Field analysis o SAW single-phase unidirectional transducers using internal floating electrodes

A coupled-mode analysis is presented of the performance of a single-phase unidirectional transducer utilizing the internal reflections of floating electrodes of electrically open circuited and shorted metal strips within an interdigital electrode. All four independent parameters (self- and mutual-coupling coefficients, transduction coefficient, and static capacitance) governing the coupled-mode equation with an electrical transduction term are analytically derived using extended Legendre polynomial expansions of electrical fields and a perturbation analysis. The frequency response of the radiation admittance and the insertion loss, and the growing surface acoustic wave (SAW) field distributions are calculated from simple closed-form solutions of the coupled-mode equation. The shift effect of reflection and transduction centers due to the asymmetric electrode structure is clarified. Experimental results are given for test devices fabricated on a 128° YX LiNbO₃ substrate, and compared with the theory. The theoretical results are in good agreement with experiments