Importance of Three-Dimensional Piezoelectric Coupling Modeling in Quantitative Analysis of Piezoelectric Actuators

This paper demonstrates the importance of three-dimensional(3-D)piezoelectric coupling in the electromechanical behavior of piezoelectric devices using three-dimensional finite element analyses based on weak and strong coupling models for a thin cantilevered piezoelectric bimorph actuator.It is found that there is a significant difference between the strong and weak coupling solutions given by coupling direct and inverse piezoelectric effects(i.e.,piezoelectric coupling effect).In addition,there is significant longitudinal bending caused by the constraint of the inverse piezoelectric effect in the width direction at the fixed end(i.e.,3-D effect).Hence,modeling of these effects or 3-D piezoelectric coupling modeling is an electromechanical basis for the piezoelectric devices,which contributes to the accurate prediction of their behavior.

A novel type of transverse surface wave propagating in a layered structure consisting of a piezoelectric layer attached to an elastic half-space

The existence and propagation of transverse surface waves in piezoelectric coupled solids is investigated, in which perfect bonding between a metal/dielectric substrate and a piezoelectric layer of finite-thickness is assumed. Dis- persion equations relating phase velocity to material con- stants for the existence of various modes are obtained in a simple mathematical form for a piezoelectric material of class 6mm. It is discovered and proved by numerical examples in this paper that a novel Bleustein-Gulyaev （B-G） type of transverse surface wave can exist in such piezoelectric cou- pled solid media when the bulk-shear-wave velocity in the substrate is less than that in the piezoelectric layer but greater than the corresponding B-G wave velocity in the same pie- zoelectric material with an electroded surface. Such a wave does not exist in such layered structures in the absence of pie- zoelectricity. The mode shapes for displacement and electric potential in the piezoelectric layer are obtained and discussed theoretically. The study extends the regime of transverse sur- face waves and may lead to potential applications to surface acoustic wave devices.

Nonlinearity analysis of piezoelectric micromachined ultrasonic transducers based on couple stress theory

This paper studies the static deformation behavior of a piezoelectric micromachined ultrasonic transducer （PMUT） actuated by a strong external electric field. The transducer membrane consists of a piezoelectric layer, a passive layer and two electrode layers. The nonlinearities of the piezoelectric layer caused by electrostriction under a strong electric field are analyzed. Because the thickness of the transducer membrane is on the microscale, the size dependence of the deformation behavior is evaluated using the couple stress theory. The results show that the optimal ratio of the top electrode diameter and the membrane diameter is around 0.674. It is also found that this optimal value does not depend on any other parameters if the thicknesses of the two electrodes are negligible compared with those of the piezo- electric and passive layers. In addition, the nonlinearities of the piezoelectric layer will become stronger along with the increase of the electric field, which means that softening of the membrane stiffness occurs when a strong external electric field is applied. Meanwhile, the optimal thickness ratio for the passive layer and the piezoelectric layer is not equal to 1.0 which is usually adopted by previous researchers. Because there exists size dependence of membrane deforma-tion, the optimal value of this thickness ratio needs to be greater than 1.0 on the microscale.

A GENERAL SOLUTION AND THE APPLICATION OF SPACE AXISYMMETRIC PROBLEM IN PIEZOELECTRIC MATERIAL

According to the structure feature of the governing equations of spaceaxisymmetric problem in transversely, isotropic piezoelectric material. using the methodof introducing potential .function one by. one, in this paper we obtain the so-calledgeneral solution of displacement and eleclric potential function denoied by uniquepoiential.function which satisfies specific partiality equations. As an applying exampleof the general solution, we solve problem of semi-infinile boodt. made of piezoelectricmaterial, on the surface of the semi-infinite body a concentrative .force is applied, andget the analytic .formulations of stress and electric displacement comiponenis. Thegeneral solution provided by this paper can be used as a tool to analyse the mechanical-electrical coupling behavior of piezoelecrtic material which conlains defects such ascavity inclusion. penny-shape crack. and so on. The result of the solved problem canbe used directly to analyse contact problems which take place between twopiezoelectric bodies or piezoelectric body. and elastic body .

Interaction of a Surface Acoustic Wave with a Two-dimensional Electron Gas

When a surface acoustic wave （SAW） propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coemcient is ~alculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is strongly dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.

Lateral-field-excitation properties of LiNbO_3 single crystal

LiNbO3 has been found attractive for lateral field excitation （LFE） applications due to its high piezoelectric coupling. In this paper, bulk acoustic wave propagation properties for LiNbO3 single crystal excited by a lateral electric field have been investigated using the extended Christoffel Bechmann method. It is found that the LFE piezoelectric coupling factor for c mode reaches its maximum value of 95.46% when ψ = 0° for both （yxl）-58° and （yxwl）±60°/58° LiNbO3. The acoustic wave phase velocity of c mode TSM （thickness shear mode） changes from 3456 m/s to 3983 m/s as a function of ψ. Here ψ represents the angle between the lateral electric field and the crystallographic X-axis in the substrate major surface. A 5 MHz LFE device of （yxl）-58° LiNbO3 with ψ = 0° was designed and tested in air. A major resonance peak was observed with the motional resistance as low as 17 Ω and the Q-factor value up to 10353. The test result is well in agreement with the theoretical analysis, and suggests that the LFE LiNbO3 device can be a good platform for high performance resonator or sensor applications.