Influence of 1-3 piezocomposite fabrications on lateral modes

International audience—Properties of 1-3 piezocomposites with periodic structure were characterized. This material can be typically fabricated in using the " dice and fill " method (DFM) and two phases were used (PMN-34.5PT ceramic and epoxy resin). The corresponding numerical simulations allowed to study the influence of spurious lateral modes on electromechanical performance of the thickness mode. This was performed in calculating the bandwidth and the sensitivity of the piezocomposite in water (emission-reception) in the frequency range 1-5 MHz. Moreover, three ceramic volume fractions between 25% and 60% were used. Finally, a comparison of these results with those obtained with a pseudo-periodic 1-3 piezocomposite was made. This composite can be fabricated by a lamination technique (LMT) and the use of a pseudo-periodic structure leads to a minimized effect of the lateral modes (confirmed on the simulated electrical impedance). Thanks to these results an optimum structure was discussed

Lead-Free Sodium Potassium Niobate Based Piezoelectric Thick Film Bimorph Structure for Energy Harvesting

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Super-Cell Piezoelectric Composite With 1–3 Connectivity

International audience— The standard fabrication method for 1–3 piezo-composites for ultrasound transducers is the " dice and fill " method (DFM) in which lateral periodicity is introduced. This contributes to the appearance of spurious modes that can drastically affect the performance of the device if they appear near its thickness mode frequency, thus limiting the effective frequency range. A new 1–3 piezocomposite fabricated with a super-cell structure [1–3 super cell (13SC)] was designed in order to overcome these limitations. It consists of the merging of several periodic cells with 47% PZT volume fraction and epoxy resin as the matrix. Two lateral periodicities in one direction are defined as well as two different kerfs. The chosen cell shape is composed of five nonaligned square section rods (1 × 1 mm 2). For comparison of performance, two regular 1–3 piezocomposites (the same materials and equivalent periodicities) were fabricated by DFM. Electroacoustic responses in water were measured for the three composites being considered as transducers. Successive regular thinnings (from 2.8 to 1.1 mm) were carried out for each sample to increase the operating frequency (from around 0.4 to 1.3 MHz) and study the evolution of the characteristics (bandwidth and sensitivity). The experimental results confirmed the behavior of those obtained with numerical simulations, showing that the 13SC composite can be used in this entire frequency range, unlike regular composites

Texturation of lead-free BaTiO₃ based piezoelectric ceramics: [Invited]

oral invitéInternational audiencePiezoelectric ceramics have been integrated for a long time in a widerange of devices, particularly in ultrasonic applications (sonar systems,medical imaging...) and most of them use Pb(Zr,Ti)O3 (PZT) materials.However, due to health care and environmental problems, lead contentmust be reduced in such applications. Among the few lead-freematerials families which can be considered for the replacement of PZT,BaTiO3 appear as interesting because of its piezoelectric properties atroom temperature and capacity to be modulated by doping, even ifCurie temperature is not very high (120°C).However, ceramics are generally limited by their isotropic nature. Forthis reason, texturing process was developed in order toimprove/optimize their electromechanical properties. The aim of thepresent study is thus to obtain textured BaTiO3 based materials byusing the templated grain growth process (TGG) and to measure theirpiezoelectric properties.Doped and undoped BaTiO3 powders were prepared by classical solidstate route while BaTiO3 templates were elaborated by a molten saltsprocess. Green ceramics were then obtained by tapecasting of a slurrycontaining templates and matrix particles dispersed in theappropriated solvent. After drying, green sheet was cut, stacked,pressed and then sintered at the appropriated temperature, in order toobtain thick or thin samples. This process allowed obtaining highlyorientedmaterials (texturation degree 70% to 90%). Piezoelectricproperties were investigated, for doped and undoped samples, and fordifferent sintering parameters. Some samples appears as veryinteresting for piezoelectric applications with d33* higher than 300 pC/N, against 180 pC/N for BaTiO3 ceramics obtained by classical way

1-3 Piezocomposites Based on Super-Cell Structuring for Transducer Applications

International audience—In ultrasound transducers, the most popular fabrication method for 1-3 piezocomposites is the « dice and fill » method where lateral periodicity p is introduced and leads to the occurrence of lateral modes. These spurious modes can drastically damage the performance of the device if they appear near its thickness (h) mode, thus limiting the operational frequency range. In order to overcome the previous limitations while maintaining a good electromechanical efficiency for the 1-3 piezocomposites, a new fabrication method based on lamination is proposed. The piezocomposite is partially regular with a super-cell structure composed of five piezoelectric rods and two different pitches in one direction. The chosen cell shape allows numerical modeling to be performed (ATILA software). This study is made in the frequency range 0.4-1.3 MHz. Experimental results (electroacoustic responses in water) confirm those obtained with the numerical simulations, showing that the super-cell composite can be used in a larger range of frequencies than regular composites, while keeping similar sensitivity and bandwidth

