RESUMO
The use of a piezoelectric ring as transformer is reported and studied in this paper. By using a concentric electrode pattern, a ring-shaped transformer can be designed to operate at its high order extensional modes. Lead zirconate titanate (PZT) ceramic rings with 12.7-mm outer diameter, 5.1-mm inner diameter and 1.2-mm thickness were used to fabricate the prototypes. Three-dimensional (3-D) finite element models are built to study and analyze the vibration characteristics of the piezoelectric transformers (PTs) using higher order modes (>3). The resonant frequencies, mean coupling effect, mode shapes, and other open-circuit characteristics are simulated and compared with experimental measurements. Prototypes of PTs using mode order three and four were fabricated and characterized. Good agreement can be obtained between experimental results and finite element model (FEM) simulations. The dimensions for the PTs using higher order symmetric extensional modes are optimized by FEM. To avoid mode coupling with the thickness mode, the ideal ring thickness has to be less than or equal to 0.6 mm. The ring PT offers advantages of simple structure and small size. It has a good potential in making low cost PT for low-voltage applications.