| 摘要 |
PURPOSE:To reduce the diametric oscillation mode or the transverse oscillation mode and its harmonic oscillation mode to reduce spurious components by sticking a load medium of large acoustic loss to the outside peripheral edge of a piezoelectric ceramic element body. CONSTITUTION:A load medium 4 of large acoustic loss is stuck to the outside peripheral edge of a piezoelectric ceramic element body 1, and many through holes 5 are formed in the thickness direction of the piezoelectric ceramic element body. Since a characteristic similar to anisotropy is given to the oscillator without reducing the dielectric constant by providing these through holes 5, the diametric oscillation mode or the transverse oscillation mode is reduced furthermore by the action of the load medium 4 of large acoustic loss to reduce spurious components. If through holes 5 are so formed that their maximum diameter l is smaller than a wavelength lambda of the acoustic wave in an acoustic medium due to a resonance frequency f0, the acoustic load is heavier apparently. Thus, when the oscillator is driven by pulses in case of radiation of ultrasonic waves into water, a mechanical quality coefficient Qm in water is smaller than that of a conventional piezoelectric oscillator, and the ultrasonic pulse width is shorter to improve the distance resolution. |
