Harmonic response of normal and rare interdigitai surface-acoustic-wave transducers with arbitrary metallisation ratios

Surface-acoustic-wave (s.a.w.) energy, radiated by short normal and rare interdigitai transducers (i.d.t.s) with arbitrary metallisation ratios, is obtained in a novel manner that has an intimate contact with the physical situation. The basic assumption used is that the static mechanical energy generated is k2 times the applied electrostatic energy in a piezoelectric insulator, where k is the appropriate electromechanical coupling factor. By comparison with other models, it is shown that k2 thus defined is equal to 2 {(vo ¿¿ vM)/v0}, where vo and vm are s.a.w. velocities on, respectively, free and metallised surfaces of the piezoelectric in the concerned direction, and that the electric field components, both normal and parallel to the direction of wave propagation in an i.d.t., are equally significant in s.a.w. excitation. Experimental results on s.a.w. amplitude radiated by a rare i.d.t. are presented in the time domain; they agree with the calculations.