RESUMO
Piezoelectric transducers are commonly operated at their resonance frequency. However, from a power dissipation standpoint, this is not the ideal driving frequency. In this paper, an optimized driving frequency in between the resonance and antiresonance frequencies is proposed for the piezo-transducer. First, the optimum driving frequency is characterized using a constant vibration velocity measurement method. The actual input power reveals the lowest power dissipation frequency between the resonance and the antiresonance frequencies, where the transducer behaves inductive. The electrical parameters of the transducer are then determined by an equivalent circuit formulation, which is useful for the electrical circuit analysis of the driver design. A Class E resonant inverter is used to design a capacitive output impedance driver at the optimized frequency by utilizing a series capacitor. Compared with the traditional resonance drive, driving at the optimized frequency reduces the required power by approximately half according to the measurements performed.
RESUMO
The acoustically agitated bubble oscillation in liquids that is considered to be related to the half-subharmonic acoustic bubble oscillations is discussed in terms of parametric decay instability. At the frequency of about 40 kHz, the half-subharmonic bubble oscillation mode should be a surface bubble oscillation that does not easily emit acoustic waves into water and confines acoustic energy from longitudinal waves. The half-subharmonic bubble oscillation is the dominant mode that leads to parametric decay instability of bubble oscillations.