Impedance‐Matching Wavefront‐Transformation Lens Based on Acoustic Metamaterials

Abstract A broadband, low‐loss, and impedance‐matching wavefront‐transformation lens in acoustics is proposed. Different from the previous planar gradient‐index lens in which the refraction index changes in one direction, the refraction index in the proposed lens changes along two directions. Thus, with one more design freedom, the lens can be designed with additional conditions. For example, based on such an idea, some functional lenses with impedance matching to surrounding material can be designed. To realize the presented lens in acoustics, sub‐wavelength artificial structures, termed as acoustic metamaterials, are used. The elastic modulus and effective density are extracted from the unit cells. A broadband and low‐loss acoustic focusing lens with impedance matching to free space is designed, fabricated, and measured. The lens is fabricated via 3D printing technology with photosensitive resin. The measured result is in good agreement with the simulation. Such an impedance‐matching lens is expected to be used in high‐efficiency acoustic imaging.