Deconvolution of acoustically detected bubble-collapse shock waves

Abstract

The shock wave emitted by the collapse of a laser-induced bubble is detected at propagation distances of 30, 40and50mm, using a PVdF needle hydrophone, with a non-flat end-of-cable frequency response, calibrated for magnitude and phase, from 125kHz to 20MHz. High-speed shadowgraphic imaging at 5×10⁶ frames per second, 10nstemporal resolution and 256 frames per sequence, records the bubble deflation from maximum to minimum radius, the collapse and shock wave generation, and the subsequent rebound in unprecedented detail, for a single sequence of an individual bubble. The Gilmore equation for bubble oscillation is solved according to the resolved bubble collapse, and simulated shock wave profiles deduced from the acoustic emissions, for comparison to the hydrophone recordings. The effects of single-frequency calibration, magnitude-only and full waveform deconvolution of the experimental data are presented, in both time and frequency domains. Magnitude-only deconvolution increases the peak pressure amplitude of the measured shock wave by approximately 9%, from single-frequency calibration, with full waveform deconvolution increasing it by a further 3%. Full waveform deconvolution generates a shock wave profile that is in agreement with the simulated profile, filtered according to the calibration bandwidth. Implications for the detection and monitoring of acoustic cavitation, where the role of periodic bubble collapse shock waves has recently been realised, are discussed.

Keywords: Bubble; Collapse; Deconvolution; Shock wave.