Alternative Designs of Acoustic Lenses Based on Nonlinear Solitary Waves

Abstract

In the last decade, there has been an increasing attention on the use of highly- and weakly-nonlinear solitary waves in engineering and physics. These waves can form and travel in nonlinear systems such as one-dimensional chains of particles. When compared to linear elastic waves, solitary waves are much slower, nondispersive, and their speed is amplitude-dependent. Moreover, they can be tuned by modifying the particles' material or size, or the chain's precompression. One interesting engineering application of solitary waves is the fabrication of acoustic lenses, which are employed in a variety of fields ranging from biomedical imaging and surgery to defense systems and damage detection in materials. In this paper, we propose the design of acoustic lenses composed by one-dimensional chains of spherical particles arranged to form a line or a circle array. We show, by means of numerical simulations and an experimental validation, that both the line and circle arrays allow the focusing of waves transmitted into a solid or liquid (the host media) and the generation of compact sound bullets of large amplitude. The advantages and limitations of these nonlinear lenses to attain accurate high-energy acoustic pulses with high signal-to-noise ratio are discussed.