Scattering of Shear Horizontal Waves by Massive Metallic Electrodes in Saw Devices

Abstract

In surface acoustic wave (SAW) devices the excitation and detection of acoustic waves is conveniently controlled by a set of metallic electrodes on the plane surface of a piezoelectric substrate [1]. An input interdigital transducer (IDT) consisting of a number of electrodes converts the electric input signal into the propagating acoustic waves, and conversely, an output IDT converts the signal carried by the acoustic waves back into the electric signal. The fundamental process behind the generation and detection of acoustic waves is the interaction of the acoustic waves with the electrodes. In many applications the electrodes are modeled as being ideal conductive, massless thin electrodes, leading to excellent simulation results compared with carefully obtained experimental data [2,3]. On the contrary, in some other applications, the above idealizations seem to be merely vague assumptions which, possibly hand-in-hand with other second- [4] or higher order effects [5], cause considerable discrepancy with experimental results. Our intention in this work is focused on the description of the massloading effect in SAW devices. In SAW devices like reflective arrays and unidirectional transducers in general, and single phase unidirectional transducers (SPUDTs) [6] in particular, the massloading effect due to the mass of the electrodes, plays a fundamental role in the functional behavior of the devices, and in this sense, it is rather primary effect.