Towards a quieter world : three-dimensional printed acoustic metamaterials for noise control

Environmental noise impacts the everyday life of millions of people and it represents a growing concern for the health of the world's population. To mitigate this impact, noise reducing materials such as foam or barriers are employed extensively with effective results. However, the efficacy of such materials is limited by the inverse relationship between the frequency of the attenuated waves and materials characteristics like thickness and density, as described by the mass-law. In order to overcome this fundamental limitation, a new challenge in acoustic engineering has emerged to design and manufacture lightweight and subwavelength materials that can break the mass-law. A potential solution to this challenge is represented by a recently discovered family of materials, called acoustic metamaterials, which show properties typically not found in nature. These materials are made of resonant building blocks that are smaller than the wavelength of the attenuated acoustic wave. When these building blocks are combined to form a metamaterial, they lead to the formation of band gaps - near their resonance frequency - that deeply attenuate the incident sound. The manufacturing of noise reducing acoustic metamaterials could also largely benefit from recent advances in three-dimensional printing technologies, as they offer the possibility to fabricate abstract shapes and to carefully choose some properties of the printed materials. The work presented in this thesis describes the modelling, fabrication and measurement of noise reducing acoustic metamaterials based on Helmholtz resonators, thin plates and active piezoelectric plates. These materials have been produced through original and innovative three-dimensional printing techniques. The results of this thesis can be applied to noise control in audio applications such as headphones, hearing aids and smart speakers. Similarly, other fields like aerospace and automotive industry or architectural acoustics could also greatly benefit from lightweight subwavelength noise reduction.Environmental noise impacts the everyday life of millions of people and it represents a growing concern for the health of the world's population. To mitigate this impact, noise reducing materials such as foam or barriers are employed extensively with effective results. However, the efficacy of such materials is limited by the inverse relationship between the frequency of the attenuated waves and materials characteristics like thickness and density, as described by the mass-law. In order to overcome this fundamental limitation, a new challenge in acoustic engineering has emerged to design and manufacture lightweight and subwavelength materials that can break the mass-law. A potential solution to this challenge is represented by a recently discovered family of materials, called acoustic metamaterials, which show properties typically not found in nature. These materials are made of resonant building blocks that are smaller than the wavelength of the attenuated acoustic wave. When these building blocks are combined to form a metamaterial, they lead to the formation of band gaps - near their resonance frequency - that deeply attenuate the incident sound. The manufacturing of noise reducing acoustic metamaterials could also largely benefit from recent advances in three-dimensional printing technologies, as they offer the possibility to fabricate abstract shapes and to carefully choose some properties of the printed materials. The work presented in this thesis describes the modelling, fabrication and measurement of noise reducing acoustic metamaterials based on Helmholtz resonators, thin plates and active piezoelectric plates. These materials have been produced through original and innovative three-dimensional printing techniques. The results of this thesis can be applied to noise control in audio applications such as headphones, hearing aids and smart speakers. Similarly, other fields like aerospace and automotive industry or architectural acoustics could also greatly benefit from lightweight subwavelength noise reduction

3D printed small-scale acoustic metamaterials based on Helmholtz resonators with tuned overtones

Acoustic metamaterials have been extensively studied in recent decades due to their ability to control acoustic waves. In this paper, we present a prototype of a small-scale acoustic metamaterial based on Helmholtz resonators fabricated with additive manufacturing technology. The results confirm that 3D printed small-scale metamaterials can break the mass law by creating band gaps where the sound is deeply attenuated. We have also introduced a modification of the resonators whereby overtones are exploited and tuned in order to broaden the band gap. The output of this research could be used to provide passive filtering for transducers, to improve noise cancelling headphones, as well as in other smart acoustic sensors and IoT audio applications

DEMO : multimodal sensing system for hearing enhancement and research

Directivity in hearing aid systems is normally achieved with the use of multiple microphones in an array fashion that aims to enhance signal processing capabilities and performance. Despite the use of binaural information (hearing with two ears), natural hearing systems (e.g. human) also rely on movements of the head to retrieve directional information and the origin of sounds [1]. This kind of natural sensing technique, which combines sound with the movements and position of the body (Fig. 1 & 2) has previously been investigated, and showed encouraging results with improved localization performance [2]. However, the concept has not been explored or exploited yet in any standard commercial hearing aid devices. Creating a hearing aid system that can also include motion sensing would be of great benefit to the hearing impaired in order to enhance directional perception of sound with other functionalities such as frequency selectivity (Fig. 3 & 4) on a wearable hearing device

