Modelagem por equivalente elétrico para dispositivos a onda acústica de superfície

Abstract

Surface Acoustic Wave (SAW) devices find extensive application in telecommunications as delay lines and highly selective filters, and they also operate as high-sensitivity sensors. This versatility arises from their ability to convert electrical signals into acoustic waves through interdigital transducers and from the strong interaction between these waves and physical or chemical perturbations in the propagation medium. Engineers typically characterize these devices using vector network analyzers, which restrict field applications and complicate integration with systems and wireless sensor networks. These limitations motivate the implementation of approaches based on open- and closed-loop electronic oscillators. However, the development of such systems faces constraints related to the acquisition of SAW devices and to their direct use in circuit simulators. As a result, researchers employ equivalent electrical models, particularly those based on resonator crystals. An extensive literature review reveals that currently available models, although simple and physically implementable, diverge in their representation of the electrical coupling between SAW ports. This aspect plays a critical role in the performance and stability of closed-loop oscillators, especially under uncontrolled environmental conditions. In this context, this work proposes the development of an equivalent electrical circuit model for SAW devices based on a resonator crystal with adjustable parameters. The proposed model more accurately represents the coupling between ports and supports applications in the calibration of SAW-based systems, integration with electronic oscillators, and laboratory testing. This approach reduces dependence on real devices and increases the feasibility of field measurements. The study derives the model from an adapted resonator crystal representation and incorporates dedicated blocks to adjust input and output impedances as well as transmission magnitude.