Acoustic Beam Forming Based on a Surface with Sinusoidally Modulated Admittance

Directional sound beam forming is an area of interest in practical acoustic applications where leaky-wave principles and techniques may provide efficient solutions. Here, we present a type of high-gain acoustic leaky antenna used for acoustic beamforming using an admittance-modulation metasurface which consists of periodic subwavelength grooves with sinusoidal depth profiles. The acoustic metasurface converts the surface waves into far-field radiating waves forming a high-gain surface wave antenna. We numerically and experimentally demonstrate far-field propagation angles of -30 degrees, 0 degrees, and 30 degrees at 19 300, 22 000, and 23 900 Hz, respectively, and show that the radiation angle and beamwidth can be independently controlled by modulating the sinusoidal profile. Also, we use a Laser Doppler Vibrometer to directly measure the surface wave damping along a circular sinusoidally modulated admittance surface (SMAS).