Underwater Sound Absorption Research Articles

Porous-Solid Metaconverters for Broadband Underwater Sound Absorption and Insulation

Existing solid composite structures composed of several viscoelastic materials and metals mainly exploit diverse resonances, damping, and scattering to realize underwater acoustic wave functionalities. However, low-frequency broadband underwater sound absorption and insulation are still hard to capture with an acoustic coating possessing subwavelength thickness and lightweight nature simultaneously. This paper reports the systematic simulated and experimental validations of a porous-solid underwater metaconverter, consisting of a rubber layer and a topology-optimized elastic metasurface to exhibit broadband functionalities of sound absorption and insulation caused by the strong reflective and transmitted longitudinal-to-transverse wave conversion, while sustaining broadband impedance matching. Various results confirm the predicted capabilities of underwater broadband high-efficiency sound absorption (>80%) or insulation (20 dB) within the range of 2–10 kHz for a large- and limited-size sample, providing an estimate of the energy-converting effect and phenomenon. The present study provides possibilities for elastic wave energy dissipation, harvesting, and underwater acoustic stealth via metasurfaces.4 MoreReceived 9 December 2022Revised 3 February 2023Accepted 28 February 2023DOI:https://doi.org/10.1103/PhysRevApplied.19.044074© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAcoustic metamaterialsAcoustic wave phenomenaArchitectural acousticsCloakingMechanical & acoustical propertiesUnderwater acousticsPhysical SystemsPorous mediaTechniquesSound wave techniquesCondensed Matter, Materials & Applied Physics

Multifunctional Integrated Underwater Sound Absorption Materials: A Review

Rapid improvements in underwater vehicle technology have led to a significant increase in the demand for underwater sound absorption materials. These materials, unlike their counterparts utilized in air, must have high hydrostatic pressure resistance, corrosion resistance, and other advantageous attributes. This necessitates the development of innovative, composite sound-absorbing materials with multifunctional properties, which presents substantial challenges for researchers. In this comprehensive review, we systematically analyze and categorize the mechanisms governing underwater sound absorption, hydrostatic pressure resistance, and corrosion prevention while considering related research advances. Furthermore, we provide an extensive overview of research advancements, existing challenges, and potential solutions pertaining to multifunctional and integrated underwater sound-absorbing materials. This review aims to serve as a valuable resource for future investigations into the development and optimization of multifunctional integrated underwater sound-absorbing materials, thereby contributing to the advancement of underwater vehicle technology.

Underwater sound absorption characteristic of the rubber core sandwich structure with funnel-shaped cavities reinforced by carbon fiber columns

This paper introduces a multi-functional rubber core sandwich structure with funnel-shaped cavities (RCSSFC) reinforced by carbon fiber columns (CFC), which has the potential to meet requirements of the pressure resistance and acoustic stealth for the underwater equipment in deep sea. A test sample of the RCSSFC with CFC is firstly manufactured and the acoustic propagation experiment is conducted by the pulse tube method to gain the sound absorption coefficient. Then the approximate theoretical model of the RCSSFC is built to predict the sound absorption performance via the layered gradient discretization of cavities, the equivalent theory of the cylindrical tube and the transfer matrix method. Both the obtained experimental and theoretical results are compared with the ones from finite element (FE) analyses conducted in the software COMSOL and the good agreements are achieved. Characteristic analyses are further done to investigate the effects of the diameter of CFC, the shape of cavities, the backing of the structure and the underwater pressure. The design of localized resonances is introduced to improve the low-frequency sound absorption performance. It is found that there are three sound absorption peaks (SAPs) on the curves at lower, middle and higher frequencies, which are respectively dominated by the longitudinal vibration of the structure, the resonances of cavities and the local vibration of the face sheet. Characteristic parameters mainly affect the sound absorption coefficients by changing the above three vibration behaviors. Besides, the CFC greatly improves the pressure resistance property, and the sound absorption performance of the RCSSFC with CFC is insensitive to the change of the pressure. Localized resonances show the excellent effect on increasing the low-frequency sound absorption of the RCSSFC with CFC.

