and optimality resulting from the conventional serial design of sonar dome structures, this paper establishes a multi-objective optimal design model for composite sandwich structures, utilising the Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The model's stability and reliability are subsequently validated. Upon this model, a structural optimization design technique is postulated for composite sandwich structures within the realm of Fluid-Structure Interaction (FSI) multi-physics coupling. This approach aims to optimize the lightweight, high-rigidity composite sandwich structure, enhancing its acoustic transmission and minimizing vibration performance under turbulent pressure pulsations. The suggested method notably enhances the efficiency of structural design while ensuring precision. The proposed method effectively addresses the deficiency of serially designed sonar domes by neglecting the synergistic effects among multiple disciplines. In summary, this approach offers technical support and new research perspectives for the design of sonar domes under the coupling of multiple physical fields.

Moiré Pattern Controlled Phonon Polarizer Based on Twisted Graphene.

Twisted van der Waals materials featuring Moiré patterns present new design possibilities and demonstrate unconventional behaviors in electrical, optical, spintronic, and superconducting properties. However, experimental exploration of thermal transport across Moiré patterns has not been as extensive, despite its critical role in nanoelectronics, thermal management, and energy technologies. Here, thefirst experimental study is conducted on thermal transport across twisted graphene, demonstrating a phonon polarizer concept from the rotational misalignment between stacked layers. The direct thermal and acoustic measurements,structural characterizations, and atomistic modeling, reveal a modulation up to 631% in thermal conductance with various Moiré angles, while maintaining a high acoustic transmission. By comparing experiments with density functional theory and molecular dynamics simulations, mode-dependent phonon transmissions are quantified based on the angle alignment of graphene band structures and attributed to the coupling among flexural phonon modes. The agreement confirms the dominant tuning mechanisms in adjusting phonon transmission from high-frequency thermal modes while having negligible effects on low-frequency acoustic modes near Brillouin zone center. This study offers crucial insights into the fundamental thermal transport in Moiré structures, opening avenues for the invention of quantum thermal devices and new design methodologies based on manipulations of vibrational band structures and phonon spectra.

Study on sound insulation performance of sonic black hole with micro-perforated plates

According to the traditional law of mass, the insulation of low-frequency sound usually requires thick, high-density materials. However, lightweight metamaterials containing acoustic structures can also achieve high acoustic transmission losses. In this study, we present a sonic black hole (SBH) device coupled with micro-perforated plates (MPPs) and intraluminal column structure to achieve high sound insulation performance with light weight. The finite element model (FEM) is developed to analyze the acoustic energy distribution and dissipation inside the SBH device to evaluate its sound transmission loss (STL), and the accuracy of the analytical model is verified by impedance tube testing. The analysis results show that the SBH device has excellent sound insulation performance in the broadband and low frequency mainly due to the energy dissipation caused by the MPPs and column structure, and wavelength compression, energy focusing caused by the SBH effect. Finally, the sound insulation capacity of SBH can be further improved by improving the structure, such as increasing the complexity of acoustic medium flow and adding the number of layers of MPPs. The numerical model and the calculation results of this paper provide a new way of thinking for the design and optimization of SBH sound insulation structures.

Using sonic crystals to separate the acoustic from the flow field of a fluidic transducer

Ultrasonic testing is a widely applied measurement method in materials research and medicine. Commonly, a transducer is coupled to the specimen directly or via a liquid coupling agent. While reducing acoustic transmission losses significantly, this procedure is time-consuming and cannot be used for sensitive specimens. Air-coupled ultrasound is a viable alternative in such cases, although suffering from very high acoustic transmission losses between transducer, air and specimen.The recently introduced fluidic transducer (FT) generates ultrasound by utilizing the instability of a supersonic air jet switched inside a fluidic amplifier. Since only air is used as the working medium and no vibrating surfaces are used for ultrasound generation, the transducer is able to efficiently generate large acoustic pressure amplitudes. The resulting acoustic field shares its directivity with the ejected high-velocity air jet. Thus, the acoustic energy needs to be redirected from the jet axis in order to make the fluidic transducer applicable to sensitive specimens.In this study, the effectivity of using sonic crystals (SCs) for this redirection is investigated using acoustic and flow measurements. SCs are air-permeable while being reflective to large acoustic frequency bands. It was shown that both a defect waveguide and a mirroring strategy successfully redirected the acoustic field from the air jet. Furthermore, the interaction of flow and SC showed strong acoustic quenching if the SC was placed too close to the FT outlet. Blockage of the jet entrainment due to the SC may result in slightly higher off-axis flow velocities locally, which should be considered in sensitive applications.

