Band Gaps of structures based on concrete-steel and concrete-molybdenum. Comparison between structures with square and hexagonal periodicities

In this article, a study of the frequency dispersion curves of a periodic structure was made. The cell units of the base model are made of steel cylinders coated with a rubber layer embedded in a concrete thin mat. The results show the existence of three band gaps which means that we have no propagation waves. In second step, the steel core has been substituted with molybdenum. A noticeable shift towards the low frequencies has been achieved together with an improvement in the relative widths of the band gaps. In addition, a comparison of band gaps was made between a finites two-dimensional structure with square periodicity and hexagonal periodicity. The results showed that a square periodicity of a two-dimensional structure is more favourable for the field of civil engineering wich is necessary to be in a low frequencies

Protection of structures subject to seismic and mechanical vibrations using periodical networks

The concept of frequency gaps in phononic crystals is widely used in physics. The feasibility and efficiency of applying this principle in damping out seismic and mechanical induced vibrations in real scale of civil engineering constructions are presented in this article through the results obtained from numerical modeling and analysis of a concrete substratum embedding steel elements (pillars) coated in a polyvinyl chloride polymer (PVC). The first configuration having the elements fully embedded into the substrate resulted in two narrow band gaps at relatively high frequencies; and when only the metallic pillars are emerging from the substrate, the band gaps shift towards the low frequencies. The results are improved and show the existence of three band gaps at medium frequencies ranging from 80 to 200 m/s when both the pillars and the polymer are emerging from the foundation. Exploring other metal-polymer pairs of materials such as "steel-rubber", "steel-silicone"," lead-rubber" and "lead-silicone", shows that a range of band gaps has shifted again towards the lower frequencies which cover part of the seismic frequency domain. Further improvement is obtained by notching the ends of the substrate in order to widen and lower the band gaps especially for "metal-rubber" pairs. These results show the potential of using periodic networks to mitigate seismic and mechanical vibration effects on large scale structures and components

Protection of structures subject to seismic and mechanical vibrations using periodical networks

The concept of frequency gaps in phononic crystals is widely used in physics. The feasibility and efficiency of applying this principle in damping out seismic and mechanical induced vibrations in real scale of civil engineering constructions are presented in this article through the results obtained from numerical modeling and analysis of a concrete substratum embedding steel elements (pillars) coated in a polyvinyl chloride polymer (PVC). The first configuration having the elements fully embedded into the substrate resulted in two narrow band gaps at relatively high frequencies; and when only the metallic pillars are emerging from the substrate, the band gaps shift towards the low frequencies. The results are improved and show the existence of three band gaps at medium frequencies ranging from 80 to 200 m/s when both the pillars and the polymer are emerging from the foundation. Exploring other metal-polymer pairs of materials such as "steel-rubber", "steel-silicone"," lead-rubber" and "lead-silicone", shows that a range of band gaps has shifted again towards the lower frequencies which cover part of the seismic frequency domain. Further improvement is obtained by notching the ends of the substrate in order to widen and lower the band gaps especially for "metal-rubber" pairs. These results show the potential of using periodic networks to mitigate seismic and mechanical vibration effects on large scale structures and components

Evidence of Ultrasonic Band Gap in Aluminum Phononic Crystal Beam

International audienceIn this paper, we prove theoretically and experimentally the existence of complete ultrasonic band gap in phononic crystal beam. The phononic beam structure studied is composed of a linear lattice array of square pillars on a beam, made with aluminum-fortal easily machinable at centimetric scale. Ultrasonic characterization of phononic beam guides shows the existence of a frequency range where the transmitted signals are strongly attenuated, due to the presence of ultrasonic band gap, in agreement with theoretical results predicted by finite element simulation. These structures present a potential for the use as energy loss reduction in micromechanical resonators at high frequency regime

Le Traitement D'image Dans Les Mems : Outil Essentiel Dans La Caractérisation Sans Contacts Des Microsystèmes

International audienceLe Traitement D'image Dans Les Mems : Outil Essentiel Dans La Caractérisation Sans Contacts Des Microsystème

Etude de Comportement Dynamique des Micropoutres MEMS : Simulation par FEM Sous COMSOL et ANSYS Multiphysiques

National audienceEtude de Comportement Dynamique des Micropoutres MEMS : Simulation par FEM Sous COMSOL et ANSYS Multiphysique

H2 sensing properties of modified silicon nanowires

It has been found that the silicon nanowires modified with noble metals can be used to fabricate an effective H2 gas sensor in the present study. The preparation and surface modification of silicon nanowires (SiNWs) were carried out by chemical methods. The morphology of the silicon nanowires unmodified and modified with nanoparticles of platinum, palladium, silver and gold was investigated using scanning electron microscopy (SEM). The chemical composition of the silicon nanowire layers was studied by secondary ion mass spectroscopy (SIMS) and energy dispersive X-ray analysis (EDX). The structures of type metal/SiNWs/p-Si/Al were fabricated. The electrical characterization (I–V) was performed in primary vacuum and H2 at different concentrations. It was found that the metal type used to modify the SiNWs strongly influenced the I–V characteristics. The response of these structures toward H2 gas was studied as a function of the metal type. Finally, the sensing characteristics and performance of the sensors were investigated

La Modélisation par Eléments Finis Comme Outil Essentiel dans la Caractérisation des Structures MEMS : Application aux Microponts

International audienceLa Modélisation par Eléments Finis Comme Outil Essentiel dans la Caractérisation des Structures MEMS : Application aux Micropont