Numerical design and optimization of metamaterials for underwater sound absorption at various hydrostatic pressures

Underwater sound absorption materials with a stable performance at various hydrostatic pressures are important for marine applications. However, most studies about underwater sound absorption materials only focused on the performance at atmospheric hydrostatic pressure, while ignoring the influence of various hydrostatic pressures. Aiming to improve the underwater sound absorption stability of a metamaterial at various hydrostatic pressures, different structures and a Nelder–Mead algorithm with an acoustic-structure fully coupled finite element method (FEM) model are developed to optimize the structure of the metamaterial at various hydrostatic pressures. In this numerical modeling, the metamaterial is a PDMS matrix embedded with periodic cylinders. Firstly, the effect of hydrostatic pressure on the metamaterial is evaluated in the frequency range [0, 8 kHz]. Secondly, different cases are designed to improve the underwater sound absorption stability at various hydrostatic pressures, including different cylinder radii, different distances between the air cylinder and the steel backing, and different void shapes. Then two layers of air and/or steel cylinders are introduced to further improve sound absorption performance under various hydrostatic pressures. The results indicate that PDMS with two layers of air cylinders have the optimal sound absorption stability performance under various hydrostatic pressures, which can be attributed to the top layer of air cylinders absorbing the main deformation. Lastly, the optimization algorithm significantly improves the sound absorption performance of the metamaterials at various hydrostatic pressures. This combination of an optimistic algorithm and FEM can guide the design of underwater sound absorption metamaterials at various hydrostatic pressures.

Multifunctional Underwater Adhesive Film Enabled by a Single-Component Poly(ionic liquid).

Tremendous efforts have been devoted to exploiting synthetic wet adhesives for real-life applications. However, developing low-cost, robust, and multifunctional wet adhesive materials remains a considerable challenge. Herein, a wet adhesive composed of a single-component poly(ionic liquid) (PIL) that enables fast and robust underwater adhesion is reported. The PIL adhesive film possesses excellent stretchability and flexibility, enabling its anchoring on target substrates regardless of deformation and water scouring. Surface force measurements show the PIL can achieve a maximum adhesion of 56.7 mN·m-1 on diverse substrates (both hydrophilic and hydrophobic substrates) in aqueous media, within ∼30 s after being applied. The adhesion mechanisms of the PIL were revealed via the force measurements, and its robust wet adhesive capacity was ascribed to the synergy of different non-covalent interactions, such as of hydrogen bonding, cation-π, electrostatic, and van der Waals interactions. Surprisingly, this PIL adhesive film exhibited impressive underwater sound absorption capacity. The absorption coefficient of a 0.7 mm-thick PIL film to 4-30 kHz sound waves could be as high as 0.80-0.92. This work reports a multifunctional PIL wet adhesive that has promising applications in many areas and provides deep insights into interfacial interaction mechanisms underlying the wet adhesion capability of PILs.

Study on the phase structure and sound absorption properties of Eucommia ulmoides gum composites

Eucommia ulmoides gum (EUG) can be used as an underwater sound-absorbing material, but the effect of the phase structure of its composites on the sound absorption performance has not been fully investigated. EUG was blended with chloroprene rubber (CR) and solution-polymerized styrene butadiene rubber (SSBR), and then epoxidized natural rubber (ENR) was added to the EUG/CR composites. The results showed that when CR was supplemented with 20% EUG, the composite showed the sea-island structure, EUG existed mainly in β-crystal form, and the average sound absorption coefficient of the composite was 0.4 at 0 MPa pressure, which was twice as high as that of pure CR. However, the sound absorption performance of the EUG/SSBR composite obtained by the same method of EUG/CR composites was reduced. In addition, the average sound absorption coefficient improved to 0.62 with the addition of ENR based on EUG/CR composites, and the compression resistance was greatly improved. The key factors for EUG to improve the underwater sound absorption performance of rubber materials lie in the generation of well-dispersed sea-island structures while retaining its own crystals. This work will provide some reference for the preparation of EUG composite sound-absorbing materials that are resistant to high water pressure.