Parametric study of a thin piezoelectric cantilever for energy harvesting applications

International audienc

Complete Electroelastic Set of Co doped Barium Titanate for Transducer Applications

International audienceBaTiO 3 ceramic doped with cobalt and calcium (BTCaCo), processed by a conventional technique with a reduced sintering temperature, is characterized. Particular attention is paid to the delivery of complete and accurate set of elastic, dielectric, and piezoelectric constants. These databases are relatively rare in the literature but are essential for numerical simulations of new devices, integrating these materials. The processed piezoelectric material exhibits an electromechanical thickness coupling factor (k t) of 45% and a relative dielectric constant of 1180, at constant strain. A 1-3 piezo-composite is successfully fabricated to improve the performance (k t =47%). Finally, BTCaCo disc is used to fabricate a transducer with a center frequency at 4.3 MHz, showing competitive performance compared to a standard PZT-based transducer

Numerical and experimental investigations of piezoelectric energy harvesters

International audienceIn order to supply low consumption electronic devices, wasted mechanical energy available in ourenvironment can be converted into useful electrical energy by piezoelectric harvesters. The two commonstructures used for vibration energy harvesting are a cantilever-based unimorph or bimorph. The unimorph isconstituted of one PZT layer bonded on an elastic one, and the bimorph is made of two PZT layers separatedwith an inner elastic shim material. Further deepening the comprehension of these mechanical energyharvesters will facilitate their design. Moreover, it is commonly known that material properties ofpiezoelectric thin films differ from bulk ones [1]. This can be a significant source of error for the devicesimulation, using analytical models or finite element (FE) models. Numerical models are powerful tools andrequire an accurate set of material properties of the PZT layer. For this purpose, an original method has beenintroduced [2], requiring only the electrical impedance measurement of the PZT layer in free-free mechanicalboundary conditions: the effective values of the electrical, mechanical and piezoelectric tensors are identifiedusing successively a one-dimensional analytical model and a three-dimensional (3D) FE model of theelectrical impedance. The pursued goal is to build a 3D FE model for the design of our harvesters.Firstly, the set of electromechanical properties of the PZT layer, taking into account mechanical anddielectric losses, is identified thanks to an original method [2], based solely on the electrical impedancecharacterization in free-free boundary conditions. But since the PZT layer is bonded on the elastic shimmaterial, and the final devices are clamped at one end, the influence of the modification of the mechanicalboundary conditions has to be determined. For this purpose, a 14μm thick layer of brass has been bondedonto a 150μm thick of PZT to form a 164μm thick unimorph structure. In the same way, another PZT layerhas been added to the unimorph structure to constitute a 314μm thick bimorph structure. For each structure, anumerical study based on the FE method has been carried out. In particular, a frequency domain study hasbeen performed on a 3D FE model in clamped-free mechanical boundary conditions to calculate theelectrical response of the considered sample in the frequency range of 60Hz-145Hz. The electricalimpedance of the sample has been measured on the same frequency range using an impedance analyzer(HIOKI IM3570, Koizumi, Ueda, Nagano, Japan) and compared to the numerical results.The electrical impedance of the samples has been computed and compared with the experiment. Thediscrepancy between modelling and experimental results is less than 4% in frequency and 16% in impedancemagnitude. This demonstrates the accuracy of our model to predict the electrical behavior of piezoelectriccantilevers in clamped-free mechanical boundary conditions. The next step of this work is to model thevibrational behavior of our clamped devices and estimate their electrical output performances (generatedvoltage, current and power as a function of the resistive load) when the clamped end of the harvester issubmitted to a vibration, with the purpose of mechanical energy harvesting

Modeling and Electrical Characterization of a Cantilever Beam for Mechanical Energy Harvesting

International audienc

Numerical and experimental study of thinned-bulk piezoelectric harvesters

International audienceBulk piezoelectric cantilever beams are mostly assembled under serial bimorph topologies where the piezoelectric material is laminated around an inner shim material. The two PZT layers exhibit an individual thickness ranging from few tens to hundreds of micrometers according to the targeted application and its miniaturization requests. Designing such devices becomes a challenge and one needs FEM (finite element model) to properly define material thicknesses and overall piezoelectric energy harvester geometries. Unfortunately, bulk piezoelectric material are characterized using thicker samples which provide results slightly different from the actual characteristics of thinned-bulk piezoelectric materials. Previous works have addressed an approach to study the thin piezoelectric material layer relying on the electrical admittance analysis. Then, the effective coefficients of thinned-bulk piezoelectric material are identified and entered in a 3D FEM of the PZT layer. The electrical admittance is calculated, showing a good agreement with the experimental measurements