Review of phononic crystals and acoustic metamaterials

As a new type of acoustic functional material, phononic crystal has great research value and application environment. It is a periodic structure of two or more elastic materials, which are derived from photonic crystals. The main research work on phononic crystals focuses on the two band gap formation mechanisms of Bragg scattering and local resonance, and some new methods of vibration reduction and noise reduction can be obtained by studying its banding mechanism. Similarly, a "metamaterial" has been proposed for the ability to achieve new vibration reduction and noise reduction, which is a composite structure or material with physical properties not available in natural materials. By analysing the acoustic metamaterials of various structures, in this work we can understand how to achieve vibration reduction and noise reduction under the local resonance mechanism

Behaviour and applications of elastic waves in structures and metamaterials

The present thesis focuses on elastic waves behaviour in ordinary structures as well as in acousto-elastic metamaterials via numerical and experimental applications. After a brief introduction on the behaviour of elastic guided waves in the framework of non-destructive evaluation (NDE) and structural health monitoring (SHM) and on the study of elastic waves propagation in acousto-elastic metamaterials, dispersion curves for thin-walled beams and arbitrary cross-section waveguides are extracted via Semi-Analytical Finite Element (SAFE) methods. Thus, a novel strategy tackling signal dispersion to locate defects in irregular waveguides is proposed and numerically validated. Finally, a time-reversal and laser-vibrometry based procedure for impact location is numerically and experimentally tested. In the second part, an introduction and a brief review of the basic definitions necessary to describe acousto-elastic metamaterials is provided. A numerical approach to extract dispersion properties in such structures is highlighted. Afterwards, solid-solid and solid-fluid phononic systems are discussed via numerical applications. In particular, band structures and transmission power spectra are predicted for 1P-2D, 2P-2D and 2P-3D phononic systems. In addition, attenuation bands in the ultrasonic as well as in the sonic frequency regimes are experimentally investigated. In the experimental validation, PZTs in a pitch-catch configuration and laser vibrometric measurements are performed on a PVC phononic plate in the ultrasonic frequency range and sound insulation index is computed for a 2P-3D phononic barrier in the sonic frequency range. In both cases the numerical-experimental results comparison confirms the existence of the numerical predicted band-gaps. Finally, the feasibility of an innovative passive isolation strategy based on giant elastic metamaterials is numerically proved to be practical for civil structures. In particular, attenuation of seismic waves is demonstrated via finite elements analyses. Further, a parametric study shows that depending on the soil properties, such an earthquake-proof barrier could lead to significant reduction of the superstructure displacement

Research of the acoustic phenomenon produced by isolated scatterers and its applicability as a noise reducing device in transport infrastructures. Search for an optimised and sustainable design.

