Photoacoustic ultrasound sources from diffusion-limited aggregates

TL;DR

This paper demonstrates that diffusion-limited aggregate (DLA) films can serve as broadband, air-coupled ultrasonic sources due to their strong photoacoustic response, enabling simple, inexpensive, and versatile acoustic devices.

Contribution

It introduces the use of DLA films as broadband photoacoustic sources and develops an optically-addressed acoustic phased array for arbitrary pattern generation.

Findings

DLA films exhibit a strong, broadband photoacoustic response.

DLA-based sources can operate in the ultrasonic regime.

The phased array can produce arbitrary acoustic patterns in air.

Abstract

Metallic diffusion-limited aggregate (DLA) films are well-known to exhibit near-perfect broadband optical absorption. We demonstrate that such films also manifest a substantial and relatively material-independent photoacoustic response, as a consequence of their random nanostructure. We theoretically and experimentally analyze photoacoustic phenomena in DLA films, and show that they can be used to create broadband air- coupled acoustic sources. These sources are inexpensive and simple to fabricate, and work into the ultrasonic regime. We illustrate the device possibilities by building and testing an optically-addressed acoustic phased array capable of producing virtually arbitrary acoustic intensity patterns in air.