The effect of pulse length on transient cavitation inception

Abstract

Most ultrasonic systems used for diagnostic purposes employ short acoustic pulse rather than cw operation in order to accomplish imaging or Doppler scanning. It is also commonly thought that these short‐pulse systems, although driven at high acoustic pressure amplitudes, do not induce cavitation effects due to the low duty cycle of the ultrasound. Although stable cavitation typically requires cw operation for its effects to be present, transient cavitation can theoretically occur in pulse lengths as short as one cycle. We have developed a detection scheme utilizing sonoluminescence to observe the cavitation produced by pulses of varying length and repetition rate. Normal detection methods that examine noise emitted by the collapsing cavity can not be used in short‐pulse excitation due to the high spectral content of the pulse itself. We have observed transient cavitation effects (sonoluminescence) in pulse lengths as low as a few tens of cycles and are modifying our apparatus to go to even shorter pulses. [Work supported in part by the ONR and the NSF.]