Tesis por compendio[ES] El control de ruido ambiental es una preocupación de primera magnitud para las sociedades avanzadas, debido a los problemas derivados que ocasionan en la salud de los ciudadanos. Una de las soluciones más extendidas para el control del ruido en su fase de transmisión en la utilización de pantallas acústicas. La aparición de nuevos materiales formados por redes de dispersores acústicos aislados, denominados cristales de sonido, está revolucionando el campo del apantallamiento acústico, posibilitando el avance tecnológico de esta área. Así, en los últimos años, las pantallas acústicas basadas en cristales de sonido se han posicionado como una alternativa viable a las pantallas acústicas tradicionales, puesto que ofrecen múltiples ventajas frente a las soluciones actuales. En el presente trabajo se muestra primeramente una recopilación de los avances realizados en el campo del apantallamiento acústico mediante esta tipología de pantallas. No obstante, aún existen líneas de investigación abiertas en esta área, que es necesario abordar para conseguir el objetivo de aplicar esta tecnología como atenuadores de sonido en las infraestructuras de transporte. Durante el periodo de formación de la doctoranda, se ha trabajado en algunas de las líneas de investigación activas en este campo del apantallamiento acústico. Una de estas investigaciones condujo al descubrimiento de interferencias entre los efectos de la resonancia y la dispersión múltiple de los cristales de sonido cuando estos efectos se producen en rangos de frecuencia cercanos. También hemos diseñado un nuevo dispositivo de reducción de ruido basado en cristales de sonido, utilizando herramientas de optimización multiobjetivo, que permitan apantallar y reflejar de forma difusa el ruido. El empleo de esta nueva herramienta de diseño identificó la necesidad de realizar un estudio comparativo de los métodos de simulación más utilizados para estimar el rendimiento de los dispositivos basados en cristales de sonido. Por último, hemos realizado un estudio psicoacústico para determinar la percepción de la reducción de molestia que proporcionan las pantallas acústicas basadas en cristales sonido y las barreras tradicionales, determinando si los parámetros objetivos que evalúan su rendimiento coinciden con la respuesta subjetiva de los usuarios.[CA] El control de soroll ambiental és una preocupació de primera magnitud per a les societats avançades, a causa dels problemes derivats que ocasionen en la salut dels ciutadans. Una de les solucions més esteses per al control del soroll en la seua fase de transmissió en la utilització de pantalles acústiques. L'aparició de nous materials formats per xarxes de dispersors acústics aïllats, denominats cristals de so, està revolucionant el camp de l'apantallament acústic, possibilitant l'avanç tecnològic d'esta àrea. Així, en els últims anys, les pantalles acústiques basades en cristals de so s'han posicionat com una alternativa viable a les pantalles acústiques tradicionals, ja que oferixen múltiples avantatges enfront de les solucions actuals. En el present treball es mostra primerament una recopilació dels avanços realitzats en el camp de l'apantallament acústic per mitjà d'esta tipologia de pantalles. No obstant això, encara hi ha línies d'investigació obertes en esta àrea, que és necessari abordar per a aconseguir l'objectiu d'aplicar esta tecnologia com a atenuadors de so en les infraestructures de transport. Durant el període de formació de la doctoranda, s'ha treballat en algunes de les línies d'investigació actives en este camp de l'apantallament acústic. Una d'estes investigacions va conduir al descobriment d'interferències entre els efectes de la ressonància i la dispersió múltiple dels cristals de so quan estos efectes es produïxen en rangs de freqüència pròxims. També hem dissenyat un nou dispositiu de reducció de soroll basat en cristals de so, utilitzant ferramentes d'optimització multiobjectiu, que permeten apantallar i reflectir de forma difusa el soroll. L'ús d'esta nova ferramenta de disseny va identificar la necessitat de realitzar un estudi comparatiu dels mètodes de simulació més utilitzats per a estimar el rendiment dels dispositius basats en cristals de so. Finalment, hem realitzat un estudi psicoacústic per a determinar la percepció de la reducció de molèstia que proporcionen les pantalles acústiques basades en cristals so i les barreres tradicionals, determinant si els paràmetres objectius que avaluen el seu rendiment coincidixen amb la resposta subjectiva dels usuaris.[EN] Control of environmental noise is a major concern for advanced societies because of the resulting problems for citizens' health. One of the most widespread solutions for controlling noise in its transmission phase is the use of acoustic screens. The emergence of new materials made up of arrays of isolated acoustic scatterers, called sonic crystals, is revolutionizing the field of acoustic screening. In recent years, acoustic screens based on sonic crystals have positioned themselves as a viable alternative to traditional acoustic screens, as they offer multiple advantages over current traditional solutions. This Doctoral dissertation compiles the advances in the field of acoustic screening using this type of sonic crystals. However, there is still active research in this area which needs to be addressed and studied in order to apply this technology as noise reduction devices in transport infrastructures. Therefore, during the PhD student's training period, we have researched the acoustic phenomena produced by isolated scatterers in order to better understand the physical phenomena behind the lasts designs of this type of screen. One of these researches led to the discovery of interferences between the effects of resonance and multiple scattering of sonic crystals when occurring in nearby frequency ranges. Also we have designed a new noise reduction device based on sonic crystals, using multi-objective optimization tools, which would block and diffuse the noise. This new designing tool identified the need for a comparative study of the most commonly used simulation methods to estimate the performance of devices based on sonic crystals. Finally, we have carried out a psychoacoustic study that determined the perception of the annoyance reduction provided by acoustic screens based on sonic crystals and traditional barriers, determining whether the objective parameters that evaluate their performance match to the subjective response of the users.Agradezco al Ministerio de Ciencia e Innovación por la ayuda concedida dentro del programa Doctores Industriales. Asimismo, a mi tutor en empresa Dr. Juan José Martín Pino, por posibilitar la realización de esta investigación dentro de la empresa BECSA. Al Departamento de Física Aplicada de la Universitat Politècnica de València, a la Comisión Académica del Programa de Doctorado de Matemáticas y al Centro de Tecnologías Físicas: Acústica, Materiales y Astrofísica.Peiró Torres, MDP. (2021). Research of the acoustic phenomenon produced by isolated scatterers and its applicability as a noise reducing device in transport infrastructures. Search for an optimised and sustainable design [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164903TESISCompendi

Broadband and intense sound transmission loss by a coupled-resonance acoustic metamaterial

The advent of acoustic metamaterials opened up a new frontier in the control of sound transmission. A key limitation, however, is that an acoustic metamaterial based on a single local resonator in the unit cell produces a restricted narrow-band attenuation peak; and when multiple local resonators are used the emerging attenuation peaks -- while numerous -- are each still narrow and separated by pass bands. Here, we present a new acoustic metamaterial concept that yields a sound transmission loss through two antiresonances -- in a single band gap -- that are fully coupled and hence provide a broadband attenuation range; this is in addition to delivering an isolation intensity that exceeds 90 decibels for both peaks. The underlying coupled resonance mechanism is realized in the form of a single-panel, single-material pillared plate structure with internal contiguous holes$-$a practical configuration that lends itself to design adjustments and optimization for a frequency range of interest, down to sub-kilohertz, and to mass fabrication

