M.Sc Thesis


M.Sc StudentBenita Shir
SubjectSurface Waves in Piezoelectric Structures for Actuators
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. David Elata


Abstract

This research considers Lamb waves in piezoelectric single crystalline layers. There are two types of Lamb waves: extensional waves and flexural waves, which are also known as symmetric and antisymmetric waves, respectively.  For an application of a surface acoustic waves (SAW) micromotor, we aim to use Lamb waves as surface waves to generate motion in a fastener that is in contact with the upper and bottom surfaces of the layer.

We show that for each one of the two types of Lamb waves, there are two varieties of waves: a prograde wave and a retrograde wave. In a prograde wave, material points at the top of the wave move in the same direction as of the wave propagation, and in a retrograde wave material points at the top of the wave move in a direction that is opposite to that of the wave propagation. In this research we seek to find a wave length in which we can excite both a prograde and a retrograde wave, using the same set of inter-digitated electrodes (IDEs). Trivially, this means that each of the two waves is excited at a different frequency, and this should allow to drive the fastener in one of the two opposite axial directions by simply switching between two distinct driving frequencies. We discuss two main parameters that affect the behavior of the wave, orbitality of motion of material particles that are on the structure surface, and maximum displacement at the surface of the wave.

In this research we examined two different materials, Quartz and Lithium Niobate. We considered those materials in different structures, as only one piezoelectric layer or with a layer of single crystalline silicon (SCS). In this work we presented prograde and retrograde waves in different configurations, and compare the qualities of the surface waves for the different configurations. In our investigation, we also perform harmonic sweep simulations that provide additional information about the waves, such as their amplitudes and the power they consume, for a given level of driving voltage. We use these simulations to demonstrate the effect of a silicon inter-layer on the strength of the waves.