Acoustic wave propagation through panels that are made of used tea bags

These days more than ever, society habits raise the necessity to consider the future of the environment. This presentation will tackle the aspect of more eco-friendly sound absorbing materials, more specifically analyzing the properties of consumed tea bags, starting from the collection up to the application and measurement of the final product. Many good options are often avoided, or not implemented for the lack of reliable properties analysis, encouraging existing materials to be chosen instead. The more information could be found about new materials, the more these could have a chance to be used, compared, or eventually improved. Sound absorbing panels that are made of tea bags were designed and developed to investigate sound transmission through tea-bag panels. Measurements were carried out on tea-bag panels in an impedance tube using a transfer function method to determine their sound absorption and transmission loss. Furthermore, the impedance gun system was used to determine acoustical properties of larger panels. Results show that 70 mm thick panels give an absorption coefficient higher than 0.8 between 500 Hz and 1600 Hz while 17 mm thick panels give an absorption coefficient that is mostly effective at higher frequencies. Up to 9 dB sound transmission loss is obtained at some frequencies

Acoustic wave propagation through eco-friendly porous panels at normal incidence

Human and non-human subjects are exposed to micro plastics through drink, food, and air. Micro-plastics propagating through atmosphere are breathable particles during inhalation and exhalation leading to deposition of them in the deep lung via the alveoli of the lungs. Teabags are made of plastics that are not recyclable and biodegradable. Therefore, we intend to remove used teabags from the natural environment by repurposing them to make sound attenuating panels for building and architectural industries, contributing in this way to a sustainable circular economy. The panels were designed and developed from consumed teabags as porous material by filling a frame to investigate acoustics wave propagation through them at normal incidence. Experimental testing was carried out on circular teabag panels in an impedance tube using a transfer function method to determine their sound absorption coefficient and transmission loss. Furthermore, the impedance gun method was used to determine the absorption properties of square panels. Results show that 75 mm thick circular panels give an absorption coefficient higher than 0.8 between 400 and 1600 Hz. Up-to 9.8 dB sound transmission loss of circular panels is obtained at higher frequencies. Absorption coefficients for square teabag panels are very good despite a coincidence-dip seen at 800 Hz. The satisfactory sound absorption and sound transmission characteristics of acoustic panels made of consumed tea bags can make this recycled material a cost-effective solution in the production of sustainable acoustic treatment in indoor spaces. The results suggest that recycling of consumed teabag as the panel could be applied as alternative sound absorbing materials

Metadiffusers for quasi-perfect and broadband sound diffusion

Sound diffusion refers to the ability of a surface to evenly scatter sound energy in both time and space. However, omnidirectional radiation of sound, or perfect diffusion, can be impractical or difficult to reach under traditional means. This is due to the considerable size required by, and the lack of tunability, of typical quarter-wavelength scattering strategies necessary for producing the required complexity of the surface acoustic impedance. As such, it can be a challenge to design sound diffusing structures that can display near perfect diffusion performance within slim dimensions. In this work, we propose a method for obtaining quasi-perfect and broadband sound diffusion coefficients using deep-subwavelength acoustic diffusers, i.e., metadiffusers. The relation between the geometry of the metasurface, the bandwidth and the diffusion performance is analytically and numerically studied. For moderate bandwidths, around 1/3 of an octave, the method results in nearly perfect sound diffusion, while for a bandwidth of 2.5 octaves a normalized diffusion coefficient of 0.8 was obtained using panels 1/30th thinner than traditional phase-grating designs. The ratio between the wavelength and the size of the unit cell was identified as a limitation of the performance. This work demonstrates the versatility and effectiveness of metadiffusers to generate diffuse reflections outperforming those of classical sound diffuser

Scattering evaluation of equivalent surface impedances of acoustic metamaterials in large FDTD volumes using RLC circuit modelling

Most simulations involving metamaterials often require complex physics to be solved through refined meshing grids. However, it can prove challenging to simulate the effect of local physical conditions created by said metamaterials into much wider computing sceneries due to the increased meshing load. We thus present in this work a framework for simulating complex structures with detailed geometries, such as metamaterials, into large Finite-Difference Time-Domain (FDTD) computing environments by reducing them to their equivalent surface impedance represented by a parallel-series RLC circuit. This reduction helps to simplify the physics involved as well as drastically reducing the meshing load of the model and the implicit calculation time. Here, an emphasis is made on scattering comparisons between an acoustic metamaterial and its equivalent surface impedance through analytical and numerical methods. Additionally, the problem of fitting RLC parameters to complex impedance data obtained from transfer matrix models is herein solved using a novel approach based on zero crossings of admittance phase derivatives. Despite the simplification process, the proposed framework achieves good overall results with respect to the original acoustic scatterer while ensuring relatively short simulation times over a vast range of frequencies

Thin film MoS2 nanocrystal based ultraviolet photodetector

Cataloged from PDF version of article.We report on the development of UV range photodetector based on molybdenum disulfide nanocrystals (MoS2-NCs). The inorganic MoS2-NCs are produced by pulsed laser ablation technique in deionized water and the colloidal MoS2-NCs are characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and UV/VIS absorption measurements. The photoresponse studies indicate that the fabricated MoS2-NCs photodetector (MoS2-NCs PD) operates well within 300-400 nm UV range, with diminishing response at visible wavelengths, due to the MoS2-NCs absorption characteristics. The structural and the optical properties of laser generated MoS2-NCs suggest promising applications in the field of photonics and optoelectronics. (C) 2012 Optical Society of Americ

Experimental validation of deep-subwavelength diffusion by acoustic metadiffusers

International audienceAn acoustic metadiffuser is a subwavelength locally resonant surface relying on slow sound propagation. Its design consists of rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators (HRs). Due to the slow sound properties, the effective thickness of the panel can therefore be dramatically reduced when compared to traditional diffusers made of quarter-wavelength resonators. The aim of this work is to experimentally validate the concept of metadiffusers from the scattering measurements of a specific metadiffuser design, i.e., a Quadratic Residue Metadiffuser (QRM). The experimental results reported herein are in a close agreement with analytical and numerical predictions, therefore showing the potential of metadiffusers for controlling sound diffusion at very low frequencies

A Survey of Social Network Forensics

Social networks in any form, specifically online social networks (OSNs), are becoming a part of our everyday life in this new millennium especially with the advanced and simple communication technologies through easily accessible devices such as smartphones and tablets. The data generated through the use of these technologies need to be analyzed for forensic purposes when criminal and terrorist activities are involved. In order to deal with the forensic implications of social networks, current research on both digital forensics and social networks need to be incorporated and understood. This will help digital forensics investigators to predict, detect and even prevent any criminal activities in different forms. It will also help researchers to develop new models / techniques in the future. This paper provides literature review of the social network forensics methods, models, and techniques in order to provide an overview to the researchers for their future works as well as the law enforcement investigators for their investigations when crimes are committed in the cyber space. It also provides awareness and defense methods for OSN users in order to protect them against to social attacks