Analysis of Sound Absorption Characteristics of Acoustic Ducts with Periodic Additional Multi-Local Resonant Cavities

With the aim of applying various Helmholtz resonant cavities to achieve low-frequency sound absorption structures, a pipe structure with periodic, additional, symmetrical, multi-local resonant cavities is proposed. A thin plate with additional mass is placed in the cylindrical Helmholtz resonant cavity structure to form a symmetric resonant cavity structure and achieve multi-local resonance. The simulation results show that the periodic structure proposed in this paper can produce multiple, high acoustic transmission loss peaks and multiple lower broadband sound absorption frequency bands in the low-frequency range. In this paper, this idea is also extended to the Helmholtz resonant cavity embedded with multiple additional mass plates. The results show that the periodic arrangement of the multi-local resonant symmetric cavity inserted into multiple plates with mass can significantly increase its transmission loss and show a better performance on low-frequency sound absorption characteristics.

Switchable asymmetric acoustic transmission based on topological insulator and metasurfaces

Dynamically switching the symmetric and asymmetric acoustic transmission (AAT) is significant in sound manipulation. In this paper, we present the design of switchable AAT in a certain frequency band, which is composed of an acoustic valley hall (AVH) topological insulator and acoustic metasurface (AMS). The underlying mechanism of AAT is attributed to the valley-selective excitation of AVH edge modes and the arbitrary refraction angle controls of the AMS. The acoustic transmission can only occur when the AVH edge modes are excited by controlling the direction of the incident sound waves with the help of AMS. By moving the AMS, the device can shift from symmetric transmission to asymmetric transmission within the designed frequency band. Importantly, the acoustic transmission through the device is topologically protected, which is robust to bends and defects. The AMS based on the spiral-coiling structure is chosen to reach a high acoustic transmission. The performance of switchable AAT is validated with full-wave simulations. Our work may open a new method for introducing the advantages of topological insulators to AAT.

Non-Hermitian complimentary acoustic metamaterials for imaging through skull

Complimentary metamaterials are designed to facilitate full acoustic transmission through highly mismatched impedance barriers. Applied to biomedical acoustics, complimentary metamaterials theoretically enable unidirectional acoustic transmission through the skull to realize noninvasive brain imaging and facilitate neural ultrasound therapies. Previously designed complimentary acoustic metamaterials relied on the realization of negative material parameters opposite to that of the skull to cancel the impedance mismatch effect. However, much of the incident acoustic energy is dissipated due to the skull’s internal porosity, preventing full energy transmission. To resolve this issue, we propose to counteract the skull’s acoustic attenuating effects with a non-Hermitian complimentary metamaterial (NHCMM) having an active gain circuit to achieve high acoustic transmission at high frequencies. In addition to the full wave simulations showing near perfect transmission from either side of the skull, the NHCMM preserves imaging information for objects inside the skull, and enhances the focused acoustic energy used for focused ultrasound therapies. By facilitating two-way acoustic transmission through the skull with NHCMMs, we lay the foundation for noninvasive brain imaging and treatment for neural disorders.

Non-Hermitian complementary acoustic metamaterials for lossy barriers

Complementary materials are designed for the suppression of strongly mismatched potential barriers to enhance wave transmission and reduce wavefront distortion through the barriers. In acoustics, complementary materials enable noninvasive brain imaging and the treatment of neural disorders by overcoming the high impedance mismatch layer that prevents ultrasound transmission. However, the porous skull layer possesses intrinsic loss that prohibits the effective use of complementary metamaterials alone. Here, we propose to apply a non-Hermitian complementary metamaterial (NHCMM) to counteract the impedance mismatch and energy attenuation effect of the skull to achieve high acoustic transmission at high frequencies. Our numerical study shows a near perfect, unidirectional transmission through the skull when the NHCMM is applied while preserving the imaging information and enhancing the acoustic energy at the focal point needed for focused ultrasound used for noninvasive therapies. The proposed acoustic NHCMM lays the foundation for noninvasive ultrasonic brain imaging through an intact skull by stimulating in-vivo deep brain circuitry research and treatments for neural disorders such as brain tumors and strokes.

A three-dimensional underwater sound propagation model for offshore wind farm noise prediction.

A three-dimensional underwater sound propagation model with realistic ocean environmental conditions has been created for assessing the impacts of noise from offshore wind farm construction and operation. This model utilizes an existing accurate numerical solution scheme to solve the three-dimensional Helmholtz wave equation, and it is compared and validated with acoustic transmission data between 750 and 1250 Hz collected during the development of the Block Island Wind Farm (BIWF), Rhode Island. The variability of underwater sound propagation conditions has been investigated in the BIWF area on a temporal scale of months and a spatial scale of kilometers. This study suggests that future offshore wind farm developments can exploit the seasonal variability of underwater sound propagation for mitigating noise impact by scheduling wind farm construction during periods of high acoustic transmission loss. Discussions on other applications of soundscape prediction, planning, and management are provided.

