Positive pressure matters in acoustic droplet vaporization

TL;DR

This paper reveals that compression waves can initiate acoustic droplet vaporization through Gouy phase shift, unifying existing theories and enabling safer ultrasound therapies.

Contribution

It introduces a unified theoretical framework explaining vaporization via compression waves and validates it through experiments and simulations.

Findings

Compression waves can induce vaporization via Gouy phase shift.

The theory identifies parameters for safe vaporization using compression waves.

Experimental and simulation results support the unified theory.

Abstract

Acoustically vaporizable droplets are phase-change agents that can improve the effectiveness of ultrasound-based therapies. In this study, we demonstrate that the compression part of an acoustic wave can generate tension that initiates the vaporization. This counter-intuitive process is explained by the occurrence of Gouy phase shift due to the focusing of the acoustic wave inside the droplet. Our analysis unifies the existing theories for acoustic droplet vaporization under a single framework and is supported by experiments and simulations. We use our theory to identify governing parameters that allow to vaporize droplets using predominantly compression waves, which are safer in medical use.