Shear-horizontal piezoelectric waves in an aluminum nitride film on a silicon substrate

The propagation of shear-horizontal waves in a piezoelectric film of aluminum nitride on a silicon substrate is studied. Three different electrode configurations are considered for thin film acoustic wave resonator application. A theoretical analysis is performed. The equations of linear piezoelectricity and anisotropic elasticity are used for the film and the substrate, respectively. Real and imaginary dispersion curves as well as electromechanical mode shapes are obtained. The effects of electrode configuration on the distribution of the electromechanical fields and the dispersion curves of long thickness-twist waves as well as energy trapping are examined.     

Effective properties of composites with embedded piezoelectric fibres

The present work deals with the modelling of 1–3 and 0–3 composites made of piezoceramic fibres embedded in a soft non-piezoelectric matrix. We especially focus on the longitudinal and transversal effective piezoelectric constants as a function of several micromechanical parameters such as the fibre volume fraction or the aspect ratio. Finite-element results, based on the concept of a cell model, are compared with results of analytical approaches. This study is restricted to linear piezoelectricity and quasistatic cases.     

Influence of water-cement ratio on the properties of 2-2 cement based piezoelectric composite

Composites with 2-2 connectivity were fabricated from plates of “PMN” ceramic embedded in a sulphoaluminate cement matrix by a cut-filling process. The influences of the water-cement ratio in the matrix on the properties of the composite were analyzed. The results show that when the water-cement ratio is less than 0.4, the piezoelectric stain factor d₃₃ and piezoelectric voltage factor g₃₃ increase smoothly. When the water-cement ratio is larger than 0.4, d₃₃ and g₃₃ increase obviously with increasing the water-cement ratio. This is attributed to a more effective contact between the active and matrix phases. d₃₃ = 322 pc N^− 1 and g₃₃ = 20.9 mV mN^− 1 at a water-cement ratio of 0.45. The planar electromechanical coupling coefficient K_p of the composite is nearly independent of the water-cement ratio. With increasing the water-cement ratio, the thickness electromechanical coupling coefficient K_t of the composite increases, while the mechanical quality factor Q_m exhibits the trend of decrease.     

A system for powder transport based on piezoelectrically excited ultrasonic progressive waves

The transport and dosage of granular materials are an important part of Process Engineering. Thereby, the food, chemical, pharmaceutical and coating industries set high demands on the transport and dosage performances of the used plants. In this context, Ultrasound Process Technology in the past years has developed itself into an attractive alternative compared to presently used classical technologies.

This paper describes the application of ultrasonic progressive waves in a powder-feeding device. The use of a specific pipe material with appropriate damping characteristics allows to generate a progressive wave using a single piezoelectric actuator. Small objects can be carried along the surface of a pipe by the elliptic motion at the surface, which is the result of a flexural progressive wave. The operational principle is the same as in travelling wave ultrasonic motors.

It was experimentally confirmed that the device can be used for feeding and supplying small amounts of powder. The powder-fed performance, however, strongly depends on environmental conditions, so that a control of the system is required. Construction and characteristics of a trial device are shown.     

Investigation of nano particle additives on lithium doped KNN lead free piezoelectric ceramics

Lead free potassium sodium niobate modified piezoelectric ceramics were synthesized through conventional mixed oxide method. Crystal structure and microstructure were analyzed by X-ray diffraction and scanning electron microscopy (SEM). The effects of nano ZnO, CuO and SnO₂ additives as the nano scale sintering aids, on microstructure and electrical properties of (K₀₅₀Na_0.50)_0.94Li_0.06NbO₃ (KNNL-6) ceramics were investigated. The optimum dielectric and piezoelectric properties of ?_r = 560, d₃₃ = 215 pC/N and tan δ = 0.008 were obtained for pure KNNL-6 that sintered at 1000 °C for 2 h. The results show that with addition of nano particle sintering aids, the piezoelectric coefficient d₃₃ of (K₀₅₀Na_0.50)_0.94Li_0.06NbO₃ ceramics was decreased. The decrease in piezoelectric charge coefficient could be due to the hardening effect, which lowers the piezoelectric charge.     

