Design and characterization of piezoelectric transformers for high power applications

A piezoelectric transformer (PT) is an electro-mechanical device that transfers electrical energy through a mechanical vibration at its resonance frequency.; To improve the piezoelectric transformers in term of high density of transfer power, two types of piezoelectric transformers, a laminated piezoelectric transformer and an unipoled disk piezoelectric transformer, with radial extensional vibration mode were studied. For the laminated piezoelectric transformer, its structure consists of uniform-poled piezoelectric ceramic plates at the input and output parts with an insulation layer between them. This type of transformer provides more high power density, simple structure, isolation between input and output terminals, and multiple output voltage levels, since the output voltage depends on the thickness ratio between individual layer in the input and output parts. For the unipoled disk piezoelectric transformer, a hard piezoelectric material, which was poled only along the thickness direction, was used. The input and output electrodes were concentrically placed in the top surface of the ceramic. The input electrode was the external electrode ring and the output electrode was the internal center dot.; This proposed research is aimed to develop a good understanding of the piezoelectric transformer designs and their related properties. The equivalent circuit and finite element modeling analysis were initially performed to analyze the piezoelectric transformer behaviors. Various characteristics, such as, voltage step-up ratio, efficiency, temperature rise, and output power were experimentally investigated. Some examples of the transformer applications provide.; We found that Stycast® 1264 is a promising bonding material to improve transformer characteristics of the laminated piezoelectric transformer in terms of mechanical quality factor, and that the bonding layer thickness provides significant change in its properties, efficiency and output power. Size and shape of the piezoelectric element also affect the transformer's performance. It showed that the power capability of piezoelectric transformer can be increased when the disk-shape and bigger size of piezoelectric elements are used. From this study, the maximum output powers of 10 and 36 W were obtained for 23.8 and 45.0 mm diameter piezoelectric transformers with the same total thickness, respectively. These laminated transformers exhibit approximately three times higher power density than a rectangular Rosen-type piezoelectric transformer with a similar volume. (Abstract shortened by UMI.)...