Particle levitation in tone-burst-excited half-wavelength ultrasonic standing waves in cylindrical microresonator

Electrical signals driving piezoelectric transducers in acoustofluidic applications are crucial for acoustic manipulation efficiency, as sinusoidal wave excitation at the resonance frequency determines the acoustic radiation force in application systems. In this study, particle levitation in half-wavelength ultrasonic standing wave fields generated by both continuous-wave and tone-burst excitations of a cylindrical microresonator was investigated by measuring the average velocity of levitating particles and their equilibrium positions. The dependence of these parameters on the characteristics of the sinusoidal voltage amplitude applied to the resonator was examined by evaluating the net force exerting on spherical fluorescent microparticles, including the time-averaged effect of tone-burst excitation. A semi-empirical correlation was proposed to predict the average energy density of the established standing wave field in the resonator. By incorporating a correction factor that quantitatively accounts for the time-averaged effect over the tone-burst repetition period, the model allows one to evaluate the average energy density of half-wavelength ultrasonic standing wave fields generated by continuous-wave and tone-burst voltage amplitudes. The predicted values in good agreement, within less than 18 % of the experimental measurements.