Beamforming with transformation acoustics in anisotropic media

Abstract

Transformation acoustics correlates complex material properties in physical space with distorted wave manipulations in virtual space, such that wave propagation patterns can be determined by mathematical coordinate transformations. These transformations allow for accurate modeling of acoustic propagation in complex materials. Such models are relevant for both biomedical ultrasound therapies and integrated on-chip systems, where muscle fibers and piezoelectric substrates act as effective anisotropic media, respectively. Without considering the anisotropic density of these sophisticated media, attempts to beamform acoustic patterns by phase engineering result in a heavily distorted signal. This distortion is detrimental to the performance of high intensity focused ultrasound acoustic tweezers for noninvasive surgeries, cell trapping, and cell sorting. Here, we demonstrate that the distortion effects can be corrected by transformation acoustics in which the phased array profile is adjusted to account for the corresponding anisotropy. We perform experiments to verify this transformation acoustic correction for arbitrary focused and self-bending beams with two-dimensional anisotropic spoof surface acoustic waves. The benefit of transformation acoustics in suppressing undesired anisotropic effects on beamformed waves improves the precision and efficacy of medical treatments that facilitate noninvasive ultrasound therapies and integrated on-chip applications.