Propagation Of Elastic Waves In Piezoelectric Semiconductor Layered Structures

Piezoelectric semiconductor(PSC)is a kind of functional materials that with multifield coupling effect among mechanics,electricity and carrier.Due to the simultaneous possessions of piezoelectricity and semiconductor properties,the PSC materials can be used as sensors,transistors,resonators as well as other PSC devices.The functional development and performance optimization of these applications call for an in-depth understanding of the dynamic behaviors of PSC composites,especially the propagation characteristics of the elastic waves in the PSC structures.PSC layered structures are the basic configurations for all kinds of PSC devices.The interaction between piezoelectric and semiconductor fields has obvious effects on the propagation characteristics of elastic waves in the PSC layered strutures.Thus,several basic problems for wave propagation in layered PSC strucutres are investigated in this dissertation,which could be very helpful as theoretical guidance for the application of PSC devices.The main contents and achievements are as follows:1.Based on the multi-field coupling effect of mechanical-electric-carrier,the propagation characteristics of elastic waves in the anistropic PSC plate are investigated.For achieve our goals,we first introduce the new extended notations to express the basic equations.Then the extended displacements and stresses are obtained by using the extended Stroh formalism.Finally,making use of the boundary conditions on the top and bottom surfaces of the plate,wave dispersion and attenuation equations are derived analytically.Numerical examples are presented to systematically study the effects of the surface boundary conditions,plate thickness,initial carrier density and biasing electric field on the wave speed and attenuation of both SH and Lamb waves in the transversely isotropic PSC plate.Numerical results show that the propagation characteristics of the normalized elastic waves in the PSC plate depend on the plate thickness.Wave amplification can be achieved relatively easily by applying a horizontal baising electric field,as compared to that by applying a vertical biasing electric field.Initial carrier density,plate thickness and biasing electric field are the key parameters which should be considered when designing a PSC device.2.The dispersion and attenuation characteristics of Love waves in the PSC thin film/elastic dielectric half-space are studied by considering the semiconductor coupling.And the effects of semiconductor characteristics,boundary conditions,thin film thickness and biasing electric field on the propagation characteristics of Love waves in the PSC thin film/elastic dielectric half-space are examined.Numerical results show that the semiconductor coupling reduces the wave speed.The Love waves can propagate with a wave speed that larger than the shear wave speed of the elastic dieletric half-space.At the critical horizontal biasing electric field,the wave speed and attenuation obtain minimum and 0,respectively.3.The propagation characteristics of Rayeligh waves in a layered structure which is composed of a PSC thin film and an elastic dielectric half-space are investigated.The analytical solutions of dispersion equation are obtained.Numerical examples first show the effect of semiconductor characteristics on the dispersion and attenuation curves,and then present the effects of initial carrier density,thin film thickness,and biasing electric field on the maximum speed of 2nd wave mode and the interaction of the first two modes.Numerical results show that the maximum wave speed of 2nd mode and the interaction between the 1st and 2nd modes are closely related with the initial carrier density,thin film thickness and biasing electric field.The semiconductor coupling reduces the wave speed of Rayleigh waves,and the 2nd dispersion curve could be discontinuous due to the zero imaginary wave speed.4.The dispersion and attenuation characteristics of SH waves in multilayered PSC plates with imperfect interfaces are investigated by using the extended Stroh formalism and the DVP(Dual variable and position)method.The effect of semiconductor coupling on the single-layer PSC plate,and the effects of stacking sequences and imperfect interfaces on the sandwich plates are studied in detail.Numerical results show that the first three modes of SH waves can propagate in the entire frequency domain without cutoff frequency.Introducing a mechanical imperfect interface would increase the real part of the wavenumber and decrease the imaginary part of wavenumber for the 1st and 2nd modes.When the interface flexibility is relatively large,the dispersion and attenuation curves no longer change significantly with the change of interface flexibility at high frequency.5.The propagation characteristics of Lamb waves in the PSC mutilayered plates with imperfect interfaces are investigated,and the impacts of semiconductor coupling on the dispersion and attenuation of PSC single-layer plate,and the stacking sequences and imperfect interfaces on the transversely isotropic PSC sandwich plates are examined.Numerical results indicate that the first three modes of Lamb waves can propagate in the entire frequency domain.The real part of the wavenumber for the first two modes increase with the interface flexibility of mechanical imperfect interface.The normal flexibility(the displacement is dicontinous along the thickness direction)almost has no influence on the wavenumber at low frequencies for the first two modes.