Development of Very High Voltage Transformers Using Piezoelectric Single Crystals

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The purpose of this research project to propose riezoelectric LiNbO_3 single-crystal transformers suitable for large amplitude operation and to develop small-size transformers with a high stepup ratio. The results obtained in this project are summarized as follows : 1. To find the optimum cuts for transformers the orientation dependence of the relevant electromechanical coupling factors was calculated. The optimum orientation turned out to be the 130。 rotated Y-cut for the longitudinal coupling output configuration and the 140。 rotated Y-cut for the transverse coupling output configuration. 2. The large-amplitude characteristics of LiNbO_3 vibrators were measured. LiNbO_3 has small losses compared to those of ceramics and exhibits little deterioration of performance under large amplitude operation. 3. The behavior of piezoelectric transformers including a rectifying circuit with nonlinear diodes and a load resistance was theoretically analyzed. The dependence of the voltage stepup ratio, output current, and output power on the load resistance was made clear. 4. A transformer of longitudinal coupling output configuration with a high stepup ratio of about 500 and with no saturation of the output voltage upto 5kV was developed. The fact that the output characteristics differed depending on the polarity of the plate surface with the output electrode was found and qualitatively explained. 5. A LiNbO_3 transformer of the transverse coupling output configuration using the 140。 rotated Y-cut was devised and demonstrated to have a high output current and a high stepup ratio about 1300.6. In 154.5。 rotated Y-cut LiNbO_3 rectangular plates, the Lame-modes which have vibration nodes at the four corners were theoretically predicted to exist and to be highly excitable. It was demonstrated that the Lame-mode transformer has a very high Q over 10000 and a high stepup ratio over 700 even if it is supported on the four edges. 7. A miniature Lame-m