Practical realization of a sub-λ/2 acoustic jet.

Area of Science:

• Acoustics and Metamaterials
• Nanoscale Physics

Background:

• Metamaterial lenses enable sub-wavelength localization in optics and acoustics.
• The 'acoustojet' concept theoretically achieves acoustic energy localization to a spot smaller than half the wavelength (λ/2).
• Previous experimental realizations of the acoustojet have struggled to achieve this sub-wavelength localization.

Purpose of the Study:

• To demonstrate experimentally and computationally that sub-λ/2 acoustic localization can be achieved.
• To translate the concept of a photonic jet into the acoustic domain for enhanced focusing.
• To explore the scalability of this phenomenon from nanoscale to macroscale.

Main Methods:

• Performed molecular dynamics (MD) and finite element method (FEM) simulations across nano- to macroscales.
• Conducted macroscale experiments using specifically designed cylindrical acoustic lenses.
• Investigated the influence of lens size and the speed-of-sound ratio between materials.

Main Results:

• Achieved an acoustic jet ('acoustic sheet') with a full width at half maximum (FWHM) less than λ/2.
• Demonstrated experimental realization using easily manufactured macroscale acoustic lenses.
• MD simulations confirmed the extension of the concept to coherent phonons at the nanoscale.

Conclusions:

• The acoustojet approach is experimentally viable for achieving sub-wavelength acoustic localization.
• This technique can be implemented with readily manufacturable acoustic lenses across various scales.
• The findings pave the way for a new era of super-resolution acoustic imaging and applications requiring tight focusing of mechanical energy.