Investigation Of Elastic Waves Propagation Properties In Piezoelectric Composite Structures And Applications For Acoustic Wave Devices With High Performance

It is well known that surface acoustic wave devices,thin film bulk acoustic resonators,piezoelectric transformers,quartz crystal microbalances and mass sensors have been widely used in many regions including acoustics,nondestructive testing,aerospace,electronic communications,medical appliances,active control and so on.In this dissertation,some kinds of imperfections,for example,weak interface,functional graded materials and inhomogeneous thickness,which are usually encountered in practical applications,are discussed from the point of view of theoretical analysis and numerical simulation by using basic kinetic equations and MATLAB software.Firstly,four cases of typical problems on imperfect interface are preceded.They are respectively the B-G waves propagating in piezoelectric composites with a weak interface,influence of imperfection of electrical boundary conditions on thickness twist waves,the visco-elastic imperfect interface existing in piezoelectric devices under electrical excitation and the new thickness twist or thickness shear wave excited by imperfect interface.We have added electrical parameter or damping coefficient of imperfect interface based on the classical shear-lag model when dealing with different problems.Theoretical analysis and numerical results show that the imperfect interface has a great effect on the performance of devices.For instance,the phase velocity and existing condition of B-G waves can be changed when an upper film imperfectly bonded on a piezoelectric substrate,and the effect of mechanical imperfection is more evident than that of electrical imperfection on thickness twist modes.The flexibility of the interface is related to resonances of piezoelectric devices,and hence affects some performance index,such as output displacement signal or transform ratio,input admittance and power density.Meanwhile,the visco-elastic parameter of weak interface has a significant influence on energy transform efficiency.Besides,a new kind of thickness twist or thickness shear wave induced by imperfect interface has been exposed by using of perturbation method and Mindlin equations,which is totally different from the case of perfect interface.Following,B-G waves in a functionally graded transversely isotropic electro-magneto-elastic half-space and thickness twist waves in a functional graded piezoelectric plate with its material coefficients varying along the length direction are respectively investigated based on plane wave expansion method and power series technique.The heterogeneity of material changes the properties of some waves in essence.For example,the B-G waves are dispersive when all material parameters in the functionally graded electro-magneto-elastic substrate possess the same exponential function variation pattern along thickness direction,which is different from a pure substrate.If piezoelectric damage makes the material parameters change along the length direction,the amplitude of thickness twist waves will focus on some region of the plate and energy trapping takes place,which can not be observed for perfect materials.Finally,the energy trapping phenomenon has been achieved by changing the usual resonator into a hyperbolic contour or alternating the thickness of additional mass layer properly in a quartz crystal microbalance.During the analysis,a two-dimensional approximate equation obtained by Professor Harry F Tiersten and Fourier series are applied respectively.It is shown that the resonance frequencies are mainly controlled by the inertial effect of additional mass layer,and the vibration is focus on the area with a thicker layer.The mass layer,which has thinner thickness at the edge than the center,will be benefit for energy trapping and the mounting of resonators.Totally,the influence of imperfect interface,functional graded materials and inhomogeneous thickness has been revealed from the point of view of physics and mechanics,which can be used to provide the foundation for the analysis and design of electronic devices and new experimental procedures in the near further.