Acoustic Magnifying Lens Based on Compact Non-Dispersive Spiral Metamaterial Array

Abstract

Acoustic magnifying lenses are utilized in a diversity of applications, from nondestructive detection of damages in materials to biomedical imaging. Acoustic metamaterials (MMs) provide powerful control over sound waves by using periodic structures made from natural materials. Existing acoustic meta-lens are commonly associated with designing dispersive metamaterial or connect with local resonator, thus resulting in inevitable deformity of waveforms. Although the four-blade spiral MMs has non-dispersive properties, how to further improve the transmission and reduce the manufacturing difficulty in a compact size is important to construction of a meta-lens. We propose a single-blade spiral metamaterial, which has higher transmission and non-dispersion properties. Based on this meta-unit, we designed and manufactured a meta-lens with the ability to amplify sound signals at the focus point. Different from previous research, the meta-lens is established by periodic meta-helicoid unit and presents great focusing ability while maintaining a compact volume. We show, both theoretically and experimentally, the thin flat acoustic magnifier can turn normally incident signals focusing on the prescribed point and augmenting pressure amplitude about three times. Moreover, the diameter of each element is only 10 mm, and the thickness of the meta-lens is 48mm. Our new strategy may offer an alternate route to the design of novel meta-lens and devices for acoustic application in the future.