Simple broadband planar acoustic lenses design with a velocity gradient structure

Abstract

Compared to curved acoustic lens, planar acoustic lens fits better with other surfaces like human body or additional lenses due to its profile. Traditional planar lens designs such as Fresnel lens and metamaterial lens suffer from poor bandwidth in frequency and complexities in fabrication, limiting the use in medical ultrasound. By curing epoxy mixtures in a 3D-print mold, a simple planar lens planar lens is designed and tested with a velocity gradient matching layer. Its Total cost is no higher than 8 dollars. Since the focusing relies on material velocity instead of wavelength, it makes the single planar lens designed for 1 MHz functions from 0.5 to 1.2 MHz (82 %). For concept validation, transducers with single circular planar lens and a lens set are fabricated and compared to traditional lens design. At 1 MHz, single planar lens reaches a focal length of 64.24 mm, which is similar to traditional concave lens design but shows less near field effect and less prone to cavitation at the interface. The planar-lens-added lens set also shows similarity to traditional lens set including a shorter focal length, a smaller focal spot and a better directivity. With the merit of easy fabrication and less cost, the proposed planar lens design strategy has the potential to be a complement of Fresnel lenses and metamaterial lenses in medical treatment applications.