A circular piezoelectric transformer with crescent shape input electrodes

For most PZT based piezoelectric materials, the shear mode electromechanical coupling constant is twice as large as the transverse mode coupling. In this study, a new disk type piezoelectric transformer was designed. Crescent shape electrodes at the input side and focused poling direction at the output side on a commercially available PZT disk were designed so that the planar and shear mode electromechanical coupling factors becomes effective rather than the transverse mode coupling. ATILA finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been dramatically improved in comparison with an equivalent rectangular type. A single layer prototype transformer 25.4 mm in diameter and 1.0 mm in thickness, operated at 93 kHz, was fabricated and its characteristics, such as step-up ratio, power transformation efficiency and temperature rise were measured.