# Ultrasound generation in water via quasi-periodically snapping polymeric core–shell micro-bead excited with radiowaves

## TL;DR

Researchers discovered that a special micro-bead can generate ultrasound in water when exposed to radio waves, opening new possibilities for imaging technology.

## Contribution

A novel core–shell micro-bead system is shown to generate ultrasound via stochastic resonance and snap-through-buckling, enabling radioacoustic imaging.

## Key findings

- The micro-bead system generates pressure oscillations via a snap-through-buckling mechanism.
- The system achieves resonance by matching optical and acoustic frequencies with a pulsed laser.
- This mechanism demonstrates high energy conversion efficiency and periodic behavior.

## Abstract

This work reports the results of a theoretical and numerical study showing the occurrence of stochastically resonating bistable dynamic in polymeric micro-bead of sub-micrometric size with stiff core and soft shell. The system, submerged in water, is excited with a pulsed laser working in the Mega-Hertz frequency range and tuned to match both an optical and acoustic resonance of the system. The laser interacts with the carbon nanotubes embedded in the shell of the polymeric micro-bead generating heat. The concurrent action of the generated heat with the standing acoustic oscillations, gives rise to a stochastically resonating bistable system. The system in fact is forced to switch between two states (identifiable with the creation and organized disruption of a quasi-hexagonal tessellation) via a snap-through-buckling mechanism. This phenomenon results in the unprecedented generation of pressure oscillations. These results open the way to develop a new type of core–shell micro-transducers for radioacoustic imaging applications able to work in the Mega-Hertz frequency range. From a more general thermodynamic perspective, the reported mechanism shows a remarkable periodicity and energy conversion efficiency.