Coupled model analysis of SAW floating electrode type unidirectional transducers

The performance of a single-phase unidirectional transducers utilizing the internal reflections of floating electrodes of electrically open and shorted metal strips within an interdigital electrode structure (FEUDT: floating electrode unidirectional transducer) is analyzed using a coupled-mode theory. All four independent parameters (the self and mutual coupling coefficient, the transduction coefficient, and the static capacitance) governing the coupling-mode equation with an electrical transduction term are analytically derived using extended Legendre polynomial expansions of electrical fields and perturbation analysis. Frequency response of radiation admittance and insertion loss, and SAW field distributions in a transducer 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 degrees C YX LiNbO/sub 3/ substrate and compared with theoretical results.<>