High-frequency acoustic wave reflective acoustic metasurface based on diffraction grating theory

Addressing the issues of near-field distortion and manufacturing difficulty arising from fluid-structure coupling effects in traditional metasurfaces for underwater MHz-range high-frequency acoustic wave manipulation, this paper proposes a reflective acoustic metagrating grounded in diffraction grating theory. By employing an integrated optimization strategy—and comprehensively accounting for both nonlocal interactions among sub-units and the fluid-structure coupling between them—we design a metallic structure featuring only two rectangular grooves per unit cell, enabling ±45° anomalous reflection of 1 MHz normally incident sound waves with a −1st-order-to-+1st-order diffraction energy ratio of 3∶1. Simulation results demonstrate that the metagrating achieves the target energy ratio of 3∶1 precisely at 1 MHz. Time-domain fluid-structure coupling simulations and underwater experimental measurements of the sound pressure amplitude ratio in the ±45° directions both confirm this 3∶1 energy ratio, showing excellent agreement with theoretical predictions. Experimental analysis reveals an energy ratio deviation of less than 5% over the frequency range of 0.98–1.02 MHz, yielding a relative working bandwidth of approximately 4%. In conclusion, the designed metagrating exhibits an exceptionally simple geometry and low fabrication complexity, enabling efficient nonlocal regulation of high-frequency underwater acoustic waves. It holds promising potential for applications in underwater sonar stealth, high-frequency ultrasonic imaging, and related fields.