Deep subwavelength hybrid metamaterial for low-frequency underwater sound absorption by quasi-Helmholtz resonance

We proposed an acoustic metamaterial with deep subwavelength thickness for low-frequency underwater sound absorption. The proposed hybrid metamaterial has a perforated facesheet, a fluid-filled square honeycomb core with inside rubber coating, and a fixed backsheet. A theoretical model is established to predict the sound absorption performance of this perforated honeycomb hybrid metamaterial based on the sound absorption theory of the micro-perforated panel and electro-acoustic analogy. The theoretical model agrees well with our finite element simulation. Results suggest that perfect sound absorption (99.9%) of the metamaterial occurs at 375 Hz, at which the thickness of the metamaterial is only 1/80 of the underwater sound wavelength. According to the simulation, most of the sound energy is consumed by the rubber coating. It can be analyzed that the rubber coating replaces the fluid in the square honeycomb resonant cavity improving the acoustic capacitance and acoustic resistance and triggering a quasi-Helmholtz resonance. This acoustic metamaterial also exhibits a broadband underwater sound absorption performance by parallel design with different perforations, which has a promising potential in engineering applications.

Recent study progress of underwater sound absorption coating

AbstractBased on the recent development of underwater sound absorption coatings, this paper analyzes the evolution of underwater sound absorption coatings from two aspects: traditional structures and metamaterials. The traditional structures are divided into three types: cavity structures, composite structures, and impedance‐matching structures. First, the development history of traditional structures, from cavities to hybrid structures, is presented, and the optimization and recent improvements in sound absorption fundamentals are explained. For different types of structures, the sound absorption effects of their respective structures are presented. At the same time, recent development progress of underwater coating metamaterials is summarized, and the sound absorption fundamentals and effects of local and nonlocal resonance types are compared. In addition, typical underwater sound absorption metamaterials are described in detail, and the application prospect of the acoustic bubble structure in practice is summarized. Moreover, this paper compares and discusses various structural types of underwater sound absorption coatings and points out the shortcomings of recent related research. Finally, it points out current open issues in the field and suggests future development directions of underwater sound absorption coatings, defining the possible development focus of underwater sound absorption coatings.

A new fabrication method of designed metamaterial based on a 3D-printed structure for underwater sound absorption applications

Effective sound absorption in a broad frequency range of thin-anechoic materials is a challenge that acoustic materials for underwater applications are still facing. This study proposes a thin-anechoic membrane for underwater applications with an innovative fabrication method for a designed metamaterial based on a 3D-printed structure with a cone-shaped cavities array. The structure is printed with thermoplastic polyurethane (TPU) and cast in a thermoset polyurethane (SPU). Three types of TPUs with different hardness were used to assess the contribution of the polymer properties to the sound absorption performance in the frequency range from 1.5 kHz to 7 kHz and hydrostatic pressure conditions from normal pressure to 1.5 MPa. The materials were characterised using FTIR, FESEM, tensile and compression testing. The FTIR results evidenced a shift of the peak absorption from 1727 cm−1 to 1701 cm−1 when the hardness of the TPU is increased, suggesting a more reinforced network structure that enhances the mechanical properties. The SEM images provided an understanding of the matrix condition given by the 3D-printing parameters, evidencing cavity characteristics that affect the filament adhesion and the mechanical response. Compression testing evidenced the strain-value change of the materials under compression stress and consequently its stability under hydrostatic pressure from 0 MPa to 1.5 MPa. The metamaterial with the designed structure shows a significant improvement in the sound absorption coefficient and more stable coefficient values under hydrostatic pressure when the 82-TPU was used in the 3D-printed structure.

Tunable composite lattice structure for low-frequency and ultra-broadband underwater sound absorption.

