Subwavelength focusing and steering of spoof acoustic surface waves with aperiodic waveguide arrays

In this study, we designed an acoustic waveguide by setting small periodic rigid plates to support spoof acoustic surface waves that can be freely controlled by tailoring the waveguide widths. When constructing acoustic waveguide arrays with parabolic refractive-index distributions, sound can be steered to focus on deep-subwavelength focal points, surpassing the diffraction limit. Theoretically, we used the Hamiltonian optics method to predict the focusing position and propagation trace of the spoof acoustic surface waves. Both simulated and experimental results demonstrate the theoretical prediction that the focusing point can be tuned lengthwise by changing the incident frequency and the lateral shifts by changing the incident angle. The results indicate that metal-like waveguide arrays can provide a feasible pathway for achieving compact and tunable sound focusing and super-resolution acoustic imaging on a subwavelength scale.