Study on the rectangular-bar-shaped multilayer piezoelectric transformer using length extensional vibration mode

The rectangular-bar-shaped multilayer piezoelectric transformer, which employs the length extensional vibration mode and interdigital internal electrodes, has been suggested and developed by us for the application to AC adapters. First, the methods of increasing the power-to-volume ratio of the transformer are investigated experimentally. As a result, it is found that using a high driving frequency and optimizing the positions of input and output parts increase the power-to-volume ratio. Second, to prevent characteristic degradation resulting from spurious vibrations in its driving frequency range, the methods of controlling such spurious vibrations are studied theoretically and experimentally. It is found that controlling the size of the transformer can widen the driving frequency range without spurious vibrations, and that using a low order length extensional vibration mode can decrease the number of spurious vibrations in its driving frequency range. Also, it is found that spurious vibrations can be eliminated or weakened by properly arranging the positions of input and output parts according to the mode pattern of the spurious vibrations.