The underwater sound absorption technique in low-frequency and broadband has far-reaching prospects since it is essential for noise reduction of deep-sea operation requirements and evading advanced underwater target detection. Here, we propose an underwater sound-absorbing composite lattice with low-frequency and ultra-broadband characteristics. The composite lattice is constructed by regular spatially stacking cells with different sizes of metallic core spheres. All the core spheres are coated with silicon rubbers, and cells are embedded in the rubber matrix. In the composite lattice stereostructure, the lattice cells convert incident longitudinal waves into transverse waves through multiple local resonance coupling and multiple scattering. The energy is localized and dissipated in the composite lattice. We analyze the relationship among the corresponding absorption spectrums, the displacement clouds, and the resonance modes of lattice cells. Then, we construct a composite lattice and realize low-frequency broadband absorption from 693 to 1106 Hz with absorptance above 0.8. Further, our investigation demonstrates that the absorption bandwidth can be extended to ultra-broadband from 1077 to 10 000 Hz, where the thickness of the composite lattice is λ/17.05. The proposed composite lattice provides a practical approach to designing ultrathin low-frequency and ultra-broadband acoustic absorption coating for underwater noise suppression.

Integration of Antifouling and Underwater Sound Absorption Properties into PDMS/MWCNT/SiO2 Coatings.

Any surface immersed in sea water will suffer from marine fouling, including underwater sound absorption coatings. Traditional underwater sound absorption coatings rely heavily on the use of toxic, biocide-containing paints to combat biofouling. In this paper, an environmentally-friendly nanocomposite with integrated antifouling and underwater sound absorption properties was fabricated by adopting MWCNTs-COOH and SiO2 into PDMS at different ratios. SEM, FTIR and XPS results demonstrated MWCNTs were mixed into PDMS, and the changes in elements were also analyzed. SiO2 nanoparticles in PDMS decreased the tensile properties of the coating, while erosion resistance was enhanced. Antibacterial properties of the coatings containing MWCNTs-COOH and SiO2 at a ratio of 1:1, 1:3, and 1:5 reached 62.02%, 72.36%, and 74.69%, respectively. In the frequency range of 1500-5000 Hz, the average sound absorption coefficient of PDMS increased from 0.5 to greater than 0.8 after adding MWCNTs-COOH and SiO2, which illustrated that the addition of nanoparticles enhanced the underwater sound absorption performance of the coating. Incorporating MWCNTs-COOH and SiO2 nanoparticles into the PDMS matrix to improve its sound absorption and surface antifouling properties provides a promising idea for marine applications.

Tunable underwater low-frequency sound absorption via locally resonant piezoelectric metamaterials

Acoustic metamaterials with passive dissipative elements have demonstrated excellent underwater low-frequency sound absorption abilities, but still suffer from the narrow bandwidth, fixed absorption frequencies and bulky size. In this research, tunable underwater low-frequency sound absorption of the locally resonant piezoelectric metamaterials (LRPM) is systematically studied. A theoretical model of underwater sound absorption based on the LRPM is established. From the perspective of effective materials, the tunable sound absorption characteristics and perfect absorption mechanism are analyzed. The theoretical results are in good agreement with the numerical ones. It is demonstrated that a thin LRPM layer can achieve perfect sound absorption at targeted low-frequency which can be actively tuned by manipulating the resonant shunt circuit. Furthermore, the negative capacitance (NC) shunt can be introduced to the resonant circuit, which significantly improves the sound absorption bandwidth. By applying causality principle to the proposed LRPM, the causal constraints are discussed, which results in an improvement of causal optimality by NC shunt. This research can provide useful guidance for the realization of efficient and widely adjustable ultra-thin underwater sound absorbers.