Broadband low-frequency sound isolation by lightweight adaptive metamaterials

Blocking broadband low-frequency airborne noises is highly desirable in lots of engineering applications, while it is extremely difficult to be realized with lightweight materials and/or structures. Recently, a new class of lightweight adaptive metamaterials with hybrid shunting circuits has been proposed, demonstrating super broadband structure-borne bandgaps. In this study, we aim at examining their potentials in broadband sound isolation by establishing an analytical model that rigorously combines the piezoelectric dynamic couplings between adaptive metamaterials and acoustics. Sound transmission loss of the adaptive metamaterial is investigated with respect to both the frequency and angular spectrum to demonstrate their sound-insulation effects. We find that efficient sound isolation can indeed be pursued in the broadband bi-spectrum for not only the case of the small resonator's periodicity where only one mode relevant to the mass-spring resonance exists, but also for the large-periodicity scenario, so that the total weight can be even lighter, in which the multiple plate-resonator coupling modes appear. In the latter case, the negative spring stiffness provided by the piezoelectric stack has been utilized to suppress the resonance-induced high acoustic transmission. Such kinds of adaptive metamaterials could open a new approach for broadband noise isolation with extremely lightweight structures.

Impedance-matching acoustic bend composed of perforated plates and side pipes

In this article, we propose a design for an impedance-matching acoustic bend. The bending structure is composed of sub-wavelength unit cells containing perforated plates and side pipes that allow the mass density and the bulk modulus of each unit cell to be tuned simultaneously. The refractive index and the impedance of the acoustic bend can therefore be modulated simultaneously to guarantee both the bending effect and high acoustic transmission. The results of simulation of the sound pressure field distribution show that the bending effect of the proposed impedance-matching acoustic bend is very good. Transmission spectra are calculated for both the impedance-matching acoustic bend and an acoustic bend composed of the perforated plates alone for comparison. The results indicate that the impedance-matching acoustic bend successfully improves the impedance ratio while also obviously increasing the transmission.

Vibroacoustics behavior of self-similarly loaded sandwich structures

The reduction of structural vibrations and acoustic radiation is increasingly challenging due to lightweight material use driven by mass reduction, particularly in the aerospace industry. Trim panels are well-known materials with high acoustic transmission and radiation. This study combines semi-analytical modeling, numerical simulations and experiments on the vibroacoustic behavior of sandwich constructions locally overloaded by a pre-fractal mass distribution. The research originality lies in the overload distribution (a self-similar pattern inspired by the Cantor set) which is directly slotted within the honeycomb core, so that the structure load-bearing capability is not altered. As the mass effect spatially localizes the vibrations, the pre-fractal pattern focuses the effect of localization on some specific frequency band gaps, which reduces the total vibrational energy and thus the acoustic radiation. Before the extension to composite plates, simulations of a homogenized beam model have been computed to form a numerical modal database. Experiments have been conducted to compare and tune the mechanical model parameters. Satisfying agreement has been obtained between simulations and experiments. Finally, acoustic radiation simulations of self-similarly loaded structures have been conducted and radiation coefficients are expected to be weaker than for classical bending beams.

A collimated focused ultrasound beam of high acoustic transmission and minimum diffraction achieved by using a lens with subwavelength structures

An acoustic focusing lens incorporated with periodically aligned subwavelength grooves corrugated on its spherical surface has been developed. It is demonstrated theoretically and experimentally that acoustic focusing achieved by using the lens can suppress the relative side-lobe amplitudes, enhance the focal gain, and minimize the shifting of the focus. Use of the lens coupled with a planar ultrasound transducer can generate an ultrasound beam with enhanced acoustic transmission and collimation effect, which offers the capability of improving the safety, efficiency, and accuracy of targeted surgery implemented by high intensity focused ultrasound.

Analytical and experimental aeroacoustic studies of open-ended three-duct perforated elements used in mufflers

Perforated element mufflers have been known to have good acoustic performance, when used on automotive exhaust systems. In the last decade and a half, plug mufflers, concentric hole resonators, and three-duct closed-end perforated elements have been studied. The present investigation concerns open-ended, three-duct perforated elements, which are known to combine high acoustic transmission loss with low back pressures. The governing equations have been solved in the frequency domain, using the decoupling approach along with appropriate boundary conditions, to derive the transfer matrix and then to calculate noise reduction and transmission loss. The predicted noise reduction values have been shown to corroborate well with experimentally observed values. Finally, parametric studies have been done to draw design curves for such mufflers.