Hilbert fractal acoustic metamaterials with negative mass density and bulk modulus on subwavelength scale

© 2019 The Authors Acoustic metamaterials (AMs) are artificially engineered composite materials, structured to have unconventional effective properties for flexibly manipulating the wave propagation, which can produce a broad range of applications such as sound cloaking and tunneling. In nature, bio-inspired fractal organization with multiple length scales has been found in various biological materials, which display enhanced dynamic properties. By introducing Hilbert curve channels, this work will design a class of topological architectures of Hilbert fractal acoustic metamaterials (HFAMs) with negative mass density and bulk modulus on subwavelength scale. In this paper, we will highlight the influences of the self-similar fractal configurations on multipole modes of HFAM. To further demonstrate multipole resonances, the pressure magnifications are assessed in the center region of HFAM with losses. Moreover, based on effective medium theory, we systematically calculate and investigate effective bulk modulus and mass density, as well as density-near-zero of HFAM, to demonstrate the negative properties and the zero-phase-difference effects of HFAMs. Numerical results show that HFAM can enable a number of applications, from sound blocking, quarter bending, sound cloaking to sound tunneling, and may further provide a possibility for the engineering guidances of the exotic properties on subwavelength scale

Efficient design of sandwich panels with cellular truss cores and large phononic band gaps using surrogate modeling and global optimization

Recent advancements in additive manufacturing technologies and topology optimization techniques have catalyzed a transformative shift in the design of architected materials, enabling increasingly complex and customized configurations. This study delves into the realm of engineered cellular materials, spotlighting their capacity to modulate the propagation of mechanical waves through the strategic creation of phononic band gaps. Focusing on the design of sandwich panels with cellular truss cores, we aim to harness these band gaps to achieve pronounced wave suppression within specific frequency ranges. Our methodology combines surrogate modeling with a comprehensive global optimization strategy, employing three machine learning algorithms—k-Nearest Neighbors (kNN), Random Forest Regression (RFR), and Artificial Neural Networks (ANN)—to construct predictive models from parameterized finite element (FE) analyses. These models, once trained, are integrated with Particle Swarm Optimization (PSO) to refine the panel designs. This approach not only facilitates the discovery of optimal truss core configurations for targeted phononic band gaps but also showcases a marked increase in computational efficiency over traditional optimization methods, particularly in the context of designing for diverse target frequencies

Development of Acoustic Metamaterial Noise Barriers and Simultaneously Harvesting Energy Using Smart Materials