Finite Element Solution for Dynamic Mechanical Parameter Influence on Underwater Sound Absorption of Polyurethane-Based Composite

Underwater noise pollution, mainly emitted by shipping and ocean infrastructure development of human activities, has produced severe environmental impacts on marine species and seabed habitats. In recent years, a polyurethane-based (PU-based) composite with excellent damping performance has been increasingly utilized as underwater sound absorption material by attaching it to equipment surfaces. As one of the key parameters of damping materials, dynamic mechanical parameters are of vital importance to evaluating the viscoelastic damping property and thus influencing the sound absorption performance. Nevertheless, lots of researchers have not checked thoroughly the relationship and the mechanism of the material dynamic mechanical parameters and its sound absorption performance. In this work, a finite element model was fabricated and verified effectively using acoustic pulse tube tests to investigate the aforementioned issues. The influence of the dynamic mechanical parameters on underwater sound absorption performance was systematically studied with the frequency domain to reveal the mechanism and the relationship between damping properties and the sound absorption of the PU-based composite. The results indicate that the internal friction of the molecular segments and the structure stiffness were the two main contributors of the PU-based composite's consumption of sound energy, and the sound absorption peak and the sound absorption coefficient could be clearly changed by adjusting the dynamic mechanical parameters of the composite. This study will provide helpful guidance to develop the fabrication and engineering applications of the PU-based composite with outstanding underwater sound absorption performance.

Low-frequency underwater sound absorption metamaterial

Air bubbles in liquid are known for exhibiting low-frequency resonance and can be considered as passive scatterers. In this paper, we design an acoustic metamaterial consisting of an air bubble in a water-filled metal shell with an opening to develop low frequency underwater sound absorber. Numerical simulation is carried out by using finite element method, and the results show that the metamaterial sound absorber achieves quasi-prefect sound absorption coefficient (up to 0.96) at the frequency of 900 Hz based on the coupling resonance between the elastic bubble and the metal shell matrix. By replacing the single unit with a 3-unit composite structure, the acoustic metamaterial absorber can extend the working frequency from 830 Hz to1330 Hz, with still high absorption coefficient above 0.8. Our design acoustic metamaterial has potential applications in underwater noise control.

Topology optimization combined with a genetic algorithm to design structured materials for underwater broadband acoustic absorption

This paper applies topology optimization in combination with a genetic algorithm to design a coating structure for sound absorption in underwater applications. The coating is designed with a high broadband acoustic absorption of 0.94 ranging from 1 to 10 kHz by optimizing the cavity topology and the dimensions of the embedded steel scatterers. This study demonstrates the application process of the topology optimization with a genetic algorithm method and the optimization results of the optimization process stages. The absorption mechanism of the topology design is analyzed. The effects of different cavity compositions, steel scatterers, design ideas, material parameters, and acoustic incident angles on the sound absorption coefficients are investigated. These acoustic structures and the method provide more ideas for the design of coating structures for underwater sound absorption.

An effective method to enhance the underwater sound absorption performance by constructing a membrane-type acoustic metamaterial

Broadband sound absorption has consistently been a challenge in designing underwater sound absorption structure (USAS). Most research of USASs achieve broadband sound absorption through structural optimization, which curbs the freedom of designing, and commonly alights it at the expense of increased thickness. In this paper, a method is reported to broaden the frequency band of the USAS by embedding a membrane-type resonator into the cavity, which forming a membrane-type underwater acoustic absorption metamaterial. We demonstrate the mechanism of membrane-type metamaterial by theory, and verify it by simulation and experiment. The experimental results show that the sound absorption coefficient in the frequency range of 2000–10 000 Hz is significantly improved after implanting the membrane-type resonator into the cavity. The average sound absorption coefficient is increased by nearly 17%, and the improvement effect of the sound absorption covers to each frequency point, which is consistent with our expectation. As the case of applying membrane-type metamaterials to the design process of underwater acoustic structures, this research possesses great application potential in acoustic wave communication and device compatibility design technologies.

