Conception de capteurs en champ proche acoustique. Applications à la caractérisation des milieux viscoélastiques

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Adaptation of the near-field acoustic sensor to the measurement of the media properties

International audienceIn this work, the geometry of the near-field acoustic (NFA) sensor has been modified and adapted to the media properties to be characterized. The NFA method consists in studying the alterations of resonance curve of a horn whose tip, the probe, is immersed in the medium to be characterized. The sensor design has been changed by variation of cylinders lengths and their sections ratio. So sensitivity in the measuring of the liquids properties as well as in the characterization of the cement setting has been increased

Ultrasonic investigation of ceramic clay membranes

International audienceClay membranes containing various percentages of coal before sintering have been manufactured in order to obtain various volume fractions of porosity. Using echographic techniques, the longitudinal ultrasonic velocity and damping have been measured between 0 and 20% of coal. These results, compared to porosity measurements show that there is a simple linkage between porosity and ultrasonic parameters. Furthermore, the anomalous behaviour of one batch of membranes has been detected with ultrasonic waves and confirmed using classical porosity measurements (triple weight method). A linear behaviour of the ultrasonic velocity versus porosity has been obtained from 38 to 60% of porosit

Performance of a dual piezoceramic cantilever for low frequency energy harvesting applications: modeling and experiment verification

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices. These applications are usually in an environment of abundant low frequency vibration, which can be collected through an appropriate energy conversion structure. However, traditional energy conversion architectures such as cantilever-cantilever type or spring-mass type have the problem of high working frequency and narrow bandwidth (limiting its use and far from the frequency found in the surrounding environment). To overcome these challenges, this work proposes a study of a piezoelectric vibration energy harvester based on a dual cantilever structure. The energy harvesting system is designed, analyzed and verified with the finite element analysis method and an experimental study. The results show that the bandwidth is enlarged of 30 Hz and a power is generated and equals to the sum of the power generated by each cantilever (190 nW) with an output voltage supplying a resistive load of 110 KΏ

Design and Construction of a Multifunction Piezoelectric Transformer

International audienceIn recent years, piezoelectric materials have particularly found advantageous field of application in electrical energy’s conversion. Especially, the piezoelectric transformers are becoming more and more usable in electrical devices owing to several advantages such as small size, high efficiency, no electromagnetic noise, and non-flammability. The purpose of this study was to investigate a transformer design that allows having multi-functionality with different efficiency and wider range of voltage gain at resonance frequency. The piezoelectric transformer construction utilizes radial mode both at the input and output port and has the unidirectional polarization in the ceramics. An electromechanical equivalent circuit model based on Mason’s equivalent circuit was developed so as to describe the characteristics of the piezoelectric transformer. Excellent matching was found between the simulation data and experimental results. Finally, the results of this study will allow to deterministically designing multifunction piezoelectric transformers with specified performance

SOLID STATE SINTERING PREPARED 0.935(Bi0.5Na0.5)TiO3-0.065BaTiO3 LEAD FREE CERAMICS: EFFECT OF POLING CONDITIONS

In this work , the influence of poling conditions (poling field, poling temperature and poling time) on the piezoelectric properties of 0.935(Bi0.5Na0.5) TiO3-0.065BaTiO3 (BNT6.5BT) lead-free ceramics was examined. Piezoelectric properties like piezoelectric constant (d33) and electromechanical factors (Kp ,Kt) depend on poling field and poling temperature, whereas different poling times, in the 5-30 min range, were not observed to have significant effect on the piezoelectric properties

Elaboration and characterization of a low frequency and wideband piezoceramic generator for energy harvesting

International audienceThe aim of this work was to efficiently convert the mechanical vibrations into electrical energy by using direct piezoelectric effect. Most mechanical vibrations occur at low frequencies varying from 50 to 120 Hz. As piezoelectric converters provide maximum energy conversion when their natural frequencies are close to the frequency of the mechanical source, it would be interesting to design piezoelectric converters operating at low resonance frequencies. For those reasons, a piezoelectric generator has been developed with multi-cantilever piezoceramics operating at low frequencies. The device was shaped using the tape casting technique followed by a laser cutting process. It was made of six piezoelectric cantilevers with different lengths and various masses at their free-ends. Its piezoelectric response was characterized and analysed. It was shown that it can operate at low and many resonant frequencies. Moreover the frequency bandwidth was widened up to 200% compared to the one obtained from a single cantilever beam. It allowed efficiently exploiting mechanical vibrations of sources exhibiting wide frequency spectrum

Elaboration and characterization of BZT lead-free ceramic prepared in chemical way and with the addition of a sintering aid (LBCU)

International audienceThe Barium Titanates are very promising materials ecologically, but still have poor piezoelectric properties compared to the Lead Zirconate Titanates. So in order to improve them, a substitution of the zirconium in our ceramic (BT) has been investigated by X-ray diffraction (XRD) and grain size distribution. After the preparation of the BZT powder in chemical way we have added a sintering aid (Li2O3 - Bi2O3-CuO) and we have tried to study our massive ceramic. The X-ray diffraction, grain size distribution and scanning electron microscope of the BZT with LBCu show a better particles arrangement and density. In other hand we have noticed an important improvement of the piezoelectric properties (d33 = 220 pC/N at 25°C) especially in comparison with other lead-free ceramics. These properties make BZT a lead-free high performance material for piezoelectric applications

Synthesis of nanosized TiO2 powder by sol gel method at low temperature

International audienceNanotechnology is all about making products from very small constituents, components or subsystems to gain greatly enhanced material properties and functionality. Nanocrystalline anatase TiO2 was prepared by a facile sol–gel route at a temperature of 50°C under mild conditions. Titanium tetraisopropoxide (TTIP) was used as a titanium precursor, and 2-propanol was used as a solvent. XRD, TEM, SEM, FT-IR and BET were applied to characterize the crystal phase. The Crystalline size of TiO2 powder has been obtained with diameter < 30 nm for anatase at 500°C using an acid