An additional concave incident surface comprised of two-dimensional (2D) sonic crystals (SCs) is employed to tune the acoustic image in the far-field region. The tunability is realized through changing the curvature of the concave surface. To explain the tuning mechanism, a simple ray-trace analysis is demonstrated based on the wave-beam negative refractive law. Then, a numerical confirmation is carried out. Results show that both the position and the intensity of the image can be tuned by the introduced concave surface.

Negative refractive collimation beam at the low frequency region is achieved in a square lattice sonic crystal with the small magnitude of effective refractive index. A simple tuning approach for such acoustic beam is also proposed by attaching an additional concave surface of incidence to the crystal slab. This can increase the propagation distance of collimation beam, enhance or suppress the beam intensity. The proposed approach is rather general and applicable to other acoustic materials as long as their effective index can be retrieved. Moreover, the results can be applied to wavefront manipulation and transmission enhancement.

No abstract

We manipulate the source distance, emission position and number of negative-index collimation beam in a two-dimensional hybrid sonic crystal by using band-gap waveguide to control the flow of acoustic waves from a point source. The desired beam manipulations can be achieved at many different frequencies by suitably selecting the first order resonant mode of two crystal components and the waveguide structures. These results have potential applications in acoustic mutifunctional directional emission and acoustic integrated circuits. The proposed approach is also applicable for the similar manipulations of other types of acoustic collimation beams.