Grating‐like anechoic layer for broadband underwater sound absorption

AbstractTo address the challenging task of effective sound absorption in the low and broad frequency band for underwater structures, we propose a novel grating‐like anechoic layer by filling rubber blocks and an air backing layer into metallic grating. The metallic gratings are incorporated into the anechoic layer as a skeleton for enhanced viscoelastic dissipation by promoting shear deformation between rubber and metal plates. The introduction of an air backing layer releases the bottom constraint of the rubber, thus intensifying its deformation under acoustic excitation. Based on the homogenization method and the transfer matrix method, a theoretical model is developed to evaluate the sound absorption performance of the proposed anechoic layer, which is validated against finite element simulation results. It is demonstrated that a sound absorption coefficient of the grating‐like anechoic layer of 0.8 can be achieved in the frequency range of 1294–10 000 Hz. Given the importance of sound absorption at varying frequencies, the weighted average method is subsequently used to comprehensively evaluate the performance of the anechoic layer. Then, with structural density taken into consideration, an integrated index is proposed to further evaluate the acoustic properties of the proposed anechoic layer. Finally, the backing conditions and the boundary conditions of finite‐size structures are discussed. The results provide helpful theoretical guidance for designing novel acoustic metamaterials with broadband low‐frequency underwater sound absorption.

Underwater sound absorption performance of exponential gradient anechoic coating

In this paper, the gradient anechoic coating whose density changes exponentially along direction of thickness is investigated. A numerical model is established by finite element method (FEM) to analyze the underwater sound absorption performance under different density distribution. The calculation results show that the exponential anechoic coating has better sound absorption performance compared with the homogeneous medium and linear anechoic coating. In addition, a discrete layered method is proposed to achieve gradient characteristics. In order to change the equivalent density of each layer, periodically distributed semi-cylindrical steel scatterers with different diameters are embedded in each layer. Therefore, the density function of the whole coating changes in exponential gradient with stepped function. Based on the sound absorption mechanism of multiple scattering and waveform conversion, the sound absorption is improved in low-frequency band from 0 Hz to 1000 Hz. The exponential gradient anechoic coating has potential applications in underwater sound absorption and vibration control.

Low-frequency underwater sound absorption of hybrid metamaterials using dissipative slow-sound

In this work, a hybrid metamaterial is proposed as a new type of underwater absorber, which is composed of carefully designed periodically arranged units. Each unit consists of a perforated panel, a water chamber and a coiled water channel coated with rubber on the channel walls. The coiled channel is designed to reduce the thickness of the structure. The introduction of the rubber coating changes the boundary condition of the coiled channel from rigid to non-rigid, resulting in dissipative slow-sound propagation in the coiled channel. The slow-sound propagation leads to the decrease of resonant frequency, and its inherent dissipation can consume sound energy, resulting in perfect low-frequency sound absorption at subwavelength thickness. Theoretical and numerical results show that the proposed hybrid metamaterial exhibits more than 99% sound energy absorption at 155 Hz, and the thickness of the structure is only 1/456 of the wavelength of sound wave. This work paves the way for the design of ultrathin underwater low-frequency absorbers.

Underwater sound absorption and insulation of elastic micro-perforated plates in impedance tubes

In this study, the underwater sound absorption and insulation performance capabilities of elastic micro-perforated plates (MPPs) in circular impedance tubes are investigated. The underwater sound absorption coefficient and the sound transmission loss (STL) of elastic MPPs are calculated by considering interaction between water and vibration of the elastic MPPs. As the frequency increases, higher order terms in addition to the plane wave solution are needed for convergence of the prediction. A comparison of the predictions from this study and the results obtained from the finite element method (FEM) shows good agreement. The fluid–structure interaction significantly affects the vibration of the MPP and the sound absorption characteristics are dominated by the vibration of the MPP, which results in sharp peaks in the sound absorption coefficient. For a low-frequency range, the characteristics of the STL are examined using a plane wave solution. The STL in water shows peaks, while that in air exhibits a wide bandwidth. For both underwater sound absorption and sound insulation, the peak frequencies remain nearly unchanged for different values of the cavity depth, and as the micro-perforation ratio increases, the peak frequencies increase.