PSEUDO AND HIGH VELOCITY PSEUDO SAWs

Abstract

This article discusses the characteristics of pseudo surface waves (PS AWs) and high velocity pseudo surface waves (HVPSAWs). The fundamental properties of these waves, the matrix method formulation, the different solution types due to crystal symmetry, early experiments on HVPSAWs, and practical applications of pseudo surface acoustic waves serve as an introduction. The solutions to the pseudo modes are discussed by analyzing the boundary condition function for several orientations. The relation between the radiating partial modes and the sagittal plane bulk slowness reveals new characteristics of the different symmetry types of H VPS AW, and helps classify and understand the pseudo modes. The acoustoelectric Poynting vector is used along different crystal symmetry orientations to reveal and discuss the pseudo SAW characteristics: penetration depth, declination of the power vector, and an estimation of power flow angle. Experimental data and numerical solutions of HVPS AW and PS AW along selected planes and orientations are discussed. This article concludes with a brief analysis of layered structures on different symmetry type substrates and a discussion of the layered pseudo surface wave properties. 203 Int. J. Hi. Spe. Ele. Syst. 2000.10:1069-1109. Downloaded from www.worldscientific.com by UNIVERSITY OF ILLINOIS AT URBANA CHAMPAIGN on 03/11/15. For personal use only.204 Int. J. Hi. Spe. Ele. Syst. 2000.10:1069-1109. Downloaded from www.worldscientific.com by UNIVERSITY OF ILLINOIS AT URBANA CHAMPAIGN on 03/11/15. For personal use only. Early Experiments on HVPSA WLike the PSAW, the experimental evidence for the HVPSAW goes back over two decades. Some of the early experiments that detected the HVPSAW classified this wave as: "longitudinal bulk wave," "surface skimming bulk wave," "shallow bulk acoustic wave," or "quasi-bulk acoustic surface wave"; mostly due to the proximity of the phase velocity to the planar longitudinal bulk wave velocity in the direction of propagation. 5 ' 6 ' 7 ' 8 ' 910 The name "surface skimming bulk wave" has also been used for both PSAW and HVPSAW in early publications. 6 ' 11 Since a bulk acoustic wave, BAW, in a piezoelectric material does not satisfy the mechanically free boundary conditions, the mode experimentally identified could not be a BAW .The existence of an independent high-velocity pseudo SAW mode was identified by researchers from Brillouin scattering experiments on cubic materials. 12 Jhunjhunwala also discussed the pseudo SAWs, grouping them as first or second order pseudo SAWs, according to the number of radiating partial modes. 13 As mentioned in 1.2, the HVPSAW might have one or two radiating partial modes, depending on the symmetry of the orientation of propagation. Therefore a classification according to the number of radiating partial modes is not appropriate. Reference 12 estimates the HVPSAW to have high loss for the gallium arsenide, GaAs, orientations discussed in that paper. This is not the case for other materials and orientations as discussed in this pape...