A flat acoustic lens to generate a Bessel-like beam.

We report a flat acoustic lens with a periodical structure to transform a divergent beam into a Bessel-like beam. Using the Schlieren imaging technique, the propagation process of acoustic wave in the periodical structure was experimentally observed. The pressure distribution in the main lobe is in good agreement with the Bessel function and the positions of the side lobes are close to the peak of the Bessel function. To observe the directivity of the beam, simulations were performed using the finite-element method. The simulation results indicated that the transmitted acoustic intensity at the central axis was several times greater with the lens than without it. The applicability of the lens for detecting the location of an acoustic source was also investigated.