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 isk2times the applied electrostatic energy in a piezoelectric insulator, wherekis the appropriate electromechanical coupling factor. By comparison with other models, it is shown thatk2thus defined is equal to 2 {(vo—vM)/v0}, wherevoandvmare 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.