压电晶体表面高速声学模式

Wide applications in UHF SAW devices has led to seek high velocity modes on the surface of a piezoelectric crystal. The so found high velocity surface acoustic mode was suggested to be the high velocity pseudo -SAW(HVPSAW) or the longitudinal leaky surface wave which has high propagation velocity close to the longitudinal bulk wave velocity and which exhibits the Δv/v effect, i.e. it possesses different velocities on the free and the metallized crystal surface. Earlier we have developed a transient surface excitation theory of the acoustical waves in a piezoelectric crystal. In the theory, acoustic head waves were predicted of which one wave can have a velocity as high as the group velocity of a longitudinal bulk wave along the crystal surface. We shall call this head wave the "surface high velocity head wave"(SHVHW). This wave does not exhibit any Δv/v effect. This project focuse on the fundamental excitation and propagation problem on half-space of piezoelectric crystal and the nature of the high velocity surface acoustics mode, the theretical and experimental investigation is performed , and important results were obtained. First of all, the criterion for surface wave is given. The general SAW and Pseudo SAW exactly satisfies the boundary condition, and their propagation velocity is different on free and metalized surface. But the high velocity surface acoustic mode does not satisfy the boundary condition, there isn't the so call high velocity Pseodo SAW or longitudianl leaky SAW, so it isn't a surface wave mode.This project give the stationary Green fuction analyse of the Pseudo SAW and the head wave. The results of theoretical and numerical shown that the first arrival wave mode is the longitudianl head wave, we call it that the high velocity head wave, its progation velocity is equal to the group velocity of the longitudinal bulk wave alone the surface no matter the surface is free or metalized, i.e., it does not have theΔv/v effect. The experimental investigation and numerical calculation is performed on some commonly used single crystals. The results are in favor that surface high velocity mode is a SHVHW instead of a HVPSAW. In addition, duo to the Green function of Pseudo SAW and longitudinal head wave is presented by this project, the theory of generalized Green function for surface excitation on piezoelectric half-space become more systematic.

压电晶体表面高速声学模式研究，无论在理论上或者实用上都是一个国际前沿课题。我们将从所建立的压电晶体表面激发理论出发，分析和判定表面高速声学模式是表面纵波头波，或者高速伪表面波：并进而给出它的特性。实验上将采用一些常用晶体，进而比较和验证。此项研究在理论上将澄清声表面波一些带根本性问题，而在实用上将推动超高频器件的发埂?..