Unidad de Vinculación Institucional con el Sector Agropecuario. Ordenamiento de las pulverizaciones en el área periurbana de la Ciudad

El continuo crecimiento del área urbana, dio lugar a la construcción de viviendas y/o barrios en lugares cada vez más cercanos a los establecimientos rurales, llevando a un estrechamiento de la zona de transición entre lo urbano y lo rural. Por lo que es cada vez más imprescindible que los actores involucrados en el sector tomen dimensión de la importancia que tiene la aplicación racional y responsable de los productos fitosanitarios en esas zonas. Es por estas razones que se debe lograr un ordenamiento de las áreas urbanas  y peri urbanas para que no interfiera con las actividades agrícolas y ganaderas. Ante este panorama la Unidad de Vinculación Institucional con el Sector Agropecuario, dependiente de la Secretaría de Extensión Universitaria de la Universidad Nacional de Rosario, junto con las Secretarías de Extensión de las Facultades de Ciencias Agrarias y Ciencias Veterinarias, pretende llevar adelante en las comunas y municipios interesados, un programa de concientización y capacitación acerca de la aplicación racional y responsable de los productos fitosanitarios. Además intenta ser el puntapié inicial para que cada localidad logre un desarrollo de las áreas urbanas y rurales a través de una planificación teniendo como premisa el  ordenamiento territorial. Palabras claves: Ordenamiento; periurbanas; aplicación; fitosanitarios; concientizació

Enhancing the sound absorption of small-scale 3D printed acoustic metamaterials based on Helmholtz resonators

Acoustic metamaterials have recently become of interest for their ability to attenuate sound by breaking the massdensity law. In this paper, acoustic metamaterials based on Helmholtz resonators and capable of attenuating sound up to 30 dB are fabricated for sound absorption applications in the smallscale. The proposed metamaterials are subwavelength at a factor of λ/12 with respect to the lateral dimension of the units. The directional response due to the position of the acoustic source on the sound attenuation provided by the metamaterial is investigated by controlling the location of a loudspeaker with a robot arm. To enhance and broaden the absorption bands, structural modifications are added such that overtones are tuned to selected frequencies, and membranes are included at the base of the resonators. This design is made possible by innovative 3D printing techniques based on stereolithography and on the use of specific UV-curable resins. These results show that these designs could be used for sound control in small-scale electroacoustic devices and sensors

Fabrication and characterization of 3D printed thin plates for acoustic metamaterials applications

This paper presents a 3D printing technique based on stereolithography and direct light processing for the fabrication of low resonance frequency thin plates suitable for acoustic metamaterials applications. It was possible to achieve a better resolution with respect to other 3D printing methods such as fusion deposition modeling and to obtain plates with a thickness of 70 μm. The plates were characterized using three different methods: laser Doppler vibrometer supported by modal analysis, impedance tube measurements backed by a transfer matrix model and nanoindentation. All results are in good agreement. The physical parameters retrieved through the characterization methods can be used for future designs and integrated into finite element analysis to better predict the noise impact of these materials. Thanks to the small radius and thickness of the plates presented in this paper and to their low resonance frequency, it is suggested that they could be arranged in various configurations and used as unit cells in acoustic metamaterials applications for noise attenuation in small-scale electroacoustic devices

Global Multidimensional Poverty Index 2021: Unmasking disparities by ethnicity, caste and gender

This report provides a comprehensive picture of acute multidimensional poverty to inform the work of countries and communities building a more just future for the global poor. Part I focuses on where we are now. It examines the levels and composition of multidimensional poverty across 109 countries covering 5.9 billion people. It also discusses trends among more than 5 billion people in 80 countries, 70 of which showed a statistically significant reduction in Multidimensional Poverty Index value during at least one of the time periods presented. While the COVID-19 pandemic's impact on developed countries is already an active area of research, this report offers a multidimensional poverty perspective on the experience of developing countries. It explores how the pandemic has affected three key development indicators (social protection, livelihoods and school attendance), in association with multidimensional poverty, with a focus predominantly on Sub-Saharan Africa. Part II profiles disparities in multidimensional poverty with new research that scrutinizes estimates disaggregated by ethnicity or race and by caste to identify who and how people are being left behind. It also explores the proportion of multidimensionally poor people who live in a household in which no female member has completed at least six years of schooling and presents disparities in multidimensional poverty by gender of the household head. Finally, it probes interconnections between the incidence of multidimensional poverty and intimate partner violence against women and girls