In our surroundings abundant energy, we either feel through component vibration or hear noises from acoustic sources. Harvesting these unused and untapped green energy in the form of ambient vibration, and acoustic sounds is an emerging field of research in recent years. Utilization of the energy within a wide band of the frequency spectrum originated from the vibrational sources alone stands as one of the most promising ways to power small electronic devices, smartphones, local structural health monitoring sensors, home, and workshop appliances. These abundant sources of green energy are available in almost all the engineering industries, workshops, manufacturing facilities, construction zones, and in our daily operations. Particularly aerospace, mechanical, and civil sectors have plenty of such scenarios where the energy used is lost through vibration and acoustic noises. Continuously running machinery in a workshop, ambient vibration in a manufacturing facility, vibrating wings of an aircraft, high dB aircraft noise near airports, noise in metallurgical plants, power plants, vehicle noise near a roadside facility, etc. are few examples of the ambient source of energy that can be harvested which are otherwise wasted. If a suitable mechanism is devised, the vibration and acoustic noise sources can be equipped to trap and reclaim the energy to create local power sources. Researchers proposed many such methods in the past two decades. However, only recently researchers including us proposed that carefully engineered metamaterials can also be used for energy harvesting. Metamaterials are man-made materials that behave uniquely and possess exclusively desired properties that are not found in natural materials. Usually, it is the combination of two or more materials and can be engineered to perform specific tasks that are not possible with traditional materials. These were initially discovered in photonics while working with electromagnetic radiation. An electromagnetic counterpart of wave propagation in mechanics, i.e. phononics with acoustic waves were found to be affected by the metamaterials. These acoustic metamaterials when carefully designed are also capable of affecting the wave propagation characteristics through fluids such as air. Many acoustic metamaterials have gone beyond its definition but still, characterize the waveguiding properties. They are classified under the passive modalities of acoustics to affect the sound and vibration mitigation. Incorporation of smart materials while constructing acoustic metamaterial, can enhance the multifunctionality of these materials in both passive and active ways. A prospective application field for such acoustic metamaterials is energy harvesting from low-frequency vibrations. Conventionally, passive acoustic metamaterials are visualized as noise barrier materials to filter roadside and industrial noises. This application can get extended to the aerospace application where mitigation of engine noise inside the cabin is challenging. Irrespective of their target applications, acoustic metamaterials integrated with smart materials can scavenge the very green energy that they are designed to absorb and mitigate. First, in this research work, a recently proposed method of creating Acoustoelastic Metamaterial (AEMM) is used to investigate further if that can be used to harvest energy from the industrial noise barriers. It is known that noise barriers are designed to minimize noise outside the boundary like the noise barriers seen beside the highways. Construction materials like concrete, steel, vinyl, wood, or earth mounds are used in the industrial sound barriers that can reduce the sound pressure level (dB) on the other side of the barriers. In this work, a novel metamaterial wall (MetaWall) is proposed to redefine the industrial sound isolation wall using the integrated AEMM units. In this part, wave isolation and energy harvesting capabilities of the acoustic metamaterial is fused to propose MetaWall unit bricks, which are made of rubber-metal-concrete composite, as an industrial building material. Secondly, it is proposed that such acousto-elastic metamaterial (AEMM) models can also be used in the aerospace industry to power the online NDE/SHM sensors, e.g. piezoelectric wafer active sensors which are widely used. Hence, further in this part, a rigorous study is made to find the actual power required by the online NDE / SHM sensors such that a similar amount of power can be harvested by the AEMM model and stored in a battery for scheduled scans. The ultimate goal of this second study is to minimize the size of the proposed AEMM model to make it suitable for aerospace applications on-board. With changes in the materials of the cell constituents, it is shown that the power outputs from a similar model can be significantly altered and further optimized. A parametric study is also performed to show the variation of the output power. Finally, based on the learning a plate-type metamaterial is proposed to harvest a required optimum amount of energy from the ambient vibration with dominant frequency as low as 100Hz. In the third section, a spiral-shaped acoustic metamaterial is proposed which has dual functionality of noise filtering and energy harvesting over a wider range of frequencies. A work in progress presented with a proposed timeline to complete the dissertation. This acoustic metamaterial has a comparatively high reflection coefficient closer to the anti-resonance frequencies, resulting in high sound transmission loss. The filtered noise is trapped inside the cell in the form of strain energy. The spiral design is also sensitive to the vibration due to trampoline shaped in highly flexible polymeric piezoelectric material attachments inside the cell. This also makes it capable of harvesting energy using vibration. This is a promising acoustoelastic metamaterial with multifunctionality properties for future applications. Hence, it is claimed that if metamaterials are employed to reduce or suppress the noise and make use of the trapped energy which is any way wasted could be harvested to power the local electronic devices. The new solution could make a transformative impact on the 21st century’s green energy solutions. Calculated placement of smart materials in the cell-matrix can help to extract the strain energy in the form of power. The acoustic metamaterial cell designs presented in this research have the capability of isolating noise and reducing diffraction by trapping sound in a wide range of frequencies and at the same time recover the trapped abundant energy in the form of electrical potential using piezoelectric materials

RAINBOW TRAPPING EFFECT IN 2D AXISYMMETRIC BROADBAND ACOUSTIC ENERGY HARVESTERS

Acoustic energy harvesters (AEHs) collect otherwise unused ambient acoustic waves for conversion into useful electrical energy. This promising technology has potential applications ranging from grid-independent electronics to structural health monitoring systems. AEHs capture specific acoustic frequencies of interest using structures with frequency-matched component geometries. Despite the multitude of potential geometries suitable for AEH structures, existing AEH research has predominantly focused on the acoustic wave trapping performance of unidimensional or linear bidimensional AEH structures. This study intended to broaden AEH bandwidth and capture efficiency by investigating the acoustic rainbow trapping performance of a novel 2D axisymmetric AEH design. A Finite Element Method (FEM) approach was employed using COMSOL Multiphysics® v5.5 to evaluate the acoustic wave trapping performance of various groove, cylindrical pillar, and circular hole-based unit cell geometries across the 100 kHz - 220 kHz frequency range. The grooved unit cell groove/plate depth ratio and overall plate depth were optimized. A FEM simulation analyzed the acoustic rainbow trapping performance of a 2D axisymmetric AEH design comprised of a gradient array of these optimized unit cells. These FEM results were validated using an array of piezoMEMS sensors mounted to an aluminum AEH prototype. The prototype displayed reliably predictable acoustic frequency trapping at defined locations. Through these results, this study demonstrated the viability of 2D axisymmetric AEHs in enhancing the acoustic rainbow trapping effect across a broadband frequency range of interest. However, there is much opportunity to refine this AEH design. This proof of concept presents a strong impetus for furthering 2D axisymmetric AEH research