電歪振動子の大振幅特性の連続測定

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The output power of electrostrictive transducers in ultrasonic power application seems to be limited by following three major factors:(1)saturation of electrostrictive driving force, (2)maximum vibrational stress amplitude not to cause electrostrictive property degradation due to large amplitude continuous vibration, and (3)mechanical fatigue limit of transducer materials. The authors have already measured the mechanical fatigue limit of transducer materials and the data about it have been presented in the previous paper. The present paper deals with electrostrictive property degradation mainly due to heat generation or temperature rise under large amplitude mechanical vibration. A method to measure continuously the change of electrostrictive stress constants h_l and e_l under large amplitude mechanical vibration is described, and the measurements were performed in order to clarify the upper limit of vibrational stress level not to cause any degradation of electrostrictive stress constants. At practical operations, dielectric loss and mechanical vibrational loss exist simultaneously in the transducer, however, because of the low value of dielectric loss factor(tanδ), dielectric loss usually remains to be small, compared with mechanical vibrational loss, except the cases in which a large electric input is required owing to a quite heavy mechanical load. Furthermore, in most cases, while dielectric loss is uniformly distributed throughout the transducer, mechanical vibrational loss depends upon the vibrational stress distribution in the transducer. In view of these circumstances, it is quite necessary to investigate the behavior of electrostrictive stress constants in connection with the vibrational stress distribution. For this purpose, the bar-shaped lead zirconate titanate transducer with three pairs of electrodes along its length was taken up, and it was used for longitudinal mode vibration, excited mechanically by another vibrating system which consists of a nickel magnetostrictive transducer, a metal resonance horn, and a vibration pick-up. Electrostrictive stress constants h_l and e_l were measured for each pair of electrodes, where values of vibrational stress differ according to the vibrational stress distribution, by the observation of open circuit voltage and short circuit current of electrodes, and this measurement was performed at a few levels of the vibrational velocity at the test transducer end which is known from the calibrated output voltage of the vibration pick-up. The vibrational stress at the center of the test transducer S_<max> was calculated from the density ρ, the longitudinal velocity c of the test transducer material, and the vibrational velocity υ at the test transducer end, and it was used to represent the vibrational stress levels of test transducer. The results of 60 minutes continuous measurement showed that any irreversible degradation did not occur at the vibrational stress levels under 2 kg/mm^2. The value of 2kg/mm^2 is less than the previously reported mechanical fatigue limit 3. 85kg/mm^2, therefore, it can be declared that this longitudinal mode transducer can operate without suffering from electrostrictive property degradation and mechanical fatigue at vibrational stress levels under 2kg/mm^2. The surface temperature distribution on the test transducer was also measured by a thermister-type thermometer, and it was made clear that the surface temperature becomes maximum at the center of the length where the vibrational stress becomes maximum and this fact indicates that mechanical vibrational loss appears according to the vibrational stress distribution. Furthermore, it turned out that the surface temperature with each pair of electrodes short circuited(A type resonance operation)is higher than that with each pair of electrodes open circuited(B type resonance operation), and this implies that mechanical vibrational loss at A type resonance is larger than that at B type resonance. It
社団法人日本音響学会の論文
1973-02-01

電歪振動子の大振幅特性の連続測定

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