A ring-shaped piezoelectric transformer operating in the third symmetric extensional vibration mode

In this study, a ring-shaped piezoelectric transformer operating in the third symmetric extensional vibration mode is proposed, and its characteristics are investigated. The transformer consists of a lead zirconate titanate (PZT) ceramic ring with st high mechanical quality factor which has an outer diameter of 12.7 mm, an inner diameter of 5.1 mm and a thickness of 1.2 mm. The transformer is poled along the thickness direction. The top surface is covered by two ring-shaped electrodes separated by a narrow annular gap, and the regions covered by the outer and inner ring electrodes serve as the input and output parts of the transformer, respectively. Its bottom surface is fully covered with a silver electrode. For a temperature rise of 20 degreesC, the transformer has an output power of 1.8 W and a power density of 14.3 W/cm(3) With a matching load resistance of 860 Omega, its maximum efficiency is 92.3%, and the maximum voltage gain is 1.9. When two ring-shaped transformers are connected in parallel, the total output power is significantly higher than that of a single ring-shaped transformer. However, the resultant maximum efficiency is slightly less than that of a single transformer, and the transformer with the lower voltage ratio determines the overall voltage gain of the parallel combination. (C) 2001 Elsevier Science B.V. All rights reserved.