Acoustic Meta-Lens for Enhanced Sensing Consisting of Single-Helicoid Array

Magnifying lenses based on acoustic metamaterials (MMs) play an important role in many practical applications requiring acoustic focusing and amplification detection. However, the current 3D meta-lenses are still plagued by low flexibility, huge volumes, and high manufacture costs. We report a 3D meta-lens composed of discretely distributed meta-helicoid element that can solve the above problems. We improve the traditional helical MMs by reducing the number of blades to increase the distance between blades, achieving higher transmission efficiency and avoiding blade adhesion during manufacture. In order to eliminate the uneven phase and pressure of single-helicoid MMs at the outlet, pipe extension method is used to unify the phase and pressure. Via adjusting the spiral pitch, the meta-helicoid can generate 0-
$2 \boldsymbol {\pi }$
phase delay with a fixed outline size while maintaining transmittance greater than 90%. Based on the small single-helicoid meta-element, we design and manufacture a low-cost 3D magnify meta-lens with compact size. We demonstrate, both theoretically and experimentally, the acoustic meta-lens can make the normally incident signals focus on the prescribed point, enhances pressure amplitude about three times, and can flexibly manipulate focus point. Moreover, the bandwidth of the meta-lens is as wide as about 5.6 kHz. Our new strategy may offer an alternate route to the design of novel meta-lens and devices for acoustic focusing and amplification detection.