Construction of a low-frequency high-power piezoelectric transformer with a specified step-up voltage transformation ratio using two identical bolt-clamped Langevin-type transducers

Abstract

We propose a low-frequency piezoelectric transformer comprising two identical bolt-clamped Langevin-type transducers (BLTs) and a stepped horn with a half-wavelength straight extension. The transformer can realize a specified step-up voltage transformation ratio as determined by the cross-sectional area ratio of the horn whose both ends the two BLTs are connected to, and the driving frequency at which the specified transformation ratio is realized can be set near its mechanical resonance. Thus, it can be mechanically held firmly at its vibratory node without affecting the mechanical vibration mode or resulting in a loss of energy. After relevant finite-element simulations, experiments were conducted for a trial-fabricated transformer of the above type. As a result, the experimental results predicted by the simulations were obtained in step-up operation. The influence of the load resistance on the deviation of the driving frequency from its total mechanical resonance of 53.1 kHz was found to be less than 130 Hz (0.24% of the resonance frequency) only. High-power performance of the piezoelectric transformer was also demonstrated.

Stable operation of a high-power piezoelectric transformer comprising two identical bolt-clamped Langevin-type transducers and a stepped horn

“…Before proceeding to the main subjects of the present paper, the design process of the high-power piezoelectric transformer 3,4) should be briefly summarized for clear discussion later. The transformer is designed with the aid of the UNIFESP, 18,19) a linear two-dimensional finite-element analysis system developed by Adachi and coworkers for the numerical investigation of piezoelectric vibratory systems.…”

“…This is a typical case of the jumping and dropping phenomena. 4,17,[20][21][22][23][24] The peculiar phenomena of the piezoelectric material were first found by Takahashi of NEC and Hirose of Yamagata University in the early 1990s, and the cause has long been ascribed merely to the elastic nonlinearity of the piezoelectric material owing to a high vibration velocity. 17,[20][21][22][23][24] However, no systematic experimental elucidation on the physical mechanism of the phenomena has ever been reported.…”

“…3) The maximum output power and power transfer efficiency obtained with the first prototype transformer we previously fabricated were 100 W and 99.2%, respectively, while maintaining the specified step-up voltage transformation ratio at the driving frequency close to its mechanical resonance of approximately 20 kHz, despite a significant change in load resistance. Since the piezoelectric transformer of this type is driven at a frequency quite near its mechanical resonance 3,4) unlike conventional (mainly monolithic) piezoelectric transformers, [5][6][7][8][9][10][11][12][13][14][15][16] the specified step-up voltage transformation ratio is determined solely by the ratio of the cross-sectional areas at both ends of the horn. Moreover, the secure mechanical support of the vibrating transformer without mechanical energy loss can be realized quite easily by fixing the rim of the flange made at the vibratory node clearly identified near the center of the horn.…”

Structure of 100 W high-efficiency piezoelectric transformer for applications in power electronics

“…Henceforth, in the case of the step-down operation, namely n < 1, realization of the transformation ratio specified in the design near the mechanical resonance of the transformer inherently becomes very difficult owing to the significant influence of the dumped capacitance of the BLT on the secondary side. 16) For this reason, experiments were carried out only for the step-up operation.…”

“…The structure is basically the same as that of the piezoelectric transformer previously developed by Adachi et al, but the size is much larger to enable high-power operation. 16) Although the vibratory energy density in a transformer of this type is relatively small in comparison to conventional piezoelectric transformers such as Rosen-type ones, the voltage transformation ratio is simply determined by the cross-sectional area ratio of the stepped horn at a specified frequency in the vicinity of its mechanical resonance frequency even if its electrical load markedly changes, and we can easily find a position for secure mechanical support of the transformer without energy dissipation. Moreover, the problem of the weakness of piezoelectric ceramic to intense tensile stress arising in highamplitude operation can be practically averted thanks to the mechanical robustness of BLTs, which is well known in the field of high-power ultrasonic engineering.…”