Elastic parameters characterization of multilayered structures by air-coupled ultrasonic transmission and genetic algorithm.

This paper describes a non-contact method to characterize isotropic and anisotropic planar multilayer structures using a genetic algorithm. The method is based on the determination of critical angles, where the maxima of the modulus of transmission coefficient of the structure appear, and which correspond to the generation of guided waves. The optimization process minimizes the error between the reference critical angles and associated amplitudes of the transmission coefficient, with the corresponding estimated ones. The estimation of elastic parameters is demonstrated for acrylic and oak plates as well as for a bi-layered structure composed of oak and a thin layer of gesso. It is shown that to obtain satisfactory optimization results, it is necessary for guided modes of higher order than the zero ones to be taken into account. Results also show that some elastic constants such as C33 and C55 retrieved from the transmission coefficient are very sensitive to the optimization.

Modeling of the Electromechanical Behavior of Barium Titanate Under Mechanical Stress and Comparison With Experimental Measurements.

Barium titanate (BaTiO3) is increasingly studied to replace lead-based piezoelectric materials, such as those which belong to the lead zirconate titanate (PZT) family, due to lead toxicity. In many applications, such as Tonpilz transducers, piezoelectric materials undergo mechanical stress simulation of which is important to control and predict electroacoustic effects. Thus, this article deals with a fully tensorial model that allows to simulate the behaviors of electrical displacements and elastic strains under mechanical stress. Simulated curves are compared with experimental ones obtained for BaTiO3 samples. It can be verified that the hysteretic curves of strains are well predicted for unpoled samples as well as for poled ones. The order of values and global behavior of the theoretical electrical displacement are also verified, even if a less precise agreement is observed. The optimized values of the physical parameters, such as d33 , are discussed, and improvements both of the model and the optimization procedure are finally proposed in order to better predict the mechanical behavior of BaTiO3.

Electromechanical Behavior of a Doped Barium Titanate Piezoceramic Under Mechanical Stress: Modeling and Comparison With Experimental Measurements.

Barium titanate (BaTiO3) is being studied extensively to replace lead-based piezoelectric materials, such as the lead zirconate titanate (PZT) family, due to lead toxicity. As a result, researchers are turning to materials such as BaTiO3 and seek to improve their properties with the use of dopants. In many applications such as Tonpilz transducers, piezoelectric materials undergo mechanical stress which is important to control and predict their electro-acoustic performance. Thus, this study deals with a fully tensorial model that allows us to simulate the behaviors of electrical displacements and elastic strains under mechanical stress. The simulated curves are compared with the experimental ones obtained for a doped BaTiO3 composition and the hysteretic curves of strains are in good agreement both for the unpoled and poled samples. The values and global behavior of the theoretical electrical displacement are also found to be in fair agreement, though some discrepancies are observed. The optimized values of the physical parameters, such as d33 , are discussed and improvements both of the model and the optimization procedure are finally proposed to better predict the mechanical behavior of the doped BaTiO3 piezoceramics.

Internal Electric Field in Co-Doped BaTiO3 With Co2+/3+, Nb5+, Li+, and F-: Impact on Functional Properties and Charge Compensation With Niobium and Fluorine Ions.

Dense barium titanate (BaTiO3) ceramics ( [Formula: see text]) with a microscale grain size are obtained at 800 °C-1100 °C by a solid-state ceramic process. BaTiO3 (BT) doped with Co2+/3+ leads to a significant improvement in the properties ( pC/N). Soft and hard characteristics of the piezoceramics are observed depending on the dopant ions. The Co/Li acceptor dopants lead to hard piezoceramics and aging phenomena. Aged BT:Co, Li exhibits double loops and a distorted hysteresis cycle for nonpoled and poled ceramics, respectively. Ceramics poled by the increasing field process at room temperature and the field cooling process present different poled and aged states, which are dependent on the thermal history and poling process. The distorted hysteresis loops for BT:Co, Li indicate an increased internal bias field with aging time. Insertion of donor dopants, such as Nb5+ ions, significantly reduces the internal field. These behaviors are related to the presence of defect dipoles ( [Formula: see text]"- [Formula: see text] due to the insertion of acceptor dopants in the B-sites following the oxygen vacancies to equilibrate charge compensation. BT:Co sintered with LiF leads to a quasi-symmetric hysteresis loop, indicating that F- may insert into an oxygen site and counteract the formation of oxygen vacancies. Dielectric drift of BT:Co, Li shows resilience to an ac electric field, which is related to the increased internal field. BT doped with 0.75 mol% Co2+/3+ and 1 mol% Li2CO3 presents hard piezoelectric behavior with a Rayleigh coefficient α = 2.53 10-7 m/V and the capability to handle high electrical stress of up to 400 [Formula: see text]/mm.