Effect of An Initial Stress on SH-Type GuidedWaves Propagating in a Piezoelectric Layer Bonded on A Piezomagnetic Substrate

Propagation of SH-type guided waves in a layered structure with an invariant initial stress is studied, where a piezoelectric thin layer is perfectly bonded on a piezomagnetic substrate. Both the layer and the substrate possess transversely isotropic property. The dispersion relations of SH waves are obtained for four kinds of different electro-magnetic boundary conditions. The effects of initial stress, thickness ratio and electro-magnetic boundary conditions on the propagation behaviors are analyzed in detail. The numerical results show that: 1) The positive initial stresses make the phase velocity increasing, while the negative initial stresses decrease the phase velocity; 2) The smaller the thickness ratio of a piezoelectric layer to a piezomagnetic substrate, the larger the phase velocity of SH-type guided wave propagating in the corresponding layered structure; 3) The electrical boundary conditions play a dominant role in the propagating characteristics. Moreover the phase velocities for the electrically shorted surface are smaller than that for the open case. The obtained results are useful for understanding and design of the electromagnetic acoustic wave and microwave devices.     

Meshless Local Petrov-Galerkin Method for Plane Piezoelectricity

Piezoelectric materials have wide range engineering applications in smart structures and devices. They have usually anisotropic properties. Except this complication electric and mechanical fields are coupled each other and the governing equations are much more complex than that in the classical elasticity. Thus, efficient computational methods to solve the boundary or the initial-boundary value problems for piezoelectric solids are required. In this paper, the Meshless local Petrov-Galerkin (MLPG) method with a Heaviside step function as the test functions is applied to solve two-dimensional (2-D) piezoelectric problems. The mechanical fields are described by the equations of motion with an inertial term. To eliminate the time-dependence in the governing partial differential equations the Laplace-transform technique is applied to the governing equations, which are satisfied in the Laplace-transformed domain in a weak-form on small subdomains. Nodal points are spread on the analyzed domain and each node is surrounded by a small circle for simplicity. The spatial variation of the displacements and the electric potential are approximated by the Moving Least-Squares (MLS) scheme. After performing the spatial integrations, one obtains a system of linear algebraic equations for unknown nodal values. The boundary conditions on the global boundary are satisfied by the collocation of the MLS-approximation expressions for the displacements and the electric potential at the boundary nodal points. The Stehfest's inversion method is applied to obtain the final time-dependent solutions.     

A piezoelectric screw dislocation in a three-phase composite cylinder model with an imperfect interface

The electroelastic coupling interaction between a piezoelectric screw dislocation and the embedded circular cross-section inclusions with imperfect interfaces in piezoelectric solids is investigated by using a three-phase composite cylinder model. By means of a complex variable technique, the explicit solutions of electroelastic fields are obtained. With the aid of the Peach-Koehler formula, the explicit expression for the image force exerted on the piezoelectric screw dislocation is derived. The image force on the dislocation and its equilibrium positions near one of the inclusions are discussed for variable parameters (interface imperfection and material electroelastic dissimilarity) and the influence of nearby inclusions is also considered. The results show that when compared with the previous solution (the perfect interface), more equilibrium positions of the screw dislocation in the matrix may be available due to the effect of the interface imperfection when the dislocation is close to the electroelastic stiff inclusion. It is also found that the magnitude of the image force exerted on the piezoelectric screw dislocation produced by multiply inclusions is always smaller than that produced by a single inclusion and the impact of nearby inclusions on the mobility of the screw dislocation is very important.     

Piezoelectric indentation of a flat circular punch accompanied by frictional sliding and applications to scanning probe microscopy

Indentation of a piezoelectric half-space by a flat circular indenter accompanied by frictional sliding is considered. Full-field electroelastic solutions in elementary functions are obtained. The solution is based on the correspondence principle between elastic and piezoelectric problems. Stiffness relations between applied load and resulting displacement are given in elementary functions. In conjunction with the conical and spherical solutions, given previously by Makagon et al. [A. Makagon, M. Kachanov, S.V. Kalinin, E. Karapetian, Indentation and frictional sliding of spherical and conical punches into piezoelectric half-space, Physical Review B 76 (2007) 064115 (14)], this work completes the set of limiting cases of tip geometries utilized in lateral force microscopy (LFM) technology. Implications for quantitative interpretation of scanning probe microscopy (SPM) data and tribological data are analyzed.