Reflective array modelling for SAW transducers

Abstract

This paper presents a new method for modelling SAW transducers with internal reflections, such as single-electrode transducers and various types of SPUDT. In the past the main method for analysing these transducers has been the coupled-mode (COM) analysis. The latter is approximate mainly because it represents the transducer (which has a discrete nature) in terms of smoothly-varying quantities governed by differential equations; also the COM is not easily related to the transducer physics. Other theoretical approaches, based on the physics, are more accurate and justifiable, but are usually inconvenient and time-consuming to compute. The Reflective Array Model (RAM) presented here gives a method more accurate and better justified than the COM, while retaining the feature of computational convenience. Reflections are analysed by a cascading technique which gives the acoustic scattering with full accuracy even if the electrode reflection coefficient is large. Transduction analysis is based on the quasi-static method used for non-reflecting transducers. Because of its derivation from the electrostatic solution, this method is very accurate, giving for example correct harmonic responses and correctly modelling the effects of changing electrode width. In contrast to COM, the RAM is accurate for short transducers and for wide analysis bands, it can give correct harmonic responses and it easily analyses weighted transducers.