Two-dimensional equations for coupled extensional, flexural and thickness-shear motions of laminated plates of piezoelectric semiconductors are obtained systematically from the three-dimensional equations by retaining lower order terms in power series expansions in the plate thickness coordinate. The equations are used to analyze extensional waves in a composite plate of piezoelectric ceramics and semiconductors. Dispersion and dissipation due to semiconduction as well as wave amplification by a dc electric field are discussed.
IntroductionPiezoelectric materials can be either dielectrics or semiconductors [1]. An acoustic wave propagating in a piezoelectric crystal is usually accompanied by an electric field. When the crystal is also semiconducting, the field produces currents and space charge resulting in dispersion and acoustic loss [2]. The interaction between a traveling acoustic wave and mobile charges in piezoelectric semiconductors is called the acoustoelectric effect which is a special case of a more general phenomenon which may be called wave-particle drag [3]. It was also found that an acoustic wave traveling in a piezoelectric semiconductor can be amplified by application of a dc electric field [4]. Acoustoelectric effect and acoustoelectric amplification of acoustic waves have led to the development of acoustoelectric devices [5][6][7][8]. The basic behavior of piezoelectric semiconductors and acoustoelectric effect can be described by a linear phenomenological theory [2, 4]. More sophisticated nonlinear theories for deformable semiconductors have also been developed [9, 10]. Acoustoelectric effect can also be produced in composites of piezoelectric insulators and nonpiezoelectric semiconductors [8]. In these composites the acoustoelectric effect is due to the combination of the piezoelectric effect and semiconduction in each component phase of the composite. Laminated plates of piezoelectric insulators and nonpiezoelectric semiconductors can be used to produce acoustoelectric effect for device applications. Due to anisotropy and field coupling, modeling of plate piezoelectric devices, single and/or multi-layered, is usually very challenging. Exact analysis from threedimensional equations is possible in idealized special cases. Two-dimensional structural theories for thin piezoelectric insulator plates have been developed [11][12][13] and proved very effective in real device modeling as discussed by Wang and Yang [14]. In this paper we study motions of thin plates of laminated piezoelectric semiconductors. The three-dimensional equations of linear piezoelectric semiconductors are summarized in Sect. 2. Two-dimensional equations for laminated plates are derived systematically from the three-dimensional equations in Sect. 3 and are truncated to a first-order theory for coupled extension, flexure and thicknessshear in Sect. 4. Propagation of extensional waves under a dc field is analyzed in Sect. 5. Finally, some conclusions are drawn in Sect. 6.